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  • 1.
    Adler, Jonas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.). Elekta, Box 7593, 103 93 Stockholm, Sweden.
    Ringh, Axel
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Öktem, Ozan
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Karlsson, Johan
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Optimeringslära och systemteori.
    Learning to solve inverse problems using Wasserstein lossManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    We propose using the Wasserstein loss for training in inverse problems. In particular, we consider a learned primal-dual reconstruction scheme for ill-posed inverse problems using the Wasserstein distance as loss function in the learning. This is motivated by miss-alignments in training data, which when using standard mean squared error loss could severely degrade reconstruction quality. We prove that training with the Wasserstein loss gives a reconstruction operator that correctly compensates for miss-alignments in certain cases, whereas training with the mean squared error gives a smeared reconstruction. Moreover, we demonstrate these effects by training a reconstruction algorithm using both mean squared error and optimal transport loss for a problem in computerized tomography.

  • 2.
    Afkham, Heydar Maboudi
    et al.
    KTH, Skolan för bioteknologi (BIO), Genteknologi.
    Ek, Carl Henrik
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Carlsson, Stefan
    KTH, Skolan för datavetenskap och kommunikation (CSC), Datorseende och robotik, CVAP.
    Gradual improvement of image descriptor quality2014Inngår i: ICPRAM 2014 - Proceedings of the 3rd International Conference on Pattern Recognition Applications and Methods, 2014, s. 233-238Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper, we propose a framework for gradually improving the quality of an already existing image descriptor. The descriptor used in this paper (Afkham et al., 2013) uses the response of a series of discriminative components for summarizing each image. As we will show, this descriptor has an ideal form in which all categories become linearly separable. While, reaching this form is not feasible, we will argue how by replacing a small fraction of these components, it is possible to obtain a descriptor which is, on average, closer to this ideal form. To do so, we initially identify which components do not contribute to the quality of the descriptor and replace them with more robust components. Here, a joint feature selection method is used to find improved components. As our experiments show, this change directly reflects in the capability of the resulting descriptor in discriminating between different categories.

  • 3.
    Agerskov, Niels
    et al.
    KTH, Skolan för teknik och hälsa (STH).
    Carrizo, Gabriel
    KTH, Skolan för teknik och hälsa (STH).
    Application for Deriving 2D Images from 3D CT Image Data for Research Purposes2016Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Karolinska University Hospital, Huddinge, Sweden, has long desired to plan hip prostheses with Computed Tomography (CT) scans instead of plain radiographs to save time and patient discomfort. This has not been possible previously as their current software is limited to prosthesis planning on traditional 2D X-ray images. The purpose of this project was therefore to create an application (software) that allows medical professionals to derive a 2D image from CT images that can be used for prosthesis planning.

    In order to create the application NumPy and The Visualization Toolkit (VTK) Python code libraries were utilised and tied together with a graphical user interface library called PyQt4. The application includes a graphical interface and methods for optimizing the images for prosthesis planning.

    The application was finished and serves its purpose but the quality of the images needs to be evaluated with a larger sample group. 

    Fulltekst (pdf)
    fulltext
  • 4.
    Alagic, Z.
    et al.
    Functional Unit for Musculoskeletal Radiology Function Imaging and Physiology, Karolinska University Hospital, Karolinska Vägen Solna, 17176 Stockholm, Sweden.
    Bujila, Robert
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Enocson, A.
    Department of Molecular Medicine and Surgery, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden.
    Srivastava, S.
    Functional Unit for Musculoskeletal Radiology Function Imaging and Physiology, Karolinska University Hospital, Karolinska Vägen Solna, 17176 Stockholm, Sweden.
    Koskinen, S. K.
    Functional Unit for Musculoskeletal Radiology Function Imaging and Physiology, Karolinska University Hospital, Karolinska Vägen Solna, 17176 Stockholm, Sweden.
    Ultra-low-dose CT for extremities in an acute setting: initial experience with 203 subjects2019Inngår i: Skeletal RadiologyArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective

    The purpose of this study was to assess if ultra-low-dose CT is a useful clinical alternative to digital radiographs in the evaluation of acute wrist and ankle fractures.

    Materials and methods

    An ultra-low-dose protocol was designed on a 256-slice multi-detector CT. Patients from the emergency department were evaluated prospectively. After initial digital radiographs, an ultra-low-dose CT was performed. Two readers independently analyzed the images. Also, the radiation dose, examination time, and time to preliminary report was compared between digital radiographs and CT.

    Results

    In 207 extremities, digital radiography and ultra-low-dose CT detected 73 and 109 fractures, respectively (p < 0.001). The odds ratio for fracture detection with ultra-low-dose CT vs. digital radiography was 2.0 (95% CI, 1.4–3.0). CT detected additional fracture-related findings in 33 cases (15.9%) and confirmed or ruled out suspected fractures in 19 cases (9.2%). The mean effective dose was comparable between ultra-low-dose CT and digital radiography (0.59 ± 0.33 μSv, 95% CI 0.47–0.59 vs. 0.53 ± 0.43 μSv, 95% CI 0.54–0.64). The mean combined examination time plus time to preliminary report was shorter for ultra-low-dose CT compared to digital radiography (7.6 ± 2.5 min, 95% CI 7.1–8.1 vs. 9.8 ± 4.7 min, 95% CI 8.8–10.7) (p = 0.002). The recommended treatment changed in 34 (16.4%) extremities.

    Conclusions

    Ultra-low-dose CT is a useful alternative to digital radiography for imaging the peripheral skeleton in the acute setting as it detects significantly more fractures and provides additional clinically important information, at a comparable radiation dose. It also provides faster combined examination and reporting times.

  • 5.
    Angelopoulos, A.
    et al.
    -.
    Apostolakis, A.
    -.
    Aslanides, E.
    -.
    Backenstoss, G.
    -.
    Bargassa, P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Bloch, P.
    -.
    Danielsson, Mats
    KTH, Tidigare Institutioner, Fysik.
    K 0–K̄0 mass and decay-width differences: CPLEAR evaluation1999Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 471, nr 2, s. 332-338Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The CPT-violation parameters Re(δ) and Im(δ) determined recently by CPLEAR are used to evaluate the K0 mass and decay-width differences, as given by the difference between the diagonal elements of the neutral-kaon mixing matrix (M−iΓ/2). The results – GeV and GeV – are consistent with CPT invariance. The CPT invariance is also shown to hold within a few times 10−3–10−4 for many of the amplitudes describing neutral-kaon decays to different final states.

  • 6.
    Angelopoulos, Angelos
    et al.
    -.
    Locher, M P
    -.
    Markushin, V E
    -.
    Danielsson, Mats
    KTH, Tidigare Institutioner (före 2005), Fysik.
    Dispersion relation analysis of the neutral kaon regeneration amplitude in carbon1999Inngår i: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 10, nr 1, s. 19-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We apply a forward dispersion relation to the regeneration amplitude for kaon scattering on 12" style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax">12C using all available data. The CPLEAR data at low energies allow the determination of the net contribution from the subthreshold region which turns out to be much smaller than earlier evaluations, solving a long standing puzzle.

  • 7.
    Apostolakis, A.
    et al.
    -.
    Aslanides, E.
    -.
    Backenstoss, G.
    -.
    Bargassa, P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Bloch, P.
    -.
    Carlson, P.
    Danielsson, Mats
    KTH, Tidigare Institutioner, Fysik.
    Measurement of the energy dependence of the form factor f+ in K 0 e3 decay2000Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 473, nr 1, s. 186-192Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neutral-kaon decays to πeν were analysed to determine the q2 dependence of the K0e3 electroweak form factor f+. Based on 365612 events, this form factor was found to have a linear dependence on q2 with a slope λ+=0.0245±0.0012stat±0.0022syst.

  • 8.
    Azami Ghadim, Sohrab
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Utilizing Multi-Core for Optimized Data Exchange Via VoIP2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In contemporary IT industry, Multi-tasking solutions are highly regarded as optimal solutions, because hardware is equipped with multi-core CPUs.  With Multi-Core technology, CPUs run with lower frequencies while giving same or better performance as a whole system of processing. This thesis work takes advantage of multi-threading architecture in order to run different tasks under different cores such as SIP signaling and messaging to establish one or more SIP calls, capture voice, medical data, and packetize them to be streamed over internet to other SIP agents. VoIP is designed to stream voice over IP. There is inter-protocol communication and cooperation such as between the SIP, SDP, RTP, and RTCP protocols in order to establish a SIP connection and- afterwards- stream media over the internet. We use the Microsoft COM technology in order to better the C++ component design. It allows us to design and develop code once and run it anywhere on different platforms. Using VC++ helps us reduce software design time and development time. Moreover, we follow software design standards setup by software engineers’ society. VoIP technology uses protocols such as the SIP signaling protocol to locate the user agents that communicate with each other. Pjsip is a library that allows developers to extend their design with SIP capability. We use the PJSIP library in order to sign up our own developed VoIP module to a SIP server over the Internet and locate other user agents. We implement and use the already-designed iRTP protocol instead of the RTP to stream media over the Internet. Thus, we can improve RTP packet delays and improve Quality of Service (QoS). Since medical data is critical and must not be lost, the iRTP guarantees no loss of medical data. If we want to stream voice only, we would not need iRTP, because RTP is a good protocol for voice applications. Due to the increasing Internet traffic, we need to use a reliable protocol that can detect packet loss of medical data. iRTP resolves the issue and leverages QoS. This thesis work focuses on streaming medical data and medical voice-calls using VoIP, even over small bandwidths and in high traffic periods. The main contribution of this thesis is in the parallel design of iRTP and the implementation of this very design in order to be used with Multi-Core technology. We do so via multi-threading technology to speed up the streaming of medical data and medical voice-calls. According to our tests, measurements, and result analyses, the parallel design of iRTP and the multithreaded implementation on VC++ leverage performance to a level where the average decrease in delay is 71.1% when using iRTP for audio and medical data instead of the nowadays applied case of using an RTP stream for audio and multiple TCPs streams for medical data .

    Fulltekst (pdf)
    thesis-outline-v5.9.4---2015-05-23
  • 9. Azar, J.C.
    et al.
    Hamid Muhammed, Hamed
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Automated Tracking of the Carotid Artery in Ultrasound Image Sequences Using a Self Organizing Neural Network2010Inngår i: Proceedings of 20th International Conference on Pattern Recognition (ICPR 2010), Istanbul, Turkey, Istanbul, Turkey, 2010, s. 2548-2551Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An automated method for the segmentation and tracking of moving vessel walls in 2D ultrasound image sequences is introduced. The method was tested on simulated and real ultrasound image sequences of the carotid artery. Tracking was achieved via a self organizing neural network known as Growing Neural Gas. This topology-preserving algorithm assigns a net of nodes connected by edges that distributes itself within the vessel walls and adapts to changes in topology with time. The movement of the nodes was analyzed to uncover the dynamics of the vessel wall. By this way, radial and longitudinal strain and strain rates have been estimated. Finally, wave intensity signals were computed from these measurements. The method proposed improves upon wave intensity wall analysis, WIWA, and opens up a possibility for easy and efficient analysis and diagnosis of vascular disease through noninvasive ultrasonic examination.

  • 10.
    Baranowski, Jacek
    et al.
    Linköping Heart Centre, University Hospital, Linköping University.
    Ahn, Henrik
    Linköping Heart Centre, University Hospital, Linköping University.
    Freter, Wolfgang
    Linköping Heart Centre, University Hospital, Linköping University.
    Nielsen, Niels-Erik
    Linköping Heart Centre, University Hospital, Linköping University.
    Nylander, Eva
    Linköping Heart Centre, University Hospital, Linköping University.
    Janerot-Sjöberg, Birgitta
    Linköping Heart Centre, University Hospital, Linköping University.
    Sandborg, Michael
    Linköping Heart Centre, University Hospital, Linköping University.
    Wallby, Lars
    Linköping Heart Centre, University Hospital, Linköping University.
    Echo-guided presentation of the aortic valve minimises contrast exposure in transcatheter valve recipients2011Inngår i: Catheterization and cardiovascular interventions, ISSN 1522-1946, E-ISSN 1522-726X, Vol. 77, nr 2, s. 272-275Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECTIVES: We have developed a method using transthoracic echocardiography in establishing optimal visualization of the aortic root, to reduce the amount of contrast medium used in each patient.

    BACKGROUND: During transcatheter aortic valve implantation, it is necessary to obtain an optimal fluoroscopic projection for deployment of the valve showing the aortic ostium with the three cusps aligned in the beam direction. This may require repeat aortic root angiograms at this stage of the procedure with a high amount of contrast medium with a risk of detrimental influence on renal function.

    METHODS: We studied the conventional way and an echo guided way to optimize visualisation of the aortic root. Echocardiography was used initially allowing easier alignment of the image intensifier with the transducer's direction.

    RESULTS: Contrast volumes, radiation/fluoroscopy exposure times, and postoperative creatinine levels were significantly less in patients having the echo-guided orientation of the optimal fluoroscopic angles compared with patients treated with the conventional approach.

    CONCLUSION: We present a user-friendly echo-guided method to facilitate fluoroscopy adjustment during transcatheter aortic valve implantation. In our series, the amounts of contrast medium and radiation have been significantly reduced, with a concomitant reduction in detrimental effects on renal function in the early postoperative phase.

  • 11. Bassan, Gioia
    et al.
    Larsson, David
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Nordenfur, Tim
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Bjällmark, Anna
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Larsson, Matilda
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Acquisition of multiple mode shear wave propagation in transversely isotropic medium using dualprobe setup2015Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 12.
    Batool, Nazre
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Chowdhury, Manish
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Smedby, Örjan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Moreno, Rodrigo
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Estimation of trabecular bone thickness in gray scale: a validation study2017Inngår i: International Journal of Computer Assisted Radiology and Surgery, Vol. 12, nr Supplement 1Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Berggren, Karl
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik. Philips Healthcare, Sweden.
    Danielsson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Fredenberg, Erik
    Philips Healthcare, Sweden.
    Rayleigh imaging in spectral mammography2016Inngår i: MEDICAL IMAGING 2016: PHYSICS OF MEDICAL IMAGING, 2016, artikkel-id 97830AKonferansepaper (Fagfellevurdert)
    Abstract [en]

    Spectral imaging is the acquisition of multiple images of an object at different energy spectra. In mammography, dual-energy imaging (spectral imaging with two energy levels) has been investigated for several applications, in particular material decomposition, which allows for quantitative analysis of breast composition and quantitative contrast-enhanced imaging. Material decomposition with dual-energy imaging is based on the assumption that there are two dominant photon interaction effects that determine linear attenuation: the photoelectric effect and Compton scattering. This assumption limits the number of basis materials, i.e. the number of materials that are possible to differentiate between, to two. However, Rayleigh scattering may account for more than 10% of the linear attenuation in the mammography energy range. In this work, we show that a modified version of a scanning multi-slit spectral photon-counting mammography system is able to acquire three images at different spectra and can be used for triple-energy imaging. We further show that triple-energy imaging in combination with the efficient scatter rejection of the system enables measurement of Rayleigh scattering, which adds an additional energy dependency to the linear attenuation and enables material decomposition with three basis materials. Three available basis materials have the potential to improve virtually all applications of spectral imaging.

  • 14.
    Bergholm, Fredrik
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Hamid Muhammed, Hamed
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Larsolle, A.
    Acquiring instantaneous multispectral imagery using a single image sensor with multiple filter mosaic2007Konferansepaper (Annet vitenskapelig)
  • 15. Bernard, Olivier
    et al.
    Bosch, J G
    Heyde, Brecht
    Alessandrini, Martino
    Barbosa, Daniel
    Camarasu-Pop, S
    Cervenansky, F
    Valette, S
    Mirea, O
    Bernier, M
    Jodoin, P M
    Domingos, J S
    Stebbing, R V
    Keraudren, K
    Oktay, O
    Caballero, J
    Shi, W
    Rueckert, D
    Milletari, F
    Ahmadi, S A
    Smistad, E
    Lindseth, F
    van Stralen, M
    Wang, Chunliang
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Smedby, Örjan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Donal, E
    Monaghan, M
    Papachristidis, A
    Geleijnse, M L
    Galli, E
    Dhooge, Jan
    Standardized evaluation system for left ventricular segmentation algorithms in 3D echocardiography.2015Inngår i: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254XArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Real-time 3D Echocardiography (RT3DE) has been proven to be an accurate tool for left ventricular (LV) volume assessment. However, identification of the LV endocardium remains a challenging task, mainly because of the low tissue/blood contrast of the images combined with typical artifacts. Several semi and fully automatic algorithms have been proposed for segmenting the endocardium in RT3DE data in order to extract relevant clinical indices, but a systematic and fair comparison between such methods has so far been impossible due to the lack of a publicly available common database. Here, we introduce a standardized evaluation framework to reliably evaluate and compare the performance of the algorithms developed to segment the LV border in RT3DE. A database consisting of 45 multivendor cardiac ultrasound recordings acquired at different centers with corresponding reference measurements from 3 experts are made available. The algorithms from nine research groups were quantitatively evaluated and compared using the proposed online platform. The results showed that the best methods produce promising results with respect to the experts' measurements for the extraction of clinical indices, and that they offer good segmentation precision in terms of mean distance error in the context of the experts' variability range. The platform remains open for new submissions.

  • 16.
    Björklund, Tomas
    KTH, Skolan för teknik och hälsa (STH).
    Automatic evaluation of breast density in mammographic images2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The goal of this master thesis is to develop a computerized method for automatic estimation of the mammographic density of mammographic images from 5 different types of mammography units.

     

    Mammographic density is a measurement of the amount of fibroglandular tissue in a breast. This is the single most attributable risk factor for breast cancer; an accurate measurement of the mammographic density can increase the accuracy of cancer prediction in mammography. Today it is commonly estimated through visual inspection by a radiologist, which is subjective and results in inter-reader variation.

     

    The developed method estimates the density as a ratio of #pixels-containing-dense-tissue over #pixels-containing-any-breast-tissue and also according to the BI-RADS density categories. To achieve this, each mammographic image is:

    • corrected for breast thickness and normalized such that some global threshold can separate dense and non-dense tissue.
    • iteratively thresholded until a good threshold is found.  This process is monitored and automatically stopped by a classifier which is trained on sample segmentations using features based on different image intensity characteristics in specified image regions.
    • filtered to remove noise such as blood vessels from the segmentation.
    • Finally, the ratio of dense tissue is calculated and a BI-RADS density class is assigned based on a calibrated scale (after averaging the ratings of both craniocaudal images for each patient). The calibration is based on resulting density ratio estimations of over 1300 training samples against ratings by radiologists of the same images.

     

    The method was tested on craniocaudal images (not included in the training process) acquired with different mammography units of 703 patients which had also been rated by radiologists according to the BI-RADS density classes. The agreement with the radiologist rating in terms of Cohen’s weighted kappa is substantial (0.73). In 68% of the cases the agreement is exact, only in 1.2% of the cases the disagreement is more than 1 class.

    Fulltekst (pdf)
    Tomas_Björklund_MSc_Thesis
  • 17. Blystad, Ida
    et al.
    Warntjes, J. B. Marcel
    Smedby, Örjan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering. Linköping University, Sweden.
    Lundberg, Peter
    Larsson, Elna-Marie
    Tisell, Anders
    Quantitative MRI for analysis of peritumoral edema in malignant gliomas2017Inngår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, nr 5, artikkel-id e0177135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background and purpose Damage to the blood-brain barrier with subsequent contrast enhancement is a hallmark of glioblastoma. Non-enhancing tumor invasion into the peritumoral edema is, however, not usually visible on conventional magnetic resonance imaging. New quantitative techniques using relaxometry offer additional information about tissue properties. The aim of this study was to evaluate longitudinal relaxation R-1, transverse relaxation R-2, and proton density in the peritumoral edema in a group of patients with malignant glioma before surgery to assess whether relaxometry can detect changes not visible on conventional images. Methods In a prospective study, 24 patients with suspected malignant glioma were examined before surgery. A standard MRI protocol was used with the addition of a quantitative MR method (MAGIC), which measured R-1, R-2, and proton density. The diagnosis of malignant glioma was confirmed after biopsy/surgery. In 19 patients synthetic MR images were then created from the MAGIC scan, and ROIs were placed in the peritumoral edema to obtain the quantitative values. Dynamic susceptibility contrast perfusion was used to obtain cerebral blood volume (rCBV) data of the peritumoral edema. Voxel-based statistical analysis was performed using a mixed linear model. Results R-1, R-2, and rCBV decrease with increasing distance from the contrast-enhancing part of the tumor. There is a significant increase in R1 gradient after contrast agent injection (P<.0001). There is a heterogeneous pattern of relaxation values in the peritumoral edema adjacent to the contrast-enhancing part of the tumor. Conclusion Quantitative analysis with relaxometry of peritumoral edema in malignant gliomas detects tissue changes not visualized on conventional MR images. The finding of decreasing R-1 and R-2 means shorter relaxation times closer to the tumor, which could reflect tumor invasion into the peritumoral edema. However, these findings need to be validated in the future.

  • 18.
    Boltshauser, Rasmus
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem.
    Zheng, Jimmy
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem.
    Automatisering av skjuvvågselastografidata för kärldiagnostisk applikation.2018Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Sammanfattning

     

    Hjärt- och kärlsjukdommar är den ledande dödsorsaken i världen. En av det vanligaste hjärt- och kärlsjukdomarna är åderförkalkning. Sjukdomen kännetecknas av förhårdning samt plackansamling i kärl och bidrar till stroke och hjärtinfarkt. Information om kärlväggens styvhet kan spela en viktig roll vid diagnostiseringen av bland annat åderförkalkning. Skjuvvågselastografi (SWE) är en noninvasiv ultraljudsbaserad metod som idag används för att mäta elasticitet och styvhet av större mjuka vävnader som lever- och bröstvävnad. Dock används inte metoden inom kärlapplikationer, då få genomgående studier har utförts på SWE för kärl. Målet med projektet är att automatisera kvantifieringen av skjuvvågshastigheten för SWE och undersöka hur automatiseringens förmåga och begränsningar beror av automatiseringsinställningar. Med verktyg erhållna från CBH (skolan för kemi, bioteknologi och hälsa) skapades ett MATLAB-program med denna förmåga. Programmet applicerades på två fantommodeller. Automatiseringsinställningarna påverkade automatiseringen av dessa modeller olika, vilket innebar att generella optimala inställningar inte kunde finnas. Optimala inställningar beror på vad automatiseringen skall undersöka.

     

    Fulltekst (pdf)
    fulltext
  • 19.
    Bornefalk, Hans
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk avbildning.
    Task-based weights for photon counting spectral x-ray imaging2011Inngår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 38, nr 11, s. 6065-6073Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose: To develop a framework for taking the spatial frequency composition of an imaging taskinto account when determining optimal bin weight factors for photon counting energy sensitivex-ray systems. A second purpose of the investigation is to evaluate the possible improvement comparedto using pixel based weights.Methods: The Fourier based approach of imaging performance and detectability index d0 is appliedto pulse height discriminating photon counting systems. The dependency of d0 on the bin weightfactors is made explicit, taking into account both differences in signal and noise transfer characteristicsacross bins and the spatial frequency dependency of interbin correlations from reabsorbedscatter. Using a simplified model of a specific silicon detector, d0 values for a high and a low frequencyimaging task are determined for optimal weights and compared to pixel based weights.Results: The method successfully identifies bins where a large point spread function degradesdetection of high spatial frequency targets. The method is also successful in determining how todownweigh highly correlated bins. Quantitative predictions for the simplified silicon detectormodel indicate that improvements in the detectability index when applying task-based weightsinstead of pixel based weights are small for high frequency targets, but could be in excess of 10%for low frequency tasks where scatter-induced correlation otherwise degrade detectability.Conclusions: The proposed method makes the spatial frequency dependency of complex correlationstructures between bins and their effect on the system detective quantum efficiency easier toanalyze and allows optimizing bin weights for given imaging tasks. A potential increase in detectabilityof double digit percents in silicon detector systems operated at typical CT energies (100kVp) merits further evaluation on a real system. The method is noted to be of higher relevancefor silicon detectors than for cadmium (zink) telluride detectors.

  • 20.
    Broomé, Michael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Frenckner, Björn
    Broman, Mikaeö
    Bjällmark, Anna
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Recirculation during veno-venous extra-corporeal membrane oxygenation: a simulation study2015Inngår i: International Journal of Artificial Organs, ISSN 0391-3988, E-ISSN 1724-6040, Vol. 38, nr 1, s. 23-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    PURPOSE:

    Veno-venous ECMO is indicated in reversible life-threatening respiratory failure without life-threatening circulatory failure. Recirculation of oxygenated blood in the ECMO circuit decreases efficiency of patient oxygen delivery but is difficult to measure. We seek to identify and quantify some of the factors responsible for recirculation in a simulation model and compare with clinical data.

    METHODS:

    A closed-loop real-time simulation model of the cardiovascular system has been developed. ECMO is simulated with a fixed flow pump 0 to 5 l/min with various cannulation sites - 1) right atrium to inferior vena cava, 2) inferior vena cava to right atrium, and 3) superior+inferior vena cava to right atrium. Simulations are compared to data from a retrospective cohort of 11 consecutive adult veno-venous ECMO patients in our department.

    RESULTS:

    Recirculation increases with increasing ECMO-flow, decreases with increasing cardiac output, and is highly dependent on choice of cannulation sites. A more peripheral drainage site decreases recirculation substantially.

    CONCLUSIONS:

    Simulations suggest that recirculation is a significant clinical problem in veno-venous ECMO in agreement with clinical data. Due to the difficulties in measuring recirculation and interpretation of the venous oxygen saturation in the ECMO drainage blood, flow settings and cannula positioning should rather be optimized with help of arterial oxygenation parameters. Simulation may be useful in quantification and understanding of recirculation in VV-ECMO.

  • 21.
    Broomé, Michael
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning.
    Maksuti, Elira
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning.
    Bjällmark, Anna
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning.
    Frenckner, Björn
    Janerot-Sjöberg, Birgitta
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning.
    Closed-loop real-time simulation model of hemodynamics and oxygen transport in the cardiovascular system2013Inngår i: Biomedical engineering online, ISSN 1475-925X, E-ISSN 1475-925X, Vol. 12, nr 1, s. 69-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Computer technology enables realistic simulation of cardiovascular physiology. The increasing number of clinical surgical and medical treatment options imposes a need for better understanding of patient-specific pathology and outcome prediction. Methods: A distributed lumped parameter real-time closed-loop model with 26 vascular segments, cardiac modelling with time-varying elastance functions and gradually opening and closing valves, the pericardium, intrathoracic pressure, the atrial and ventricular septum, various pathological states and including oxygen transport has been developed. Results: Model output is pressure, volume, flow and oxygen saturation from every cardiac and vascular compartment. The model produces relevant clinical output and validation of quantitative data in normal physiology and qualitative directions in simulation of pathological states show good agreement with published data. Conclusion: The results show that it is possible to build a clinically relevant real-time computer simulation model of the normal adult cardiovascular system. It is suggested that understanding qualitative interaction between physiological parameters in health and disease may be improved by using the model, although further model development and validation is needed for quantitative patient-specific outcome prediction.

  • 22.
    Brusini, Irene
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Jörgens, Daniel
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Smedby, Örjan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Moreno, Rodrigo
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Dependency of neural tracts'€™ curvature estimations on tractography methods2017Konferansepaper (Fagfellevurdert)
  • 23.
    Brusini, Irene
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Jörgens, Daniel
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Smedby, Örjan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Moreno, Rodrigo
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Influence of Tractography Algorithms and Settings on Local Curvature Estimations2017Konferansepaper (Fagfellevurdert)
  • 24.
    Brusini, Irene
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Jörgens, Daniel
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Smedby, Örjan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Moreno, Rodrigo
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Medicinsk avbildning.
    Voxel-Wise Clustering of Tractography Data for Building Atlases of Local Fiber Geometry2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper aims at proposing a method to generate atlases of white matter fibers’ geometry that consider local orientation and curvature of fibers extracted from tractography data. Tractography was performed on diffusion magnetic resonance images from a set of healthy subjects and each tract was characterized voxel-wise by its curvature and Frenet–Serret frame, based on which similar tracts could be clustered separately for each voxel and each subject. Finally, the centroids of the clusters identified in all subjects were clustered to create the final atlas. The proposed clustering technique showed promising results in identifying voxel-wise distributions of curvature and orientation. Two tractography algorithms (one deterministic and one probabilistic) were tested for the present work, obtaining two different atlases. A high agreement between the two atlases was found in several brain regions. This suggests that more advanced tractography methods might only be required for some specific regions in the brain. In addition, the probabilistic approach resulted in the identification of a higher number of fiber orientations in various white matter areas, suggesting it to be more adequate for investigating complex fiber configurations in the proposed framework as compared to deterministic tractography.

  • 25.
    Cahn, R N
    et al.
    -.
    Cederström, B.
    -.
    Danielsson, Mats
    KTH, Tidigare Institutioner, Fysik.
    Hall, A.
    -.
    Lundqvist, M.
    -.
    Nygren, D.
    -.
    Detective quantum efficiency dependence on x-ray energy weighting in mammography1999Inngår i: Medical physics, Vol. 26, nr 12, s. 2680-2683Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An evaluation of the dependence of detective quantum efficiency (DQE) on the incident energy spectrum has been made for mammography. The DQE dependence on the energy spectrum has been evaluated for energy-integrating detectors, photon-counting detectors, and detectors that measure the energy of each photon. To isolate the effect of the x-ray energy spectrum the detector has been assumed to be ideal, i.e., all noise sources are assumed to be zero except for quantum fluctuations. The result shows that the improvement in DQE, if the energy-integrating detector is compared to a single-photon counting detector, is of the order of 10%. Comparing the energy-integrating detector and the detector measuring the energy for each photon the improvement is around 30% using a molybdenumanodespectrum typical in mammography. It is shown that the optimal weight factors to combine the data in the case the energy is measured are very well approximated if the weight factors are proportional to E&#x2212;3." style="position: relative;" tabindex="0" id="MathJax-Element-1-Frame" class="MathJax">E−3. Another conclusion is that in calculating the DQE, a detector should be compared to one that uses ideal energy weighting for each photon since this provides the best signal-to-noise ratio. This has generally been neglected in the literature.

  • 26.
    Carrizo, Gabriel
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Organ Segmentation Using Deep Multi-task Learning with Anatomical Landmarks2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This master thesis is the study of multi-task learning to train a neural network to segment medical images and predict anatomical landmarks. The paper shows the results from experiments using medical landmarks in order to attempt to help the network learn the important organ structures quicker. The results found in this study are inconclusive and rather than showing the efficiency of the multi-task framework for learning, they tell a story of the importance of choosing the tasks and dataset wisely. The study also reflects and depicts the general difficulties and pitfalls of performing a project of this type.

    Fulltekst (pdf)
    fulltext
  • 27. Chew, MS
    et al.
    Brandberg, J
    Janerot-Sjöberg, Birgitta
    Linköping University Hospital, Sweden.
    Sloth, E
    Hasenkam, JM
    Ask, P
    Color Doppler flow measurements using surface integration of velocity vectors (SIVV): Effect of colour flow gain, pulse repetition frequency and number of imaging planes2008Inngår i: Open Medical Imaging Journal, ISSN 1874-3471, Vol. 2, s. 56-61Artikkel i tidsskrift (Fagfellevurdert)
  • 28.
    Chowdhury, Manish
    et al.
    KTH, Skolan för teknik och hälsa (STH).
    Jörgens, Daniel
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Wang, Chunliang
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering. KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildteknik.
    Smedby, Örjan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Moreno, Rodrigo
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Segmentation of Cortical Bone using Fast Level Sets2017Inngår i: MEDICAL IMAGING 2017: IMAGE PROCESSING / [ed] Styner, MA Angelini, ED, SPIE - International Society for Optical Engineering, 2017, artikkel-id UNSP 1013327Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cortical bone plays a big role in the mechanical competence of bone. The analysis of cortical bone requires accurate segmentation methods. Level set methods are usually in the state-of-the-art for segmenting medical images. However, traditional implementations of this method are computationally expensive. This drawback was recently tackled through the so-called coherent propagation extension of the classical algorithm which has decreased computation times dramatically. In this study, we assess the potential of this technique for segmenting cortical bone in interactive time in 3D images acquired through High Resolution peripheral Quantitative Computed Tomography (HR-pQCT). The obtained segmentations are used to estimate cortical thickness and cortical porosity of the investigated images. Cortical thickness and Cortical porosity is computed using sphere fitting and mathematical morphological operations respectively. Qualitative comparison between the segmentations of our proposed algorithm and a previously published approach on six images volumes reveals superior smoothness properties of the level set approach. While the proposed method yields similar results to previous approaches in regions where the boundary between trabecular and cortical bone is well defined, it yields more stable segmentations in challenging regions. This results in more stable estimation of parameters of cortical bone. The proposed technique takes few seconds to compute, which makes it suitable for clinical settings.

  • 29.
    Chowdhury, Manish
    et al.
    KTH, Skolan för teknik och hälsa (STH).
    Klintström, Benjamin
    KTH, Skolan för teknik och hälsa (STH). Linköping University, Sweden.
    Klintström, E.
    Smedby, Örjan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering. Linköping University, Sweden.
    Moreno, Rodrigo
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Granulometry-based trabecular bone segmentation2017Inngår i: 20th Scandinavian Conference on Image Analysis, SCIA 2017, Springer, 2017, Vol. 10270, s. 100-108Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The accuracy of the analyses for studying the three dimensional trabecular bone microstructure rely on the quality of the segmentation between trabecular bone and bone marrow. Such segmentation is challenging for images from computed tomography modalities that can be used in vivo due to their low contrast and resolution. For this purpose, we propose in this paper a granulometry-based segmentation method. In a first step, the trabecular thickness is estimated by using the granulometry in gray scale, which is generated by applying the opening morphological operation with ball-shaped structuring elements of different diameters. This process mimics the traditional sphere-fitting method used for estimating trabecular thickness in segmented images. The residual obtained after computing the granulometry is compared to the original gray scale value in order to obtain a measurement of how likely a voxel belongs to trabecular bone. A threshold is applied to obtain the final segmentation. Six histomorphometric parameters were computed on 14 segmented bone specimens imaged with cone-beam computed tomography (CBCT), considering micro-computed tomography (micro-CT) as the ground truth. Otsu’s thresholding and Automated Region Growing (ARG) segmentation methods were used for comparison. For three parameters (Tb.N, Tb.Th and BV/TV), the proposed segmentation algorithm yielded the highest correlations with micro-CT, while for the remaining three (Tb.Nd, Tb.Tm and Tb.Sp), its performance was comparable to ARG. The method also yielded the strongest average correlation (0.89). When Tb.Th was computed directly from the gray scale images, the correlation was superior to the binary-based methods. The results suggest that the proposed algorithm can be used for studying trabecular bone in vivo through CBCT.

  • 30.
    Chowdhury, Manish
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Rota Bulò, S.
    Moreno, Rodrigo
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    Kundu, M.K.
    Smedby, Örjan
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk bildbehandling och visualisering.
    An Efficient Radiographic Image Retrieval System Using Convolutional Neural Network2016Inngår i: 2016 23rd International Conference on Pattern Recognition (ICPR), Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 3134-3139, artikkel-id 7900116Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Content-Based Medical Image Retrieval (CBMIR) is an important research field in the context of medical data management. In this paper we propose a novel CBMIR system for the automatic retrieval of radiographic images. Our approach employs a Convolutional Neural Network (CNN) to obtain high- level image representations that enable a coarse retrieval of images that are in correspondence to a query image. The retrieved set of images is refined via a non-parametric estimation of putative classes for the query image, which are used to filter out potential outliers in favour of more relevant images belonging to those classes. The refined set of images is finally re-ranked using Edge Histogram Descriptor, i.e. a low-level edge-based image descriptor that allows to capture finer similarities between the retrieved set of images and the query image. To improve the computational efficiency of the system, we employ dimensionality reduction via Principal Component Analysis (PCA). Experiments were carried out to evaluate the effectiveness of the proposed system on medical data from the “Image Retrieval in Medical Applications” (IRMA) benchmark database. The obtained results show the effectiveness of the proposed CBMIR system in the field of medical image retrieval.

    Fulltekst (pdf)
    fulltext
  • 31.
    da Silva, Joakim
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Grönberg, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik. Prismatic Sensors AB, Stockholm, Sweden.
    Cederström, Björn
    Persson, Mats
    Sjölin, Martin
    Alagic, Zlatan
    Bujila, Robert
    KTH, Skolan för teknikvetenskap (SCI), Fysik. Karolinska University Hospital, Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden.
    Danielsson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik. Prismatic Sensors AB, Stockholm, Sweden.
    Resolution characterization of a silicon-based, photon-counting computed tomography prototype capable of patient scanning2019Inngår i: Journal of Medical Imaging, ISSN 2329-4302, E-ISSN 2329-4310, Vol. 6, nr 4, artikkel-id 043502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Photon-counting detectors are expected to bring a range of improvements to patient imaging with x-ray computed tomography (CT). One is higher spatial resolution. We demonstrate the resolution obtained using a commercial CT scanner where the original energy-integrating detector has been replaced by a single-slice, silicon-based, photon-counting detector. This prototype constitutes the first full-field-of-view silicon-based CT scanner capable of patient scanning. First, the pixel response function and focal spot profile are measured and, combining the two, the system modulation transfer function is calculated. Second, the prototype is used to scan a resolution phantom and a skull phantom. The resolution images are compared to images from a state-of-the-art CT scanner. The comparison shows that for the prototype 19 lp∕cm are detectable with the same clarity as 14 lp∕cm on the reference scanner at equal dose and reconstruction grid, with more line pairs visible with increasing dose and decreasing image pixel size. The high spatial resolution remains evident in the anatomy of the skull phantom and is comparable to that of other photon-counting CT prototypes present in the literature. We conclude that the deep silicon-based detector used in our study could provide improved spatial resolution in patient imaging without increasing the x-ray dose.

    Fulltekst (pdf)
    fulltext
  • 32.
    Darvish, Darvish
    et al.
    KTH, Skolan för teknik och hälsa (STH).
    Öçba, F.Nadideh
    KTH, Skolan för teknik och hälsa (STH).
    Presentation and evaluation of gated-SPECT myocardial perfusion images: Radial Slices - data reduction without  loss  of  information2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

     

    Single photon emission tomography (SPECT) data from myocardial perfusion imaging (MPI) are normally displayed as a set of three slices orthogonal to the left ventricular (LV) long axis for both ECG-gated (GSPECT) and non-gated SPECT studies. The total number of slices presented for assessment depends on the size of the heart, but is typically in excess of 30. 

    A requirement for data presentation is that images should be orientated about the LV axis; therefore, a set of radial slice would fulfill this need. Radial slices are parallel to the LV long axis and arranged diametrically. They could provide a suitable alternative to standard orthogonal slices, with the advantage of requiring far fewer slices to adequately represent the data.

    In this study a semi-automatic method was developed for displaying MPI SPECT data as a set of radial slices orientated about the LV axis, with the aim of reducing the number of slices viewed, without loss of information and independent on the size of the heart. Input volume data consisted of standard short axis slices orientated perpendicular to the LV axis chosen at the time of reconstruction.

     The true LV axis was determined by first determining the boundary on a central long axis slice, the axis being in the direction of the y-axis in the matrix. The skeleton of the myocardium were found and the true LV axis determined for that slice. The angle of this axis with respect to the y-axis was calculated. The process was repeated for an orthogonal long axis slice. The input volume was then rotated by the angles calculated.

    Radial slices generated for presentation were integrated over a sector equivalent to the imaging resolution (1.2 cm); assuming the diameter of the heart is about 8cm then non-gated data could be represented by 20 radial slices integrated over an 18 degree section. Gated information could be represented with four slices spaced at 45 intervals, integrated over a 30 degree sector.

    Fulltekst (pdf)
    Presentation and evaluation of gated-SPECT
  • 33.
    del Aguila Pla, Pol
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Inverse problems in signal processing: Functional optimization, parameter estimation and machine learning2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Inverse problems arise in any scientific endeavor. Indeed, it is seldom the case that our senses or basic instruments, i.e., the data, provide the answer we seek. It is only by using our understanding of how the world has generated the data, i.e., a model, that we can hope to infer what the data imply. Solving an inverse problem is, simply put, using a model to retrieve the information we seek from the data.

    In signal processing, systems are engineered to generate, process, or transmit signals, i.e., indexed data, in order to achieve some goal. The goal of a specific system could be to use an observed signal and its model to solve an inverse problem. However, the goal could also be to generate a signal so that it reveals a parameter to investigation by inverse problems. Inverse problems and signal processing overlap substantially, and rely on the same set of concepts and tools. This thesis lies at the intersection between them, and presents results in modeling, optimization, statistics, machine learning, biomedical imaging and automatic control.

    The novel scientific content of this thesis is contained in its seven composing publications, which are reproduced in Part II. In five of these, which are mostly motivated by a biomedical imaging application, a set of related optimization and machine learning approaches to source localization under diffusion and convolutional coding models are presented. These are included in Publications A, B, E, F and G, which also include contributions to the modeling and simulation of a specific family of image-based immunoassays. Publication C presents the analysis of a system for clock synchronization between two nodes connected by a channel, which is a problem of utmost relevance in automatic control. The system exploits a specific node design to generate a signal that enables the estimation of the synchronization parameters. In the analysis, substantial contributions to the identifiability of sawtooth signal models under different conditions are made. Finally, Publication D brings to light and proves results that have been largely overlooked by the signal processing community and characterize the information that quantized linear models contain about their location and scale parameters.

    Fulltekst (pdf)
    delAguilaPla_PhDthesis.pdf
  • 34.
    del Aguila Pla, Pol
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Cell detection by functional inverse diffusion and non-negative group sparsity – Part I: Modeling and Inverse Problems2018Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 66, nr 20, s. 5407-5421Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this two-part paper, we present a novel framework and methodology to analyze data from certain image-based biochemical assays, e.g., ELISPOT and Fluorospot assays. In this first part, we start by presenting a physical partial differential equations (PDE) model up to image acquisition for these biochemical assays. Then, we use the PDEs' Green function to derive a novel parametrization of the acquired images. This parametrization allows us to propose a functional optimization problem to address inverse diffusion. In particular, we propose a non-negative group-sparsity regularized optimization problem with the goal of localizing and characterizing the biological cells involved in the said assays. We continue by proposing a suitable discretization scheme that enables both the generation of synthetic data and implementable algorithms to address inverse diffusion. We end Part I by providing a preliminary comparison between the results of our methodology and an expert human labeler on real data. Part II is devoted to providing an accelerated proximal gradient algorithm to solve the proposed problem and to the empirical validation of our methodology.

    Fulltekst (pdf)
    fulltext
  • 35.
    del Aguila Pla, Pol
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Cell detection by functional inverse diffusion and non-negative group sparsity – Part II: Proximal optimization and Performance evaluation2018Inngår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 66, nr 20, s. 5422-5437Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this two-part paper, we present a novel framework and methodology to analyze data from certain image-based biochemical assays, e.g., ELISPOT and Fluorospot assays. In this second part, we focus on our algorithmic contributions. We provide an algorithm for functional inverse diffusion that solves the variational problem we posed in Part I. As part of the derivation of this algorithm, we present the proximal operator for the non-negative group-sparsity regularizer, which is a novel result that is of interest in itself, also in comparison to previous results on the proximal operator of a sum of functions. We then present a discretized approximated implementation of our algorithm and evaluate it both in terms of operational cell-detection metrics and in terms of distributional optimal-transport metrics.

    Fulltekst (pdf)
    fulltext
  • 36.
    del Aguila Pla, Pol
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Cell detection on image-based immunoassays2018Inngår i: 2018 IEEE 15th International Symposium on Biomedical Imaging (ISBI 2018), IEEE, 2018, s. 431-435Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cell detection and counting in the image-based ELISPOT and Fluorospot immunoassays is considered a bottleneck.The task has remained hard to automatize, and biomedical researchers often have to rely on results that are not accurate.Previously proposed solutions are heuristic, and data-based solutions are subject to a lack of objective ground truth data. In this paper, we analyze a partial differential equations model for ELISPOT, Fluorospot, and assays of similar design. This leads us to a mathematical observation model forthe images generated by these assays. We use this model to motivate a methodology for cell detection. Finally, we provide a real-data example that suggests that this cell detection methodology and a human expert perform comparably.

    Fulltekst (pdf)
    delAguilaPla_Jalden_2018
  • 37.
    del Aguila Pla, Pol
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Saxena, Vidit
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Jaldén, Joakim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    SpotNet – Learned iterations for cell detection in image-based immunoassays2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Accurate cell detection and counting in the image-based ELISpot and FluoroSpot immunoassays is a challenging task. Recently proposed methodology matches human accuracy by leveraging knowledge of the underlying physical process of these assays and using proximal optimization methods to solve an inverse problem. Nonetheless, thousands of computationally expensive iterations are often needed to reach a near-optimal solution. In this paper, we exploit the structure of the iterations to design a parameterized computation graph, SpotNet, that learns the patterns embedded within several training images and their respective cell information. Further, we compare SpotNet to a convolutional neural network layout customized for cell detection. We show empirical evidence that, while both designs obtain a detection performance on synthetic data far beyond that of a human expert, SpotNet is easier to train and obtains better estimates of particle secretion for each cell.

    Fulltekst (pdf)
    ISBI2019_delAguilaPla_Saxena_Jalden
  • 38.
    Demeulemeester, Kilian
    KTH, Skolan för datavetenskap och kommunikation (CSC).
    Needle Localization in Ultrasound Images: FULL NEEDLE AXIS AND TIP LOCALIZATION IN ULTRASOUND IMAGES USING GPS DATA AND IMAGE PROCESSING2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Many medical interventions involve ultrasound based imaging systems to safely localize and navigate instruments into the patient body. To facilitate visual tracking of the instruments, we investigate the techniques and methodologies best suited for solving the problem of needle localization in ultrasound images.

    We propose a robust procedure that automatically determines the position of a needle in 2D ultrasound images. Such a task is decomposed into the localization of the needle axis and its tip. A first estimation of the axis position is computed with the help of multiple position sensors, including one embedded in the transducer and another in the needle. Based on this, the needle axis is computed using a RANSAC algorithm. The tip is detected by analyzing the intensity along the axis and a Kalman filter is added to compensate for measurement uncertainties.

    The algorithms were experimentally verified on real ultrasound images acquired by a 2D scanner scanning a portion of a cryogel phantom that contained a thin metallic needle. The experiments shows that the algorithms are capable of detecting a needle at millimeter accuracy.The computational time of the order of milliseconds permits real time needle localization.

    Fulltekst (pdf)
    fulltext
  • 39.
    Elmstedt, Nina
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Prenatal Tisse Velocity Imaging of the Heart: A new approach to assess fetal myocardial function2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The general aim of this thesis has been to evaluate color‐coded tissue velocity imaging (TVI) as an approach to developing a new, non‐invasive assessment method for fetal myocardial function. Such a method could hypothetically give early indications of fetal pathology, as myocardial dysfunction is often the consequence when the circulation tries to adapt to deteriorating situations. This would be beneficial in clinical decision making when evaluating fetal well‐being in a wide range of pregnancy associated conditions, to facilitate risk assessment and to monitor the benefit of therapeutic interventions.

    TVI is an ultrasound technique that enables quantification of longitudinal myocardial motion with high temporal resolution, which is essential in the identification of fetal myocardial movements of short duration. Furthermore, the longitudinal motion is mainly determined by subendocardial fibers that usually become abnormal in the very early stages of cardiac dysfunction as they are sensitive to milder degrees of hypoxia. Thus, TVI has the potential to give early indications of impaired fetal myocardial function and hypothetically facilitate the detection of intrauterine hypoxia. Hypoxia is a common phenomenon of many pathological conditions in pregnancy, from which a substantial number of children either die or acquire permanent brain injury during delivery every year.

    After having established optimal sampling requirements and ensured an acceptable reproducibility for TVI measurements of the fetal myocardium, normal reference values were determined feasible and sensitive enough to provide insight into maturational changes in myocardial function. This provided a foundation that should enable further investigations and was partly accomplished using the cardiac state diagram (CSD) to accurately time the myocardial events during a cardiac cycle according to the motion shifts of the atrioventricular plane.

    The demonstrated results are promising and the general conclusion of this thesis is that TVI contributes to increasing the knowledge and understanding of fetal myocardial function and dysfunction. Used together with CSD this technique has great potential as an assessment method. However, further testing of the clinical potential is needed in larger study populations concerning the pathological or physiological questions at issue, and additional development of the method is required to render the method simple enough to be of potential aid in clinical practice.

    Fulltekst (pdf)
    fulltext
  • 40.
    Elmstedt, Nina
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Johnson, Jonas
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Lind, Britta
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Ferm-Widlund, Kjerstin
    CFM, Karolinska Universitetssjukhuset.
    Westgren, Magnus
    CFM, Karolinska Universitetssjukhuset.
    Brodin, Lars-Åke
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Reference values for fetal tissue velocity imaging and a new approach to evaluate fetal myocardial function2013Inngår i: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 11, nr 1, s. 29-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: Myocardial function can be evaluated using color-coded tissue velocity imaging (TVI) to analyze the longitudinal myocardial velocity profile, and by expressing the motion of the atrioventricular plane during a cardiac cycle as coordinated events in the cardiac state diagram (CSD). The objective of this study was to establish gestational age specific reference values for fetal TVI measurements and to introduce the CSD as a potential aid in fetal myocardial evaluation. Methods: TVI recordings from 125 healthy fetuses, at 18 to 42 weeks of gestation, were performed with the transducer perpendicular to the apex to provide a four-chamber view. The myocardial velocity data was extracted from the basal segment of septum as well as the left and right ventricular free wall for subsequent offline analysis. Results: During a cardiac cycle the longitudinal peak velocities of septum increased with gestational age, as did the peak velocities of the left and right ventricular free wall, except for the peak velocity of post ejection. The duration of rapid filling and atrial contraction increased during pregnancy while the duration of post ejection decreased. The duration of pre ejection and ventricular ejection did not change significantly with gestational age. Conclusion: Evaluating fetal systolic and diastolic performance using TVI together with CSD could contribute to increase the knowledge and understanding of fetal myocardial function and dysfunction. The pre and post ejection phases are the variables most likely to indicate fetuses with abnormal myocardial function.

  • 41.
    Elmstedt, Nina
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Lind, Britta
    KTH, Skolan för teknik och hälsa (STH).
    Ferm-Widlund, Kjerstin
    CFM, Karolinska Universitetssjukhuset.
    Westgren, Magnus
    CFM, Karolinska Universitetssjukhuset.
    Brodin, Lars-Åke
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Reproducibility and variability in the assessment of color-coded tissue velocity imaging of the fetal myocardium2013Inngår i: Journal of biomedical graphics and computing, ISSN 1925-4008, Vol. 3, nr 2Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: The introduction of color-coded tissue velocity imaging (TVI) in fetal medicine is quite recent, and as this method is presently evaluated and developed in regard to diagnostic precision it is of outmost importance to evaluate the reproducibility for adequate clinical use. In this study, reproducibility and intra- and inter-observer variability was assessed for offline analysis as well as echocardiography investigations. Also, we evaluated the importance of exact placement of the region of interest (ROI).

    Methods: TVI recordings from 21 fetuses, at a gestational age of 27 to 41 weeks, were acquired at 208-239 frames/s for subsequent offline analysis. All recordings were performed with the transducer positioned to provide an apical four-chamber view and the myocardial velocity data was obtained from basal inferoseptum. The data set was analyzed according to Bland-Altman and reproducibility was expressed as the standard error of a single determination, estimated from duplicate determinations in percentage of the total.

    Results: The variation of reproducibility for the echocardiography investigation ranged from 2.0% to 9.8%. The duration of left ventricular ejection, and the peak velocities of early diastolic filling and atrial contraction being the most robust events measured. The variation of inter-observer variability for the echocardiography investigation ranged from 1.5% to 8.4%, and the variation of intra- and inter-observer variability for the offline analysis ranged from 1.2% to 10.4%. Least robust were the events of shortest duration, including isovolumetric contraction and relaxation.

    Conclusion: We believe that TVI measurements of the fetal myocardium could be performed in the clinical routine with acceptable reproducibility.

  • 42.
    Gasser, T. Christian
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Bringing vascular biomechanics into clinical practice. Simulation-based decisions for elective abdominal aortic aneurysms repair2012Inngår i: Lecture Notes in Computational Vision and Biomechanics, ISSN 2212-9391, E-ISSN 2212-9413, Vol. 5, s. 1-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vascular diseases are the leading cause of death in the industrialized countries and some of the associated risk factors are increasing. A multi-disciplinary approach including biomechanics is needed to better understand and more effectively treat these diseases. Despite the tremendous progress made in modeling the biomechanics of the vasculature, so far this research has accomplished only very limited clinical relevance or acceptance. Establishing vascular biomechanical simulations in the clinical work-flow requires integrating (i) a robust reconstruction of vascular bodies from medical images, (ii) a non-linear biomechanical analysis and (iii) a clinically relevant interpretation of the derived results. Such an approach is outlined for the biomechanical rupture risk assessment of Abdominal Aortic Aneurysms (AAAs), i.e. a local dilatation of the infrarenal aorta that may form through irreversible pathological remodeling of the aortic wall. Rupture of an AAA is a frequent cause of death in the elderly male population and assessing this risk plays a central role in the clinical management of aneurysms. Specifically, the present chapter details an operator-insensitive method to reconstruct vascular bodies from Computer Tomography-Angiography data. The approach is based on beam and shell-like deformable (active) contour models and allows a hexahedral-dominated mesh generation for an efficient Finite Element computation. Laboratory experiments and histo-mechanical constitutive modeling of AAA tissue are reviewed. Finally, the clinical application of the biomechanical rupture risk assessment is demonstrated through the especially developed software A4clinics. Most critically, individual biomechanical parameters are related to the ‘average AAA patient’, which in turn provides a biomechanics-based index for elective AAA repair indication. © 2012, Springer Science+Business Media Dordrecht.

  • 43.
    Grishenkov, Dmitry
    et al.
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning. Karolinska Institute, Sweden.
    Adrian, Gonon
    Karolinska University Hospital, Sweden.
    Janerot Sjöberg, Birgitta
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik, Medicinsk avbildning. Karolinska Institute, Sweden.
    In search of the optimal ultrasound heart perfusion imaging platform2015Inngår i: Journal of ultrasound in medicine, ISSN 0278-4297, E-ISSN 1550-9613, Vol. 34, nr 9, s. 1599-1605Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective

    Quantification of the myocardial perfusion by contrast echocardiography (CEC) remains a challenge. Existing imaging phantoms used to evaluate the performance of ultrasound scanners do not comply with perfusion basics in the myocardium, where perfusion and motion are inherently coupled.

    Methods

    To contribute towards an improvement, we developed a CEC perfusion imaging platform based on isolated rat heart coupled to the ultrasound scanner. Perfusion was assessed using three different types of contrast agent: dextran-based Promiten®, phospholipid-shelled SonoVue®, and polymer-shelled MB-pH5-RT. The myocardial video-intensity was monitored over time from contrast administration to peak and two characteristic constants were calculated using exponential fit (A representing capillary volume and b representing inflow velocity).

    Results

    Acquired experimental evidence demonstrates that the application of all three types of contrast agent allow ultrasonic estimation of myocardial perfusion in the isolated rat heart. Video-intensity maps show that an increase in contrast concentration increases the late plateau values, A, mimicking increased capillary volume. Estimated values of the flow, proportional to Axb, increase when the pressure of the perfusate column increases from 80 to 110 cm of water. This finding is in agreement with the true values of the coronary flow increase measured by the flowmeter attached to the aortic cannula.

    Conclusions

    The described CEC perfusion imaging platform holds promise for standardized evaluation and optimization of ultrasound contrast perfusion imaging where real time inflow curves at low acoustic power semi-quantitatively reflect coronary flow.

  • 44.
    Grönberg, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Persson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Bornefalk, Hans
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Image reconstruction based on energy-resolved image data from a photon-counting multi-bin detector2015Patent (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    There is provided a method of image reconstruction based on energy-resolved image data from a photon-counting multi-bin detector or an intermediate storage. The method comprises processing (S1) the energy-resolved image data by performing at least two separate basis decompositions using different number of basis functions for modeling linear attenuation, wherein a first basis decomposition is performed using a first smaller set of basis functions to obtain at least one first basis image representation, and wherein a second basis decomposition is performed using a second larger set of basis functions to obtain at least one second basis image representation. The method also comprises reconstructing a first image based on said at least one first basis image representation obtained from the first basis decomposition, and combining the first image with information representative of said at least one second basis image representation.

  • 45.
    Grönberg, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Persson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Bornefalk, Hans
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Third material separation in spectral CT with basis decomposition2015Konferansepaper (Annet vitenskapelig)
  • 46.
    Grönberg, Fredrik
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Sjölin, Martin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Danielsson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Medicinsk bildfysik.
    Count statistics and pileup correction for nonparalyzable photon counting detectors with finite pulse length2018Inngår i: Medical Imaging 2018: Physics Of Medical Imaging / [ed] Lo, JY Schmidt, TG Chen, GH, SPIE - International Society for Optical Engineering, 2018, artikkel-id UNSP 105730ZKonferansepaper (Fagfellevurdert)
    Abstract [en]

    Photon counting detectors are expected to be the next big step in the development of medical computed tomography. Accurate modeling of the behavior of photon counting detectors in the high count rate regime is therefore important for detector performance evaluations and the development of accurate image reconstruction methods. The commonly used ideal nonparalyzable detector model is based on the assumption that photon interactions are converted to pulses with zero extent in time, which is too simplistic to accurately predict the behavior of photon counting detectors in both low and high count rate regimes. In this work we develop a statistical count model for a nonparalyzable detector with finite pulse length and use it to derive the asymptotic mean and variance of the output count distribution using tools from renewal theory. We use the statistical moments of the distribution to construct an estimator of the true number of counts for pileup correction. We con firm the accuracy of the model and evaluate the pileup correction using Monte Carlo simulations. The results show that image quality is preserved for surprisingly high count rates.

  • 47.
    Gyllencreutz, E.
    et al.
    Karolinska Inst, Stockholm, Sweden.;Ostersund Hosp, Dept Obstet & Gynecol, Ostersund, Sweden..
    Lu, Ke
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Hälsoinformatik.
    Lindecrantz, Kaj
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Hälsoinformatik. Karolinska Inst, Stockholm, Sweden.
    Lindqvist, P.
    Karolinska Inst, Stockholm, Sweden..
    Nordström, L.
    Karolinska Inst, Stockholm, Sweden..
    Holzmann, M.
    Karolinska Inst, Stockholm, Sweden.;Karolinska Univ Hosp, Dept Obstet & Gynecol, Stockholm, Sweden..
    Abtahi, F.
    Karolinska Inst, Stockholm, Sweden.;Karolinska Univ Hosp, Dept Clin Physiol, Stockholm, Sweden..
    Validation of a computerised algorithm to quantify fetal heart rate deceleration area: An observational study2018Inngår i: British Journal of Obstetrics and Gynecology, ISSN 1470-0328, E-ISSN 1471-0528, Vol. 125, s. 54-54Artikkel i tidsskrift (Annet vitenskapelig)
  • 48.
    Hamid Muhammed, Hamed
    KTH, Skolan för teknik och hälsa (STH), Medicinsk teknik.
    Image Enhancement Combined with Reduction of X-Ray Dose During PCI-Operations2010Konferansepaper (Annet vitenskapelig)
  • 49.
    Hamid Muhammed, Hamed
    et al.
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap, Systemsäkerhet och organisation.
    Azar, Jimmy C
    Centre for Image Analysis, Uppsala University.
    Semi-Automated Classification of the Physiological Condition of the Carotid Artery in 2D Ultrasound Image Sequences2014Inngår i: WSEAS Transactions on Biology and Biomedicine, ISSN 1109-9518, E-ISSN 2224-2902, ISSN E-ISSN 2224-2902, Vol. 11, s. 35-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract: -A novel automated method for the classification of the physiological condition of the carotid arteryin 2D ultrasound image sequences is introduced. Unsupervised clustering was applied for the segmentationprocess in which both spatial and temporal information was utilized. Radial distension is then measured in theinner surface of the vessel wall, and this characteristic signal is extracted to reveal the detailed radial motion ofthe variable inner part of the vessel wall that is in contact with flowing blood. Characteristic differences in thistime signal were noticed among healthy young, healthy elderly and pathological elderly cases. The discreteFourier transform of the radial distension signal is then computed, and the area subtended by the transform iscalculated and utilized as a diagnostic feature. The method was tested successfully and could differentiateamong the categories of patients mentioned above. Therefore, this computer-aided method would significantlysimplify the task of medical specialists in detecting any defects in the carotid artery and thereby in detectingearly cardiovascular symptoms. The significance of the proposed method is that it is intuitive, semi-automatic,reproducible, and significantly reduces the reliance upon subjective measures.

    Fulltekst (pdf)
    fulltext
  • 50.
    Hamid Muhammed, Hamed
    et al.
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap.
    Darvish, Niloufar
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap.
    Öçba, Fatma Nadide
    KTH, Skolan för teknik och hälsa (STH), Hälso- och systemvetenskap.
    Bone, Dianna
    Karolinska Hospital, SE-17671 Stockholm, Sweden.
    A New Approach to the Presentation of Myocardial SPECT Images: Radial Slices—Data Reduction without Loss of Information2013Inngår i: Engineering, ISSN 1947-394X, Vol. 5, nr 10BArtikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: SPECT data from myocardial perfusion imaging (MPI) are normally displayed as a set of three slices orthogonal to the left ventricular (LV) long axis. For data presentation, the images are orientated about the LV long axis. Therefore, radial slices provide a suitable alternative to standard orthogonal slices, with the advantage of requiring fewer slices to adequately represent the data. In this study, a semi-automatic method is developed for displaying MPI SPECT data as a set of radial slices orientated about the LV axis. The aim is to reduce the number of slices viewed without loss of information and independently from the heart size. Method: Standard short axis slices, orientated perpendicular to the LV axis, are utilized.The skeleton of the segmented myocardium is found and the true LV axis is determined in each central long slice. The LV axis of the whole volume is determined by aligning the axes of all slices. Result: Radial slices centered about this axis were generated by integration over a sector equal to the resolution of the imaging system which was of the order of 1.2 cm. Therefore, assuming a mean LV diameter of 8 cm, 20 slices were sufficient to represent a non-gated study. Gated information could be adequately displayed with 4 slices integrated over an angle of 45. Conclusion: A semi-automatic method for generating radial slices from SPECT MPI short axis slices has been developed.

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