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  • 1. Aleman, Dionne M.
    et al.
    Glaser, Daniel
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Romeijn, H. Edwin
    Dempsey, James F.
    Interior point algorithms: guaranteed optimality for fluence map optimization in IMRT2010In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 55, no 18, p. 5467-5482Article in journal (Refereed)
    Abstract [en]

    One of the most widely studied problems of the intensity-modulated radiation therapy (IMRT) treatment planning problem is the fluence map optimization (FMO) problem, the problem of determining the amount of radiation intensity, or fluence, of each beamlet in each beam. For a given set of beams, the fluences of the beamlets can drastically affect the quality of the treatment plan, and thus it is critical to obtain good fluence maps for radiation delivery. Although several approaches have been shown to yield good solutions to the FMO problem, these solutions are not guaranteed to be optimal. This shortcoming can be attributed to either optimization model complexity or properties of the algorithms used to solve the optimization model. We present a convex FMO formulation and an interior point algorithm that yields an optimal treatment plan in seconds, making it a viable option for clinical applications.

  • 2.
    Bergenwall, B.
    et al.
    Department of Radiation Sciences, Uppsala University, Box 535, S-751 21 Uppsala, Sweden..
    Ataç, Ayşe
    Department of Radiation Sciences, Uppsala University, Box 535, S-751 21 Uppsala, Sweden..
    Kullander, S.
    Department of Radiation Sciences, Uppsala University, Box 535, S-751 21 Uppsala, Sweden..
    Experimental kerma coefficients for carbon deduced from microscopic cross sections at 96 MeV incident neutron energy2004In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 49, no 19, p. 4523-4542Article in journal (Refereed)
    Abstract [en]

    The double-differential cross sections for (n, px), (n, dx), (n, tx), (n, (3)Hex) and (n, alphax) reactions in carbon have been measured at 96 MeV incident neutron energy. The various charged particles (inclusive spectra) were identified using A E-E techniques. From the experimental data, energy- and angle-differential as well as production cross sections were determined, and subsequently the partial and total kerma coefficients. The deduced partial and total kerma coefficients were compared to previous experimental results and theoretical calculations. The findings indicate that the deduced kerma coefficients for the hydrogen isotopes are in good agreement with those deduced from a previous measurement, and that the kerma coefficient values, in particular of the hydrogen isotopes, are systematically higher than values obtained from recent model calculations, which consequently resulted in a total kerma coefficient which is up to 30% higher than predicted by the calculations.

  • 3.
    Berggren, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Royal Inst Technol KTH, Dept Phys, Stockholm, Sweden.;Philips Mammog Solut, Kista, Sweden..
    Eriksson, Mikael
    Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden..
    Hall, Per
    Karolinska Inst, Dept Med Epidemiol & Biostat, Stockholm, Sweden.;South Gen Hosp, Dept Oncol, Stockholm, Sweden..
    Walliss, Matthew G.
    Addenbrookes Hosp, Cambridge Breast Unit, Cambridge, England.;Addenbrookes Hosp, NIHR Cambridge Biomed Res Ctr, Cambridge, England..
    Fredenberg, Erik
    Philips Res, Kista, Sweden..
    In vivo measurement of the effective atomic number of breast skin using spectral mammography2018In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, no 21, article id 215023Article in journal (Refereed)
    Abstract [en]

    X-ray characteristics of body tissues are of crucial importance for developing and optimizing x-ray imaging techniques, in particular for dosimetry and spectral imaging applications. For breast imaging, the most important tissues are fibro-glandular, adipose and skin tissue. Some work has and is being done to better characterize these tissue types, in particular fibro-glandular and adipose tissue. In the case of breast skin, several recent studies have been published on the average skin thickness, but with regards to x-ray attenuation, the only published data, to the knowledge of the authors, is the elemental composition analysis of Hammerstein et al (1979 Radiology 130 485-91). This work presents an overview of breast skin thickness studies and a measurement of the effective atomic number (Z(eff)) of breast skin using spectral mammography. Z(eff), which together with the density forms the attenuation, is used to validate the work by Hammerstein et al, and the dependence of clinical parameters on Z(eff) is explored. Measurements were conducted on the skin edge of spectral mammograms using clinical data from a screening population (n = 709). The weighted average of breast skin thickness reported in studies between 1997 and 2013 was found to be 1.56 +/- 0.28 mm. Mean Z(eff) was found to be 7.365 (95% CI: 7.364,7.366) for normal breast skin and 7.441 (95% CI: 7.440,7.442) for the nipple and areola. Z(eff) of normal breast skin is in agreement with Hammerstein et al, despite the different methods and larger sample size used. A small but significant increase in Z(eff) was found with age, but the increase is too small to be relevant for most applications. We conclude that normal breast skin is well described by a 1.56 mm skin layer and the elemental composition presented by Hammerstein et al (1979 Radiology 130 485-91) and recommend using these characteristics when modelling breast skin.

  • 4.
    Bokrantz, Rasmus
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed approximation of Pareto surfaces in multicriteria radiation therapy treatment planning2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 11, p. 3501-3516Article in journal (Refereed)
    Abstract [en]

    We consider multicriteria radiation therapy treatment planning by navigationover the Pareto surface, implemented by interpolation between discretetreatment plans. Current state of the art for calculation of a discreterepresentation of the Pareto surface is to sandwich this set between inner andouter approximations that are updated one point at a time. In this paper, wegeneralize this sequential method to an algorithm that permits parallelization.The principle of the generalization is to apply the sequential method to anapproximation of an inexpensive model of the Pareto surface. The informationgathered from the model is sub-sequently used for the calculation of pointsfrom the exact Pareto surface, which are processed in parallel. The model isconstructed according to the current inner and outer approximations, and givena shape that is difficult to approximate, in order to avoid that parts of the Paretosurface are incorrectly disregarded. Approximations of comparable quality tothose generated by the sequential method are demonstrated when the degree ofparallelization is up to twice the number of dimensions of the objective space.For practical applications, the number of dimensions is typically at least five,so that a speed-up of one order of magnitude is obtained.

  • 5.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Synthetic Hounsfield units from spectral CT data2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 7, p. N83-N87Article in journal (Refereed)
    Abstract [en]

    Beam-hardening-free synthetic images with absolute CT numbers that radiologists are used to can be constructed from spectral CT data by forming 'dichromatic' images after basis decomposition. The CT numbers are accurate for all tissues and the method does not require additional reconstruction. This method prevents radiologists from having to relearn new rules-of-thumb regarding absolute CT numbers for various organs and conditions as conventional CT is replaced by spectral CT. Displaying the synthetic Hounsfield unit images side-by-side with images reconstructed for optimal detectability for a certain task can ease the transition from conventional to spectral CT.

  • 6.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Photon-counting spectral computed tomography using silicon strip detectors: a feasibility study2010In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 55, no 7, p. 1999-2022Article in journal (Refereed)
    Abstract [en]

    We show how the spectral imaging framework should be modified to account for a high fraction of Compton interactions in low Z detector materials such as silicon. Using this framework, where deposited energies differ from actual photon energies, we compare the performance of a silicon strip detector, including the influence of scatter inside the detector and charge sharing but disregarding signal pileup, with an ideal energy integrating detector. We show that although the detection efficiency for silicon rapidly drops for the acceleration voltages encountered in clinical computed tomography practice, silicon detectors could perform on a par with ideal energy integrating detectors for routine imaging tasks. The use of spectrally sensitive detectors opens up the possibility for decomposition techniques such as k-edge imaging, and we show that the proposed modification of the spectral imaging framework is beneficial for such imaging tasks.

  • 7.
    Chen, Han
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Size-dependent scanning parameters (kVp and mAs) for photon-counting spectral CT system in pediatric imaging: simulation study2016In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 61, no 11Article in journal (Refereed)
    Abstract [en]

    We are developing a photon-counting spectral CT detector with small pixel size of 0.40.5 mm2, o ering a potentialadvantage for better visualization of small structures in pediatric patients. The purpose of this study is to determinethe patient size dependent scanning parameters (kVp and mAs) for pediatric CT in two imaging cases: adipose imagingand iodinated blood imaging.Cylindrical soft-tissue phantoms of diameters between 10-25 cm were used to mimic patients of di erent ages from 0-15 y. For adipose imaging, a 5-mm-diameter adipose sphere was assumed as an imaging target, while an iodinated bloodsphere of 1 mm in diameter was assumed in the case of iodinated imaging. By applying the geometry of a commercial CTscanner (GE LightSpeed VCT), simulations were carried out to calculate the detectability index,d02, with tube potentialsvarying from 40 to 140 kVp. The optimal kVp for each phantom in each imaging case was determined such that the dose-normalized detectability index,d02=dose, is maximized. With the assumption that image quality in pediatric imagingis required the same as in typical adult imaging, the value of mAs at optimal kVp for each phantom was selected toachieve a reference detectability index that was obtained by scanning an adult phantom (30 cm in diameter) in a typicaladult CT procedure (120 kVp and 200 mAs) using a modeled energy-integrating system.For adipose imaging, the optimal kVps are 50, 60, 80, and 120 kVp, respectively, for phantoms of 10, 15, 20, and25-cm in diameter. The corresponding mAs values required to achieve the reference detectability index are only 9%,23%, 24%, and 54% of the mAs that is used for adult patients at 120 kVp, for 10, 15, 20, and 25-cm-diameter phantoms,respectively. In the case of iodinated imaging, a tube potential of 60 kVp was found optimal for all phantoms investigated,and the mAs values required to achieve the reference detectability index are 2%, 9%, 37%, and 109% of the adult mAs.The results also indicate that with the use of respective optimal kVps, the photon-counting spectral system o ers up to30% higherd02=dose than the modeled energy-integrating system for adipose imaging, and 70% for iodinated imaging.

  • 8.
    Engberg, Lovisa
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. RaySearch Labs, Sveavagen 44, SE-10365 Stockholm, Sweden..
    Eriksson, Kjell
    RaySearch Labs, Sveavagen 44, SE-10365 Stockholm, Sweden..
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Increased accuracy of planning tools for optimization of dynamic multileaf collimator delivery of radiotherapy through reformulated objective functions2018In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, no 12, article id 125012Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to examine in a clinical setting a novel formulation of objective functions for intensity-modulated radiotherapy treatment plan multicriteria optimization (MCO) that we suggested in a recent study. The proposed objective functions are extended with dynamic multileaf collimator (DMLC) delivery constraints from the literature, and a tailored interior point method is described to efficiently solve the resulting optimization formulation. In a numerical planning study involving three patient cases, DMLC plans Pareto optimal to the MCO formulation with the proposed objective functions are generated. Evaluated based on pre-defined plan quality indices, these DMLC plans are compared to conventionally generated DMLC plans. Comparable or superior plan quality is observed. Supported by these results, the proposed objective functions are argued to have a potential to streamline the planning process, since they are designed to overcome the methodological shortcomings associated with the conventional penalty-based objective functions assumed to cause the current need for time-consuming trial-and-error parameter tuning. In particular, the increased accuracy of the planning tools imposed by the proposed objective functions has the potential to make the planning process less complicated. These conclusions position the proposed formulation as an alternative to existing methods for automated planning.

  • 9. Fredenberg, Erik
    et al.
    Kilburn-Toppin, Fleur
    Willsher, Paula
    Moa, Elin
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Dance, David R.
    Young, Kenneth C.
    Wallis, Matthew G.
    Measurement of breast-tissue x-ray attenuation by spectral mammography: solid lesions2016In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 61, no 7, p. 2595-2612Article in journal (Refereed)
    Abstract [en]

    Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature.

  • 10.
    Fredriksson, Albin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Automated improvement of radiation therapy treatment plans by optimization under reference dose constraints2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 23, p. 7799-7811Article in journal (Refereed)
    Abstract [en]

    A method is presented that automatically improves upon previous treatment plans by optimization under reference dose constraints. In such an optimization, a previous plan is taken as reference and a new optimization is performed toward some goal, such as minimization of the doses to healthy structures under the constraint that no structure can become worse off than in the reference plan. Two types of constraints that enforce this are discussed: either each voxel or each dose-volume histogram of the improved plan must be at least as good as in the reference plan. These constraints ensure that the quality of the dose distribution cannot deteriorate, something that constraints on conventional physical penalty functions do not. To avoid discontinuous gradients, which may restrain gradient-based optimization algorithms, the positive part operators that constitute the optimization functions are regularized. The method was applied to a previously optimized plan for a C-shaped phantom and the effects of the choice of regularization parameter were studied. The method resulted in reduced integral dose and reduced doses to the organ at risk while maintaining target homogeneity. It could be used to improve upon treatment plans directly or as a means of quality control of plans.

  • 11.
    Fredriksson, Albin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Bokrantz, Rasmus
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Deliverable navigation for multicriteria IMRT treatment planning by combining shared and individual apertures2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 21, p. 7683-7697Article in journal (Refereed)
    Abstract [en]

    We consider the problem of deliverable Pareto surface navigation for step-and-shoot intensity-modulated radiation therapy. This problem amounts to calculation of a collection of treatment plans with the property that convex combinations of plans are directly deliverable. Previous methods for deliverable navigation impose restrictions on the number of apertures of the individual plans, or require that all treatment plans have identical apertures. We introduce simultaneous direct step-and-shoot optimization of multiple plans subject to constraints that some of the apertures must be identical across all plans. This method generalizes previous methods for deliverable navigation to allow for treatment plans with some apertures from a collective pool and some apertures that are individual. The method can also be used as a post-processing step to previous methods for deliverable navigation in order to improve upon their plans. By applying the method to subsets of plans in the collection representing the Pareto set, we show how it can enable convergence toward the unrestricted (non-navigable) Pareto set where all apertures are individual.

  • 12. Holstensson, Maria
    et al.
    Smedby, Örjan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Medical Imaging.
    Poludniowski, Gavin
    Sanches Crespo, Alejandro
    Savitcheva, Irina
    Öberg, Michael
    Grybäck, Per
    Gabrielson, Stefan
    Sandqvist, Patricia
    Bartholdson, Erika
    Axelsson, Rimma
    Comparison of acquisition protocols for ventilation/perfusion SPECT - a Monte Carlo study.2019In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560Article in journal (Refereed)
    Abstract [en]

    One of the most commonly used imaging techniques for diagnosing pulmonary embolism (PE) is ventilation/perfusion (V/P) scintigraphy. The aim of this study was to evaluate the performance of the currently used imaging protocols for V/P single photon emission computed tomography (V/P SPECT) at two nuclear medicine department sites and to investigate the effect of altering important protocol parameters. 
 
 The Monte Carlo technique was used to simulate 4D digital phantoms with perfusion defects. Six imaging protocols were included in the study and a total of 72 digital patients were simulated. Six dually trained radiologists/nuclear medicine physicians reviewed the images and reported all perfusion mismatch findings. The radiologists also visually graded the image quality. 
 
 No statistically significant differences in diagnostic performance were found between the studied protocols, but visual grading analysis pointed out one protocol as significantly superior to four of the other protocols. Considering the study results, we have decided to harmonize our clinical protocols for imaging patients with suspected PE. The administered Technegas and macro aggregated albumin activities have been altered, a low energy all purpose collimator is used instead of a low energy high resolution collimator and the acquisition times have been lowered.

  • 13.
    Janek Strååt, Sara
    et al.
    Karolinska Institutet and Stockholm University.
    Andreassen, Björn
    Karolinska Institutet and Stockholm University.
    Johansson, Cathrine
    Karolinska University Hospital Solna, Sweden.
    Noz, Marilyn E.
    New York University, Department of Radiology.
    Maguire Jr., Gerald Q.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Näfstadius, Peder
    Karolinska University Hospital.
    Näslund, Ingemar
    Karolinska Institutet.
    Schoenahl, Frederic
    University Hospital of Geneva, Geneva, Switzerland .
    Brahme, Anders
    Karolinska Institute.
    Clinical application of in vivo treatment delivery verification based on PET/CT imaging of positron activity induced at high energy photon therapy2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 16, p. 5541-5553Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to investigate in vivo verification of radiation treatment with high energy photon beams using PET/CT to image the induced positron activity. The measurements of the positron activation induced in a preoperative rectal cancer patient and a prostate cancer patient following 50 MV photon treatments are presented. A total dose of 5 and 8 Gy, respectively, were delivered to the tumors. Imaging was performed with a 64-slice PET/CT scanner for 30 min, starting 7 min after the end of the treatment. The CT volume from the PET/CT and the treatment planning CT were coregistered by matching anatomical reference points in the patient. The treatment delivery was imaged in vivo based on the distribution of the induced positron emitters produced by photonuclear reactions in tissue mapped on to the associated dose distribution of the treatment plan. The results showed that spatial distribution of induced activity in both patients agreed well with the delivered beam portals of the treatment plans in the entrance subcutaneous fat regions but less so in blood and oxygen rich soft tissues. For the preoperative rectal cancer patient however, a 2 +/- (0.5) cm misalignment was observed in the cranial-caudal direction of the patient between the induced activity distribution and treatment plan, indicating a beam patient setup error. No misalignment of this kind was seen in the prostate cancer patient. However, due to a fast patient setup error in the PET/CT scanner a slight mis-position of the patient in the PET/CT was observed in all three planes, resulting in a deformed activity distribution compared to the treatment plan. The present study indicates that the induced positron emitters by high energy photon beams can be measured quite accurately using PET imaging of subcutaneous fat to allow portal verification of the delivered treatment beams. Measurement of the induced activity in the patient 7 min after receiving 5 Gy involved count rates which were about 20 times lower than that of a patient undergoing standard F-18-FDG treatment. When using a combination of short lived nuclides such as O-15 (half-life: 2 min) and C-11 (half-life: 20 min) with low activity it is not optimal to use clinical reconstruction protocols. Thus, it might be desirable to further optimize reconstruction parameters as well as to address hardware improvements in realizing in vivo treatment verification with PET/CT in the future. A significant improvement with regard to O-15 imaging could also be expected by having the PET/CT unit located close to the radiation treatment room.

  • 14.
    Larsson, Jakob C.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Vogt, Carmen
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Vågberg, William
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Toprak, Muhammet
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Dzieran, Johanna
    Arsenian-Henriksson, Marie
    Hertz, Hans
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    High-spatial-resolution x-ray fluorescence tomography with spectrally matched nanoparticles2018In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, p. 164001-Article in journal (Refereed)
    Abstract [en]

    Present macroscopic biomedical imaging methods provide either morphology with high spatial resolution (e.g. CT) or functional/molecular information with lower resolution (e.g. PET). X-ray fluorescence (XRF) from targeted nanoparticles allows molecular or functional imaging but sensitivity has so far been insufficient resulting in low spatial resolution, despite long exposure times and high dose. In the present paper, we show that laboratory XRF tomography with metal-core nanoparticles (NPs) provides a path to functional/molecular biomedical imaging with ~100 µm resolution in living rodents. The high sensitivity and resolution rely on the combination of a high-brightness liquid-metal-jet x-ray source, pencil-beam optics, photon-counting energy-dispersive detection, and spectrally matched NPs. The method is demonstrated on mice for 3D tumor imaging via passive targeting of in-house-fabricated molybdenum NPs. Exposure times, nanoparticle dose, and radiation dose agree well with in vivo imaging.

  • 15.
    Larsson, Matilda
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. University of Leuven, Belgium .
    Verbrugghe, Peter
    Smoljkić, Marija
    Verhoeven, Jelle
    Heyde, Brecht
    Famaey, Nele
    Herijgers, Paul
    D'hooge, Jan
    Strain assessment in the carotid artery wall using ultrasound speckle tracking: validation in a sheep model.2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 3, p. 1107-Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to validate carotid artery strain assessment in-vivo using ultrasound speckle tracking. The left carotid artery of five sheep was exposed and sonomicrometry crystals were sutured onto the artery wall to obtain reference strain. Ultrasound imaging was performed at baseline and stress, followed by strain estimation using an in-house speckle tracking algorithm tuned for vascular applications. The correlation between estimated and reference strain was r = 0.95 (p < 0.001) and r = 0.87 (p < 0.01) for longitudinal and circumferential strain, respectively. Moreover, acceptable limits of agreement were found in Bland-Altman analysis (longitudinally: -0.15 to 0.42%, circumferentially: -0.54 to 0.50%), which demonstrates the feasibility of estimating carotid artery strain using ultrasound speckle tracking. However, further studies are needed to test the algorithm on human in-vivo data and to investigate its potential to detect subclinical cardiovascular disease and characterize atherosclerotic plaques.

  • 16.
    Lundström, Ulf
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Larsson, Daniel H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Burvall, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Scott, L.
    Westermark, U. K.
    Wilhelm, M.
    Henriksson, M. Arsenian
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    X-ray phase-contrast CO2 angiography for sub-10 mu m vessel imaging2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 22, p. 7431-7441Article in journal (Refereed)
    Abstract [en]

    X-ray in-line phase contrast has recently been combined with CO2 angiography for high-resolution small-animal vascular imaging at low radiation dose. In this paper we further investigate the potential and limitations of this method and demonstrate observation of vessels down to 8 mu m in diameter, considerably smaller than the 60 mu m previously reported. Our in-line phase-contrast imaging system is based on a liquid-metal-jet-anode x-ray source and utilizes free-space propagation to convert phase shifts, caused by refractive index variations, into intensity differences. Enhanced refractive index variations are obtained through injection of CO2 gas into the vascular system to replace the blood. We show rat-kidney images with blood vessels down to 27 mu m in diameter and mouse-ear images with vessels down to 8 mu m. The minimum size of observable blood vessels is found to be limited by the penetration of gas into the vascular system and the signal-to-noise ratio, i.e. the allowed dose. The diameters of vessels being gas-filled depend on the gas pressure and follow a simple model based on surface tension. A theoretical signal-to-noise comparison shows that this method requires 1000 times less radiation dose than conventional iodine-based absorption contrast for observing sub-50 mu m vessels.

  • 17.
    Lundström, Ulf
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Larsson, Daniel H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Burvall, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Takman, Per A. C.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Scott, L.
    Brismar, H.
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    X-ray phase contrast for CO2 microangiography2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 9, p. 2603-2617Article in journal (Refereed)
    Abstract [en]

    We demonstrate a laboratory method for imaging small blood vessels using x-ray propagation-based phase-contrast imaging and carbon dioxide (CO2) gas as a contrast agent. The limited radiation dose in combination with CO2 being clinically acceptable makes the method promising for small-diameter vascular visualization. We investigate the possibilities and limitations of the method for small-animal angiography and compare it with conventional absorption-based x-ray angiography. Photon noise in absorption-contrast imaging prevents visualization of blood vessels narrower than 50 mu m at the highest radiation doses compatible with living animals, whereas our simulations and experiments indicate the possibility of visualizing 20 mu m vessels at radiation doses as low as 100 mGy. Experimental computed tomography of excised rat kidney shows blood vessels of diameters down to 60 mu m with improved image quality compared to absorption-based methods. With our present prototype x-ray source, the acquisition time for a tomographic dataset is approximately 1 h, which is long compared to the 1-20 min common for absorption-contrast micro-CT systems. Further development of the liquid-metal-jet microfocus x-ray sources used here and high-resolution x-ray detectors shows promise to reduce exposure times and make this high-resolution method practical for imaging of living animals.

  • 18.
    Lundström, Ulf
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Westermark, Ulrica K.
    Larsson, Daniel H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Burvall, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Arsenian Henriksson, Marie
    Hertz, Hans M.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    X-ray phase contrast with injected gas for tumor microangiography2014In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, no 11, p. 2801-2811Article in journal (Refereed)
    Abstract [en]

    We show that the microvasculature of mouse tumors can be visualized using propagation-based phase-contrast x-ray imaging with gas as the contrast agent. The large density difference over the gas-tissue interface provides high contrast, allowing the imaging of small-diameter blood vessels with relatively short exposure times and low dose using a compact liquid-metal-jet x-ray source. The method investigated is applied to tumors (E1A/Ras-transformed mouse embryonic fibroblasts) grown in mouse ears, demonstrating sub-15-mu m-diameter imaging of their blood vessels. The exposure time for a 2D projection image is a few seconds and a full tomographic 3D map takes some minutes. The method relies on the strength of the vasculature to withstand the gas pressure. Given that tumor vessels are known to be more fragile than normal vessels, we investigate the tolerance of the vasculature of 12 tumors to gas injection and find that a majority withstand 200 mbar pressures, enough to fill 12-mu m-diameter vessels with gas. A comparison of the elasticity of tumorous and non-tumorous vessels supports the assumption of tumor vessels being more fragile. Finally, we conclude that the method has the potential to be extended to the imaging of 15 mu m vessels in thick tissue, including mouse imaging, making it of interest for, e.g., angiogenesis research.

  • 19.
    Maguire Jr., Gerald Q.
    et al.
    Columbia University, Computer Science.
    Noz, Marilyn E.
    New York University, Department of Radiology.
    Image Formats: Five Years after the AAPM Standard Format for Digital Image Interchange1988In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 33, no Supplement, p. 116-Article in journal (Refereed)
  • 20.
    Maksuti, Elira
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering.
    Bini, Fabiano
    Fiorentini, Stefano
    Blasi, Giulia
    Urban, Matthew W
    Marinozzi, Franco
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering.
    Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study.2017In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 7, p. 2694-2718Article in journal (Refereed)
    Abstract [en]

    Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. Arterial shear wave elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D) vary with age and pathology and may influence the shear wave propagation. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated. In this study the influence of geometry on the estimated mechanical properties of plates (h  =  0.5-3 mm) and hollow cylinders (h  =  1, 2 and 3 mm, D  =  6 mm) was assessed by experiments in phantoms and by finite element method simulations. In addition, simulations in hollow cylinders with wall thickness difficult to achieve in phantoms were performed (h  =  0.5-1.3 mm, D  =  5-8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency range 200-1000 Hz and showed good agreement (R (2)  =  0.80  ±  0.07 for plates and R (2)  =  0.82  ±  0.04 for hollow cylinders). Wall thickness had a larger effect than diameter on the dispersion curves, which did not have major effects above 400 Hz. An underestimation of 0.1-0.2 mm in wall thickness introduces an error 4-9 kPa in hollow cylinders with shear modulus of 21-26 kPa. Therefore, wall thickness should correctly be measured in arterial SWE applications for accurate mechanical properties estimation.

  • 21.
    Marlevi, David
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems. Karolinska Inst, Dept Clin Sci, Stockholm, Sweden..
    Maksuti, Elira
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems.
    Urban, Matthew W.
    Mayo Clin, Coll Med, Dept Radiol, Rochester, MN USA..
    Winter, Reidar
    Karolinska Inst, Dept Clin Sci, Stockholm, Sweden..
    Larsson, Matilda
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems.
    Plaque characterization using shear wave elastography-evaluation of differentiability and accuracy using a combined ex vivo and in vitro setup2018In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 63, no 23, article id 235008Article in journal (Refereed)
    Abstract [en]

    Ultrasound elastography has shown potential for improved plaque risk stratification. However, no clear consensus exists on what output metric to use, or what imaging parameters would render optimal plaque differentiation. For this reason we developed a combined ex vivo and in vitro setup, in which the ability to differentiate phantom plaques of varying stiffness was evaluated as a function of plaque geometry, push location, imaging plane, and analysed wave speed metric. The results indicate that group velocity or phase velocity >= 1 kHz showed the highest ability to significantly differentiate plaques of different stiffness, successfully classifying a majority of the 24 analysed plaque geometries, respectively. The ability to differentiate plaques was also better in the longitudinal views than in the transverse view. Group velocity as well as phase velocities <1 kHz showed a systematic underestimation of plaque stiffness, stemming from the confined plaque geometries, however, despite this group velocity analysis showed lowest deviation in estimated plaque stiffness (0.1 m s(-1) compared to 0.2 m s(-1) for phase velocity analysis). SWE results were also invariant to SWE push location, albeit apparent differences in signal-to-noise ratio (SNR) and generated plaque particle velocity. With that, the study has reinforced the potential of SWE for successful plaque differentiation; however the results also highlight the importance of choosing optimal imaging settings and using an appropriate wave speed metric when attempting to differentiate different plaque groups.

  • 22.
    Miettinen, Kaisa
    et al.
    Dept. of Mathematical Information Technology, University of Jyväskylä.
    Ruotsalainen, Henri
    Department of Physics and Mathematics, University of Eastern Finland, Kuopio.
    Palmgren, Jan-Erik
    Lahtinen, Tapani
    Department of Oncology, Kuopio University Hospital.
    Interactive Multiobjective Optimization for Anatomy based Three-Dimensinal HDR Brachytherapy2010In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 55, no 16, p. 4703-4719Article in journal (Refereed)
    Abstract [en]

    In this paper, we present an anatomy-based three-dimensional dose optimization approach for HDR brachytherapy using interactive multiobjective optimization (IMOO). In brachytherapy, the goals are to irradiate a tumor without causing damage to healthy tissue. These goals are often conflicting, i.e. when one target is optimized the other will suffer, and the solution is a compromise between them. IMOO is capable of handling multiple and strongly conflicting objectives in a convenient way. With the IMOO approach, a treatment planner’s knowledge is used to direct the optimization process. Thus, the weaknesses of widely used optimization techniques (e.g. defining weights, computational burden and trial-and-error planning) can be avoided, planning times can be shortened and the number of solutions to be calculated is small. Further, plan quality can be improved by finding advantageous trade-offs between the solutions. In addition, our approach offers an easy way to navigate among the obtained Pareto optimal solutions (i.e. different treatment plans). When considering a simulation model of clinical 3D HDR brachytherapy, the number of variables is significantly smaller compared to IMRT, for example. Thus, when solving the model, the CPU time is relatively short. This makes it possible to exploit IMOO to solve a 3D HDR brachytherapy optimization problem. To demonstrate the advantages of IMOO, two clinical examples of optimizing a gynecologic cervix cancer treatment plan are presented.

  • 23.
    Nguyen, Hang Tuan
    et al.
    NeuroSpin, CEA Saclay Center, 91191 Gif-sur-Yvette Cedex, France.
    Grebenkov, Denis
    Laboratoire de Physique de la Matière Condensée, CNRS—Ecole Polytechnique, F-91128 Palaiseau Cedex, France.
    Nguyen, Van Dang
    INRIA Saclay-Equipe DEFI, CMAP, Ecole Polytechnique, Route de Saclay, Palaiseau Cedex, 91128, France.
    Poupon, Cyril
    NeuroSpin, CEA Saclay Center, 91191 Gif-sur-Yvette Cedex, France.
    Le Bihan, Denis
    NeuroSpin, CEA Saclay Center, 91191 Gif-sur-Yvette Cedex, France.
    Li, Jing-Rebecca
    INRIA Saclay-Equipe DEFI, CMAP, Ecole Polytechnique Route de Saclay, 91128, Palaiseau Cedex, France.
    Parameter estimation using macroscopic diffusion MRI signal models2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 8, p. 3389-3413Article in journal (Refereed)
    Abstract [en]

    Macroscopic models of the diffusion MRI (dMRI) signal can be helpful in understanding the relationship between the tissue microstructure and the dMRI signal. We study the least squares problem associated with estimating tissue parameters such as the cellular volume fraction, the residence times and the effective diffusion coefficients using a recently developed macroscopic model of the dMRI signal called the Finite Pulse Kärger model that generalizes the original Kärger model to non-narrow gradient pulses. In order to analyze the quality of the estimation in a controlled way, we generated synthetic noisy dMRI signals by including the effect of noise on the exact signal produced by the Finite Pulse Kärger model. The noisy signals were then fitted using the macroscopic model. Minimizing the least squares, we estimated the model parameters. The bias and standard deviations of the estimated model parameters as a function of the signal to noise ratio (SNR) were obtained. We discuss the choice of the b-values, the least square weights, the extension to experimentally obtained dMRI data as well as noise correction.

  • 24. Nowik, Patrik
    et al.
    Bujila, Robert
    KTH, School of Engineering Sciences (SCI), Physics.
    Kull, Love
    Andersson, Jonas
    Poludniowski, Gavin
    The dosimetric impact of including the patient table in CT dose estimates2017In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 62, no 23, p. N538-N547Article in journal (Refereed)
    Abstract [en]

    he purpose of this study was to evaluate the dosimetric impact of including the patient table in Monte Carlo CT dose estimates for both spiral scans and scan projection radiographs (SPR). CT scan acquisitions were simulated for a Siemens SOMATOM Force scanner (Siemens Healthineers, Forchheim, Germany) with and without a patient table present. An adult male, an adult female and a pediatric female voxelized phantom were simulated. The simulated scans included tube voltages of 80 and 120 kVp. Spiral scans simulated without a patient table resulted in effective doses that were overestimated by approximately 5% compared to the same simulations performed with the patient table present. Doses in selected individual organs (breast, colon, lung, red bone marrow and stomach) were overestimated by up to 8%. Effective doses from SPR acquired with the x-ray tube stationary at 6 o'clock (posterior-anterior) were overestimated by 14-23% when the patient table was not included, with individual organ dose discrepancies (breast, colon, lung red bone marrow and stomach) all exceeding 13%. The reference entrance skin dose to the back were in this situation overestimated by 6-15%. These results highlight the importance of including the patient table in patient dose estimates for such scan situations.

  • 25. Omar, A.
    et al.
    Bujila, Robert
    KTH, School of Engineering Sciences (SCI), Physics. Karolinska University Hospital, Stockholm, Sweden.
    Fransson, A.
    Andreo, P.
    Poludniowski, G.
    A framework for organ dose estimation in x-ray angiography and interventional radiology based on dose-related data in DICOM structured reports2016In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 61, no 8, p. 3063-3083Article in journal (Refereed)
    Abstract [en]

    Although interventional x-ray angiography (XA) procedures involve relatively high radiation doses that can lead to deterministic tissue reactions in addition to stochastic effects, convenient and accurate estimation of absorbed organ doses has traditionally been out of reach. This has mainly been due to the absence of practical means to access dose-related data that describe the physical context of the numerous exposures during an XA procedure. The present work provides a comprehensive and general framework for the determination of absorbed organ dose, based on non-proprietary access to dose-related data by utilizing widely available DICOM radiation dose structured reports. The framework comprises a straightforward calculation workflow to determine the incident kerma and reconstruction of the geometrical relation between the projected x-ray beam and the patient's anatomy. The latter is difficult in practice, as the position of the patient on the table top is unknown. A novel patient-specific approach for reconstruction of the patient position on the table is presented. The proposed approach was evaluated for 150 patients by comparing the estimated position of the primary irradiated organs (the target organs) with their position in clinical DICOM images. The approach is shown to locate the target organ position with a mean (max) deviation of 1.3 (4.3), 1.8 (3.6) and 1.4 (2.9) cm for neurovascular, adult and paediatric cardiovascular procedures, respectively. To illustrate the utility of the framework for systematic and automated organ dose estimation in routine clinical practice, a prototype implementation of the framework with Monte Carlo simulations is included.

  • 26. Persson, M.
    et al.
    Bone, D.
    Elmqvist, Håkan
    Total variation norm for three-dimensional iterative reconstruction in limited view angle tomography2001In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 46, no 3, p. 853-866Article in journal (Refereed)
    Abstract [en]

    An iterative Bayesian reconstruction algorithm for limited view angle tomography, or ectomography, based on the three-dimensional total variation (TV) norm has been developed. The TV norm has been described ill the literature as a method for reducing noise in two-dimensional images while preserving edges, without introducing ringing or edge artefacts. It has also been proposed as a 2D regularization function in Bayesian reconstruction, implemented in an expectation maximization algorithm (TV-EM). The TV-EM was developed for 2D single photon emission computed tomography imaging, and the algorithm is capable of smoothing noise while maintaining edges without introducing artefacts. The TV norm was extended from 2D to 3D and incorporated into an ordered subsets expectation maximization algorithm for limited view angle geometry. The algorithm, called TV3D-EM, was evaluated using a modelled point spread function and digital phantoms. Reconstructed images were compared with those reconstructed with the 2D filtered backprojection algorithm currently used in ectomography. Results show a substantial reduction in artefacts related to the limited view angle geometry, and noise levels were also improved. Perhaps most important, depth resolution was improved by at least 45%. In conclusion, the proposed algorithm has been shown to improve the perceived image quality.

  • 27.
    Persson, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Huber, Ben
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Liu, Xuejin
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Chen, Han
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Yveborg, Moa
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Energy-resolved CT imaging with a photon-counting silicon-strip detector2014In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, no 22, p. 6709-6727Article in journal (Refereed)
    Abstract [en]

    Photon-counting detectors are promising candidates for use in the next generation of x-ray computed tomography (CT) scanners. Among the foreseen benefits are higher spatial resolution, better trade-off between noise and dose and energy discriminating capabilities. Silicon is an attractive detector material because of its low cost, mature manufacturing process and high hole mobility. However, it is sometimes overlooked for CT applications because of its low absorption efficiency and high fraction of Compton scatter. The purpose of this work is to demonstrate that silicon is a feasible material for CT detectors by showing energy-resolved CT images acquired with an 80 kVp x-ray tube spectrum using a photon-counting silicon-strip detector with eight energy thresholds developed in our group. We use a single detector module, consisting of a linear array of 50 0.5 x 0.4 mm detector elements, to image a phantom in a table-top lab setup. The phantom consists of a plastic cylinder with circular inserts containing water, fat and aqueous solutions of calcium, iodine and gadolinium, in different concentrations. By using basis material decomposition we obtain water, calcium, iodine and gadolinium basis images and demonstrate that these basis images can be used to separate the different materials in the inserts. We also show results showing that the detector has potential for quantitative measurements of substance concentrations.

  • 28.
    Sjölin, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Improved signal-to-noise ratio for non-perpendicular detection angles in x-ray fluorescence computed tomography (XFCT)2014In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, no 21, p. 6507-6520Article in journal (Refereed)
    Abstract [en]

    The standard imaging setup in x-ray fluorescence computed tomography detects the fluorescence emission at a right angle with respect to the axis of the excitation beam. In this paper we have studied how the detection angle affects the signal-to-noise ratio (S/N), which is a major factor influencing the low-contrast sensitivity of the imaging system. This is done for an imaging setup using a collimated detector and a pencil beam of excitation x-rays. An ideal detection process is simulated for a generalized imaging case with gold/platinum tracers and experimental measurements are performed using a diagnostic x-ray tube. For monochromatic excitation, the results indicate that order-of-magnitude improvements of the S/N can be achieved by optimizing the detection angle. The maximal S/N, when exciting with an energy just above the K-edge, is achieved for large detection angles, i.e. with the detector close to the source. The improvements also transfer to polychromatic excitation sources and the experimental results show up to four-fold improvements of the S/N when changing the detection angle from 90 degrees to 150 degrees. Also, the changes of the S/N behavior when switching the fluorescent tracer is briefly demonstrated. These results suggest that the choice of detection angle should be taken seriously in the design of future XFCT imaging systems.

  • 29.
    Tibbelin, Sandra
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Simulation of HyperSPECT: a high-resolution small-animal system with in-line x-ray optics2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 6, p. 1617-1629Article in journal (Refereed)
    Abstract [en]

    SPECT has become an important tool in pre-clinical applications. Small-animal imaging systems based on the use of one or more pinhole collimators now reach sub-half-mm resolution but unfortunately suffer from a compromise between sensitivity and resolution due to the pinhole collimators. We propose a small-animal SPECT system based not on pinholes but on in-line x-ray optics, which is rare in medical imaging systems for nuclear medicine. The x-ray lenses are optimized for 27 keV for low-energy imaging with iodine-125. We believe that this new system, HyperSPECT, can simultaneously improve on sensitivity and resolution compared to today's state-of-the-art systems. A full three-dimensional simulation of the system has been performed including the prism-array lenses, pre-and post-collimators and scintillator-based detector. Images of capillary phantoms have been reconstructed using an iterative image reconstruction method. Sensitivity was uniformly 0.37% throughout the 1 cm diameter spherical field of view and rod sizes of around 100 mu m diameter were distinguishable in the images of simulated capillary phantoms. These results indicate an increase in resolution by a factor of 5 during a simultaneous increase in sensitivity by a factor of 2 compared to the current state-of-the-art small-animal SPECT systems.

  • 30.
    Widman, Erik
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Department of Molecular Medicine and Surgery, Karolinska Institutet, Solna, Sweden .
    Maksuti, Elira
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, David
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Urban, M W
    Bjallmark, Anna
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Department of Molecular Medicine and Surgery, Karolinska Institutet, Solna, Sweden .
    Shear wave elastography plaque characterization with mechanical testing validation: a phantom study.2015In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 60, no 8, p. 3151-3174Article in journal (Refereed)
    Abstract [en]

    Determining plaque vulnerability is critical when selecting the most suitable treatment for patients with atherosclerotic plaque. Currently, clinical non-invasive ultrasound-based methods for plaque characterization are limited to visual assessment of plaque morphology and new quantitative methods are needed. In this study, shear wave elastography (SWE) was used to characterize hard and soft plaque mimicking inclusions in six common carotid artery phantoms by using phase velocity analysis in static and dynamic environments. The results were validated with mechanical tensile testing. In the static environment, SWE measured a mean shear modulus of 5.8±0.3kPa and 106.2±17.2kPa versus 3.3±0.5kPa and 98.3±3.4kPa measured by mechanical testing in the soft and hard plaques respectively. Furthermore, it was possible to measure the plaques' shear moduli throughout a simulated cardiac cycle. The results show good agreement between SWE and mechanical testing and indicate the possibility for in vivo arterial plaque characterization using SWE.

  • 31.
    Yveborg, Moa
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Performance evaluation of a sub-millimetre spectrally resolved CT system on high- and low-frequency imaging tasks: a simulation2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 8, p. 2373-2391Article in journal (Refereed)
    Abstract [en]

    We are developing a photon-counting silicon strip detector with 0.4 x 0.5 mm(2) detector elements for clinical CT applications. Except for the limited detection efficiency of approximately 0.8 for a spectrum of 80 kVp, the largest discrepancies from ideal spectral behaviour have been shown to be Compton interactions in the detector and electronic noise. Using the framework of cascaded system analysis, we reconstruct the 3D MTF and NPS of a silicon strip detector including the influence of scatter and charge sharing inside the detector. We compare the reconstructed noise and signal characteristics with a reconstructed 3D MTF and NPS of an ideal energy-integrating detector system with unity detection efficiency, no scatter or charge sharing inside the detector, unity presampling MTF and 1 x 1 mm(2) detector elements. The comparison is done by calculating the dose-normalized detectability index for some clinically relevant imaging tasks and spectra. This work demonstrates that although the detection efficiency of the silicon detector rapidly drops for the acceleration voltages encountered in clinical computed tomography practice, and despite the high fraction of Compton interactions due to the low atomic number, silicon detectors can perform on a par with ideal energy-integrating detectors for routine imaging tasks containing low-frequency components. For imaging tasks containing high-frequency components, the proposed silicon detector system can perform approximately 1.1-1.3 times better than a fully ideal energy-integrating system.

  • 32.
    Yveborg, Moa
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Crafoord, Joakim
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Eliminated risk of iodine contrast cancellation with multibin spectral CT2013In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 58, no 14, p. N201-N209Article in journal (Refereed)
    Abstract [en]

    This note compares the extent of contrast cancellation induced by iodinated contrast agents in energy integrating and photon counting multibin CT images. The contrast between a hypodense target and soft tissue is modeled for the two systems for a range of iodine concentrations and tube voltages. In energy integrating systems, we show that the contrast vanishes for low concentrations of iodine whereas the same effect is not seen in multibin systems. We conclude that it is the ability of multibin systems to apply weighting schemes post-acquisition that allows the operator to eliminate the risk of contrast cancellation between iodinated targets and the background.

1 - 32 of 32
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