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  • 1.
    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    KTH, Superseded Departments, Physics.
    K 0–K̄0 mass and decay-width differences: CPLEAR evaluation1999In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 471, no 2, 332-338 p.Article in journal (Refereed)
    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.

  • 2.
    Angelopoulos, Angelos
    et al.
    -.
    Apostolakis, A.
    -.
    Aslanides, E.
    -.
    Backenstoss, Gerhard
    -.
    Bargassa, P.
    -.
    Bee, C P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Physics at CPLEAR2003In: Physics Reports, Vol. 374, no 3, 165-270 p.Article in journal (Refereed)
    Abstract [en]

    LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

  • 3.
    Angelopoulos, Angelos
    et al.
    -.
    Aslanides, E.
    -.
    Backenstoss, G.
    -.
    Bargassa, P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Bloch, P.
    -.
    Carlson, P.
    -.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    K0⇋ K̄0 transitions monitored by strong interactions: a new determination of the K L–K S mass difference2001In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 503, no 1, 49-57 p.Article in journal (Refereed)
    Abstract [en]

    The CPLEAR set-up (modified) has been used to determine the KL–KS mass difference by a method where neutral-kaon strangeness oscillations are monitored through kaon strong interactions, rather than semileptonic decays, thus requiring no assumptions on CPT invariance for the decay amplitudes. The result, Δm=(0.5343±0.0063stat±0.0025syst)×1010ℏ/s, provides a valuable input for CPT tests.

  • 4.
    Angelopoulos, Angelos
    et al.
    -.
    Locher, M P
    -.
    Markushin, V E
    -.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Dispersion relation analysis of the neutral kaon regeneration amplitude in carbon1999In: The European Physical Journal C-Particles and Fields, ISSN 434-6044, Vol. 10, no 1, 19-25 p.Article in journal (Refereed)
    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.

  • 5. Apostolakis, A
    et al.
    Aslanides, E.
    -.
    Backenstoss, G.
    -.
    Bargassa, P.
    -.
    Behnke, O.
    -.
    Benelli, A.
    -.
    Bertin, V.
    -.
    Blanc, F.
    -.
    Bloch, P.
    -.
    Carlson, P.
    KTH, School of Engineering Sciences (SCI).
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    A determination of the CP violation parameter η+- from the decay of strangeness-tagged neutral kaons1999In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 458, no 4, 545-552 p.Article in journal (Refereed)
    Abstract [en]

    LEAR offered unique opportunities to study the symmetries which exist between matter and antimatter. At variance with other approaches at this facility, CPLEAR was an experiment devoted to the study of CP, T and CPT symmetries in the neutral-kaon system. A variety of measurements allowed us to determine with high precision the parameters which describe the time evolution of the neutral kaons and their antiparticles, including decay amplitudes, and the related symmetry properties. Limits concerning quantum-mechanical predictions (EPR, coherence of the wave function) or the equivalence principle of general relativity have been obtained. An account of the main features of the experiment and its performances is given here, together with the results achieved.

  • 6.
    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, Superseded Departments, Physics.
    Measurement of the energy dependence of the form factor f+ in K 0 e3 decay2000In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 473, no 1, 186-192 p.Article in journal (Refereed)
    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.

  • 7. Aslund, M.
    et al.
    Fredenberg, Erik
    KTH, School of Engineering Sciences (SCI), Physics.
    Telman, M.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Detectors for the future of X-ray imaging2010In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 139, no 1-3, 327-333 p.Article in journal (Refereed)
    Abstract [en]

    In recent decades, developments in detectors for X-ray imaging have improved dose efficiency. This has been accomplished with for example, structured scintillators such as columnar CsI, or with direct detectors where the X rays are converted to electric charge carriers in a semiconductor. Scattered radiation remains a major noise source, and fairly inefficient anti-scatter grids are still a gold standard. Hence, any future development should include improved scatter rejection. In recent years, photon-counting detectors have generated significant interest by several companies as well as academic research groups. This method eliminates electronic noise, which is an advantage in low-dose applications. Moreover, energy-sensitive photon-counting detectors allow for further improvements by optimising the signal-to-quantum-noise ratio, anatomical background subtraction or quantitative analysis of object constituents. This paper reviews state-of-the-art photon-counting detectors, scatter control and their application in diagnostic X-ray medical imaging. In particular, spectral imaging with photon-counting detectors, pitfalls such as charge sharing and high rates and various proposals for mitigation are discussed.

  • 8.
    Berggren, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Philips Healthcare, Sweden.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Fredenberg, Erik
    Philips Healthcare, Sweden.
    Rayleigh imaging in spectral mammography2016In: MEDICAL IMAGING 2016: PHYSICS OF MEDICAL IMAGING, 2016, 97830AConference paper (Refereed)
    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.

  • 9.
    Berggren, Karl
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Philips Healthcare, S-17141 Solna, Sweden.
    Lundqvist, Mats
    Cederstrom, Bjorn
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Fredenberg, Erik
    Physical characterization of photon-counting tomosynthesis2015Conference paper (Refereed)
    Abstract [en]

    Tomosynthesis is emerging as a next generation technology in mammography. Combined with photon-counting detectors with the ability for energy discrimination, a novel modality is enabled - spectral tomosynthesis. Further advantages of photon-counting detectors in the context of tomosynthesis include elimination of electronic noise, efficient scatter rejection (in some geometries) and no lag. Fourier-based linear-systems analysis is a well-established method for optimizing image quality in two-dimensional x-ray systems. The method has been successfully adapted to three-dimensional imaging, including tomosynthesis, but several areas need further investigation. This study focuses on two such areas: 1) Adaption of the methodology to photon-counting detectors, and 2) violation of the shift-invariance and stationarity assumptions in non-cylindrical geometries. We have developed a Fourier-based framework to study the image quality in a photon-counting tomosynthesis system, assuming locally linear, stationary, and shift-invariant system response. The framework includes a cascaded-systems model to propagate the modulation-transfer function (MTF) and noise-power spectrum (NPS) through the system. The model was validated by measurements of the MTF and NPS. High degrees of non-shift invariance and non-stationarity were observed, in particular for the depth resolution as the angle of incidence relative the reconstruction plane varied throughout the imaging volume. The largest effects on image quality in a given point in space were caused by interpolation from the inherent coordinate system of the x-rays to the coordinate system that was used for reconstruction. This study is part of our efforts to fully characterize the spectral tomosynthesis system, we intend to extend the model further to include the detective-quantum efficiency, observer modelling, and spectral effects.

  • 10.
    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, 1999-2022 p.Article 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.

  • 11. Bornefalk, Hans
    et al.
    Lewin, John M.
    Danielsson, Mats
    Lundqvist, Mats
    Single-shot dual-energy subtraction mammography with electronic spectrum splitting: Feasibility2006In: European Journal of Radiology, ISSN 0720-048X, E-ISSN 1872-7727, Vol. 60, no 2, 275-278 p.Article in journal (Refereed)
    Abstract [en]

    We present a single-shot dual-energy subtraction mammography technique using an energy sensitive photon counting detector. An electronic threshold near the middle of the X-ray spectrum discriminates between high- and low-energy photons, and allows the simultaneous acquisition of high- and low-energy images which can be combined to suppress anatomical clutter. By setting the electronic threshold close to 33.2 keV (the k-edge of iodine) the system is optimized for dual-energy contrast-enhanced imaging of breast tumors. This method eliminates the need for separate exposures which might otherwise lead to motion artifacts. The method is illustrated in phantom images.

  • 12.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Allowable forward model misspecification for accurate basis decomposition in a silicon detector based spectral CT2015In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 34, no 3, 788-795 p.Article in journal (Refereed)
    Abstract [en]

    Material basis decomposition in the sinogram domain requires accurate knowledge of the forward model in spectral computed tomography (CT). Misspecifications over a certain limit will result in biased estimates and make quantum limited (where statistical noise dominates) quantitative CT difficult. We present a method whereby users can determine the degree of allowed misspecification error in a spectral CT forward model and still have quantification errors that are limited by the inherent statistical uncertainty. For a particular silicon detector based spectral CT system, we conclude that threshold determination is the most critical factor and that the bin edges need to be known to within 0.15 keV in order to be able to perform quantum limited material basis decomposition. The method as such is general to all multibin systems.

  • 13.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Necessary forward model specification accuracy for basis material decomposition in spectral CT2014In: Medical Imaging 2014: Physics of Medical Imaging, SPIE - International Society for Optical Engineering, 2014, 90332I- p.Conference paper (Refereed)
    Abstract [en]

    Material basis decomposition in the sinogram domain requires accurate knowledge of the forward model in spectral CT. Misspecifications over a certain limit will result in biased estimates and make quantum limited quantitative CT difficult. We present a method whereby users can determine the degree of allowed misspecification error in a spectral CT forward model, and still have quantification errors that are quantum limited.

  • 14.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, Christer
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Effect of Temperature Variation on the Energy Response of a Photon Counting Silicon CT Detector2013In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 2, 1442-1449 p.Article in journal (Refereed)
    Abstract [en]

    The effect of temperature variation on pulse height determination accuracy is determined for a photon counting multibin silicon detector developed for spectral CT. Theoretical predictions of the temperature coefficient of the gain and offset are similar to values derived from synchrotron radiation measurements in a temperature controlled environment. By means of statistical modeling, we conclude that temperature changes affect all channels equally and with separate effects on gain and threshold offset. The combined effect of a 1 degrees C temperature increase is to decrease the detected energy by 0.1 keV for events depositing 30 keV. For the electronic noise, no statistically significant temperature effect was discernible in the data set, although theory predicts a weak dependence. The method is applicable to all x-ray detectors operating in pulse mode.

  • 15.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Xu, Cheng
    Svensson, Christer
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Design considerations to overcome cross talk in a photon counting silicon strip detector for computed tomography2010In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 621, no 1-3, 371-378 p.Article in journal (Refereed)
    Abstract [en]

    This article presents a Monte Carlo simulation of the detector energy response in the presence of pileup in a segmented silicon microstrip detector designed for high flux spectral computed tomography with sub-millimeter pixel size. Currents induced on the collection electrode of a pixel segment are explicitly modeled and signals emanating from events in neighboring pixels are superimposed together with electronic noise before the entire pulse train is processed by a model of the readout electronics to obtain the detector energy response function. The article shows how the lower threshold and the time constant of the electronic filters need to be set in order to minimize the detrimental influence of cross talk from neighboring pixel segments, an issue that is aggravated by the sub-millimeter pixel size and the proposed segmented detector design. (C) 2010 Elsevier B.V. All rights reserved.

  • 16.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, Christer
    Division of Electronic Devices, Linköping University.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Simulation study of an energy sensitive photon counting silicon strip detector for computed tomography: identifying strengths and weaknesses and developing work-arounds2010In: MEDICAL IMAGING 2010: PHYSICS OF MEDICAL IMAGING / [ed] Samei E; Pelc NJ, 2010, Vol. 7622Conference paper (Refereed)
    Abstract [en]

    We model the effect of signal pile-up on the energy resolution of a photon counting silicon detector designed for high flux spectral CT with sub-millimeter pixel size. Various design parameters, such as bias voltage, lower threshold level for discarding of electronic noise and the entire electronic read out chain are modeled and realistic parameter settings are determined. We explicitly model the currents induced on the collection electrodes of a pixel and superimpose signals emanating from events in neighboring pixels, either due to charge sharing or signals induced during charge collection. Electronic noise is added to the pulse train before feeding it through a model of the read out electronics where the pulse height spectrum is saved to yield the detector energy response function. The main result of this study is that a lower threshold of 5 keV and a rather long time constant of the shaping filter (tau(0) = 30 ns) are needed to discard induced pulses from events in neighboring pixels. These induction currents occur even if no charge is being deposited in the analyzed pixel from the event in the neighboring pixel. There is also only a limited gain in energy resolution by increasing the bias voltage to 1000 V from 600 V. We show that with these settings the resulting energy resolution, as measured by the FWHM/E of the photo peak, is 5% at 70 keV.

  • 17. Brahme, A.
    et al.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Iacobaeus, C.
    Ostling, J.
    Peskov, V.
    Wallmark, M.
    Evaluation of a GEM and CAT-based detector for radiation therapy beam monitoring2000In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 454, no 1, 136-141 p.Article in journal (Refereed)
    Abstract [en]

    We are developing a radiation therapy beam monitor for the Karolinska Institute. This monitor will consist of two consecutive detectors confined in one gas chamber: a keV-photon detector, which will allow diagnostic quality visualization of the patient, and a MeV-photon detector, that will measure the absolute intensity of the therapy beam and its position with respect to the patient. Both detectors are based on highly radiation resistant gas and solid photon to electron converters, combined with GEMs and a CAT as amplification structures. We have performed systematic studies of the high-rate characteristics of the GEM and the CAT, as well as tested the electron transfer through these electron multipliers and various types of converters. The tests show that the GEM and the CAT satisfy all requirements for the beam monitoring system. As a result of these studies we successfully developed and tested a full section of the beam monitor equipped with a MeV-photon converter placed between the GEM and the CAT.

  • 18.
    Cahn, R N
    et al.
    -.
    Cederström, B.
    -.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Hall, A.
    -.
    Lundqvist, M.
    -.
    Nygren, D.
    -.
    Detective quantum efficiency dependence on x-ray energy weighting in mammography1999In: Medical physics, Vol. 26, no 12, 2680-2683 p.Article in journal (Refereed)
    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−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.

  • 19. Cederström, B.
    et al.
    Fredenberg, E.
    Berggren, Karl
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. Mammography Solutions, Philips, Sweden.
    Erhard, K.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Wallis, M.
    Lesion characterization in spectral photon-counting tomosynthesis2017In: Medical Imaging 2017: Physics of Medical Imaging, SPIE - International Society for Optical Engineering, 2017, Vol. 10132, 1013205Conference paper (Refereed)
    Abstract [en]

    It has previously been shown that 2D spectral mammography can be used to discriminate between (likely benign) cystic and (potentially malignant) solid lesions in order to reduce unnecessary recalls in mammography. One limitation of the technique is, however, that the composition of overlapping tissue needs to be interpolated from a region surrounding the lesion. The purpose of this investigation was to demonstrate that lesion characterization can be done with spectral tomosynthesis, and to investigate whether the 3D information available in tomosynthesis can reduce the uncertainty from the interpolation of surrounding tissue. A phantom experiment was designed to simulate a cyst and a tumor, where the tumor was overlaid with a structure that made it mimic a cyst. In 2D, the two targets appeared similar in composition, whereas spectral tomosynthesis revealed the exact compositional difference. However, the loss of discrimination signal due to spread from the plane of interest was of the same strength as the reduction of anatomical noise. Results from a preliminary investigation on clinical tomosynthesis images of solid lesions yielded results that were consistent with the phantom experiments, but were still to some extent inconclusive. We conclude that lesion characterization is feasible in spectral tomosynthesis, but more data, as well as refinement of the calibration and discrimination algorithms, are needed to draw final conclusions about the benefit compared to 2D.

  • 20.
    Cederström, Björn
    et al.
    KTH, Superseded Departments, Physics.
    Cahn, R. N.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Lundqvist, M.
    Nygren, D. R.
    Focusing hard X-rays with old LPs2000In: Nature, ISSN 0028-0836, Vol. 404, no 6781, 951-951 p.Article in journal (Refereed)
  • 21.
    Chen, Han
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    A photon-counting silicon-strip detector for digital mammography with an ultrafast 0.18-mu m CMOS ASIC2014In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 749, 1-6 p.Article in journal (Refereed)
    Abstract [en]

    We have evaluated a silicon-strip detector with a 0.18-mu m CMOS application specific integrated circuits (ASIC) containing 160 channels for use in photon-counting digital mammography. Measurements were performed at the Elettra light source using monochromatic X-ray beams with different energies and intensities. Energy resolution, Delta E/E-in, was measured to vary between 0.10 and 0.23 in the energy range of 15-40 keV. Pulse pileup has shown little effect on energy resolution.

  • 22.
    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.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    On imaging with or without grid in digital mammography2014In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, Vol. 9033, 903346- p.Article in journal (Refereed)
    Abstract [en]

    The grids used in digital mammography to reduce scattered radiation from the breast are not perfect and lead to partial absorption of primary radiation at the same time as not all of the scattered radiation is absorbed. It has therefore lately been suggested to remove the grids and correct for effects of scattered radiation by post-processing the images. In this paper, we investigated the dose reduction that might be achieved if the gird were to be removed. Dose reduction is determined as a function of PMMA thickness by comparing the contrast-to-noise ratios (CNRs) of images acquired with and without grid at a constant exposure. We used a theoretical model validated with Monte Carlo simulations and phantom studies. To evaluate the CNR, we applied aluminum filters of two different sizes, 4x8 cm2 and 1x1 cm 2. When the large Al filter was used, the resulting CNR value for the grid-less images was overestimated as a result of a difference in amount of scattered radiation in the background region and of the region covered by the filter, a difference that could be eliminated by selecting a region of interest close to the edge of the filter. The optimal CNR when the PMMA thickness was above about 4 cm was obtained with a grid, whereas removing the grid leaded to a dose saving in thinner PMMAs. The results suggest not removing grids in breast cancer screening.

  • 23.
    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.

  • 24.
    Chen, Han
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics.
    On image quality metrics and the usefulness of grids in digital mammography2015In: Journal of medical imaging (Bellingham, Wash.), ISSN 2329-4302, Vol. 2, no 1, 013501-013501 p.Article in journal (Refereed)
    Abstract [en]

    Antiscatter grids are used in digital mammography to reduce the scattered radiation from the breast and improve image contrast. They are, however, imperfect and lead to partial absorption of primary radiation, as well as failing to absorb all scattered radiation. Nevertheless, the general consensus has been that antiscatter grids improve image quality for the majority of breast types and sizes. There is, however, inconsistency in the literature, and recent results show that a substantial image quality improvement can be achieved even for thick breasts if the grid is disposed of. The purpose of this study was to investigate if differences in the considered imaging task and experimental setup could explain the different outcomes. We estimated the dose reduction that can be achieved if the grid were to be removed as a function of breast thickness with varying geometries and experimental conditions. Image quality was quantified by the signal-difference-to-noise ratio (SDNR) measured using an aluminum (Al) filter on blocks of poly(methyl methacrylate) (PMMA), and images were acquired with and without grid at a constant exposure. We also used a theoretical model validated with Monte Carlo simulations. Both theoretically and experimentally, the main finding was that when a large [Formula: see text] Al filter was used, the SDNR values for the gridless images were overestimated up to 25% compared to the values for the small [Formula: see text] filter, and gridless imaging was superior for any PMMA thickness. For the small Al filter, gridless imaging was only superior for PMMAs thinner than 4cm. This discrepancy can be explained by a different sensitivity to and sampling of the angular scatter spread function, depending on the size of the contrast object. The experimental differences were eliminated either by using a smaller region of interest close to the edge of the large filter or by applying a technique of scatter correction by subtracting the estimated scatter image. These results explain the different conclusions reported in the literature and show the importance of the selection of measurement methods. Since the interesting structures in mammography are below the 1-cm scale, we advocate the use of smaller contrast objects for assessment of antiscatter grid performance.

  • 25.
    Chen, Han
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Optimization Of Beam Quality For Photon-Counting Spectral Computed Tomography In Head Imaging: Simulation Study2015In: Journal of Medical Imaging, ISSN 2329-4302, E-ISSN 2329-4310, Vol. 2, no 4, 043504-1-043504-16 p., 043504Article in journal (Refereed)
    Abstract [en]

    Head computed tomography (CT) plays an important role in the comprehensive evaluation of acutestroke. Photon-counting spectral detectors, as promising candidates for use in the next generation of x-ray CTsystems, allow for assigning more weight to low-energy x-rays that generally contain more contrast information.Most importantly, the spectral information can be utilized to decompose the original set of energy-selectiveimages into several basis function images that are inherently free of beam-hardening artifacts, a potential ad-vantage for further improving the diagnosis accuracy. We are developing a photon-counting spectral detector forCT applications. The purpose of this work is to determine the optimal beam quality for material decomposition intwo head imaging cases: nonenhanced imaging and K-edge imaging. A cylindrical brain tissue of 16-cm diam-eter, coated by a 6-mm-thick bone layer and 2-mm-thick skin layer, was used as a head phantom. The imagingtarget was a 5-mm-thick blood vessel centered in the head phantom. In K-edge imaging, two contrast agents,iodine and gadolinium, with the same concentration (5mg∕mL) were studied. Three parameters that affect beamquality were evaluated: kVp settings (50 to 130 kVp), filter materials (Z¼13to 83), and filter thicknesses [0 to 2half-value layer (HVL)]. The image qualities resulting from the varying x-ray beams were compared in terms oftwo figures of merit (FOMs): squared signal-difference-to-noise ratio normalized by brain dose (SDNR2∕BD) andthat normalized by skin dose (SDNR2∕SD). For nonenhanced imaging, the results show that the use of the 120-kVp spectrum filtered by 2 HVL copper (Z¼29) provides the best performance in both FOMs. When iodine isused in K-edge imaging, the optimal filter is 2 HVL iodine (Z¼53) and the optimal kVps are 60 kVp in terms ofSDNR2∕BD and 75 kVp in terms of SDNR2∕SD. A tradeoff of 65 kVp was proposed to lower the potential riskof skin injuries if a relatively long exposure time is necessarily performed in the iodinated imaging. In the case ofgadolinium imaging, both SD and BD can be minimized at 120 kVp filtered with 2 HVL thulium (Z¼69). Theresults also indicate that with the same concentration and their respective optimal spectrum, the values ofSDNR2∕BD and SDNR2∕SD in gadolinium imaging are, respectively, around 3 and 10 times larger thanthose in iodine imaging. However, since gadolinium is used in much lower concentrations than iodine in theclinic, iodine may be a preferable candidate for K-edge imaging.

  • 26.
    Dahlman, Nils
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Fredenberg, Erik
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Aslund, Magnus
    Lundqvist, Mats
    Diekmann, Felix
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Evaluation of photon-counting spectral breast tomosynthesis2011In: MEDICAL IMAGING 2011: PHYSICS OF MEDICAL IMAGING / [ed] Pelc, NJ; Samei, E; Nishikawa, RM, 2011, Vol. 7961Conference paper (Refereed)
    Abstract [en]

    We have designed a mammography system that for the first time combines photon-counting spectral imaging with tomosynthesis. The present study is a comprehensive physical evaluation of the system; tomosynthesis, spectral imaging, and the combination of both are compared using an ideal-observer model that takes anatomical noise into account. Predictions of signal and noise transfer through the system are verified by contrast measurements on a tissue phantom and 3D measurements of MTF and NPS. Clinical images acquired with the system are discussed in view of the model predictions.

  • 27.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    A collimator arrangement for varying the exposed surface of an x-ray detector in an x-ray imaging system includes an arrangement of two relatively displaceable parts having overlapping slots producing an adjustable slot width2000Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    In an x-ray imaging system, a variable exposure of a semiconductor, gas or sensitive film x-ray detector (43) to x-rays from a source is provided by a collimator (42). The collimator is arranged as two parts (42a, 42b) that are displaceable relative to each other, each having several identical slots in different planes that overlap. Relative displacement by a motor/actuator produces a variable width slot (45) that is adjustable between fully closed and open positions.

  • 28.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Challenges and Opportunities with Photon Counting CT2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 6, 3989-3989 p.Article in journal (Other academic)
  • 29.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Collimator element2001Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A beam collimator arrangement for scanned-slot x-ray imaging having one or several collimators in an x-ray apparatus is disclosed. The beam collimator arrangement includes an x-ray source; an x-ray image receiver positioned to receive x-rays from the x-ray source; a compressor or means for compressing a female breast to be examined where the compressor is positionable between the x-ray source and the x-ray image receiver; and the beam collimator is positioned between the x-ray source and the compressor. The beam collimator arrangement is arranged on a carrying structure to displace the beam collimator arrangement between a first position when no x-ray exposure is conducted and a second position before x-ray exposure is initiated.

  • 30.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    MAMMOGRAPHY SHIFTS TOWARD SPECTRAL IMAGING-Photon counting is an intuitive way to detect x-rays, which by nature are digital and have a color spectrum2009In: Diagnostic Imaging, Vol. 25, no 7Article in journal (Refereed)
  • 31.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Method and apparatus for simplified alignment in x-ray imaging1999Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The invention relates to a method and an apparatus for simplified alignment in scanned slot x-ray imaging. The apparatus has a first collimator (102) and a second collimator (104) arranged in a first distance (a) and a second distance (b), respectively, from a radiation source (100). Each collimator is provided with a slot (102a, 104a) and a detector (106) is located under the second collimator slot, said slot of said second collimator being wider than the said slot of said first collimator and said detector under the second slot is wider than the first collimator slot and the second collimator slot. The slot (104a) of said second collimator has a width (y') not less than a safety margin and the product of the width (x) of the slot (102a) of said first collimator (102) and said second distance (b) divided with the said first distance (a) for allowing a misalignment with respect to a central symmetry line (105) of said slots (102a, 104a).

  • 32.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Metod och anordning att genom etsning anordna ett blockerande medel för att förhindra laddningsdelning mellan näraliggande röntgensensorer: [Method and arrangement relating to x-ray imaging]2000Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A detector (200) comprises a number of spaced-apart sensor strips (220) arranged on a substrate, while a blocking arrangement is in the form of strips (230) covering the spaces between the sensor strips. The blocking strips also cover parts of the sensor strips and are made of a material such as wolfram, lead etc. which can be arranged as strips directly on the sensors. AN Independent claim is included for an arrangement for detecting signals from converted photons.

  • 33.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    MO‐D‐210A‐01: Photon Counting Detectors for Mammography2009In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 36, no 6, 2699-2699 p.Article in journal (Refereed)
    Abstract [en]

    Mammography is currently one of the most common x‐ray imaging examinations. More than 100 million women worldwide are screened every year and early detection of breast cancer through mammography has proven to be a key to significantly reduced mortality. The requirement on spatial resolution as well as contrast resolution is very high in order to detect and diagnose the cancer. Moreover, because of the large number of women going through this procedure and the fact that more than 99 % are healthy, it also becomes very important to minimize the radiation dose. Photon counting may be one way to meet the demands and mammography is the first modality in x‐ray imaging to implement photon counting detectors. FDA approval is still pending but they are currently in routine clinical use in more than 15 countries. The photon counting enables a discrimination of all electronic noise and a more optimum use of the information in each x‐ray. The absence of electronic noise is particularly important in low dose applications, in for example tomosynthesis a number of exposures from different angles are required and since the dose in each projection is just a fraction of the total dose for a mammogram the sensitivity to electronic noise will increase. Using the spectral information for each x‐ray it is in principle possible to deduce the elemental composition of an object in the breast. This could for example be used to enhance microcalcifications relative to soft tissue and differentiate water from fat in cysts. Recently contrast mammography has attracted significant attention. In this application Iodine is used as a contrast media to visualize the vascular structure. As in breast MRI the cancer stand out because of the leaky vessels resulting from its angiogenesis. A photon counting detector gives a unique opportunity to image the Iodine through spectral imaging by adjusting one of the thresholds to its K‐edge. Challenges for photon counting in mammography are high rates of x‐rays, both to generate the required flux at the source and to handle the rates at the detector without pile‐up. Even more difficult to handle are the charge sharing between detector pixels which, if not corrected for, will compromise the energy information. The current status of photon counting detectors in mammography will be described together with strategies to overcome the pit‐falls. Also future possibilities with spectral imaging in mammography will be investigated and examples from ongoing clinical trials will be given. Learning Objectives: 1. Status of photon counting detectors in mammography 2. Pit‐falls and opportunities with photon counting detectors for mammography 3. Future applications based on spectral detectors for mammography.

  • 34.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Philips Microdose Mammography - the Technology and Physics Behind the First FDA Approved Photon Counting X-Ray Imaging System2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 6, 4017-4017 p.Article in journal (Other academic)
    Abstract [en]

    Purpose: To validate the use of 4D‐Computed Tomography (4D‐CT) for pre‐treatment evaluation of fractional regional ventilation in patients with lung cancer by benchmarking its performance against scintigraphy V/Q imaging, the current gold‐standard. The second aim is to further corroborate the results of 4D‐CT estimation of lung aeration against the results of Pulmonary Function Testing. Methods: Scintigraphy V/Q and 4D‐CT studies were acquired in four lung cancer patients prior to treatment with radiation therapy. PFTs were acquired in 3 out of the 4 patients. 4D‐CT images were used to create 3D fractional regional ventilation maps by applying a ‘mass correction’ and subtracting the spatially matched end‐exhale and end‐inhale images. Ventilation maps were then collapsed in the anterior‐posterior dimension to create a coronal 2D projection image consistent with the scintigraphy V/Q images. The left and right lung fields were isolated on the projection image and divided into 3 sections of equal height. Summation of the signal intensity in each of the sections was carried out on the maps analogous to the analysis performed on V/Q scans and statistically compared using the Kendall's tau rank correlation. Results: The non‐parametric Kendall's tau estimate ranged between 0.87–0.95 for N=4, with corresponding p‐values ranging between 0.005–0.0002. Mean functional residual capacities (FRC) from the PFTs (N=3) versus calculated FRCs was 2.7 +/− 0.6 L and 2.4 +/− 0.7 L, and the null hypothesis could not be rejected (p = 0.61). The mean fractional regional ventilation versus the ratio of tidal‐volume/FRC was 0.24 +/− 0.11 and 0.22 +/− 0.08, and the null hypothesis could not be rejected (p=0.73). Conclusions: There was a strong correlation between 4D‐CT and scintigraphy V/Q. The similarity between the calculated and measured FRCs further validates the utility of 4D‐CT and supports its use in evaluating lung ventilation in patients with pulmonary neoplasms.

  • 35.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    System and method for imaging using radio-labeled substances, especially suitable for studying of biological processes2006Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    An imaging system is based on in-line x-ray optics arranged in combination with an X-ray detector to detect radiation from radio-labeled substances within an object to be imaged. This arrangement will provide a nuclear imaging device with potentially orders of magnitude higher resolution and efficiency and it will moreover be relatively easy to align and to produce and assemble in large quantities.

  • 36.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    TH‐A‐217BCD‐01: Challenges and Opportunities with Photon Counting CT2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 6, 3989-3989 p.Article in journal (Refereed)
    Abstract [en]

    There is currently a large interest in photon counting CT detector research in both academia and industry. There are several detector systems and strategies to handle major challenges such as the very high count‐rate, while the energy information for each photon is retained. Another challenge is cross talk, which may compromise the energy estimation for the photons and can cause double counts, which gets worse with smaller pixel size. If implemented in the clinic, photon counting CT will likely enable a dose reduction when this is important, as for example in pediatric CT. Photon counting CT will also make possible quantitative measurements, energy weighting and/or tissue decomposition techniques that can be of great importance for a number of imaging tasks.

  • 37.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    TH‐E‐217A‐01: Philips Microdose Mammography ‐ the Technology and Physics Behind the First FDA Approved Photon Counting X‐Ray Imaging System2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 6, 4017-4017 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: To validate the use of 4D‐Computed Tomography (4D‐CT) for pre‐treatment evaluation of fractional regional ventilation in patients with lung cancer by benchmarking its performance against scintigraphy V/Q imaging, the current gold‐standard. The second aim is to further corroborate the results of 4D‐CT estimation of lung aeration against the results of Pulmonary Function Testing. Methods: Scintigraphy V/Q and 4D‐CT studies were acquired in four lung cancer patients prior to treatment with radiation therapy. PFTs were acquired in 3 out of the 4 patients. 4D‐CT images were used to create 3D fractional regional ventilation maps by applying a ‘mass correction’ and subtracting the spatially matched end‐exhale and end‐inhale images. Ventilation maps were then collapsed in the anterior‐posterior dimension to create a coronal 2D projection image consistent with the scintigraphy V/Q images. The left and right lung fields were isolated on the projection image and divided into 3 sections of equal height. Summation of the signal intensity in each of the sections was carried out on the maps analogous to the analysis performed on V/Q scans and statistically compared using the Kendall's tau rank correlation. Results: The non‐parametric Kendall's tau estimate ranged between 0.87–0.95 for N=4, with corresponding p‐values ranging between 0.005–0.0002. Mean functional residual capacities (FRC) from the PFTs (N=3) versus calculated FRCs was 2.7 +/− 0.6 L and 2.4 +/− 0.7 L, and the null hypothesis could not be rejected (p = 0.61). The mean fractional regional ventilation versus the ratio of tidal‐volume/FRC was 0.24 +/− 0.11 and 0.22 +/− 0.08, and the null hypothesis could not be rejected (p=0.73). Conclusions: There was a strong correlation between 4D‐CT and scintigraphy V/Q. The similarity between the calculated and measured FRCs further validates the utility of 4D‐CT and supports its use in evaluating lung ventilation in patients with pulmonary neoplasms.

  • 38.
    Danielsson, Mats
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Bohm, Christian
    3rd International Conference on Imaging Techniques in Subatomic Physics, Astrophysics, Medicine, Biology and Industry - Stockholm, Sweden, June 27-30, 2006: Preface2007In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 580, no 2, V-V p.Article in journal (Other academic)
  • 39.
    Danielsson, Mats
    et al.
    KTH, Superseded Departments, Physics.
    Fonte, P.
    Francke, T.
    Iacobaeus, C.
    Östling, J.
    Peskov, V.
    Novel gaseous detectors for medical imaging2004In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 518, no 1-2, 406-410 p.Article in journal (Refereed)
    Abstract [en]

    We have developed and successfully tested prototypes of two new types of gaseous detectors for medical imaging purposes. The first one is called the Electronic Portal Imaging Device (EPID). It is oriented on monitoring and the precise alignment of the therapeutic cancer treatment beam (pulsed gamma radiation) with respect to the patient's tumor position. The latest will be determined from an X-ray image of the patient obtained in the time intervals between the gamma pulses. The detector is based on a sandwich of hole-type gaseous detectors (GEM and glass microcapillary plates) with metallic gamma and X-ray converters coated with CsI layers. The second detector is an X-ray image scanner oriented on mammography and other radiographic applications. It is based on specially developed by us high rate RPCs that are able to operate at rates of 10(5) HZ/mm(2) with a position resolution better than 50 mum at 1 atm. The quality of the images obtained with the latest version of this device were in most cases more superior than those obtained from commercially available detectors.

  • 40. Danielsson, Mats
    et al.
    Hjärn, Torbjörn
    X-ray protection device2002Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The present invention relates a shielding arrangement (27, 47, 57, 77) in an x-ray apparatus (20, 40, 400), preferably for mammography examination, at least comprising an x-ray source (21, 41), a collimator arrangement (22, 42) and a detector assembly (23, 43), whereby said collimator is arranged between said x-ray source and said detector assembly and through which x-rays pass. The shielding arrangement (27, 47), at least partly made of x-ray blocking material and provided for blocking scattering and/or reflecting x-rays is arranged, at least partly, in a space between in said x-ray source (21, 41) and collimator (22, 42).

  • 41.
    Danielsson, Mats
    et al.
    KTH, Superseded Departments, Physics.
    Lammroth, Theresa
    Rapp, Lennart
    Beam collimator arrangement for scanned-slot mammography has x-ray source, x-ray image receiver and female breast compression paddles2001Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    The apparatus comprises an x-ray source (21) and an x-ray image receiver (25). The breast (26) to be examined is placed between compression paddles (23,24) which flatten it, maximizing breast exposure to allow a sufficient contrast to be obtained. The collimator arrangement (22) can be moved to a parking position (P) when no x-ray exposure is conducted, and an active position (A) before x-ray exposure is initiated. The beam collimator is positioned between the x-ray source and the compressor paddles. An Independent claim is included for a mammography apparatus.

  • 42. Eriksson, Ulf
    et al.
    Danielsson, Mats
    KTH, Superseded Departments, Physics.
    Arrangement relating to an X-ray imaging apparatus for adjusting a number of settings when performing recurrent mammography using recorded settings from recent X-rays2000Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    f a patient has been examined before and the relevant data have been stored in the database (21), the system is activated by entering the patient identity through an input device (20) and a main control unit (15) controls sub-control units (16-19) according to the data, to position an X-ray source (11) at the correct height and to position pedals (13) at the correct height to enclose a breast. The pedals are moved by a motor (19) to compress the breast. AN Independent claim is included for a method of adjusting settings of an X-ray device.

  • 43.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Energy filtering with x-ray lenses: Optimization for photon-counting mammography2010In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 139, 339-342 p.Article in journal (Refereed)
    Abstract [en]

    Chromatic properties of the multi-prism and prism-array x-ray lenses (MPL and PAL) can potentially be utilized for efficient energy filtering and dose reduction in mammography. The line-shaped foci of the lenses are optimal for coupling to photon-counting silicon strip detectors in a scanning system. A theoretical model was developed and used to investigate the benefit of two lenses compared to an absorption-filtered reference system. The dose reduction of the MPL filter was 15% compared to the reference system at matching scan time, and the spatial resolution was higher. The dose of the PAL-filtered system was found to be 20% lower than for the reference system at equal scan time and resolution, and only 20% higher than for a monochromatic beam. An investigation of some practical issues remains, including the feasibility of brilliant-enough x-ray sources and manufacturing of a polymer PAL.

  • 44.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Lundqvist, Mats
    Ribbing, Carolina
    Åslund, Magnus
    Diekmann, Felix
    Nishikawa, Robert
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Contrast-enhanced dual-energy subtraction imaging using electronic spectrum-splitting and multi-prism x-ray lenses2008In: Medical Imaging 2008 - Physics of Medical Imaging: PTS 1-3 / [ed] Hsieh, J; Samei, E, 2008, Vol. 6913, 91310-91310 p.Conference paper (Refereed)
    Abstract [en]

    Dual-energy subtraction imaging (DES) is a method to improve the detectability of contrast agents over a lumpy background. Two images, acquired at x-ray energies above and below an absorption edge of the agent material, are logarithmically subtracted, resulting in suppression of the signal from the tissue background and a relative enhancement of the signal from the agent. Although promising, DES is still not widely used in clinical practice. One reason may be the need for two distinctly separated x-ray spectra that are still close to the absorption edge, realized through dual exposures which may introduce motion unsharpness. In this study, electronic spectrum-splitting with a silicon-strip detector is theoretically and experimentally investigated for a mammography model with iodinated contrast agent. Comparisons are made to absorption imaging and a near-ideal detector using a signal-to-noise ratio that includes both statistical and structural noise. Similar to previous studies, heavy absorption filtration was needed to narrow the spectra at the expense of a large reduction in x-ray flux. Therefore, potential improvements using a chromatic multi-prism x-ray lens (MPL) for filtering were evaluated theoretically. The MPL offers a narrow tunable spectrum, and we show that the image quality can be improved compared to conventional filtering methods.

  • 45.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Ribbing, Carolina
    Uppsala Univ..
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    A low-absorption x-ray energy filter for small-scale applications2009In: Optics Express, ISSN 1094-4087, Vol. 17, no 14, 11388-11398 p.Article in journal (Refereed)
    Abstract [en]

    We present an experimental and theoretical evaluation of an x-ray energy filter based on the chromatic properties of a prism-array lens (PAL). It is intended for small-scale applications such as medical imaging. The PAL approximates a Fresnel lens and allows for high efficiency compared to filters based on ordinary refractive lenses, however at the cost of a lower energy resolution. Geometrical optics was found to provide a good approximation for the performance of a flawless lens, but a field-propagation model was used for quantitative predictions. The model predicted a 0.29 ΔE/E energy resolution and an intensity gain of 6.5 for a silicon PAL at 23.5 keV. Measurements with an x-ray tube showed good agreement with the model in energy resolution and peak energy, but a blurred focal line contributed to a 29% gain reduction. We believe the blurring to be caused mainly by lens imperfections, in particular at the periphery of the lens.

  • 46.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Ribbing, Carolina
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Prism-array lenses for energy filtering in medical X-ray imaging: Physics of Medical Imaging, Pts 1-32007In: Medical Imaging 2007: Physics of Medical Imaging, Pts 1-3 / [ed] Hsieh, J; Flynn, MJ, BELLINGHAM: SPIE-INT SOC OPTICAL ENGINEERING , 2007, Vol. 6510, U270-U281 p.Conference paper (Refereed)
    Abstract [en]

    Conventional energy filters for x-ray imaging are based on absorbing materials which attenuate low energy photons, sometimes combined with an absorption edge, thus also discriminating towards 'photons of higher energies. These filters are fairly inefficient, in particular for photons of higher energies, and other methods for achieving a narrower bandwidth have been proposed. Such methods include various types of monochromators, based on for instance mosaic crystals or refractive multi-prism x-ray lenses (MPL's). Prism-array lenses (PAL's) are similar to MPL's, but are shorter, have larger apertures, and higher transmission. A PAL consists of a number of small prisms arranged in columns perpendicular to the optical axis. The column height decreases along the optical axis so that the projection of lens material is approximately linear with a Resnel phase-plate pattern superimposed on it. The focusing effect is one dimensional, and the lens is chromatic. Hence, unwanted energies can be blocked by placing a slit in the image plane of a desired energy. We present the first experimental and theoretical results on an energy filter based on a silicon PAL. The study includes an evaluation of the spectral shaping properties of the filter as well as a quantification of the achievable increase in dose efficiency compared to standard methods. Previously, PAL's have been investigated with synchrotron radiation, but in this study a medical imaging setup, based on a regular x-ray tube, is considered.

  • 47.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Åslund, Magnus
    KTH, School of Engineering Sciences (SCI), Physics.
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    An efficient pre-object collimator based on an x-ray lens2009In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 36, no 2, 626-633 p.Article in journal (Refereed)
    Abstract [en]

    A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31–1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45–1.54 gain in resolution.

  • 48.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Åslund, Magnus
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Lundqvist, Mats
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Imaging with multi-prism x-ray lenses2008In: Medical Imaging 2008 - Physics of Medical Imaging: PTS 1-3 / [ed] Hsieh, J; Samei, E, 2008, Vol. 6913, 91308-91308 p.Conference paper (Refereed)
    Abstract [en]

    The multi-prism lens (MPL) is a refractive x-ray lens consisting of two rows of prisms facing each other at an angle. Rays entering the lens at the periphery will encounter a larger number of prisms than will central ones, hence experiencing a greater refraction. The focusing effect of the MPL can be used to gather radiation from a large aperture onto a smaller detector, and accordingly to make better use of the available x-ray flux in medical x-ray imaging. Potential advantages of a better photon economy include shorter acquisition times, a reduced tube loading, or an improved resolution. Since the focusing effect is one-dimensional it matches the design of scanning systems. In this study we present the first images acquired with an MPL instead of the pre-breast slit collimator in a scanning mammography system. According to the measurements, the MPL is able to increase the flux 32% at equal resolution compared to the slit collimator, or to improve the resolution 2.4 mm(-1) at equal flux. If used with a custom-made absorption filter in a clinical set-up, the gain of flux of the MPL is expected to be at least 45%, and the corresponding improvement in resolution to be 3 mm(-1).

  • 49.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Åslund, Magnus
    Ribbing, Carolina
    Uppsala universitet.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    A Tunable Energy Filter for Medical X-Ray Imaging2008In: X-Ray Optics and Instrumentation, ISSN 1687-7632, Vol. 2008Article in journal (Refereed)
    Abstract [en]

    A multiprism lens (MPL) is a refractive X-ray lens, and its chromatic properties can be employed in an energy filtering setup to obtain a narrow tunable X-ray spectrum. We present the first evaluation of such a filter for medical X-ray imaging. The experimental setup yields a 6.6 gain of flux at 20 keV, and we demonstrate tunability by altering the energy spectrum to center also around 17 and 23 keV. All measurements are found to agree well with ray-tracing and a proposed geometrical model. Compared to a model mammography system with absorption filtering, the experimental MPL filter reduces dose 13–25% for 3–7 cm breasts if the spectrum is centered around the optimal energy. Additionally, the resolution is improved 2.5 times for a 5 cm breast. The scan time is increased 3 times but can be reduced with a slightly decreased energy filtering and resolution.

  • 50.
    Fredenberg, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Stayman, J. Webster
    Siewerdsen, Jeffrey H.
    Åslund, Magnus
    Ideal-observer detectability in photon-counting differential phase-contrast imaging using a linear-systems approach2012In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, no 9, 5317-5335 p.Article in journal (Refereed)
    Abstract [en]

    Purpose: To provide a cascaded-systems framework based on the noise-power spectrum (NPS), modulation transfer function (MTF), and noise-equivalent number of quanta (NEQ) for quantitative evaluation of differential phase-contrast imaging (Talbot interferometry) in relation to conventional absorption contrast under equal-dose, equal-geometry, and, to some extent, equal-photon-economy constraints. The focus is a geometry for photon-counting mammography. Methods: Phase-contrast imaging is a promising technology that may emerge as an alternative or adjunct to conventional absorption contrast. In particular, phase contrast may increase the signal-difference-to-noise ratio compared to absorption contrast because the difference in phase shift between soft-tissue structures is often substantially larger than the absorption difference. We have developed a comprehensive cascaded-systems framework to investigate Talbot interferometry, which is a technique for differential phase-contrast imaging. Analytical expressions for the MTF and NPS were derived to calculate the NEQ and a task-specific ideal-observer detectability index under assumptions of linearity and shift invariance. Talbot interferometry was compared to absorption contrast at equal dose, and using either a plane wave or a spherical wave in a conceivable mammography geometry. The impact of source size and spectrum bandwidth was included in the framework, and the trade-off with photon economy was investigated in some detail. Wave-propagation simulations were used to verify the analytical expressions and to generate example images. Results: Talbot interferometry inherently detects the differential of the phase, which led to a maximum in NEQ at high spatial frequencies, whereas the absorption-contrast NEQ decreased monotonically with frequency. Further, phase contrast detects differences in density rather than atomic number, and the optimal imaging energy was found to be a factor of 1.7 higher than for absorption contrast. Talbot interferometry with a plane wave increased detectability for 0.1-mm tumor and glandular structures by a factor of 3-4 at equal dose, whereas absorption contrast was the preferred method for structures larger than similar to 0.5 mm. Microcalcifications are small, but differ from soft tissue in atomic number more than density, which is favored by absorption contrast, and Talbot interferometry was barely beneficial at all within the resolution limit of the system. Further. Talbot interferometry favored detection of "sharp" as opposed to "smooth" structures, and discrimination tasks by about 50% compared to detection tasks. The technique was relatively insensitive to spectrum bandwidth, whereas the projected source size was more important. If equal photon economy was added as a restriction, phase-contrast efficiency was reduced so that the benefit for detection tasks almost vanished compared to absorption contrast, but discrimination tasks were still improved close to a factor of 2 at the resolution limit. Conclusions: Cascaded-systems analysis enables comprehensive and intuitive evaluation of phase-contrast efficiency in relation to absorption contrast under requirements of equal dose, equal geometry, and equal photon economy. The benefit of Talbot interferometry was highly dependent on task, in particular detection versus discrimination tasks, and target size, shape, and material. Requiring equal photon economy weakened the benefit of Talbot interferometry in mammography.

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