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  • 1.
    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, E-ISSN 1094-4087, Vol. 17, no 14, p. 11388-11398Article 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.

  • 2.
    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, p. 626-633Article 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.

  • 3.
    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, p. 91308-91308Conference 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).

  • 4.
    Mi, Wujun
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Holmberg, Anders
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Fabrication of circular sawtooth gratings using focused UV lithography2016In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 26, no 3, article id 035001Article in journal (Refereed)
    Abstract [en]

    AbstractThis paper presents a novel micro-fabrication method using focused ultraviolet (UV) light to manufacture three-dimensional sawtooth structures in ultra-thick negative photoresist to fabricate a novel multi-prism x-ray lens. The method uses a lens to shape the UV beam instead of the photomask conventionally used in UV lithography. Benefits of this method include the ability to manufacture sawtooth structures in free form, for example in circular shapes as well as arrays of these shapes, and in resist that is up to 76 μm thick.To verify the method, initially a simple simulation based on Fourier optics was done to predict the exposure energy distribution in the photoresist. Furthermore, circular sawtooth gratings were manufactured in a 76 μm SU-8 resist. The UV lens was fabricated using electron beam lithography and then used to expose the SU-8 with UV light. This paper details the complete developed process, including pre-exposure with an e-beam and cold development, which creates stable sawtooth structures. The measured profile was compared to the ideal sawtooth and the simulation. The main discrepancy was in the smallest feature size, the sawtooth tips, which were wider than the desired structures, as would be expected by simulation.

  • 5.
    Mi, Wujun
    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.
    Efficient proximity effect correction method based on multivariate adaptive regression splines for grayscale e-beam lithography2014In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 32, no 3, p. 031602-Article in journal (Refereed)
    Abstract [en]

    Grayscale electron beam lithography is an important technique to manufacture three-dimensional (3D) micro- and nano-structures, such as diffractive optical devices and Fresnel lenses. However, the proximity effect due to the scattering of electrons may cause significant error to the desired 3D structure. Conventional proximity correction methods depend on the exposure energy distribution which sometimes is difficult to obtain. In this study, the authors develop a novel proximity effect correction method based on multivariate adaptive regression splines, which takes exposure energy and development into consideration simultaneously. To evaluate the method, a Fresnel lens was fabricated through simulation and experiment. The measurements demonstrate the feasibility and validity of the method.

  • 6.
    Nillius, Peter
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Geometric scattering in prism-array lenses for hard x-rays: Measurements, simulations and models2012In: X-Ray Optics And Microanalysis, American Institute of Physics (AIP), 2012, Vol. 1437, p. 111-115Conference paper (Refereed)
    Abstract [en]

    This work investigates the properties of off-axis focusing of prism-array lenses. Raytracing simulations are in agreement with measurements on a planar silicon prism-array lens at 13.4 keV. The simulations show that refractions and reflections on the paraxial side of the prisms cause scattering. This geometric scattering is the main impacting factor when focusing sources that are off the optical axis. For low-attenuating materials it also limits the effective aperture on axis. A new analytical model that is able to predict the amount of scattering is presented. Such a model is for example useful when optimising optical systems, but also to understand the limits and possibilities prism-array lenses.

  • 7.
    Nillius, Peter
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Image Analysis using the Physics of Light Scattering2004Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    Any generic computer vision algorithm must be able to copewith the variations in appearance of objects due to differentillumination conditions. While these variations in the shadingof a surface may seem a nuisance, they in fact containinformation about the world. This thesis tries to provide anunderstanding what information can be extracted from theshading in a single image and how to achieve this. One of thechallenges lies in finding accurate models for the wide varietyof conditions that can occur.

    Frequency space representations are powerful tools foranalyzing shading theoretically. Surfaces act as low-passfilters on the illumination making the reflected lightband-limited. Hence, it can be represented by a finite numberof components in the Fourier domain, despite having arbitraryillumination. This thesis derives a basis for shading byrepresenting the illumination in spherical harmonics and theBRDF in a basis for isotropic reflectance. By analyzing thecontributing variance of this basis it is shown how to createfinite dimensional representations for any surface withisotropic reflectance.

    The finite representation is used to analytically derive aprincipal component analysis (PCA) basis of the set of imagesdue to the variations in the illumination and BRDF. The PCA isperformed model-based so that the variations in the images aredescribed by the variations in the illumination and the BRDF.This has a number of advantages. The PCA can be performed overa wide variety of conditions, more than would be practicallypossible if the images were captured or rendered. Also, thereis an explicit mapping between the principal components and theillumination and BRDF so that the PCA basis can be used as aphysical model.

    By combining a database of captured illumination and adatabase of captured BRDFs a general basis for shading iscreated. This basis is used to investigate materialclassification from a single image with known geometry butarbitrary unknown illumination. An image is classified byestimating the coecients in this basis and comparing them to adatabase. Experiments on synthetic data show that materialclassification from reflectance properties is hard. There aremis-classifications and the materials seem to cluster intogroups. The materials are grouped using a greedy algorithm.Experiments on real images show promising results.

    Keywords:computer vision, shading, illumination,reflectance, image irradiance, frequency space representations,spherical harmonics, analytic PCA, model-based PCA, materialclassification, illumination estimation

  • 8.
    Nillius, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Theoretical Bounds and Optimal Configurations for Multi-Pinhole SPECT2009In: 2008 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (2008 NSS/MIC), 2009, p. 5020-5022Conference paper (Refereed)
    Abstract [en]

    The pinhole geometry in SPECT has an inherent trade-off between resolution and sensitivity. High resolution requires a small aperture which on the other hand directly reduces the rate of detected photons. Recent systems overcome this to some extent by using multiple pinholes spread out around the imaging object, effectively increasing the sensitivity with a factor equal to the number of pinholes. The images of each pinhole must fit on the detector without overlap. This creates another trade-off between resolution, sensitivity and the field-of-view (FOV) of the system. The present work analytically analyzes the properties of the multi-pinhole SPECT geometry. Optimal configurations are identified and characterized. One of the main results is that there exists a theoretical upper bound for the sensitivity given the resolution and the FOV. This upper bound is proportional to the square of the resolution and inversely proportional to the square FOV diameter. This means that if we want to improve the resolution by a factor of ten, the sensitivity will go down a factor 100, unless we decrease the FOV an equal amount. The bound can not be broken even if the detector sphere is infinitely large. One important parameter when designing a system is how close it will be to its theoretical bound. The closer to the bound the more extreme the system will be, in terms of size and number of pinholes. A moderate distance away from the bound the proportions of the system are more realistic.

  • 9.
    Nillius, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Theoretical Bounds and System Design for Multipinhole SPECT2010In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 29, no 7, p. 1390-1400Article in journal (Refereed)
    Abstract [en]

    The pinhole camera in single photon emission computed tomography (SPECT) has an inherent trade-off between resolution and sensitivity. Recent systems overcome this to some extent by utilizing multiple pinholes distributed around the imaging object. The present work is a theoretical study on how to optimally construct such systems. We use an analytic model to analyze the multipinhole SPECT geometry and identify the underlying trade-offs. One of the results is the derivation of the upper bound for the sensitivity, given the geometric resolution and field-of-view (FOV). Reaching this bound requires an infinitely large detector. However, a sensitivity very close to the upper bound can be achieved by a system with realistic proportions. We show that it is usually possible to get a sensitivity that is 95%-99% of the upper bound. Further analysis reveals a trade-off between sensitivity, magnification, and the number of pinholes. Based on this new theory, we develop a strategy for multipinhole SPECT design, from which a number of example systems are computed. Penetration in the pinhole knife edge is accounted for by using the resolution and sensitivity equivalent apertures.

  • 10.
    Nillius, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Fredenberg, Erik
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Large-aperture focusing of high-energy x rays with a rolled polyimide film2011In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 36, no 4, p. 555-557Article in journal (Refereed)
    Abstract [en]

    We describe a point-focusing x-ray lens made of a rolled polyimide film with etched prisms. The resulting lens is a cylinder with a large number of prisms forming an internal conic structure. The method allows for the manufacturing of lenses with large apertures and short focal lengths, for energies up to at least 100 keV. In order to evaluate the concept, we have hand-rolled a few lenses and evaluated them at a synchrotron source. The measured performance of the prototype is promising, and deviations from the theoretical limits are quantitatively explained. (C) 2011 Optical Society of America

  • 11.
    Nillius, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Klamra, Wlodek
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sibczynski, Pawel
    Sharma, Diksha
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Badano, Aldo
    Light output measurements and computational models of microcolumnar CsI scintillators for x-ray imaging2015In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 42, no 2, p. 600-605Article in journal (Refereed)
    Abstract [en]

    Purpose: The authors report on measurements of light output and spatial resolution of microcolumnar CsI:Tl scintillator detectors for x-ray imaging. In addition, the authors discuss the results of simulations aimed at analyzing the results of synchrotron and sealed-source exposures with respect to the contributions of light transport to the total light output. Methods: The authors measured light output from a 490-mu m CsI:Tl scintillator screen using two setups. First, the authors used a photomultiplier tube (PMT) to measure the response of the scintillator to sealed-source exposures. Second, the authors performed imaging experiments with a 27-keV monoenergetic synchrotron beam and a slit to calculate the total signal generated in terms of optical photons per keV. The results of both methods are compared to simulations obtained with hybrid MANTIS, a coupled x-ray, electron, and optical photon Monte Carlo transport package. The authors report line response (LR) and light output for a range of linear absorption coefficients and describe a model that fits at the same time the light output and the blur measurements. Comparing the experimental results with the simulations, the authors obtained an estimate of the absorption coefficient for the model that provides good agreement with the experimentally measured LR. Finally, the authors report light output simulation results and their dependence on scintillator thickness and reflectivity of the backing surface. Results: The slit images from the synchrotron were analyzed to obtain a total light output of 48 keV(-1) while measurements using the fast PMT instrument setup and sealed-sources reported a light output of 28 keV-1. The authors attribute the difference in light output estimates between the two methods to the difference in time constants between the camera and PMT measurements. Simulation structures were designed to match the light output measured with the camera while providing good agreement with the measured LR resulting in a bulk absorption coefficient of 5x10(-5) mu m(-1). Conclusions: The combination of experimental measurements for microcolumnar CsI:Tl scintillators using sealed-sources and synchrotron exposures with results obtained via simulation suggests that the time course of the emission might play a role in experimental estimates. The procedure yielded an experimentally derived linear absorption coefficient for microcolumnar Cs:Tl of 5x10(-5) mu m(-1). To the author's knowledge, this is the first time this parameter has been validated against experimental observations. The measurements also offer insight into the relative role of optical transport on the effective optical yield of the scintillator with microcolumnar structure.

  • 12.
    Nillius, Peter
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Sullivan, Josephine
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Argyros, Antonis
    Shading models for illumination and reflectance invariant shape detectors2008In: 2008 IEEE Conference On Computer Vision And Pattern Recognition: Vols 1-12, 2008, p. 3353-3360Conference paper (Refereed)
    Abstract [en]

    Many objects have smooth surfaces of a fairly uniform color, thereby exhibiting shading patterns that reveal information about its shape, an important clue to the nature of the object. This papers explores extracting this information from images, by creating shape detectors based on shading. Recent work has derived low-dimensional models of shading that can handle realistic unknown lighting conditions and surface reflectance properties. We extend this theory by also incorporating variations in the surface shape. In doing so it enables the creation of very general models for the 2D appearance of objects, not only coping with variations in illumination and BRDF but also in shape alterations such as small scale and pose changes. Using this framework we propose a scheme to build shading models that can be used for shape detection in a bottom up fashion without any a priori knowledge about the scene. From the developed theory we construct detectors for two basic shape primitives, spheres and cylinders. Their performance is evaluated by extensive synthetic experiments as well as experiments on real images.

  • 13.
    Nillius, Peter
    et al.
    Institute of Computer Science - FORTH.
    Sullivan, Josephine
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Carlsson, Stefan
    KTH, School of Computer Science and Communication (CSC), Numerical Analysis and Computer Science, NADA.
    Multi-Target Tracking -- Linking Identities using Bayesian Network Inference2006In: Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition, Los Alamitos, CA, USA: IEEE Computer Society, 2006, p. 2187-2194Conference paper (Refereed)
    Abstract [en]

    Multi-target tracking requires locating the targets and labeling their identities. The latter is a challenge when many targets, with indistinct appearances, frequently occlude one another, as in football and surveillance tracking. We present an approach to solving this labeling problem.

    When isolated, a target can be tracked and its identity maintained. While, if targets interact this is not always the case. This paper assumes a track graph exists, denoting when targets are isolated and describing how they interact. Measures of similarity between isolated tracks are defined. The goal is to associate the identities of the isolated tracks, by exploiting the graph constraints and similarity measures.

    We formulate this as a Bayesian network inference problem, allowing us to use standard message propagation to find the most probable set of paths in an efficient way. The high complexity inevitable in large problems is gracefully reduced by removing dependency links between tracks. We apply the method to a 10 min sequence of an international football game and compare results to ground truth.

  • 14.
    Peter, Nillius
    et al.
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Eklundh, Jan Olof
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Classifying materials from their reflectance properties2004In: COMPUTER VISION: ECCV 2004, PT 4, BERLIN: SPRINGER , 2004, Vol. 2034, p. 366-376Conference paper (Refereed)
    Abstract [en]

    We explore the possibility of recognizing the surface material from a single image with unknown illumination, given the shape of the surface. Model-based PCA is used to create a low-dimensional basis to represent the images. Variations in the illumination create manifolds in the space spanned by this basis. These manifolds are learnt using captured illumination maps and the CUReT database. Classification of the material is done by finding the manifold closest to the point representing the image of the material. Testing on synthetic data shows that the problem is hard. The materials form groups where the materials in a group often are mis-classifed as one of the other materials in the group. With a grouping algorithm we find a grouping of the materials in the CUReT database. Tests on images of real materials in natural illumination settings show promising results.

  • 15.
    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.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    HyperSPECT: a new system for pre-clinical imaging in vivo2009In: Medical Imaging 2009: Physics of Medical Imaging, SPIE - International Society for Optical Engineering, 2009, Vol. 7258, no 1Conference paper (Refereed)
    Abstract [en]

    Imaging in general is becoming increasingly important in the medical science. At the cell level it is possible to label and trace almost individual molecules in vivo to study biochemical reactions using microscopy. In vivo imaging of living organisms is today mainly accomplished by PET, SPECT and fMRI. The problem is that the spatial resolution for realistic image acquisition times is of the order 1-3 mm, which is a serious limitation. We propose a new imaging modality, based on the same principles as SPECT but with drastically improved efficiency and spatial resolution. This is achieved by incorporating a large number of x-ray lenses between the detectors and the object. In current SPECT a pin-hole geometry is standard, involving an unfortunate trade-off between efficiency and spatial resolution, our solution would change this. The agent for radiolabelling is assumed to be 125I, with an emission peak at 27 keV, since it is widely used and easy to handle. The large area, photon counting detectors will consist of a columnar CsI scintillator coupled to a CMOS integrated circuit for electronic read-out. Our simulations of the entire system and of the detector indicate that a resolution of 50 μm for the system is possible.

  • 16.
    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.

1 - 16 of 16
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