A photon-counting detector for dual-energy breast tomosynthesis

Fredenberg, Erik; Lundqvist, Mats; Åslund, Magnus; Hemmendorff, Magnus; Cederström, Björn; Danielsson, Mats

doi:10.1117/12.813037

Cited by 21 publications

(19 citation statements)

References 21 publications

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“…Compared to conventional fluence detectors that integrate absorbed energy information over an entire image frame, PCDs offer many advantages such as improving image quality through reduction of Swank noise and electronic noise, and providing inherent spectral information by means of multiple energy discriminating windows. Such devices are presently in clinical use for mammographic imaging (Lundqvist et al , 2003) and are under development for breast tomosynthesis (Fredenberg et al , 2009). PCDs are also being explored for other imaging modalities such as computed tomography (Shikhaliev and Fritz, 2011; Taguchi and Iwanczyk, 2013; Schlomka et al , 2008).…”

Section: Introductionmentioning

confidence: 99%

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

et al. 2016

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Photon counting arrays (PCAs), defined as pixelated imagers which measure the absorbed energy of x-ray photons individually and record this information digitally, are of increasing clinical interest. A number of PCA prototypes with a 1 mm pixel-to-pixel pitch have recently been fabricated with polycrystalline silicon (poly-Si) — a thin-film technology capable of creating monolithic imagers of a size commensurate with human anatomy. In this study, analog and digital simulation frameworks were developed to provide insight into the influence of individual poly-Si transistors on pixel circuit performance — information that is not readily available through empirical means. The simulation frameworks were used to characterize the circuit designs employed in the prototypes. The analog framework, which determines the noise produced by individual transistors, was used to estimate energy resolution, as well as to identify which transistors contribute the most noise. The digital framework, which analyzes how well circuits function in the presence of significant variations in transistor properties, was used to estimate how fast a circuit can produce an output (referred to as output count rate). In addition, an algorithm was developed and used to estimate the minimum pixel pitch that could be achieved for the pixel circuits of the current prototypes. The simulation frameworks predict that the analog component of the PCA prototypes could have energy resolution as low as 8.9% FWHM at 70 keV; and the digital components should work well even in the presence of significant TFT variations, with the fastest component having output count rates as high as 3 MHz. Finally, based on conceivable improvements in the underlying fabrication process, the algorithm predicts that the 1 mm pitch of the current PCA prototypes could be reduced significantly, potentially to between ~240 and 290 μm.

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Section: Introductionmentioning

confidence: 99%

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

et al. 2016

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“…The latter can be achieved by increasing the x-ray flux, by using a higher Talbot order, and by improving the fringe visibility of the system. Furthermore, energy resolved detection, [25][26][27] as supported by the next generation MicroDose system, can further improve the SNR. [28][29][30] Since our ultimate goal is phase-contrast mammography, future work will also include the imaging of breast samples.…”

Section: Discussionmentioning

confidence: 99%

Slit‐scanning differential x‐ray phase‐contrast mammography: Proof‐of‐concept experimental studies

et al. 2015

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Purpose: The purpose of this work is to investigate the feasibility of grating-based, differential phase-contrast, full-field digital mammography (FFDM) in terms of the requirements for field-ofview (FOV), mechanical stability, and scan time. Methods: A rigid, actuator-free Talbot interferometric unit was designed and integrated into a state-of-the-art x-ray slit-scanning mammography system, namely, the Philips MicroDose L30 FFDM system. A dedicated phase-acquisition and phase retrieval method was developed and implemented that exploits the redundancy of the data acquisition inherent to the slit-scanning approach to image generation of the system. No modifications to the scan arm motion control were implemented. Results: The authors achieve a FOV of 160 × 196 mm consisting of two disjoint areas measuring 77 × 196 mm with a gap of 6 mm between them. Typical scanning times vary between 10 and 15 s and dose levels are lower than typical FFDM doses for conventional scans with identical acquisition parameters due to the presence of the source-grating G 0 . Only minor to moderate artifacts are observed in the three reconstructed images, indicating that mechanical vibrations induced by other system components do not prevent the use of the platform for phase contrast imaging. Conclusions: To the best of our knowledge, this is the first attempt to integrate x-ray gratings hardware into a clinical mammography unit. The results demonstrate that a scanning differential phase contrast FFDM system that meets the requirements of FOV, stability, scan time, and dose can be build. C 2015 American Association of Physicists in Medicine. [http://dx

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“…Si-strip PCDs have entered clinical use in scanning-slot mammography (Fredenberg et al 2010b), where an edge-on configuration is used to compensate for the relatively low stopping power of Si at x-ray energies. To accommodate the readout electronics, a sparse arrangement of linear sensors is used, causing gaps in coverage of the detector plane that are significantly larger than those present in tiled CMOS/CCD detectors (Fredenberg et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Volumetric CT with sparse detector arrays (and application to Si-strip photon counters)

et al. 2015

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Novel x-ray medical imaging sensors, such as photon counting detectors (PCDs) and large area CCD and CMOS cameras can involve irregular and/or sparse sampling of the detector plane. Application of such detectors to CT involves undersampling that is markedly different from the commonly considered case of sparse angular sampling. This work investigates volumetric sampling in CT systems incorporating sparsely sampled detectors with axial and helical scan orbits and evaluates performance of model-based image reconstruction (MBIR) with spatially varying regularization in mitigating artifacts due to sparse detector sampling. Volumetric metrics of sampling density and uniformity were introduced. Penalized-likelihood MBIR with a spatially varying penalty that homogenized resolution by accounting for variations in local sampling density (i.e. detector gaps) was evaluated. The proposed methodology was tested in simulations and on an imaging bench based on a Si-strip PCD (total area 5 cm × 25 cm) consisting of an arrangement of line sensors separated by gaps of up to 2.5 mm. The bench was equipped with translation/rotation stages allowing a variety of scanning trajectories, ranging from a simple axial acquisition to helical scans with variable pitch. Statistical (spherical clutter) and anthropomorphic (hand) phantoms were considered. Image quality was compared to that obtained with a conventional uniform penalty in terms of structural similarity index (SSIM), image uniformity, spatial resolution, contrast, and noise. Scan trajectories with intermediate helical width (~10 mm longitudinal distance per 360° rotation) demonstrated optimal tradeoff between the average sampling density and the homogeneity of sampling throughout the volume. For a scan trajectory with 10.8 mm helical width, the spatially varying penalty resulted in significant visual reduction of sampling artifacts, confirmed by a 10% reduction in minimum SSIM (from 0.88 to 0.8) and a 40% reduction in the dispersion of SSIM in the volume compared to the constant penalty (both penalties applied at optimal regularization strength). Images of the spherical clutter and wrist phantoms confirmed the advantages of the spatially varying penalty, showing a 25% improvement in image uniformity and 1.8 × higher CNR (at matched spatial resolution) compared to the constant penalty. The studies elucidate the relationship between sampling in the detector plane, acquisition orbit, sampling of the reconstructed volume, and the resulting image quality. They also demonstrate the benefit of spatially varying regularization in MBIR for scenarios with irregular sampling patterns. Such findings are important and integral to the incorporation of a sparsely sampled Si-strip PCD in CT imaging.

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A photon-counting detector for dual-energy breast tomosynthesis

Cited by 21 publications

References 21 publications

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

Performance of in-pixel circuits for photon counting arrays (PCAs) based on polycrystalline silicon TFTs

Slit‐scanning differential x‐ray phase‐contrast mammography: Proof‐of‐concept experimental studies

Volumetric CT with sparse detector arrays (and application to Si-strip photon counters)

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