Model-based iterative reconstruction for flat-panel cone-beam CT with focal spot blur, detector blur, and correlated noise

Tilley, Steven; Siewerdsen, Jeffrey H.; Stayman, J. Webster

doi:10.1088/0031-9155/61/1/296

Cited by 50 publications

(64 citation statements)

References 44 publications

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“…Future work will involve optimization of reconstruction algorithms for trabecular imaging. Of particular interest are novel model‐based iterative reconstruction (MBIR) algorithms incorporating models of system blur . Such algorithm are able to account for noise correlations due to blur, to incorporate shift‐variant source blur and potentially to model blur due to gantry rotation.…”

Section: Discussionmentioning

confidence: 99%

“…Of particular interest are novel model‐based iterative reconstruction (MBIR) algorithms incorporating models of system blur . Such algorithm are able to account for noise correlations due to blur, to incorporate shift‐variant source blur and potentially to model blur due to gantry rotation. This may improve trabecular imaging by achieving resolution recovery with better resolution‐noise properties then using standard deblurring methods.…”

Section: Discussionmentioning

confidence: 99%

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Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

et al. 2017

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Purpose: Quantitative assessment of trabecular bone microarchitecture in extremity cone-beam CT (CBCT) would benefit from the high spatial resolution, low electronic noise, and fast scan time provided by complementary metal-oxide semiconductor (CMOS) x-ray detectors. We investigate the performance of CMOS sensors in extremity CBCT, in particular with respect to potential advantages of thin (<0.7 mm) scintillators offering higher spatial resolution. Methods: A cascaded systems model of a CMOS x-ray detector incorporating the effects of CsI:Tl scintillator thickness was developed. Simulation studies were performed using nominal extremity CBCT acquisition protocols (90 kVp, 0.126 mAs/projection). A range of scintillator thickness (0.35-0.75 mm), pixel size (0.05-0.4 mm), focal spot size (0.05-0.7 mm), magnification (1.1-2.1), and dose (15-40 mGy) was considered. The detectability index was evaluated for both CMOS and aSi:H flat-panel detector (FPD) configurations for a range of imaging tasks emphasizing spatial frequencies associated with feature size a obj . Experimental validation was performed on a CBCT test bench in the geometry of a compact orthopedic CBCT system (SAD = 43.1 cm, SDD = 56.0 cm, matching that of the Carestream OnSight 3D system). The test-bench studies involved a 0.3 mm focal spot x-ray source and two CMOS detectors (Dalsa Xineos-3030HR, 0.099 mm pixel pitch) -one with the standard CsI:Tl thickness of 0.7 mm (C700) and one with a custom 0.4 mm thick scintillator (C400). Measurements of modulation transfer function (MTF), detective quantum efficiency (DQE), and CBCT scans of a cadaveric knee (15 mGy) were obtained for each detector. Results: Optimal detectability for high-frequency tasks (feature size of~0.06 mm, consistent with the size of trabeculae) was~49 for the C700 CMOS detector compared to the a-Si:H FPD at nominal system geometry of extremity CBCT. This is due to~59 lower electronic noise of a CMOS sensor, which enables input quantum-limited imaging at smaller pixel size. Optimal pixel size for high-frequency tasks was <0.1 mm for a CMOS, compared to~0.14 mm for an a-Si:H FPD. For this fine pixel pitch, detectability of fine features could be improved by using a thinner scintillator to reduce light spread blur. A 22% increase in detectability of 0.06 mm features was found for the C400 configuration compared to C700. An improvement in the frequency at 50% modulation (f 50 ) of MTF was measured, increasing from 1.8 lp/mm for C700 to 2.5 lp/mm for C400. The C400 configuration also achieved equivalent or better DQE as C700 for frequencies above~2 mm À1. Images of cadaver specimens confirmed improved visualization of trabeculae with the C400 sensor. Conclusions: The small pixel size of CMOS detectors yields improved performance in high-resolution extremity CBCT compared to a-Si:H FPDs, particularly when coupled with a custom 0.4 mm thick scintillator. The results indicate that adoption of a CMOS detector in extremity CBCT can benefit applications in quantitative imaging of trabecular microstr...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

et al. 2017

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“…Translation of the CMOS-based imaging chain onto the CBCT gantry is ongoing, with anticipated deployment in pilot clinical studies within ~1 year. Through the application of an optimized CMOS sensor and novel deblurring and motion correction algorithms 12,13 , this new generation of extremity CBCT will provide a comprehensive platform for in-vivo assessment of bone health at spatial scales ranging from gross morphology to trabecular microarchitecture.…”

Section: Discussionmentioning

confidence: 99%

High-resolution extremity cone-beam CT with a CMOS detector: task-based optimization of scintillator thickness

Cao

Brehler

Sisniega

et al. 2017

Medical Imaging 2017: Physics of Medical Imaging

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Purpose CMOS x-ray detectors offer small pixel sizes and low electronic noise that may support the development of novel high-resolution imaging applications of cone-beam CT (CBCT). We investigate the effects of CsI scintillator thickness on the performance of CMOS detectors in high resolution imaging tasks, in particular in quantitative imaging of bone microstructure in extremity CBCT. Methods A scintillator thickness-dependent cascaded systems model of CMOS x-ray detectors was developed. Detectability in low-, high- and ultra-high resolution imaging tasks (Gaussian with FWHM of ~250 μm, ~80 μm and ~40 μm, respectively) was studied as a function of scintillator thickness using the theoretical model. Experimental studies were performed on a CBCT test bench equipped with DALSA Xineos3030 CMOS detectors (99 μm pixels) with CsI scintillator thicknesses of 400 μm and 700 μm, and a 0.3 FS compact rotating anode x-ray source. The evaluation involved a radiographic resolution gauge (0.6–5.0 lp/mm), a 127 μm tungsten wire for assessment of 3D resolution, a contrast phantom with tissue-mimicking inserts, and an excised fragment of human tibia for visual assessment of fine trabecular detail. Results Experimental studies show ~35% improvement in the frequency of 50% MTF modulation when using the 400 μm scintillator compared to the standard nominal CsI thickness of 700 μm. Even though the high-frequency DQE of the two detectors is comparable, theoretical studies show a 14% to 28% increase in detectability index (d′2) of high- and ultrahigh resolution tasks, respectively, for the detector with 400 μm CsI compared to 700 μm CsI. Experiments confirm the theoretical findings, showing improvements with the adoption of 400 μm panel in the visibility of the radiographic pattern (2× improvement in peak-to-through distance at 4.6 lp/mm) and a 12.5% decrease in the FWHM of the tungsten wire. Reconstructions of the tibial plateau reveal enhanced visibility of trabecular structures with the CMOS detector with 400 μm scinitllator. Conclusion Applications on CMOS detectors in high resolution CBCT imaging of trabecular bone will benefit from using a thinner scintillator than the current standard in general radiography. The results support the translation of the CMOS sensor with 400 μm CsI onto the clinical prototype of CMOS-based extremity CBCT.

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“…The multiresolution framework can be further expanded to support other applications where computationally expensive forward models (e.g. modeling of detector blur (Tilley II et al 2015)) are applied only to a sub-region of the field-of-view. The algorithm permits application of different regularization strengths in the regions of coarse and fine grid, enabling reconstructions in which the sampling and regularization are individually optimized depending on the clinical task in each image region.…”

Section: Discussionmentioning

confidence: 99%

Multiresolution iterative reconstruction in high-resolution extremity cone-beam CT

et al. 2016

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Application of model-based iterative reconstruction (MBIR) to high resolution cone-beam CT (CBCT) is computationally challenging because of the very fine discretization (voxel size <100 µm) of the reconstructed volume. Moreover, standard MBIR techniques require that the complete transaxial support for the acquired projections is reconstructed, thus precluding acceleration by restricting the reconstruction to a region-of-interest. To reduce the computational burden of high resolution MBIR, we propose a multiresolution Penalized-Weighted Least Squares (PWLS) algorithm, where the volume is parameterized as a union of fine and coarse voxel grids as well as selective binning of detector pixels. We introduce a penalty function designed to regularize across the boundaries between the two grids. The algorithm was evaluated in simulation studies emulating an extremity CBCT system and in a physical study on a test-bench. Artifacts arising from the mismatched discretization of the fine and coarse sub-volumes were investigated. The fine grid region was parameterized using 0.15 mm voxels and the voxel size in the coarse grid region was varied by changing a downsampling factor. No significant artifacts were found in either of the regions for downsampling factors of up to 4×. For a typical extremities CBCT volume size, this downsampling corresponds to an acceleration of the reconstruction that is more than five times faster than a brute force solution that applies fine voxel parameterization to the entire volume. For certain configurations of the coarse and fine grid regions, in particular when the boundary between the regions does not cross high attenuation gradients, downsampling factors as high as 10× can be used without introducing artifacts, yielding a ~50× speedup in PWLS. The proposed multiresolution algorithm significantly reduces the computational burden of high resolution iterative CBCT reconstruction and can be extended to other applications of MBIR where computationally expensive, high-fidelity forward models are applied only to a sub-region of the field-of-view.

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Model-based iterative reconstruction for flat-panel cone-beam CT with focal spot blur, detector blur, and correlated noise

Cited by 50 publications

References 44 publications

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

Modeling and evaluation of a high‐resolution CMOS detector for cone‐beam CT of the extremities

High-resolution extremity cone-beam CT with a CMOS detector: task-based optimization of scintillator thickness

Multiresolution iterative reconstruction in high-resolution extremity cone-beam CT

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