Abstract:Objective: A dedicated cone-beam breast computed tomography (BCT) using a high-resolution, low-noise detector operating in offset-detector geometry has been developed. This study investigates the effects of varying detector offsets and image reconstruction algorithms to determine the appropriate combination of detector offset and reconstruction algorithm. Approach: Projection datasets (300 projections in 360°) of 30 breasts containing calcified lesions that were acquired using a prototype cone-beam BCT system… Show more
“…The short-scan trajectory in cone-beam CT (CBCT) imaging effectively decreases the scan time and the patient dose by excluding the redundant measurements. Also, the offset scan geometry improves the efficacy of the detector utilization by achieving the larger field-of-view (FOV) than the normal use [1][2][3][4]. However, the asymmetric HU value recovery in the sinus of the patient has been consistently observed whenever we use the short-scan trajectory with offset detector.…”
The short-scan trajectory in cone-beam CT (CBCT) imaging effectively decreases the scan time and the patient dose by excluding the redundant measurements. Also, the offset scan geometry improves the efficacy of the detector utilization by achieving the larger field-of-view (FOV) than the normal use. However, the asymmetric HU value recovery in the sinus of the patient has been consistently observed whenever we use the short-scan trajectory with offset detector. Typically, the reconstruction of short-scan CBCT with an offset detector may lead to inaccuracies in the CT attenuation values within the reconstructed image. This is particularly noticeable away from the beam center due to insufficient data consistency. Also, other physical factors (ex) beam-hardening, scattering effect) and truncation artifact due to the small FOV may contribute to asymmetric sinus representation. In this study, we investigate the potential causes of the asymmetric sinus representation through the artifact study. We used a Monte-Carlo (MC) simulation to reproduce asymmetric HU value for the ease artifact study.
“…The short-scan trajectory in cone-beam CT (CBCT) imaging effectively decreases the scan time and the patient dose by excluding the redundant measurements. Also, the offset scan geometry improves the efficacy of the detector utilization by achieving the larger field-of-view (FOV) than the normal use [1][2][3][4]. However, the asymmetric HU value recovery in the sinus of the patient has been consistently observed whenever we use the short-scan trajectory with offset detector.…”
The short-scan trajectory in cone-beam CT (CBCT) imaging effectively decreases the scan time and the patient dose by excluding the redundant measurements. Also, the offset scan geometry improves the efficacy of the detector utilization by achieving the larger field-of-view (FOV) than the normal use. However, the asymmetric HU value recovery in the sinus of the patient has been consistently observed whenever we use the short-scan trajectory with offset detector. Typically, the reconstruction of short-scan CBCT with an offset detector may lead to inaccuracies in the CT attenuation values within the reconstructed image. This is particularly noticeable away from the beam center due to insufficient data consistency. Also, other physical factors (ex) beam-hardening, scattering effect) and truncation artifact due to the small FOV may contribute to asymmetric sinus representation. In this study, we investigate the potential causes of the asymmetric sinus representation through the artifact study. We used a Monte-Carlo (MC) simulation to reproduce asymmetric HU value for the ease artifact study.
“…1 a,b) can be used to maintain the FOV without modifying the system magnification. In full-scan, the truncated projection data acquired using an offset detector can be compensated using weighting functions owing to the inherent data redundancy of fan-beam data 4 , 9 – 13 . The feasibility of an offset detector geometry in full-scan cone-beam bCT using the Feldkamp-Davis-Kress (FDK) algorithm 4 and a compressed sensing-based iterative reconstruction algorithm 13 has been demonstrated.…”
Section: Introductionmentioning
confidence: 99%
“…In full-scan, the truncated projection data acquired using an offset detector can be compensated using weighting functions owing to the inherent data redundancy of fan-beam data 4 , 9 – 13 . The feasibility of an offset detector geometry in full-scan cone-beam bCT using the Feldkamp-Davis-Kress (FDK) algorithm 4 and a compressed sensing-based iterative reconstruction algorithm 13 has been demonstrated. Figure 1 The proposed reconstruction pipeline ( d – f ) for a short-scan and offset-detector geometry (a-b) in cone-beam breast CT. ( a ) The half cone-beam geometry in cone-angle view.…”
The feasibility of full-scan, offset-detector geometry cone-beam CT has been demonstrated for several clinical applications. For full-scan acquisition with offset-detector geometry, data redundancy from complementary views can be exploited during image reconstruction. Envisioning an upright breast CT system, we propose to acquire short-scan data in conjunction with offset-detector geometry. To tackle the resulting incomplete data, we have developed a self-supervised attenuation field network (AFN). AFN leverages the inherent redundancy of cone-beam CT data through coordinate-based representation and known imaging physics. A trained AFN can query attenuation coefficients using their respective coordinates or synthesize projection data including the missing projections. The AFN was evaluated using clinical cone-beam breast CT datasets (n = 50). While conventional analytical and iterative reconstruction methods failed to reconstruct the incomplete data, AFN reconstruction was not statistically different from the reference reconstruction obtained using full-scan, full-detector data in terms of image noise, image contrast, and the full width at half maximum of calcifications. This study indicates the feasibility of a simultaneous short-scan and offset-detector geometry for dedicated breast CT imaging. The proposed AFN technique can potentially be expanded to other cone-beam CT applications.
“…To date, scatter mitigation approaches in bCT have included the addition of hardware components to the imaging apparatus (such as anti-scatter grids, 5,6 bow-tie filters, [7][8][9] beamstop arrays [10][11][12] ), changes to system geometry (e.g., increasing the gap between the object and imager), 13 application of scatter correction algorithms during postprocessing, 10, [14][15][16][17][18][19] or utilizing displaced (also known as "offset") flat-panel detector strategies. 20,21 While these efforts lead to an effective management of the acquired scatter, none are without limitation or undesirable consequence. Usage of anti-scatter grids, for example, is typically prohibitive in a low-dose CT image acquisition technique due to the dose penalty associated with using a grid.…”
Section: Introductionmentioning
confidence: 99%
“…Because of this, scatter components of a projection cannot be reliably identified and targeted for correction or removal. To date, scatter mitigation approaches in bCT have included the addition of hardware components to the imaging apparatus (such as anti‐scatter grids, 5,6 bow‐tie filters, 7–9 beam‐stop arrays 10–12 ), changes to system geometry (e.g., increasing the gap between the object and imager), 13 application of scatter correction algorithms during postprocessing, 10,14–19 or utilizing displaced (also known as “offset”) flat‐panel detector strategies 20,21 …”
Background
In breast CT, scattered photons form a large portion of the acquired signal, adversely impacting image quality throughout the frequency response of the imaging system. Prior studies provided evidence for a new image acquisition design, dubbed Narrow Beam Breast CT (NB‐bCT), in preventing scatter acquisition.
Purpose
Here, we report the design, implementation, and initial characterization of the first NB‐bCT prototype.
Methods
The imaging system's apparatus is composed of two primary assemblies: a dynamic Fluence Modulator (collimator) and a photon‐counting line detector. The design of the assemblies enables them to operate in lockstep during image acquisition, converting sourced x‐rays into a moving narrow beam. During a projection, this narrow beam sweeps the entire fan angle coverage of the imaging system. The assemblies are each comprised of a metal housing, a sensory system, and a robotic system. A controller unit handles their relative movements. To study the impact of fluence modulation on the signal received in the detector, three physical breast phantoms, representative of small, average, and large size breasts, were developed and imaged, and acquired projections analyzed. The scatter acquisition in each projection as a function of breast phantom size was investigated. The imaging system's spatial resolution at the center and periphery of the field of view was measured.
Results
Minimal acquisition of scattered rays occurs during image acquisition with NB‐bCT; results in minimal scatter to primary ratios in small, average, and large breast phantoms imaged were 0.05, 0.07, and 0.9, respectively. System spatial resolution of 5.2 lp/mm at 10% max MTF and 2.9 lp/mm at 50% max MTF at the center of the field of view was achieved, with minimal loss with the shift toward the corner (5.0 lp/mm at 10% max MTF and 2.5 lp/mm at 50% max MTF).
Conclusion
The disclosed development, implementation, and characterization of a physical NB‐bCT prototype system demonstrates a new method of CT‐based image acquisition that yields high spatial resolution while minimizing scatter‐components in acquired projections. This methodology holds promise for high‐resolution CT‐imaging applications in which reduction of scatter contamination is desirable.
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