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Featured researches published by S Yan.


nuclear science symposium and medical imaging conference | 2010

Regional SPECT imaging using sampling Principles and Multiple Pinholes

James E. Bowsher; J Roper; S Yan; W Giles; Fang-Fang Yin

There may be many SPECT imaging applications in which a small region is primarily of interest. One such case is imaging in the radiation therapy treatment room, as the patient is on the treatment table in position for radiation therapy. This onboard imaging is currently performed by cone-beam CT. The purpose of this onboard imaging is to fine tune localization of the tumor target. It has been proposed that onboard SPECT could be useful for target localization and also for imaging biological function for the purpose of real-time re-planning of therapy beams. Onboard imaging would need to be accomplished within about 5 minutes. Herein we propose that this might be done by regional SPECT imaging in which multi-pinhole collimation is used to concentrate a large detector surface on a small (e.g. 7cm-diameter) region. Pinhole trajectories are designed in accord with recent developments regarding complete sampling in the presence of truncation. A 9-pinhole system is found to outperform two single-pinhole systems as well as a smaller, reference parallel-hole-collimated detector. Realistic computer-aided design (CAD) studies are shown to illustrate how an onboard SPECT system could be implemented.


Medical Physics | 2013

Onboard functional and molecular imaging: A design investigation for robotic multipinhole SPECT

James E. Bowsher; S Yan; J Roper; W Giles; Fang-Fang Yin

PURPOSE Onboard imaging-currently performed primarily by x-ray transmission modalities-is essential in modern radiation therapy. As radiation therapy moves toward personalized medicine, molecular imaging, which views individual gene expression, may also be important onboard. Nuclear medicine methods, such as single photon emission computed tomography (SPECT), are premier modalities for molecular imaging. The purpose of this study is to investigate a robotic multipinhole approach to onboard SPECT. METHODS Computer-aided design (CAD) studies were performed to assess the feasibility of maneuvering a robotic SPECT system about a patient in position for radiation therapy. In order to obtain fast, high-quality SPECT images, a 49-pinhole SPECT camera was designed which provides high sensitivity to photons emitted from an imaging region of interest. This multipinhole system was investigated by computer-simulation studies. Seventeen hot spots 10 and 7 mm in diameter were placed in the breast region of a supine female phantom. Hot spot activity concentration was six times that of background. For the 49-pinhole camera and a reference, more conventional, broad field-of-view (FOV) SPECT system, projection data were computer simulated for 4-min scans and SPECT images were reconstructed. Hot-spot localization was evaluated using a nonprewhitening forced-choice numerical observer. RESULTS The CAD simulation studies found that robots could maneuver SPECT cameras about patients in position for radiation therapy. In the imaging studies, most hot spots were apparent in the 49-pinhole images. Average localization errors for 10-mm- and 7-mm-diameter hot spots were 0.4 and 1.7 mm, respectively, for the 49-pinhole system, and 3.1 and 5.7 mm, respectively, for the reference broad-FOV system. CONCLUSIONS A robot could maneuver a multipinhole SPECT system about a patient in position for radiation therapy. The system could provide onboard functional and molecular imaging with 4-min scan times.


Medical Physics | 2013

A line‐source method for aligning on‐board and other pinhole SPECT systems

S Yan; James E. Bowsher; Fang-Fang Yin

PURPOSE In order to achieve functional and molecular imaging as patients are in position for radiation therapy, a robotic multipinhole SPECT system is being developed. Alignment of the SPECT system-to the linear accelerator (LINAC) coordinate frame and to the coordinate frames of other on-board imaging systems such as cone-beam CT (CBCT)-is essential for target localization and image reconstruction. An alignment method that utilizes line sources and one pinhole projection is proposed and investigated to achieve this goal. Potentially, this method could also be applied to the calibration of the other pinhole SPECT systems. METHODS An alignment model consisting of multiple alignment parameters was developed which maps line sources in three-dimensional (3D) space to their two-dimensional (2D) projections on the SPECT detector. In a computer-simulation study, 3D coordinates of line-sources were defined in a reference room coordinate frame, such as the LINAC coordinate frame. Corresponding 2D line-source projections were generated by computer simulation that included SPECT blurring and noise effects. The Radon transform was utilized to detect angles (α) and offsets (ρ) of the line-source projections. Alignment parameters were then estimated by a nonlinear least squares method, based on the α and ρ values and the alignment model. Alignment performance was evaluated as a function of number of line sources, Radon transform accuracy, finite line-source width, intrinsic camera resolution, Poisson noise, and acquisition geometry. Experimental evaluations were performed using a physical line-source phantom and a pinhole-collimated gamma camera attached to a robot. RESULTS In computer-simulation studies, when there was no error in determining angles (α) and offsets (ρ) of the measured projections, six alignment parameters (three translational and three rotational) were estimated perfectly using three line sources. When angles (α) and offsets (ρ) were provided by the Radon transform, estimation accuracy was reduced. The estimation error was associated with rounding errors of Radon transform, finite line-source width, Poisson noise, number of line sources, intrinsic camera resolution, and detector acquisition geometry. Statistically, the estimation accuracy was significantly improved by using four line sources rather than three and by thinner line-source projections (obtained by better intrinsic detector resolution). With five line sources, median errors were 0.2 mm for the detector translations, 0.7 mm for the detector radius of rotation, and less than 0.5° for detector rotation, tilt, and twist. In experimental evaluations, average errors relative to a different, independent registration technique were about 1.8 mm for detector translations, 1.1 mm for the detector radius of rotation (ROR), 0.5° and 0.4° for detector rotation and tilt, respectively, and 1.2° for detector twist. CONCLUSIONS Alignment parameters can be estimated using one pinhole projection of line sources. Alignment errors are largely associated with limited accuracy of the Radon transform in determining angles (α) and offsets (ρ) of the line-source projections. This alignment method may be important for multipinhole SPECT, where relative pinhole alignment may vary during rotation. For pinhole and multipinhole SPECT imaging on-board radiation therapy machines, the method could provide alignment of SPECT coordinates with those of CBCT and the LINAC.


Medical Physics | 2014

SU-E-I-79: Effect of Number of Pinholes in Onboard Robotic Multi-Pinhole SPECT System

M Touch; James E. Bowsher; S Yan; F Yin

PURPOSE To study the effect of number of pinholes for a novel Single Photon Emission Computed Tomography (SPECT) system for onboard molecular and functional imaging. METHODS Comparison studies were performed using simulation for the 49-pinhole SPECT system and a series of reductions in number of pinholes. Trajectories about the breast of a supine patient were considered. Minimum distances, radii of rotation (RORs), were determined by requirements to fully view the region of interest (ROI) and to avoid collision between the detector and the patient. Reductions in RORs translate into improvements in sensitivity. Starting from the 49-pinhole system, pinholes were removed pod by pod. The furthest two end pods in the Sup-Inf direction were removed first for their higher likelihood of alleviating the collision avoidance criteria. After iterating through different combinations of pinhole pods, and selecting three combinations, the corresponding RORs were used to analytically calculate sensitivities. RESULTS Based on the Methods procedure, 3 combination of pods removal were identified: 1) Superior peripheral pod 2) Inferior peripheral pod 3) both pods. RORs were reduced at only one multi-pinhole stop. Analytic calculation showed that sensitivities were reduced from 0.032 for the 49-pinhole system to 0.028 for 42-pinhole and to 0.023 for 39-pinhole system respectively. The sensitivity per pinhole detector was approximately the same for all three cases. CONCLUSION For the trajectories considered, only minimal improvements in RORs were identified by removing pinhole pods. Consequently, sensitivities decreased in proportion to the number of pinholes. Studies of other anatomical sites are needed to determine if in some cases sensitivity per pinhole can be improved by removing some pinholes. PHS/NIH/NCI grant R21-CA156390-01A1.


Medical Physics | 2014

MO-G-17A-02: Computer Simulation Studies for On-Board Functional and Molecular Imaging of the Prostate Using a Robotic Multi-Pinhole SPECT System

Lin Cheng; James E. Bowsher; S Yan; F Yin

PURPOSE To investigate prostate imaging onboard radiation therapy machines using a novel robotic, 49-pinhole Single Photon Emission Computed Tomography (SPECT) system. METHODS Computer-simulation studies were performed for region-of-interest (ROI) imaging using a 49-pinhole SPECT collimator and for broad cross-section imaging using a parallel-hole SPECT collimator. A male XCAT phantom was computersimulated in supine position with one 12mm-diameter tumor added in the prostate. A treatment couch was added to the phantom. Four-minute detector trajectories for imaging a 7cm-diameter-sphere ROI encompassing the tumor were investigated with different parameters, including pinhole focal length, pinhole diameter and trajectory starting angle. Pseudo-random Poisson noise was included in the simulated projection data, and SPECT images were reconstructed by OSEM with 4 subsets and up to 10 iterations. Images were evaluated by visual inspection, profiles, and Root-Mean- Square-Error (RMSE). RESULTS The tumor was well visualized above background by the 49-pinhole SPECT system with different pinhole parameters while it was not visible with parallel-hole SPECT imaging. Minimum RMSEs were 0.30 for 49-pinhole imaging and 0.41 for parallelhole imaging. For parallel-hole imaging, the detector trajectory from rightto- left yielded slightly lower RMSEs than that from posterior to anterior. For 49-pinhole imaging, near-minimum RMSEs were maintained over a broader range of OSEM iterations with a 5mm pinhole diameter and 21cm focal length versus a 2mm diameter pinhole and 18cm focal length. The detector with 21cm pinhole focal length had the shortest rotation radius averaged over the trajectory. CONCLUSION On-board functional and molecular prostate imaging may be feasible in 4-minute scan times by robotic SPECT. A 49-pinhole SPECT system could improve such imaging as compared to broadcross-section parallel-hole collimated SPECT imaging. Multi-pinhole imaging can be improved by considering pinhole focal length, pinhole diameter, and trajectory starting angle. The project is supported by the NIH grant 5R21-CA156390.


Medical Physics | 2014

A hardware investigation of robotic SPECT for functional and molecular imaging onboard radiation therapy systems

S Yan; James E. Bowsher; MengHeng Tough; Lin Cheng; Fang-Fang Yin

PURPOSE To construct a robotic SPECT system and to demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch, as a step toward onboard functional and molecular imaging in radiation therapy. METHODS A robotic SPECT imaging system was constructed utilizing a gamma camera detector (Digirad 2020tc) and a robot (KUKA KR150 L110 robot). An imaging study was performed with a phantom (PET CT Phantom(TM)), which includes five spheres of 10, 13, 17, 22, and 28 mm diameters. The phantom was placed on a flat-top couch. SPECT projections were acquired either with a parallel-hole collimator or a single-pinhole collimator, both without background in the phantom and with background at 1/10th the sphere activity concentration. The imaging trajectories of parallel-hole and pinhole collimated detectors spanned 180° and 228°, respectively. The pinhole detector viewed an off-centered spherical common volume which encompassed the 28 and 22 mm spheres. The common volume for parallel-hole system was centered at the phantom which encompassed all five spheres in the phantom. The maneuverability of the robotic system was tested by navigating the detector to trace the phantom and flat-top table while avoiding collision and maintaining the closest possible proximity to the common volume. The robot base and tool coordinates were used for image reconstruction. RESULTS The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector radius of rotation. Without background, all five spheres were visible in the reconstructed parallel-hole image, while four spheres, all except the smallest one, were visible in the reconstructed pinhole image. With background, three spheres of 17, 22, and 28 mm diameters were readily observed with the parallel-hole imaging, and the targeted spheres (22 and 28 mm diameters) were readily observed in the pinhole region-of-interest imaging. CONCLUSIONS Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frames could be an effective means to estimate detector pose for use in SPECT image reconstruction.


Medical Physics | 2014

TH-C-17A-06: A Hardware Implementation and Evaluation of Robotic SPECT: Toward Molecular Imaging Onboard Radiation Therapy Machines

S Yan; James E. Bowsher; M Touch; Lin Cheng; F Yin

PURPOSE To construct a robotic SPECT system and demonstrate its capability to image a thorax phantom on a radiation therapy flat-top couch. The system has potential for on-board functional and molecular imaging in radiation therapy. METHODS A robotic SPECT imaging system was developed utilizing a Digirad 2020tc detector and a KUKA KR150-L110 robot. An imaging study was performed with the PET CT Phantom, which includes 5 spheres: 10, 13, 17, 22 and 28 mm in diameter. Sphere-tobackground concentration ratio was 6:1 of Tc99m. The phantom was placed on a flat-top couch. SPECT projections were acquired with a parallel-hole collimator and a single pinhole collimator. The robotic system navigated the detector tracing the flat-top table to maintain the closest possible proximity to the phantom. For image reconstruction, detector trajectories were described by six parameters: radius-of-rotation, x and z detector shifts, and detector rotation θ, tilt ϕ and twist γ. These six parameters were obtained from the robotic system by calibrating the robot base and tool coordinates. RESULTS The robotic SPECT system was able to maneuver parallel-hole and pinhole collimated SPECT detectors in close proximity to the phantom, minimizing impact of the flat-top couch on detector-to-COR (center-ofrotation) distance. In acquisitions with background at 1/6th sphere activity concentration, photopeak contamination was heavy, yet the 17, 22, and 28 mm diameter spheres were readily observed with the parallel hole imaging, and the single, targeted sphere (28 mm diameter) was readily observed in the pinhole region-of-interest (ROI) imaging. CONCLUSION Onboard SPECT could be achieved by a robot maneuvering a SPECT detector about patients in position for radiation therapy on a flat-top couch. The robot inherent coordinate frame could be an effective means to estimate detector pose for use in SPECT image reconstruction. PHS/NIH/NCI grant R21-CA156390-01A1.


Medical Physics | 2014

SU-E-T-514: Simultaneously Determination of Radiation Isocentricity of Gantry, Collimator and Couch Using a Commercial Three-Dimensional Dosimetry QA Apparatus.

S Yan; H Song; Q Wu

PURPOSE Radiation isocentricity is an important benchmark for a LINAC and is typically determined by 3 separate film star-shots. We developed a technique to simultaneously determine the radiation isocenter of gantry, collimator and couch with a commercial 3D QA apparatus. METHODS The ArcCHECK from SunNuclear was used on two LINACs. It was aligned with room lasers. For gantry rotation, collimator and couch were set to zero and gantry was placed to 0, 49, 213 and 311 degrees. Similarly, a set of collimator/couch angles were chosen with the other two axes at neutral positions. The measured dose matrices were analyzed by an in-house MATLAB program. For each shot, the central axis was determined by computing the FWHM of the diode arrays. The largest inscribed circle from these central axis lines was used to determine isocenter: the radius as the benchmark of isocentricity and the coordinates of the center as the discrepancy of radiation isocenter to the origin defined by lasers. To validate the method, the couch was shifted by ~5 mm in all three directions and measurements were repeated. RESULTS The radius of the largest inscribed circle for gantry, collimator and couch are (0.3, 0.5, 0.2) mm for one LINAC and (0.2, 0.3, 0.1) mm for the other, in agreement with the film star-shots at annual QA. The discrepancies of radiation isocenter are generally within 1 mm, except gantry rotation on one LINAC due to the drift of foot laser. The differences in positions detected are consistent with the intentional predefined shift. CONCLUSION We have demonstrated a technique for the simultaneous measurement of gantry, collimator, and couch isocentricity with a set of carefully chosen irradiation parameters based on the specific construction geometry of the 3D detector ArcCheck. This can replace the standard film star-shots. The future work includes improving operation efficiency.


Medical Physics | 2013

SU‐D‐500‐06: On‐Board Robotic Multi‐Pinhole SPECT System for Prone Breast Imaging

S Yan; James E. Bowsher; S Yoo; Fang-Fang Yin

PURPOSE To investigate a novel Single Photon Emission Computed Tomography (SPECT) system for on-board molecular and functional imaging in partial breast radiation therapy of prone patients. METHODS Computer-simulation studies were performed for on-board robotic 49-pinhole and reference conventional clinical parallel-hole collimated SPECT systems. A female XCAT phantom was simulated in prone position with nine tumors of 10mm diameter in the left breast. The simulations included two commercial prone breast boards, 24 and 7 cm thick. Four-minute trajectories of the 49-pinhole and parallel-hole systems were designed to image a 7cm-diameter target region encompassing the tumors. Noisy Poisson-distributed projection data were drawn from these simulated projections, and SPECT images were reconstructed by OSEM with up to 10 iterations. Images were evaluated by visual inspection, profiles, and root mean squared error (RMSE). Results were correlated with trajectory radii of rotation. Commercial CAD programs were utilized to evaluate the feasibility of robot and detector trajectories about the patient, treatment table, prone breast board and LINAC gantry. RESULTS With 4-minute scans of the proposed 49-pinhole SPECT system, using the thinner prone breast board, almost all of the 9 tumors were well visualized above background. Few if any of the tumors were apparent in the parallel-hole images. With the thinner board, lowest RMSE values, across all iterations, were 0.206 for 49-pinhole and 0.251 for parallel-hole. For the thicker board, these RMSE results were 0.234 and 0.260 respectively. These results correspond to smaller radii of rotation with the thinner board. CAD simulations indicate feasibility in terms of geometrical considerations. CONCLUSION The proposed on-board robotic multi-pinhole SPECT approach shows promising results for targeted molecular and functional imaging of the breast as patients are in prone position for radiation therapy, especially with breast boards that allow closer detector proximity. PHS/NIH/NCI grant R21-CA156390-01A1.


Medical Physics | 2013

TH‐A‐WAB‐04: Respiratory Sorted Imaging Using Region‐Of‐Interest Robotic Multi‐Pinhole SPECT System

S Yan; James E. Bowsher; Fang-Fang Yin

PURPOSE Single Photon Emission Computed Tomography (SPECT) may provide important information on tumors in the thorax and abdomen. Respiratory sorted imaging using conventional full cross-section methods is generally degraded by noise. The purpose is to investigate noise reduction by region-of-interest (ROI) SPECT. METHODS The 4D XCAT phantom was computer simulated with a 10mm diameter tumor added in the right lung. Respiratory motion was simulated for 6 and 10 phases, accomplished by simulating 30 frames in one 5sec respiratory cycle. A non-sorted phantom was generated by summing the 30 phantoms to mimic motion blur. A static phantom with no respiratory motion was simulated using one of the 30 phantoms. The maximum tumor motion was 2cm Sup/Inf and 1.2cm AP. Projections were computer simulated for 4-minute scans with a reference conventional parallel-hole collimated SPECT and a 49-pinhole SPECT that was optimized to image a 7cm diameter region-of-interest(ROI) encompassing the tumor and its motion. Noisy projections were then generated with random Poisson noise. The SPECT images were reconstructed by OSEM with up to 7 iterations. Images were evaluated as a function of phase by visual inspection and root mean squared error (RMSE). RESULTS The tumor was visualized well above background in most phases for the 49-pinhole SPECT scan. Visual quality was not as good for the parallel-hole scan. The 49-pinhole SPECT resulted in smaller RMSEs than the broader cross-section parallel-hole detector. RMSE values were around 0.11 for the 49-pinhole SPECT scan and 0.18 for the parallel-hole SPECT scan. The RMSEs for 10 respiratory phases were similar to that of 6 phases. CONCLUSION The higher sensitivity and resolution of ROI imaging can alleviate noise effects of respiratory sorted imaging, provided the motion range is within the ROI. The specific ROI SPECT system could enable this gated imaging on-board radiation therapy machines. PHS/NIH/NCI grant R21-CA156390-01A1.

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