[Objective] Single-photon emission computed tomography (SPECT) is still considered a nonquantitative imaging modality because it cannot perform attenuation correction. To acquire a quantitative SPECT image, Beijing Novel Medical Equipment Co., Ltd. developed a domestic SPECT/CT system, Insight NM/CT Pro. It was equipped with dual digital detectors and enabled various scanning geometries. In addition to better spatial resolution, the system can correct attenuation effects in SPECT and realize quantitative reconstruction using CT. In this study, we evaluated the imaging accuracy of this domestic SPECT/CT system and compared it with advanced abroad systems. [Methods] To obtain quantitatively correct results, physical effects, including collimator blurring, object attenuation, scatter, and radionuclide decay, were modeled and corrected in the reconstruction algorithm. Moreover, a large cylindrical phantom was employed to obtain the calibration factor for the system so that we could convert the reconstruction result to a quantitative image in terms of Bq/mL. Then, the performance of CT-based attenuation correction was tested according to testing method for SPECT imaging based on CT-attenuation correction (YY/T 1546—2017). A cylinder phantom with three cylindrical inserts corresponding to air, nonradioactive water, and bone was filled with a radioactive solution for imaging. The biases inside the air, water, and bone regions of the reconstructed image were calculated to evaluate the performance of CT-based attenuation correction. In addition, the quantitative accuracy of the equipment was tested using the Notional Electrical Manufactures Association (NEMA) torso phantom according to performance measurements of Gamma cameras (NEMA NU 1—2018). Six fillable spheres with different diameters were set as targets for recovery evaluation, and the target-to-background concentration ratio was approximately 8∶1. A large volume of interest (VOI) was placed in the background region to calculate the quantitative bias of the reconstruction. VOIs with the same size of six spheres were drawn based on the registered CT to evaluate recovery coefficients of different sizes. Radionuclide technetium-99m and a low-energy, high-resolution collimator with Insight NM/CT Pro were used for all these tests, and the evaluation results were compared with those of the GE Discovery NM/CT 670. [Results] For attenuation accuracy testing, the biases inside the air, water, and bone regions of Insight NM/CT Pro were 7.84%, 8.38%, and 4.66%, respectively, whereas the corresponding biases in GE Discovery NM/CT 670 were 16.64%, 18.01%, and 11.02%, respectively. For quantitative accuracy testing, in GE discovery NM/CT 670, the quantitative recovery coefficients of the hot spheres with diameters of 13, 17, 22, and 28 mm were 31.04%, 51.36%, 59.91%, and 66.39%, respectively, and the background concentration bias was 10.84%. Insight NM/CT Pro achieved higher recovery coefficients and lower bias. The recovery coefficients were 38.22%, 50.98%, 66.55%, and 71.32% for 13, 17, 22, and 28 mm hot rods, respectively, and the bias in the background region was 7.95%. [Conclusions] Phantom studies have demonstrated that the domestic Insight NM/CT Pro imaging system can obtain smaller biases after CT attenuation correction and achieve quantitative images with high accuracy. The reliability of the Insight NM/CT Pro system for quantitative imaging is validated in this study, and its performance is comparable to that of the advanced GE Discovery NM/CT 670 imaging system.

[Objective] Iodine-131 SPECT (single photon emission computed tomography) planar imaging has been widely used in the clinical diagnosis and treatment evaluation of thyroid cancer. Because of the high-energy emissions of iodine-131, the photons have a high probability of penetrating the collimator septa of SPECT, causing "spoke" artifacts in the final result. The "spoke" artifacts make it difficult to distinguish accurate concentration regions of iodine-131, and they may obscure lower uptake regions nearby, such as metastatic spread to lymph nodes. In this paper, a deconvolution method based on the point spread function was combined with a priori regularization to suppress the spoke artifacts and to improve the diagnostic accuracy in clinical studies.[Methods] This study is based on the NET632 SPECT system with the corresponding high-energy general purpose collimator. The collected data follow the Poisson distribution, and they consist of two parts, a forward projection of the true activity distribution and the scatter data. The forward projection progress can be well modeled using a shift-invariant PSF (point spread function). An objective function is built based on the aforementioned approximation, and a priori function is introduced to regularize the reconstruction. A monotonic and convergent algorithm is derived to iteratively solve the objective function. In contrast, the conventional deconvolution method regularizes the solution using a total variation term, and the objective function is optimized based on the "one-step-late" algorithm; thus, nonnegativity and convergence can not be guaranteed. The triple-energy window method is employed to estimate scattering data, and PSFs of different sizes are generated based on Monte Carlo simulations. Simulated NEMA torso phantom data are reconstructed with different parameters to validate the monotonicity and convergence of the proposed method. Moreover, the dataset is also used to evaluate the effects of PSF size and regularization strength on reconstruction images. Normalized spoke counts and background noise are calculated for quantitative comparison. Simulation data are also used to compare the reconstruction performance of the proposed method and the conventional deconvolution method. With the optimized parameters determined by simulation data, the proposed method is further validated by clinical point data and volunteer data.[Results] With different reconstruction parameters, the objective function value increased monotonically, and the image differences between two adjacent iterations rapidly reduced to a value close to zero. The simulation study also demonstrated that a 127?27 PSF size could provide performance similar to a 255?55 PSF size, which was significantly better than 63?3 and 31?1 PSF sizes. A study on different regularization strengths suggested an optimized regularization parameter, 0.01. When the PSF size and regularization parameter were set as 127?27 and 0.01, the mean spoke counts could be reduced to 4% of the original value with a low background noise level. A comparison study based on simulation data showed the superiority of the proposed method over the conventional deconvolution method. The clinical point data and volunteer data also validated the performance of the proposed method, and the mean spoke counts could be reduced to 35% and 28% of the original values, respectively.[Conclusions] The proposed method suppresses the spoke artifacts in iodine-131 imaging using a PSF that models the physical response, and it also introduces a priori regularization to suppress noise amplified by deconvolution. The derived algorithm can guarantee the monotonicity and convergence of the iterative reconstruction. Studies on simulation data and clinical data have demonstrated that the proposed method can achieve the desired performance and is expected to improve the diagnostic accuracy in clinical studies.

[Objective] Single photon emission computed tomography (SPECT) is an important imaging method of radionuclide bone imaging. It can obtain noninvasive three-dimensional functional images for early diagnosis and staged prognostic evaluation of disease by detecting γ photons emitted by radioactive drugs in the human body. According to the results of the national nuclear medicine census in 2020, more than 60% of SPECT clinical examinations in China are bone system examinations, indicating a great demand for bone imaging. Bone system examination generally refers to bone scanning, which is a nuclear medical imaging examination for systemic bones and can effectively diagnose various primary or secondary bone tumors. However, the low-energy general-purpose parallel-hole collimator, which is clinically used for SPECT bone scanning, has a low detection sensitivity, which leads to low patient comfort and scanning efficiency. Thus, this study aimes to optimize the detection sensitivity of SPECT system for bone imaging in clinical practice, which can not only reduce bone scanning time but also improve bone scanning efficiency and increase clinical-conomic benefits.[Methods] Based on the clinical dual-head SPECT system, this paper designed a specific collimator for bone imaging with high detection sensitivity. This study focuses on simulation experiments, including the construction of an overall simulation system, design of collimator parameters, and performance evaluation. The overall simulation system refers to the parameters of the SPECT system developed by this paper's cooperative company. In collimator parameter design, based on the formula derived in theory, which guides this paper in identifying the factors related to the detection sensitivity and resolution of SPECT system, different collimator parameters are tested by changing the collimator thickness, hole spacing, and hole diameter. Then, a Monte Carlo simulation, which is supported by center of high performance computing, Tsinghua University, is conducted with a point source for performance evaluation, including the detection sensitivity and image spatial resolution.[Results] The results indicates that the relationship between the geometric parameters and performance of the collimator matched well with the theoretical formula:as the increase of hole septal increases, the effective area of photon penetration on the collimator decreases, which reduces the detection sensitivity, while there is no obvious change in the image resolution. As the aperture increases, the collimation effect of the collimator is weakened, resulting in a serious decline in resolution. However, more scintillation photons will reach the scintillation crystal, there by hugely improving the detection sensitivity. When the aperture becomes larger, the improvement in detection sensitivity cannot make up for the loss brought by the reduction in resolution. When the collimator thickens, the collimation effect is enhanced, and the number of oblique incident photons that can be detected is reduced, so the detection sensitivity shows a downward trend. However, the image resolution can be improved.[Conclusions] Thinning the collimator and hole diameter is feasible in designing the SPECT collimator for bone scanning. According to the results of the performance evaluation, a collimator design (collimator thickness, 25.5 mm; hole septal, 0.15 mm; hole diameter, 0.5 mm) is empirically selected. It has a detection sensitivity of 183 cpm/μCi and a spatial resolution of 13.6 mm, which can significantly reduce the bone scanning acquisition time while ensuring image quality. The imaging effect of the collimator is evaluated using a hot-rod phantom experiment. The results show that hot rods with a 5.5-mm diameter could be distinguished, demonstrating the imaging performance of our proposed dedicated collimator design for bone scanning.

This study analyzed the collimator parameters of a large animal single photon emission computed tomography (SPECT) detector. Six collimator design schemes were chosen by thoretical calculation of the spatial resolution, the sensitivity at the field of view (FOV) center and the projection overlap ratio with specified constraints. A performance evaluation method was used to evaluate the six collimator design schemes by calculating the contrast recovery coefficient (CRC) and the variance of the local impulse response of selected pixels to find the best design scheme. The imaging effect of the design scheme was verified by numerical simulations of imaging experiments of a hotrod phantom. The theoretical calculations and the numerical simulations demonstrate that the design scheme gives a spatial resolution of the hotrod phantom that is better than 3.0 mm with better than 0.03% sensitivity at the FOV center, which meets the technical requirements.