Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
J Appl Clin Med Phys. 2011 Nov 15;12(4):3459. doi: 10.1120/jacmp.v12i4.3459.
The purpose of this study was to evaluate the effects of voxel size and iterative reconstruction parameters on the radial and tangential resolution for 99mTc SPECT as a function of radial distance from isocenter. SPECT/CT scans of eight coplanar point sources of size smaller than 1 mm3 containing high concentration 99mTc solution were acquired on a SPECT/CT system with 5/8 inch NaI(Tl) detector and low-energy, high-resolution collimator. The tomographic projection images were acquired in step-and-shoot mode for 360 views over 360° with 250,000 counts per view, a zoom of 2.67, and an image matrix of 256 × 256 pixels that resulted in a 0.9 × 0.9 × 0.9 mm3 SPECT voxel size over 230 mm field-of-view. The projection images were also rebinned to image matrices of 128 × 128 and 64 × 64 to yield SPECT voxel sizes of 1.8 × 1.8 × 1.8 and 3.6 × 3.6 × 3.6 mm3, respectively. The SPECT/CT datasets were reconstructed using the vendor-supplied iterative reconstruction software that incorporated collimator-specific resolution recovery, CT-based attenuation correction, and dual-energy window-based scatter correction using different combinations of iterations and subsets. SPECT spatial resolution was estimated as the full width at half maximum of the radial and tangential profiles through the center of each point source in reconstructed SPECT images. Both radial and tangential resolution improved with higher iterations and subsets, and with smaller voxel sizes. Both radial and tangential resolution also improved with radial distance further away from isocenter. The magnitude of variation decreased for smaller voxel sizes and for higher number of iterations and subsets. Tangential resolution was found not to be equal to the radial resolution, and the nature of the anisotropy depended on the distribution of the radionuclide and on the reconstruction parameters used. The tangential resolution converged faster than the radial resolution, with higher iterations and subsets. SPECT resolution was isotropic and independent of radial distance when reconstructed using filtered back-projection. SPECT spatial resolution and therefore quantification of SPECT uptake via partial-volume correction in clinical images were found to depend on the nature of activity distribution within the SPECT field-of-view and on the specific choice of iterative reconstruction parameters.
本研究旨在评估体素大小和迭代重建参数对 99mTc SPECT 径向和切向分辨率的影响，作为与等中心径向距离的函数。使用具有 5/8 英寸 NaI(Tl)探测器和低能、高分辨率准直器的 SPECT/CT 系统，对包含高浓度 99mTc 溶液的八个小于 1mm3 的共面点状源进行 SPECT/CT 扫描。断层投影图像以步进和拍摄模式采集，在 360°范围内采集 360 个视图，每个视图的计数为 250,000 个，放大率为 2.67，图像矩阵为 256×256 像素，从而在 230mm 视野范围内得到 0.9×0.9×0.9mm3 的 SPECT 体素大小。投影图像也被重排到 128×128 和 64×64 的图像矩阵，分别得到 1.8×1.8×1.8 和 3.6×3.6×3.6mm3 的 SPECT 体素大小。使用供应商提供的迭代重建软件对 SPECT/CT 数据集进行重建，该软件结合了准直器特定的分辨率恢复、基于 CT 的衰减校正以及使用不同迭代和子集的双能窗口散射校正。通过重建 SPECT 图像中每个点源中心的径向和切向轮廓的半高全宽来估计 SPECT 空间分辨率。随着迭代次数和子集的增加，以及体素尺寸的减小，径向和切向分辨率都得到了提高。随着与等中心距离的增加，径向和切向分辨率都得到了提高。对于较小的体素尺寸和较高的迭代次数和子集，变化幅度减小。切向分辨率不等于径向分辨率，各向异性的性质取决于放射性核素的分布和使用的重建参数。随着迭代次数和子集的增加，切向分辨率的收敛速度比径向分辨率快。使用滤波反投影进行重建时，SPECT 分辨率是各向同性的，与径向距离无关。通过部分容积校正对临床图像中的 SPECT 摄取进行定量时，SPECT 空间分辨率发现取决于 SPECT 视野内活性分布的性质和迭代重建参数的具体选择。
