LaCroix K J, Tsui B M, Hasegawa B H
Department of Biomedical Engineering, The University of North Carolina at Chapel Hill, 27599, USA.
J Nucl Med. 1998 Mar;39(3):562-74.
This study compared attenuation compensated, myocardial SPECT images reconstructed from 180 degrees and 360 degrees data to determine if either data acquisition method might yield improved image quality. Specifically, this study analyzed how the use of either 180 degrees or 360 degrees data affects: (a) the relative count density distribution, (b) defect contrast and (c) level of statistical noise in the left ventricular (LV) wall in the reconstructed SPECT images.
Using the three-dimensional MCAT phantom simulating 201Tl uptake in the upper torso and the SIMSET Monte Carlo code, noise-free projection datasets for both 180 degrees (45 degrees LPO to 45 degrees RAO) and 360 degrees acquisition were generated with the effects of nonuniform attenuation, collimator-detector response and scatter. In addition, low-noise experimental phantom data were acquired over 180 degrees and 360 degrees. Assuming the same total acquisition time, four sets of noisy projection data were simulated from scaled noise-free, simulated data for the following acquisitions: (a) 180 degrees and (b) 360 degrees data acquired on a 90 degrees dual-detector system and (c) 180 degrees and (d) 360 degrees data acquired on a 120 degrees triple-detector system. For each of the four acquisition schemes, 400 realizations of noisy projection data were generated, and the normalized s.d. in the reconstructed images was calculated for five ROIs in the LV wall. Images were reconstructed with nonuniform attenuation compensation using ML-EM algorithm for 25, 50 and 75 iterations.
Both the simulated noise-free and experimental low-noise images reconstructed from 180 degrees and 360 degrees data showed nearly identical count densities and defect contrasts in the LV wall. For the 90 degrees dual-detector system, 180 degrees images showed less noise, while for the 120 degrees triple-detector system, 360 degrees showed less noise; however, these differences in noise level were extremely small after a smoothing filter was applied. The 180 degrees images acquired with the 90 degrees dual-detector system showed the same noise level as the 360 degrees images acquired with the 120 degrees triple-detector system, so neither system geometry had an advantage with respect to reduced noise in the SPECT images.
When nonuniform attenuation compensation is included in the reconstruction, the count density in the LV wall is nearly identical for 180 degrees and 360 degrees SPECT images, and the 90 degrees dual-detector and 120 degrees triple-detector SPECT systems produced similar SPECT images for the same total acquisition time.
本研究比较了从180度和360度数据重建的衰减校正心肌SPECT图像，以确定两种数据采集方法是否能产生更好的图像质量。具体而言，本研究分析了使用180度或360度数据如何影响：(a)相对计数密度分布，(b)缺损对比度，以及(c)重建SPECT图像中左心室（LV）壁的统计噪声水平。
使用模拟上半身201Tl摄取的三维MCAT体模和SIMSET蒙特卡罗代码，生成了180度（从左前斜45度到右前斜45度）和360度采集的无噪声投影数据集，并考虑了非均匀衰减、准直器 - 探测器响应和散射的影响。此外，还采集了180度和360度的低噪声实验体模数据。假设总采集时间相同，从按比例缩放的无噪声模拟数据中模拟了四组有噪声投影数据，用于以下采集：(a) 180度，(b) 在90度双探测器系统上采集的360度数据，(c) 180度，以及(d) 在120度三探测器系统上采集的360度数据。对于这四种采集方案中的每一种，生成了400次有噪声投影数据的实现，并计算了LV壁中五个感兴趣区域（ROI）在重建图像中的归一化标准差。使用ML - EM算法对图像进行非均匀衰减校正重建，迭代次数为25、50和75次。
从180度和360度数据重建的模拟无噪声和实验低噪声图像在LV壁中显示出几乎相同的计数密度和缺损对比度。对于90度双探测器系统，180度图像显示出的噪声较少，而对于120度三探测器系统，360度图像显示出的噪声较少；然而，在应用平滑滤波器后，这些噪声水平的差异极小。在90度双探测器系统上采集的180度图像与在120度三探测器系统上采集的360度图像显示出相同的噪声水平，因此在降低SPECT图像噪声方面，两种系统几何结构均无优势。
当在重建中包括非均匀衰减校正时，180度和360度SPECT图像中LV壁的计数密度几乎相同，并且在相同的总采集时间下，90度双探测器和120度三探测器SPECT系统产生的SPECT图像相似。
