van Velden Floris H P, Kloet Reina W, van Berckel Bart N M, Lammertsma Adriaan A, Boellaard Ronald
Department of Nuclear Medicine & PET Research, VU University medical center, Amsterdam, The Netherlands.
J Nucl Med. 2009 Jan;50(1):72-80. doi: 10.2967/jnumed.108.052985. Epub 2008 Dec 17.
The high-resolution research tomograph (HRRT) is a dedicated human brain PET scanner. At present, iterative reconstruction methods are preferred for reconstructing HRRT studies. However, these iterative reconstruction algorithms show bias in short-duration frames. New algorithms such as the shifted Poisson ordered-subsets expectation maximization (SP-OSEM) and ordered-subsets weighted least squares (OSWLS) showed promising results in bias reduction, compared with the recommended ordinary Poisson OSEM (OP-OSEM). The goal of this study was to evaluate quantitative accuracy of these iterative reconstruction algorithms, compared with 3-dimensional filtered backprojection (3D-FBP).
The 3 above-mentioned 3D iterative reconstruction methods were implemented for the HRRT. To evaluate the various 3D iterative reconstruction techniques quantitatively, several phantom studies and a human brain study (n=5) were performed.
OSWLS showed a low and almost linearly increasing coefficient of variation (SD over average activity concentration), with decreasing noise-equivalent count rates. In decay studies, OSWLS showed good agreement with the 3D-FBP gray matter (GM)-to-white matter (WM) contrast ratio (<4%), and OP-OSEM and SP-OSEM showed agreement within 6% and 7%, respectively. For various frame durations, both SP-OSEM and OP-OSEM showed the fewest errors in GM-to-WM contrast ratios, varying 75% between different noise-equivalent count rates; this variability was much higher for other iterative methods (>92%). 3D-FBP showed the least variability (34%). Visually, OSWLS hardly showed any artifacts in parametric images and showed good agreement with 3D-FBP data for parametric images, especially in the case of reference-tissue kinetic methods (slope, 1.02; Pearson correlation coefficient, 0.99).
OP-OSEM, SP-OSEM, and OSWLS showed good performance for phantom studies. In addition, OSWLS showed better results for parametric analysis of clinical studies and is therefore recommended for quantitative HRRT brain PET studies.
高分辨率研究断层扫描仪（HRRT）是一种专门用于人体脑部的正电子发射断层显像（PET）扫描仪。目前，迭代重建方法在重建HRRT研究中更受青睐。然而，这些迭代重建算法在短时间帧中显示出偏差。与推荐的普通泊松有序子集期望最大化（OP-OSEM）相比，诸如移位泊松有序子集期望最大化（SP-OSEM）和有序子集加权最小二乘法（OSWLS）等新算法在减少偏差方面显示出有前景的结果。本研究的目的是与三维滤波反投影（3D-FBP）相比，评估这些迭代重建算法的定量准确性。
对HRRT实施上述三种三维迭代重建方法。为了定量评估各种三维迭代重建技术，进行了多项体模研究和一项人体脑部研究（n = 5）。
OSWLS显示出较低且几乎呈线性增加的变异系数（标准差除以平均活度浓度），随着噪声等效计数率降低。在衰变研究中，OSWLS与3D-FBP灰质（GM）与白质（WM）对比度比值显示出良好一致性（<4%），OP-OSEM和SP-OSEM分别在6%和7%以内显示出一致性。对于各种帧持续时间，SP-OSEM和OP-OSEM在GM与WM对比度比值方面的误差最少，在不同噪声等效计数率之间变化75%；其他迭代方法的这种变异性更高（>92%）。3D-FBP显示出最小的变异性（34%）。在视觉上，OSWLS在参数图像中几乎未显示出任何伪影，并且与参数图像的3D-FBP数据显示出良好一致性，特别是在参考组织动力学方法的情况下（斜率，1.02；皮尔逊相关系数，0.99）。
OP-OSEM、SP-OSEM和OSWLS在体模研究中表现良好。此外，OSWLS在临床研究的参数分析中显示出更好的结果，因此推荐用于定量HRRT脑部PET研究。
