Suljic Alen, Tomse Petra, Jensterle Luka, Skrk Damijan
Faculty of Health Sciences, University of Ljubljana, Slovenia.
Department for Nuclear Medicine, University Medical Centre Ljubljana, Slovenia.
Radiol Oncol. 2015 Aug 21;49(3):227-33. doi: 10.1515/raon-2015-0014. eCollection 2015 Sep.
The aim of the study was to explore the influence of various time-of-flight (TOF) and non-TOF reconstruction algorithms on positron emission tomography/computer tomography (PET/CT) image quality.
Measurements were performed with a triple line source phantom, consisting of capillaries with internal diameter of ∼ 1 mm and standard Jaszczak phantom. Each of the data sets was reconstructed using analytical filtered back projection (FBP) algorithm, iterative ordered subsets expectation maximization (OSEM) algorithm (4 iterations, 24 subsets) and iterative True-X algorithm incorporating a specific point spread function (PSF) correction (4 iterations, 21 subsets). Baseline OSEM (2 iterations, 8 subsets) was included for comparison. Procedures were undertaken following the National Electrical Manufacturers Association (NEMA) NU-2-2001 protocol.
Measurement of spatial resolution in full width at half maximum (FWHM) was 5.2 mm, 4.5 mm and 2.9 mm for FBP, OSEM and True-X; and 5.1 mm, 4.5 mm and 2.9 mm for FBP+TOF, OSEM+TOF and True-X+TOF respectively. Assessment of reconstructed Jaszczak images at different concentration ratios showed that incorporation of TOF information improves cold contrast, while hot contrast only slightly, however the most prominent improvement could be seen in background variability - noise reduction.
On the basis of the results of investigation we concluded, that incorporation of TOF information in reconstruction algorithm mostly affects reduction of the background variability (levels of noise in the image), while the improvement of spatial resolution due to incorporation of TOF information is negligible. Comparison of traditional and modern reconstruction algorithms showed that analytical FBP yields comparable results in some parameter measurements, such as cold contrast and relative count error. Iterative methods show highest levels of hot contrast, when TOF and PSF corrections were applied simultaneously.
本研究旨在探讨各种飞行时间（TOF）和非TOF重建算法对正电子发射断层扫描/计算机断层扫描（PET/CT）图像质量的影响。
使用三线源体模（由内径约1mm的毛细管组成）和标准Jaszczak体模进行测量。每个数据集均使用解析滤波反投影（FBP）算法、迭代有序子集期望最大化（OSEM）算法（4次迭代，24个子集）以及结合特定点扩散函数（PSF）校正的迭代True-X算法（4次迭代，21个子集）进行重建。纳入基线OSEM（2次迭代，8个子集）用于比较。按照美国国家电气制造商协会（NEMA）NU-2-2001协议进行操作。
FBP、OSEM和True-X的半高宽（FWHM）空间分辨率测量值分别为5.2mm、4.5mm和2.9mm；FBP+TOF、OSEM+TOF和True-X+TOF的测量值分别为5.1mm、4.5mm和2.9mm。对不同浓度比下重建的Jaszczak图像进行评估显示，纳入TOF信息可改善冷对比度，而热对比度改善较小，但最显著的改善体现在背景变异性——噪声降低方面。
基于研究结果我们得出结论，在重建算法中纳入TOF信息主要影响背景变异性（图像中的噪声水平）的降低，而由于纳入TOF信息导致的空间分辨率改善可忽略不计。传统和现代重建算法的比较表明，解析FBP在一些参数测量（如冷对比度和相对计数误差）中产生可比结果。当同时应用TOF和PSF校正时，迭代方法显示出最高水平的热对比度。
