Department of Radiological Sciences, School of Health Science, International University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara, Tochigi, 324-8501, Japan.
Research Team for Neuroimaging, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
Ann Nucl Med. 2020 Oct;34(10):762-771. doi: 10.1007/s12149-020-01500-8. Epub 2020 Jul 4.
Many advances in PET/CT technology can potentially improve image quality and the ability to detect small lesions. A new digital TOF-PET/CT scanner based on silicon photomultipliers (SiPM) integrated with a Bayesian penalized likelihood (BPL) PET reconstruction algorithm (Q.Clear; GE Healthcare) has been introduced into clinical practice. The present study aimed to quantify the ability of a digital TOF-PET/CT scanner combined with BPL reconstruction to detect small lesions, and to determine the optimal penalization factor (β) in BPL to accurately detect such lesions.
All PET data were acquired from a NEMA body phantom using a Discovery MI (DMI) PET/CT system (GE Healthcare). The phantom included six spheres with diameters of 4, 5, 6, 8, 10, and 13 mm, and contained a background activity level of 5.3 kBq/mL, with target-to-background ratios (TBR) of 4:1 and 8:1. Images were reconstructed using a baseline OSEM algorithm, with OSEM + PSF, OSEM + TOF, OSEM + PSF + TOF, and BPL + PSF + TOF (β: 50-400). The matrix size was 192 × 192 and 384 × 384. Data acquired in 100-min list mode were re-binned into acquisition times ranging from 2 to 100 min. The quantitative accuracy and detectability of small hot spheres were evaluated by physical assessment of a recovery coefficient (RC) and a detectability index (DI), as well as visual assessment of PET images at each acquisition time.
The RC and DI of sub-centimeter spheres were improved, because the digital TOF-PET/CT scanner has a larger TOF performance gain due to better timing resolution. The RC and DI were higher with BPL in sub-centimeter spheres, than with other OSEM-based types of reconstruction. The BPL for an 8-mm sphere overestimated uptake due to edge artifact overshoot induced by PSF modeling. The variability of RC and DI for acquisition times and TBR differed considerably according to β values. The RC for ~ 8-mm spheres were > 1 at β values between 50 and 100, but were close to 1 at β value of 200. The visual scores for β = 200 in BPL were maximal, whereas those for spheres that were ≥ 6 mm exceeded the criterion of 3.
The BPL in the digital TOF-PET/CT scanner improved the quantitation and detectability of sub-centimeter spheres compared with OSEM-based reconstruction. Optimization of the β value in BPL might allow the detection of lesions ≤ 6 mm, although detectability depended on the TBR of lesions. A β value of 200 seemed optimal for detecting sub-centimeter lesions.
PET/CT 技术的许多进步都有可能提高图像质量和检测小病灶的能力。一种新的基于硅光电倍增管（SiPM）的数字 TOF-PET/CT 扫描仪，结合贝叶斯惩罚似然（BPL）PET 重建算法（Q.Clear；GE 医疗）已投入临床使用。本研究旨在量化数字 TOF-PET/CT 扫描仪结合 BPL 重建检测小病灶的能力，并确定 BPL 中准确检测此类病灶的最佳惩罚因子（β）。
所有 PET 数据均使用 Discovery MI（DMI）PET/CT 系统（GE 医疗）从 NEMA 体模中采集。该体模包含六个直径为 4、5、6、8、10 和 13 毫米的球体，背景活动水平为 5.3kBq/mL，靶标与背景比（TBR）为 4:1 和 8:1。图像使用基线 OSEM 算法、OSEM+PSF、OSEM+TOF、OSEM+PSF+TOF 和 BPL+PSF+TOF（β：50-400）进行重建。矩阵大小为 192×192 和 384×384。在 100 分钟的列表模式下采集的数据被重新分配到 2 到 100 分钟的采集时间。通过物理评估恢复系数（RC）和检测指数（DI），以及在每个采集时间评估 PET 图像的视觉评估，评估小热球的定量准确性和检测能力。
由于更好的时间分辨率，数字 TOF-PET/CT 扫描仪的 TOF 性能增益更大，亚厘米球体的 RC 和 DI 得到了提高。与其他基于 OSEM 的重建类型相比，BPL 在亚厘米球体中的 RC 和 DI 更高。由于 PSF 建模引起的边缘伪影过冲，BPL 对 8 毫米球体的摄取量估计过高。RC 和 DI 的采集时间和 TBR 变化值差异较大。β值在 50 到 100 之间时，约 8 毫米球体的 RC 大于 1，但在β值为 200 时接近 1。BPL 中β值为 200 时的视觉评分最高，而 TBR 为 6 或更大的球体的评分超过 3。
与基于 OSEM 的重建相比，数字 TOF-PET/CT 扫描仪中的 BPL 提高了亚厘米球体的定量和检测能力。优化 BPL 中的β值可能允许检测到≤6mm 的病灶，尽管检测能力取决于病灶的 TBR。β值为 200 似乎是检测亚厘米病灶的最佳选择。
