Radiology and Nuclear Medicine, University Medical Center Utrecht, P.O. Box 85500, 3508 GA, Utrecht, Netherlands.
Image Sciences Institute, Utrecht University and University Medical Center Utrecht, P.O. Box 85500, 3508 GA, Utrecht, Netherlands.
Med Phys. 2019 Jan;46(1):345-355. doi: 10.1002/mp.13253. Epub 2018 Nov 13.
The efficiency of radioembolization procedures could be greatly enhanced if results of the Tc-MAA pretreatment procedure were immediately available in the interventional suite, enabling 1-day procedures as a result of direct estimation of the hepatic radiation dose and lung shunt fraction. This would, however, require a relatively fast, but still quantitative, SPECT procedure, which might be achieved with acquisition protocols using nonuniform durations of the projection images.
SPECT liver images of the 150-MBq Tc-MAA pretreatment procedure were simulated for eight different lesion locations and two different lesion sizes using the digital XCAT phantom for both single- and dual-head scanning geometries with respective total acquisition times of 1, 2, 5, 10, and 30 min. Three nonuniform projection-time acquisition protocols ("half-circle SPECT (HCS)," "nonuniform SPECT (NUS) I," and "NUS II") for fast quantitative SPECT of the liver were designed and compared with the standard uniform projection-time protocol. Images were evaluated in terms of contrast-to-noise ratio (CNR), activity recovery coefficient (ARC), tumor/non-tumor (T/N) activity concentration ratio, and lung shunt fraction (LSF) estimation. In addition, image quality was verified with a physical phantom experiment, reconstructed with both clinical and Monte Carlo-based reconstruction software.
Simulations showed no substantial change in image quality and dosimetry by usage of a nonuniform projection-time acquisition protocol. Upon shortening acquisition times, CNR dropped, but ARC, T/N ratio, and LSF estimates were stable across all simulated acquisition times. Results of the physical phantom were in agreement with those of the simulations.
Both uniform and nonuniform projection-time acquisition liver SPECT protocols yield accurate dosimetric metrics for radioembolization treatment planning in the interventional suite within 10 min, without compromising image quality. Consequently, fast quantitative SPECT of the liver in the interventional suite is feasible.
如果 Tc-MAA 预处理程序的结果能够在介入室立即获得，那么放射栓塞程序的效率将大大提高，从而可以直接估计肝辐射剂量和肺分流分数，实现 1 天的程序。然而，这需要一个相对较快但仍然定量的 SPECT 程序，这可以通过使用投影图像非均匀持续时间的采集协议来实现。
使用数字 XCAT 体模，针对单探头和双探头扫描几何结构，分别模拟了 150MBq Tc-MAA 预处理程序的 SPECT 肝脏图像，对于 8 种不同的病变位置和 2 种不同的病变大小，各自的总采集时间分别为 1、2、5、10 和 30 分钟。设计了三种用于快速定量 SPECT 肝脏的非均匀投影时间采集协议（“半圆 SPECT（HCS）”、“非均匀 SPECT（NUS）I”和“NUS II”），并与标准均匀投影时间协议进行了比较。通过对比噪声比（CNR）、活性回收系数（ARC）、肿瘤/非肿瘤（T/N）活性浓度比和肺分流分数（LSF）估计值，对图像进行了评估。此外，还通过物理体模实验进行了图像质量验证，该实验使用了临床和基于蒙特卡罗的重建软件进行了重建。
模拟结果表明，使用非均匀投影时间采集协议不会对图像质量和剂量学产生实质性影响。随着采集时间的缩短，CNR 降低，但 ARC、T/N 比值和 LSF 估计值在所有模拟采集时间内都保持稳定。物理体模的结果与模拟结果一致。
在 10 分钟内，均匀和非均匀投影时间采集的 SPECT 肝脏协议都可以为介入室中的放射栓塞治疗计划提供准确的剂量学指标，而不会影响图像质量。因此，在介入室中进行快速定量 SPECT 肝脏检查是可行的。
