Department of Medical Physics and Radiation Protection, Gurutzeta-Cruces University Hospital/ Biocruces Bizkaia Health Research Institute, Plaza Cruces s/n, E-48903 Barakaldo, Spain.
Faculty of Engineering, Department of Applied Physics, UPV/EHU, Bilbao, Spain.
Phys Med Biol. 2023 Jun 16;68(12). doi: 10.1088/1361-6560/acd982.
The aim was to theoretically and experimentally investigate recovery in SPECT images with objects of different shapes. Furthermore, the accuracy of volume estimation by thresholding was studied for those shapes.Nine spheres, nine oblate spheroids, and nine prolate spheroids phantom inserts were used, of which the six smaller spheres were part of the NEMA IEC body phantom and the rest of the inserts were 3D-printed. The inserts were filled withTc andLu. When filled withTc, SPECT images were acquired in a Siemens Symbia Intevo Bold gamma camera and when filled withLu in a General Electric NM/CT 870 DR gamma camera. The signal rate per activity (SRPA) was determined for all inserts and represented as a function of the volume-to-surface ratio and of the volume-equivalent radius using VOIs defined according to the sphere dimensions and VOIs defined using thresholding. Experimental values were compared with theoretical curves obtained analytically (spheres) or numerically (spheroids), starting from the convolution of a source distribution with a point-spread function. Validation of the activity estimation strategy was performed using four 3D-printed ellipsoids. Lastly, the threshold values necessary to determine the volume of each insert were obtained.Results showed that SRPA values for the oblate spheroids diverted from the other inserts, when SRPA were represented as a function of the volume-equivalent radius. However, SRPA values for all inserts followed a similar behaviour when represented as a function of the volume-to-surface ratio. Results for ellipsoids were in agreement with those results. For the three types of inserts the volume could be accurately estimated using a threshold method for volumes larger than 25 ml.Determination of SRPA independently of lesion or organ shape should decrease uncertainties in estimated activities and thereby, in the long term, be beneficial to patient care.
目的是从理论和实验两方面研究不同形状物体的 SPECT 图像的恢复。此外，还研究了用阈值法对这些形状的体积进行估计的准确性。使用了九个球体、九个扁球体和九个长球体的幻影插入物，其中六个较小的球体是 NEMA IEC 体幻影的一部分，其余的插入物是 3D 打印的。插入物中填充了Tc 和Lu。当填充Tc 时，使用 Siemens Symbia Intevo Bold 伽马相机获取 SPECT 图像，当填充Lu 时，使用 General Electric NM/CT 870 DR 伽马相机获取 SPECT 图像。所有插入物的信号率与活性（SRPA）都被确定，并表示为体积-表面积比和体积等效半径的函数，使用根据球体尺寸定义的 VOI 和使用阈值定义的 VOI。实验值与从源分布与点扩散函数卷积得到的理论曲线进行了比较（球体）或数值比较（椭球体）。使用四个 3D 打印的椭球体进行了活性估计策略的验证。最后，获得了确定每个插入物体积所需的阈值。结果表明，当 SRPA 表示为体积等效半径的函数时，扁球体的 SRPA 值与其他插入物偏离。然而，当 SRPA 表示为体积-表面积比的函数时，所有插入物的 SRPA 值都表现出相似的行为。椭球体的结果与这些结果一致。对于三种类型的插入物，对于大于 25 毫升的体积，可以使用阈值方法准确估计体积。独立于病变或器官形状确定 SRPA 应降低估计活性的不确定性，从而长期有益于患者护理。
