Magota Keiichi, Numata Naoto, Shinyama Daiki, Katahata Junya, Munakata Yamato, Maniawski Piotr J, Kobayashi Kentaro, Manabe Osamu, Hirata Kenji, Tateishi Ukihide, Kudo Kohsuke, Shiga Tohru
Division of Medical Imaging and Technology, Hokkaido University Hospital, Sapporo, Japan.
Philips Japan, Tokyo, Japan.
EJNMMI Phys. 2020 Nov 13;7(1):66. doi: 10.1186/s40658-020-00333-8.
Halo artifacts from urinary catheters can occur due to inaccurate scatter correction, and the artifacts affect the tumor visibility in F-FDG PET/CT images. We investigated the incidence rate and the mechanisms of halo-artifact generation and explored several scatter correction techniques to prevent artifacts.
We conducted patient and phantom studies. (1) We retrospectively reviewed the cases of patients who had undergone F-FDG PET/CT scans. To determine the frequency of halo-artifact generation, we used the patients' PET images with a standard scatter correction based on a tail-fitted single-scatter simulation (TF-SSS) using 4-mm voxel μ-maps (TFS 4-mm). (2) We performed phantom studies to evaluate the effects of a urine catheter and two scatter correction techniques, i.e., TF-SSS with 2-mm voxel μ-maps (TFS 2-mm) and a Monte Carlo-based single-scatter simulation (MC-SSS) using 4-mm voxel μ-maps (MCS 4-mm). The average standardized uptake values (SUVs) were measured for axial PET images. (3) Using the patients' data, we investigated whether TFS 2-mm and MCS 4-mm can eliminate the artifacts in the clinical images.
(1) There were 61 patients with urinary catheters; in five (8.2%), halo artifacts were observed in the TFS 4-mm PET images. (2) The phantom study clearly reproduced the halo artifacts in the TFS 4-mm PET images. The halo artifacts were generated when urine moved in the interval between the CT and PET imaging, and when the urinary catheter was placed in a circular shape. The SUVs for the TFS 4-mm and TFS-2mm PET images were underestimated at the halo-artifact regions, whereas the SUVs for the MCS 4-mm PET images were close to the true values. (3) The halo artifacts disappeared in the TFS 2-mm PET images in 4/5 patients but not 1/5 patient, whereas the halo artifacts were completely absent in the MCS 4-mm PET images in 5/5 patients.
These data suggest that halo artifacts are caused if the PET images do not correspond to the physical material in the μ-maps, which induces the scatter correction error. With the MC-SSS, it was possible to accurately estimate the scatter without generating halo artifacts.
导尿管产生的晕状伪影可能由于散射校正不准确而出现，且这些伪影会影响F-FDG PET/CT图像中肿瘤的可见性。我们调查了晕状伪影的发生率及产生机制，并探索了几种散射校正技术以预防伪影。
我们开展了患者和体模研究。（1）我们回顾性分析了接受F-FDG PET/CT扫描患者的病例。为确定晕状伪影的产生频率，我们使用基于4毫米体素μ图的尾部拟合单散射模拟（TF-SSS）进行标准散射校正的患者PET图像（TFS 4毫米）。（2）我们进行了体模研究，以评估导尿管以及两种散射校正技术的效果，即基于2毫米体素μ图的TF-SSS（TFS 2毫米）和基于4毫米体素μ图的蒙特卡洛单散射模拟（MC-SSS）（MCS 4毫米）。测量轴向PET图像的平均标准化摄取值（SUV）。（3）利用患者数据，我们研究了TFS 2毫米和MCS 4毫米能否消除临床图像中的伪影。
（1）有61例患者使用了导尿管；在5例（8.2%）患者中，TFS 4毫米PET图像中观察到晕状伪影。（2）体模研究清楚地再现了TFS 4毫米PET图像中的晕状伪影。当尿液在CT和PET成像之间的时间间隔内移动，以及导尿管呈圆形放置时，会产生晕状伪影。晕状伪影区域的TFS 4毫米和TFS-2毫米PET图像的SUV被低估，而MCS 4毫米PET图像的SUV接近真实值。（3）5例患者中有4例患者的TFS 2毫米PET图像中的晕状伪影消失，但有1例未消失，而5例患者的MCS 4毫米PET图像中完全没有晕状伪影。
这些数据表明，如果PET图像与μ图中的物理材料不对应，就会导致散射校正误差，进而产生晕状伪影。使用MC-SSS，可以准确估计散射而不产生晕状伪影。
