Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA.
J Nucl Med. 2010 Oct;51(10):1501-6. doi: 10.2967/jnumed.110.079145. Epub 2010 Sep 16.
Assessing tumor involvement in the rectal region can sometimes be complicated by what appears to be an artifact on (18)F-FDG PET/CT images. This artifact manifests as a high-intensity region on the PET image, extending posterior to the bladder in the area around the rectum. The aim of this study was to describe this artifact, which-as far as we are aware-has not been previously reported, and to investigate its cause.
One hundred (18)F-FDG PET/CT studies (ordered-subsets expectation maximization reconstruction, CT attenuation correction) of patients with no known malignancy in the pelvis were retrospectively reviewed. Localized regions of apparently high uptake posterior to the bladder were considered an artifact when there was a discrepancy between attenuation-corrected (asymmetric appearance) and non-attenuation-corrected images (symmetric appearance). In addition, an experiment was performed using a body phantom containing 2 cylindric inserts simulating the bladder and a region of low-attenuation rectal gas. Attenuation-corrected images were reconstructed with different amounts of spatial misregistration intentionally introduced between the CT and PET images.
The artifact was observed in 15 of 100 patient studies and had a mean maximum standardized uptake value of 4.8 ± 2.7. When fused with sequentially acquired CT images, the artifact always appeared to be in the perirectal region near the bladder and an area of rectal gas. The phantom study indicated this artifact was consistent with an attenuation-correction problem caused by misregistration between CT and PET. Movement of gas within the rectum can cause an air pocket to be present during the PET acquisition at a location where CT indicated soft tissue. The resulting localized overcorrection for attenuation at the margin of the rectum and the extremely high activity concentration in the nearby bladder contributed to the artifact.
Movement of gas within the rectum between acquisition of CT and PET images can lead to an artifact in attenuation-corrected PET images in the perirectal region. An awareness of this artifact and reference to non-attenuation-corrected images will aid in the interpretation of (18)F-FDG pelvis studies.
描述一种在直肠区域评估肿瘤累及情况时可能出现的、尚未见文献报道的（18）F-FDG PET/CT 图像伪影，并探讨其发生原因。
回顾性分析 100 例（18）F-FDG PET/CT 检查结果（有序子集期望最大化重建，CT 衰减校正），这些患者均无盆腔恶性肿瘤病史。当膀胱后区出现与衰减校正（不对称表现）和非衰减校正（对称表现）图像不一致的局灶性高摄取区时，将其视为伪影。此外，还使用包含 2 个模拟膀胱和直肠低衰减气区的圆柱状插入物的体模进行了实验，在 CT 和 PET 图像之间有意引入不同程度的空间配准错误。
15 例患者的 100 例研究中观察到该伪影，其最大标准化摄取值的平均值为 4.8±2.7。与顺序采集的 CT 图像融合时，伪影始终出现在膀胱附近的直肠周围区域和直肠气区。体模研究表明，这种伪影与 CT 和 PET 之间配准错误引起的衰减校正问题一致。直肠内气体的运动可导致在 PET 采集期间在 CT 指示软组织的位置存在气袋。直肠边缘局部过度校正衰减和附近膀胱内极高的活性浓度导致了这种伪影。
CT 和 PET 图像采集期间直肠内气体的运动可导致直肠周围区域衰减校正 PET 图像出现伪影。了解这种伪影并参考非衰减校正图像将有助于（18）F-FDG 盆腔研究的解读。
