Alessio Adam M, Kohlmyer Steve, Branch Kelley, Chen Grace, Caldwell James, Kinahan Paul
Department of Radiology, University of Washington, Seattle, WA 98195-7987, USA.
J Nucl Med. 2007 May;48(5):794-801. doi: 10.2967/jnumed.106.035717.
In dual-modality PET/CT systems, the CT scan provides the attenuation map for PET attenuation correction. The current clinical practice of obtaining a single helical CT scan provides only a snapshot of the respiratory cycle, whereas PET occurs over multiple respiratory cycles. Misalignment of the attenuation map and emission image because of respiratory motion causes errors in the attenuation correction factors and artifacts in the attenuation-corrected PET image. To rectify this problem, we evaluated the use of cine CT, which acquires multiple low-dose CT images during a respiratory cycle. We evaluated the average and the intensity-maximum image of cine CT for cardiac PET attenuation correction.
Cine CT data and cardiac PET data were acquired from a cardiac phantom and from multiple patient studies. The conventional helical CT, cine CT, and PET data of an axially translating phantom were evaluated with and without respiratory motion. For the patient studies, we acquired 2 cine CT studies for each PET acquisition in a rest-stress (13)N-ammonia protocol. Three readers visually evaluated the alignment of 74 attenuation image sets versus the corresponding emission image and determined whether the alignment provided acceptable or unacceptable attenuation-corrected PET images.
In the phantom study, the attenuation correction from helical CT caused a major artifactual defect in the lateral wall on the PET image. The attenuation correction from the average and from the intensity-maximum cine CT images reduced the defect by 20% and 60%, respectively. In the patient studies, 77% of the cases using the average of the cine CT images had acceptable alignment and 88% of the cases using the intensity maximum of the cine CT images had acceptable alignment.
Cine CT offers an alternative to helical CT for compensating for respiratory motion in the attenuation correction of cardiac PET studies. Phantom studies suggest that the average and the intensity maximum of the cine CT images can reduce potential respiration-induced misalignment errors in attenuation correction. Patient studies reveal that cine CT provides acceptable alignment in most cases and suggest that the intensity-maximum cine image offers a more robust alternative to the average cine image.
在双模态PET/CT系统中，CT扫描为PET衰减校正提供衰减图。当前获取单层螺旋CT扫描的临床实践仅提供呼吸周期的一个快照，而PET扫描跨越多个呼吸周期。由于呼吸运动导致的衰减图与发射图像的不对准会引起衰减校正因子的误差以及衰减校正后的PET图像中的伪影。为纠正此问题，我们评估了电影CT的应用，其在一个呼吸周期内采集多个低剂量CT图像。我们评估了电影CT的平均图像和强度最大值图像用于心脏PET衰减校正的情况。
电影CT数据和心脏PET数据来自心脏模型以及多个患者研究。对轴向平移模型的传统螺旋CT、电影CT和PET数据在有和无呼吸运动的情况下进行了评估。对于患者研究，在静息-负荷（13）N-氨方案中，每次PET采集我们获取了2次电影CT研究。三位阅片者通过视觉评估74组衰减图像集与相应发射图像的对准情况，并确定该对准是否提供了可接受或不可接受的衰减校正后的PET图像。
在模型研究中，螺旋CT的衰减校正导致PET图像侧壁出现一个主要的伪影缺陷。平均电影CT图像和强度最大值电影CT图像的衰减校正分别将缺陷减少了20%和60%。在患者研究中，使用电影CT图像平均值的病例中有77%对准情况可接受，使用电影CT图像强度最大值的病例中有88%对准情况可接受。
电影CT为心脏PET研究的衰减校正中补偿呼吸运动提供了一种替代螺旋CT的方法。模型研究表明，电影CT图像的平均值和强度最大值可减少衰减校正中潜在的呼吸诱导不对准误差。患者研究表明，电影CT在大多数情况下提供了可接受的对准情况，并表明强度最大值电影图像为平均电影图像提供了一种更可靠的替代方法。
