Chin Bennett B, Nakamoto Yuji, Kraitchman Dara L, Marshall Laura, Wahl Richard
Department of Radiology, Division of Nuclear Medicine Johns Hopkins University School of Medicine, Baltimire, MD, USA.
Mol Imaging Biol. 2003 Mar-Apr;5(2):57-64. doi: 10.1016/s1536-1632(03)00044-1.
Using combined positron emission tomography (PET) and computerized tomography (CT) instrumentation, PET measurements of myocardial tracer uptake performed with CT attenuation correction may differ from estimates using 68Germanium transmission correction due to differences in respiratory motion during acquisition. The purpose of this study is to evaluate the effects of respiratory motion on the CT acquisition and emission corrected images, and to evaluate the correlation of diaphragm position with regional differences in myocardial 2-deoxy-2-[18F]fluoro-D-glucose (FDG) uptake in clinical studies.
A canine myocardial FDG-PET study was performed with controlled ventilation. Attenuation correction was performed with CT scans acquired at end expiration and end inspiration, and throughout multiple respiratory cycles with conventional 68Germanium transmission scan. The mean myocardial FDG activity was evaluated in multiple short axis regions of interest (n=40) using each of these three AC maps. Differences in emission during CT acquisitions were identified and expressed as bias (%) compared to 68Germanium corrected data. Ten patient studies with high myocardial FDG uptake were retrospectively selected from a clinical population referred for whole body oncology studies. All subjects had both CT and 68Germanium AC. After analysis for diaphragm misregistration defined by imaging and diaphragm position, subjects were divided into two groups: Group A controls (n=5) with no or mild misregistration, and Group B (n=5) with moderate or severe diaphragm misregistration. Regional emission bias (n=400 regions) from CT correction was defined by using the 68Germanium attenuation corrected emission as the standard.
The canine study using end-expiration CT for attenuation correction showed regional overestimation of activity (1.8%+/-0.7% for inferior; 2.0%+/-0.5% for inferolateral) compared to the 68Germanium corrected images. Conversely, the study using end-inspiration CT attenuation correction showed underestimation (-3.9%+/-0.5% for inferior; -4.0%+/-0.6% for inferolateral) of myocardial activity compared to 68Germanium corrected images. In subjects, Group B showed significant relative underestimation of FDG myocardial activity compared to Group A in the regions adjacent to the diaphragm including the inferior (P=0.0003), inferoseptal (P=0.008), and inferolateral (P<0.0001) regions.
In canine myocardium, differences in respiration influenced CT attenuation maps and subsequent CT attenuation corrected PET images in the inferolateral and lateral regions. In clinical PET-CT studies, diaphragm misregistration is associated with relative decreased emission activity in inferior, inferoseptal, and inferolateral walls. Nonuniformity of bias in the emission data can affect quantitative accuracy, and therefore, the interpretation of myocardial viability. Further studies are required to determine if the frequency of these findings warrants the use of 68Germanium transmission attenuation correction in myocardial FDG-PET. The quantitative differences between these techniques were typically modest.
使用正电子发射断层扫描（PET）与计算机断层扫描（CT）相结合的仪器设备时，采用CT衰减校正进行的心肌示踪剂摄取PET测量结果可能与使用68锗传输校正的估计值有所不同，这是由于采集过程中呼吸运动存在差异。本研究的目的是评估呼吸运动对CT采集图像和发射校正图像的影响，并在临床研究中评估膈肌位置与心肌2-脱氧-2-[18F]氟-D-葡萄糖（FDG）摄取区域差异之间的相关性。
进行一项犬类心肌FDG-PET研究，采用控制通气。分别使用呼气末和吸气末采集的CT扫描以及传统的68锗传输扫描在多个呼吸周期内进行衰减校正。使用这三种衰减校正图中的每一种，在多个短轴感兴趣区域（n = 40）评估平均心肌FDG活性。确定CT采集过程中发射的差异，并以相对于68锗校正数据的偏差（%）表示。从临床接受全身肿瘤学研究的人群中回顾性选择10例心肌FDG摄取较高的患者研究。所有受试者均进行了CT和68锗衰减校正。在分析由成像和膈肌位置定义的膈肌配准错误后，将受试者分为两组：A组为无或轻度配准错误的对照组（n = 5），B组为中度或重度膈肌配准错误组（n = 5）。以68锗衰减校正发射作为标准，定义CT校正的区域发射偏差（n = 400个区域）。
与68锗校正图像相比，犬类研究中使用呼气末CT进行衰减校正显示活动区域高估（下壁为1.8%±0.7%；下外侧壁为2.0%±0.5%）。相反，与68锗校正图像相比，使用吸气末CT衰减校正的研究显示心肌活动低估（下壁为-3.9%±0.5%；下外侧壁为-4.0%±0.6%）。在受试者中，B组在与膈肌相邻的区域，包括下壁（P = 0.0003）、下间隔（P = 0.008）和下外侧壁（P < 0.0001），与A组相比，FDG心肌活动明显相对低估。
在犬类心肌中，呼吸差异影响下外侧和外侧区域的CT衰减图以及随后的CT衰减校正PET图像。在临床PET-CT研究中，膈肌配准错误与下壁、下间隔和下外侧壁的相对发射活性降低有关。发射数据偏差的不均匀性会影响定量准确性，进而影响心肌活力的评估。需要进一步研究以确定这些发现的频率是否足以证明在心肌FDG-PET中使用68锗传输衰减校正的合理性。这些技术之间的定量差异通常较小。
