Cook Russell A H, Carnes Greg, Lee Ting-Yim, Wells R Glenn
Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada.
J Nucl Med. 2007 May;48(5):811-8. doi: 10.2967/jnumed.106.034199. Epub 2007 Apr 27.
Heart disease is a leading cause of death in North America. With the increased availability of PET/CT scanners, CT is now commonly used as a transmission source for attenuation correction. Because of the differences in scan duration between PET and CT, respiration-induced motion can create inconsistencies between the PET and CT data and lead to incorrect attenuation correction and, thus, artifacts in the final reconstructed PET images. This study compared respiration-averaged CT and 4-dimensional (4D) CT for attenuation correction of cardiac PET in an in vivo canine model as a means of removing these inconsistencies.
Five dogs underwent respiration-gated cardiac (18)F-FDG PET and 4D CT. The PET data were reconstructed with 3 methods of attenuation correction that differed only in the CT data used: The first method was single-phase CT at either end-expiration, end-inspiration, or the middle of a breathing cycle; the second was respiration-averaged CT, which is CT temporally averaged over the entire respiratory cycle; and the third was phase-matched CT, in which each PET phase is corrected with the matched phase from 4D CT. After reconstruction, the gated PET images were summed to produce an ungated image. Polar plots of the PET heart images were generated, and percentage differences were calculated with respect to the phase-matched correction for each dog. The difference maps were then averaged over the 5 dogs.
For single-phase CT correction at end-expiration, end-inspiration, and mid cycle, the maximum percentage differences were 11% +/- 4%, 7% +/- 3%, and 5% +/- 2%, respectively. Conversely, the maximum difference for attenuation correction with respiration-averaged CT data was only 1.6% +/- 0.7%.
Respiration-averaged CT correction produced a maximum percentage difference 7 times smaller than that obtained with end-expiration single-phase correction. This finding indicates that using respiration-averaged CT may accurately correct for attenuation on respiration-ungated cardiac PET.
心脏病是北美地区主要的死亡原因。随着正电子发射断层扫描/计算机断层扫描（PET/CT）扫描仪的普及，CT现在通常用作衰减校正的透射源。由于PET和CT扫描持续时间的差异，呼吸引起的运动可能会导致PET和CT数据之间出现不一致，从而导致不正确的衰减校正，进而在最终重建的PET图像中产生伪影。本研究在活体犬模型中比较了呼吸平均CT和四维（4D）CT用于心脏PET衰减校正的情况，以此作为消除这些不一致性的一种方法。
五只犬接受了呼吸门控心脏（18）F-氟代脱氧葡萄糖（FDG）PET和4D CT检查。PET数据采用三种仅在所用CT数据上有所不同的衰减校正方法进行重建：第一种方法是在呼气末、吸气末或呼吸周期中间的单相CT；第二种是呼吸平均CT，即CT在整个呼吸周期内进行时间平均；第三种是相位匹配CT，其中每个PET相位用来自4D CT的匹配相位进行校正。重建后，将门控PET图像求和以生成非门控图像。生成PET心脏图像的极坐标图，并计算每只犬相对于相位匹配校正的百分比差异。然后将差异图在五只犬中进行平均。
对于呼气末、吸气末和周期中间的单相CT校正，最大百分比差异分别为11%±4%、7%±3%和5%±2%。相反，使用呼吸平均CT数据进行衰减校正的最大差异仅为1.6%±0.7%。
呼吸平均CT校正产生的最大百分比差异比呼气末单相校正小7倍。这一发现表明，使用呼吸平均CT可能会准确校正呼吸非门控心脏PET的衰减。
