Xia Ting, Alessio Adam M, Kinahan Paul E
Departments of Bioengineering and Radiology at the University of Washington, Seattle, WA.
IEEE Nucl Sci Symp Conf Rec (1997). 2010 Jan 29;2009(Oct. 24 2009-Nov. 1 2009):3074-3079. doi: 10.1109/NSSMIC.2009.5401665.
We present an analysis of the effects of ultra-low dose X-ray computerized tomography (CT) based attenuation correction for positron emission tomography (PET). By ultra low dose we mean less than approximately 5 mAs or 0.5 mSv total effective whole body dose. The motivation is the increased interest in using respiratory motion information acquired during the CT scan for both phase-matched CT-based attenuation correction and for motion estimation. Since longer duration CT scans are desired, radiation dose to the patient can be a limiting factor. In this study we evaluate the impact of reducing photon flux rates in the CT data on the reconstructed PET image by using the CATSIM simulation tool for the CT component and the ASIM simulation tool for the PET component. The CT simulation includes effects of the x-ray tube spectra, beam conditioning, bowtie filter, detector noise, and bean hardening correction. The PET simulation includes the effect of attenuation and photon counting. Noise and bias in the PET image were evaluated from multiple realizations of test objects. We show that techniques can be used to significantly reduce the mAs needed for CT based attenuation correction if the CT is not used for diagnostic purposes. The limiting factor, however, is not the noise in the CT image but rather the bias introduced by CT sinogram elements with no detected flux. These results constrain the methods that can be used to lower CT dose in a manner suitable for attenuation correction of PET data. We conclude that ultra-low-dose CT for attenuation correction of PET data is feasible with current PET/CT scanners.
我们对基于超低剂量X射线计算机断层扫描（CT）的正电子发射断层扫描（PET）衰减校正效果进行了分析。所谓超低剂量，是指总有效全身剂量小于约5 mAs或0.5 mSv。其动机在于，人们越来越关注利用CT扫描期间获取的呼吸运动信息进行基于相位匹配的CT衰减校正和运动估计。由于需要更长时间的CT扫描，患者所接受的辐射剂量可能成为一个限制因素。在本研究中，我们通过使用针对CT组件的CATSIM模拟工具和针对PET组件的ASIM模拟工具，评估了降低CT数据中光子通量率对重建PET图像的影响。CT模拟包括X射线管光谱、光束调节、蝴蝶结滤波器、探测器噪声和束硬化校正的影响。PET模拟包括衰减和光子计数的影响。从测试对象的多次实现中评估PET图像中的噪声和偏差。我们表明，如果CT不用于诊断目的，可使用一些技术显著降低基于CT的衰减校正所需的mAs。然而，限制因素并非CT图像中的噪声，而是由未检测到通量的CT正弦图元素引入的偏差。这些结果限制了可用于以适合PET数据衰减校正的方式降低CT剂量的方法。我们得出结论，使用当前的PET/CT扫描仪进行用于PET数据衰减校正的超低剂量CT是可行的。
