Liew S C, Hasegawa B H
Department of Radiology, University of California, San Francisco 94143.
Med Phys. 1991 Sep-Oct;18(5):1002-15. doi: 10.1118/1.596643.
A prototype Emission-Transmission Computed Tomography (ETCT) system is being developed that will acquire single-slice x-ray transmission CT images simultaneously with single photon emission computed tomography (SPECT) images. This system will permit the correlation of anatomical information from x-ray CT with functional information from SPECT images. The patient-specific attenuation map derived from the x-ray CT images can be used to perform attenuation correction of the SPECT images, so that accurate quantitative information can be obtained. The fan-beam scanning geometry and the use of a segmented HPGe detector array impose special constraints on the design of the collimator for the system. Based on a signal detection model, an efficiency-resolution figure of merit (ERFM) as a function of the collimator geometric efficiency, system resolution width, and object diameter is defined. The ERFM is proportional to the square of the detection signal-to-noise ratio. The collimator design parameters can then be optimized by optimizing the ERFM for an anticipated object diameter. The collimator point-spread function, geometric efficiency, and resolution are calculated. The collimator optimized for the detection of a 1-cm object will have a single-slice point source efficiency of 1.2 X 10(-4), and a FWHM of 6.5 mm at the center of the reconstruction circle, at 12 cm from the collimator face. The minimum object contrast which will give a detection SNR of 5 is 74%, for a total accumulated count per slice of 2 X 10(6).
一种发射 - 透射计算机断层扫描（ETCT）原型系统正在研发中，该系统将同时获取单层X射线透射CT图像和单光子发射计算机断层扫描（SPECT）图像。该系统将使X射线CT的解剖学信息与SPECT图像的功能信息相互关联。从X射线CT图像得出的患者特异性衰减图可用于对SPECT图像进行衰减校正，从而获得准确的定量信息。扇形束扫描几何结构以及分段HPGe探测器阵列的使用对该系统准直器的设计施加了特殊限制。基于信号检测模型，定义了作为准直器几何效率、系统分辨率宽度和物体直径函数的效率 - 分辨率品质因数（ERFM）。ERFM与检测信噪比的平方成正比。然后可以通过针对预期物体直径优化ERFM来优化准直器设计参数。计算了准直器的点扩散函数、几何效率和分辨率。针对检测1厘米物体优化的准直器在距准直器表面12厘米处的重建圆中心处，单层点源效率为1.2×10⁻⁴，半高宽为6.5毫米。对于每切片2×10⁶的总累积计数，给出检测信噪比为5的最小物体对比度为74%。
