Wang H, Smith M F, Stone C D, Jaszczak R J
Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Med Phys. 1998 Aug;25(8):1493-501. doi: 10.1118/1.598325.
A filtered backprojection algorithm is developed for single photon emission computed tomography (SPECT) imaging with an astigmatic collimator having a displaced center of rotation. The astigmatic collimator has two perpendicular focal lines, one that is parallel to the axis of rotation of the gamma camera and one that is perpendicular to this axis. Using SPECT simulations of projection data from a hot rod phantom and point source arrays, it is found that a lack of incorporation of the mechanical shift in the reconstruction algorithm causes errors and artifacts in reconstructed SPECT images. The collimator and acquisition parameters in the astigmatic reconstruction formula, which include focal lengths, radius of rotation, and mechanical shifts, are often partly unknown and can be determined using the projections of a point source at various projection angles. The accurate determination of these parameters by a least squares fitting technique using projection data from numerically simulated SPECT acquisitions is studied. These studies show that the accuracy of parameter determination is improved as the distance between the point source and the axis of rotation of the gamma camera is increased. The focal length of the focal line perpendicular to the axis of rotation is determined more accurately than the focal length to the focal line parallel to this axis.
针对具有偏心旋转中心的散光准直器的单光子发射计算机断层扫描（SPECT）成像，开发了一种滤波反投影算法。该散光准直器有两条相互垂直的焦线，一条平行于γ相机的旋转轴，另一条垂直于该轴。通过对热棒体模和点源阵列的投影数据进行SPECT模拟发现，重建算法中未纳入机械偏移会在重建的SPECT图像中产生误差和伪影。散光重建公式中的准直器和采集参数，包括焦距、旋转半径和机械偏移，通常部分未知，可以使用点源在不同投影角度的投影来确定。研究了使用数值模拟SPECT采集的投影数据通过最小二乘法拟合技术准确确定这些参数的方法。这些研究表明，随着点源与γ相机旋转轴之间距离的增加，参数确定的准确性会提高。垂直于旋转轴的焦线的焦距比平行于该轴的焦线的焦距确定得更准确。
