Bequé Dirk, Nuyts Johan, Bormans Guy, Suetens Paul, Dupont Patrick
Department of Nuclear Medicine, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
IEEE Trans Med Imaging. 2003 May;22(5):599-612. doi: 10.1109/TMI.2003.812258.
A method is presented to estimate the acquisition geometry of a pinhole single photon emission computed tomography (SPECT) camera with a circular detector orbit. This information is needed for the reconstruction of tomographic images. The calibration uses the point source projection locations of a tomographic acquisition of three point sources located at known distances from each other. It is shown that this simple phantom provides the necessary and sufficient information for the proposed calibration method. The knowledge of two of the distances between the point sources proves to be essential. The geometry is estimated by fitting analytically calculated projections to the measured ones, using a simple least squares Powell algorithm. Some mild a priori knowledge is used to constrain the solutions of the fit. Several of the geometrical parameters are however highly correlated. The effect of these correlations on the reconstructed images is evaluated in simulation studies and related to the estimation accuracy. The highly correlated detector tilt and electrical shift are shown to be the critical parameters for accurate image reconstruction. The performance of the algorithm is finally demonstrated by phantom measurements. The method is based on a single SPECT scan of a simple calibration phantom, executed immediately after the actual SPECT acquisition. The method is also applicable to cone-beam SPECT and X-ray CT.
本文提出了一种用于估计具有圆形探测器轨道的针孔单光子发射计算机断层扫描（SPECT）相机采集几何结构的方法。断层图像重建需要此信息。校准使用位于彼此已知距离处的三个点源的断层采集的点源投影位置。结果表明，这种简单的体模为所提出的校准方法提供了必要且充分的信息。事实证明，点源之间两个距离的知识至关重要。通过使用简单的最小二乘鲍威尔算法，将解析计算的投影拟合到测量投影来估计几何结构。使用一些适度的先验知识来约束拟合的解。然而，几个几何参数高度相关。在模拟研究中评估了这些相关性对重建图像的影响，并将其与估计精度相关联。高度相关的探测器倾斜和电偏移被证明是准确图像重建的关键参数。最后通过体模测量证明了该算法的性能。该方法基于在实际SPECT采集之后立即执行的简单校准体模的单次SPECT扫描。该方法也适用于锥束SPECT和X射线CT。
