Schwarzband Gil, Kiryati Nahum
School of Electrical Engineering, Tel Aviv University, Ramat Aviv 69978, Israel.
Phys Med Biol. 2005 Nov 21;50(22):5307-22. doi: 10.1088/0031-9155/50/22/007. Epub 2005 Nov 1.
Computed tomography (CT) scanners are usually described by their in-plane resolution and slice-sensitivity profile (SSP). Other imaging systems are characterized by their point spread function (PSF). The PSF is an excellent basis for the analysis, design and enhancement of imaging systems. The 3D PSF of CT systems has rarely been considered, and has usually been approximated by a 3D Gaussian. We present mathematical analysis of the PSF of single-slice and multi-slice fan-beam and cone-beam CT, for major reconstruction algorithms. We show that the PSF has a complicated, non-separable 3D shape. It is anisotropic in the xy plane and twisted in the z direction. Furthermore, the PSF is space variant in all three axes. In particular, it rotates as the input impulse function moves in the z direction. The PSF may also have effective discontinuities that can lead to streaking artefacts. Indirect measurements of the PSF can be misleading. We support the theoretical results by direct experimental measurements of the PSF.
计算机断层扫描（CT）扫描仪通常根据其平面分辨率和层厚灵敏度曲线（SSP）来描述。其他成像系统则以其点扩散函数（PSF）为特征。PSF是成像系统分析、设计和增强的绝佳基础。CT系统的三维PSF很少被考虑，通常用三维高斯函数来近似。我们针对主要的重建算法，对单层和多层扇束及锥束CT的PSF进行了数学分析。我们表明，PSF具有复杂的、不可分离的三维形状。它在xy平面上是各向异性的，在z方向上是扭曲的。此外，PSF在所有三个轴向上都是空间可变的。特别是，当输入脉冲函数在z方向上移动时，它会旋转。PSF也可能有有效的不连续性，这可能导致条纹伪影。PSF的间接测量可能会产生误导。我们通过对PSF的直接实验测量来支持理论结果。
