Kijewski M F, Judy P F
Med Phys. 1983 Mar-Apr;10(2):169-75. doi: 10.1118/1.595237.
Misregistration of the projections in 360 degrees computed tomographic (CT) scanners has been found to blur the image without generating artifacts. The effects of this error were investigated by analytical methods and by reconstruction of real and simulated data. The point-spread function which results from shifting each projection by a constant distance epsilon consists of a two-dimensional impulse function surrounding a region of negative density. The locus of the impulse function is a circle for parallel-beam geometry and a sixth-order curve for fanbeam geometry. The anisotropy and position dependence of the point-spread function in fanbeam geometry have been characterized. The line-spread function due to the error in parallel-beam geometry consists of two delta functions located at +/- epsilon. In fanbeam geometry, the line-spread function consists of two delta functions separated by approximately 2 epsilon, with the locations of the impulses dependent on the position and orientation of the line. This error, combined with other sources of blurring, results in a system edge-response function which contains a flat region at one-half the maximum density.
已发现360度计算机断层扫描（CT）扫描仪中的投影配准错误会使图像模糊但不产生伪影。通过分析方法以及对真实数据和模拟数据的重建来研究此误差的影响。将每个投影移动恒定距离ε所产生的点扩散函数由围绕负密度区域的二维脉冲函数组成。对于平行束几何结构，脉冲函数的轨迹是一个圆；对于扇形束几何结构，脉冲函数的轨迹是一条六次曲线。已对扇形束几何结构中点扩散函数的各向异性和位置依赖性进行了表征。平行束几何结构中由于误差导致的线扩散函数由位于±ε处的两个δ函数组成。在扇形束几何结构中，线扩散函数由两个间隔约为2ε的δ函数组成，脉冲的位置取决于线的位置和方向。此误差与其他模糊源相结合，会导致系统边缘响应函数在最大密度的一半处包含一个平坦区域。
