Hu H, Fox S H
GE Medical Systems, Milwaukee, Wisconsin 53201, USA.
Med Phys. 1996 Dec;23(12):1943-54. doi: 10.1118/1.597774.
A model is presented in this paper to describe how the contrast of a reconstructed object and slice sensitivity profile are affected by (1) the table speed or helical pitch, (2) the x-ray collimations, (3) the size of the object, (4) the alignment between the reconstructed slice and the object, (5) the distance of the object from the axis of rotation, and (6) the helical CT reconstruction algorithm employed. This contrast model is validated by both computer simulations and experiments. With this model, the contrast of a reconstructed object, slice sensitivity profile, and the longitudinal MTF can be accurately predicted. The optimal scan strategy and the point of diminishing returns can be determined prior to scanning. Several conclusions can be drawn from this model. First, overlapping reconstruction significantly improves overall scan contrast sensitivity of helical CT. Second, with a given x-ray collimation, low pitch helical scans provide better longitudinal resolutions. Third, with a given volume coverage rate (i.e., a given table speed), narrow collimation high pitch helical scans provide better longitudinal resolutions than wide collimation low pitch ones and therefore are recommended for high-contrast thin-slice applications. A lesion conspicuity model is also established.
本文提出了一个模型，用于描述重建物体的对比度和切片灵敏度分布如何受到以下因素的影响：(1) 检查床速度或螺旋 pitch；(2) X射线准直；(3) 物体大小；(4) 重建切片与物体之间的对齐；(5) 物体到旋转轴的距离；以及(6) 所采用的螺旋CT重建算法。该对比度模型通过计算机模拟和实验得到了验证。利用这个模型，可以准确预测重建物体的对比度、切片灵敏度分布和纵向调制传递函数(MTF)。可以在扫描前确定最佳扫描策略和收益递减点。从这个模型可以得出几个结论。首先，重叠重建显著提高了螺旋CT的整体扫描对比度灵敏度。其次，在给定X射线准直的情况下，低pitch螺旋扫描提供更好的纵向分辨率。第三，在给定的容积覆盖率(即给定的检查床速度)下，窄准直高pitch螺旋扫描比宽准直低pitch螺旋扫描提供更好的纵向分辨率，因此推荐用于高对比度薄层应用。还建立了一个病变可见性模型。
