Graduate School of Health Sciences, Niigata University, 2-746 Asahimachi-dori, Chuo-ku Niigata, 951-8518, Japan.
Department of Clinical Support, Niigata University Medical and Dental Hospital, 1-746 Asahimachi-dori, Chuo-ku Niigata, 951-8510, Japan.
Med Phys. 2021 Mar;48(3):1125-1130. doi: 10.1002/mp.14668. Epub 2021 Jan 14.
A method for measuring the slice sensitivity profile (SSP) of computed tomography (CT) images reconstructed with iterative reconstruction (IR) algorithms was reported by the AAPM Task Group 233 (TG233). In this method, the phantom plane edge is slightly slanted with respect to the scan plane to obtain a composite oversampled edge-spread function (ESF). However, it is expected that a fine-sampled ESF can be obtained directly from images reconstructed with a small slice increment without slanting the edge plane. This study aimed to investigate the validity of using a non-slanted edge plane.
In the proposed non-slanted edge method, the phantom was positioned so that the plane edge was perpendicular to the longitudinal z-axis, and images were reconstructed with a 1-mm slice thickness and 0.1-mm increment. The mean CT value was obtained in each slice and plotted as a function of slice position along the z-axis, thereby generating the ESF. The SSP was calculated from the ESF by differentiation. In the TG 233-recommended slanted edge method, the SSP was obtained by following the procedure described in the TG233 report. To validate the methodology, we first used filtered back projection (FBP) images to compare SSPs obtained using the non-slanted edge method, slanted edge method, and a standard method using a high-contrast thin object (coin). Next, for two types of IR algorithms, we compared the SSPs obtained using the non-slanted and slanted edge methods.
For the FBP images, the SSP measured using the non-slanted edge method agreed well with SSPs measured using the coin and slanted edge methods. For the IR images, the SSPs measured using the non-slanted and slanted edge methods showed good agreement.
The non-slanted edge method was demonstrated to be valid. The simplicity and practicality of the method allows routine and accurate determination of the SSP.
AAPM 工作组 233（TG233）报道了一种用于测量使用迭代重建（IR）算法重建的计算机断层扫描（CT）图像的切片灵敏度分布（SSP）的方法。在该方法中，相对于扫描平面，使体模平面边缘稍微倾斜以获得复合过采样边缘扩展函数（ESF）。然而，预期可以直接从使用小切片增量重建的图像中获得精细采样的 ESF，而无需倾斜边缘平面。本研究旨在探讨使用非倾斜边缘平面的有效性。
在提出的非倾斜边缘方法中，将体模定位使得平面边缘垂直于纵向 z 轴，并且使用 1mm 切片厚度和 0.1mm 增量重建图像。在每个切片中获得平均 CT 值，并将其绘制为沿 z 轴的切片位置的函数，从而生成 ESF。通过微分从 ESF 计算 SSP。在 TG 233 推荐的倾斜边缘方法中，按照 TG233 报告中描述的程序获得 SSP。为了验证方法的有效性，我们首先使用滤波反投影（FBP）图像来比较使用非倾斜边缘方法，倾斜边缘方法和使用高对比度薄物体（硬币）的标准方法获得的 SSP。接下来，对于两种类型的 IR 算法，我们比较了使用非倾斜和倾斜边缘方法获得的 SSP。
对于 FBP 图像，使用非倾斜边缘方法测量的 SSP 与使用硬币和倾斜边缘方法测量的 SSP 吻合良好。对于 IR 图像，使用非倾斜和倾斜边缘方法测量的 SSP 吻合良好。
证明了非倾斜边缘方法的有效性。该方法简单实用，可常规且准确地确定 SSP。
