一种用于计算机断层扫描的非平稳数据的新冗余加权方案。

A new redundancy weighting scheme for nonstationary data for computed tomography.

作者信息

Taguchi Katsuyuki, Cammin Jochen

机构信息

Division of Medical Imaging Physics, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287.

出版信息

Med Phys. 2015 May;42(5):2659-67. doi: 10.1118/1.4915954.

DOI:10.1118/1.4915954

PMID:25979064

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC4443724/

Abstract

PURPOSE

The same projection data (or line integrals) are often measured multiple times, e.g., twice from opposite directions during one gantry rotation. The redundant data must be normalized by applying redundancy weighting such as the halfscan algorithm, which assumes that the noise of the data is uniform. This assumption, however, is not correct when a tube current modulation technique is employed. The variance of line integrals, which is inversely related to the tube current, could vary significantly. The purpose of this work is to improve how the projection data are used during analytical reconstruction when the tube current is modulated during the scan.

METHODS

The authors developed a new redundancy weighting scheme. It not only takes into account the data statistics but also can control how much to weigh the statistics from 100% (αs = 1.0) to 0% (αs = 0.0) by a parameter αs. The proposed weighting scheme reduces to the conventional redundancy weighting scheme when αs = 0.0. The authors evaluated the performance of the proposed scheme using computer simulations targeting at myocardial perfusion CT imaging. The image quality was evaluated in terms of the image noise and halfscan artifacts, and perfusion defect detection performance was evaluated by the positive predictive value (PPV) and the area-under-the-receiver operating characteristic-curve (AUC) value.

RESULTS

Results showed a tradeoff between the image noise and halfscan artifacts. The normalized noise standard deviation was 1.00 with halfscan, 0.89 with αs = 1.0, 0.97 with αs = 0.5, and 1.20 with αs = 0.0 when projections over one rotation (75% of projections are acquired with full dose, 25% with 1/10 of the full dose) are used. The halfscan artifacts were 13.4 Hounsfield unit (HU) with halfscan, 8.2 HU with αs = 1.0, 4.5 HU with αs = 0.5, and 3.1 HU with αs = 0.0. Both the PPVs and AUCs were improved from the halfscan method: PPV, 69.0%-70.6% vs 58.0%, P < 0.003; AUC, 0.935-0.938 vs 0.908, P < 0.003.

CONCLUSIONS

The new redundancy weight allows for decreasing the image noise and controlling the tradeoff between the image noise and artifacts.

摘要

目的

相同的投影数据（或线积分）通常会被多次测量，例如，在一次机架旋转过程中从相反方向测量两次。必须通过应用诸如半扫描算法之类的冗余加权来对冗余数据进行归一化，该算法假定数据的噪声是均匀的。然而，当采用管电流调制技术时，这一假设并不正确。与管电流成反比的线积分方差可能会有显著变化。这项工作的目的是改进在扫描过程中管电流被调制时，解析重建过程中投影数据的使用方式。

方法

作者开发了一种新的冗余加权方案。它不仅考虑了数据统计，还可以通过参数αs控制对统计权重的取值范围，从100%（αs = 1.0）到0%（αs = 0.0）。当αs = 0.0时，所提出的加权方案简化为传统的冗余加权方案。作者使用针对心肌灌注CT成像的计算机模拟评估了所提出方案的性能。根据图像噪声和半扫描伪影评估图像质量，并通过阳性预测值（PPV）和受试者操作特征曲线下面积（AUC）值评估灌注缺损检测性能。

结果

结果表明图像噪声和半扫描伪影之间存在权衡。当使用一圈的投影数据（75%的投影以全剂量采集，25%以全剂量的1/10采集）时，半扫描的归一化噪声标准差为1.00，αs = 1.0时为0.89，αs = 0.5时为0.97，αs = 0.0时为1.20。半扫描伪影在半扫描时为13.4亨氏单位（HU），αs = 1.0时为8.2 HU，αs = 0.5时为4.5 HU，αs = 0.0时为3.1 HU。PPV和AUC均比半扫描方法有所提高：PPV，69.0% - 70.6%对58.0%，P < 0.003；AUC，0.935 - 0.938对0.908，P < 0.003。