Rapid measurement of the low contrast detectability of CT scanners.
Rapid measurement of the low contrast detectability of CT scanners.
复制标题
CT扫描仪低对比度检测能力的快速测量。
DOI：
10.1002/mp.14657
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发表时间：
2021-03
期刊：
影响因子：
3.8
通讯作者：
Hsieh SS
中科院分区：
文献类型：
--
作者：
Omigbodun A;Vaishnav JY;Hsieh SS
低对比度可检测性（LCD）是计算机断层扫描（CT）成像的一项重要指标。尽管如此，在非线性数据处理的背景下，其测量是具有挑战性的。我们介绍了一个新的框架，客观表征LCD与一个特殊用途的幻影和自动分析软件的单次扫描。分析软件的输出是一个“机器LCD”度量，它比比噪比（CNR）更能代表LCD。它并不打算取代人类观察者或模型观察者的研究。根据初步模拟，我们制造了一个包含数百个低对比度珠子的幻影。这些微球是丙烯酸球（1.6 mm，净对比度~10 HU），悬浮在尼龙颗粒和等衰减盐水的背景基质中，随机分散。任务是寻找和定位这些珠子。采用一种改进的匹配滤波器对重建图像进行自动扫描，并选择不同置信度的候选头部定位。将这些与高剂量参考扫描确定的脑头位置进行比较，以产生自由反应的ROC曲线。我们比较了40 - 240 ma多个剂量水平下的迭代重建（IR）和滤波反向传播（FBP）。在60ma、120ma和180ma下分别进行三次扫描，以估计不确定度。实验扫描证明了我们技术的可行性。我们对机器LCD的度量是FROC曲线指数变换下的面积（AUC）。AUC从40 ma时的0.21单调增加到240 ma时的0.84。AUC的样本标准差约为0.02。AUC的测量不确定度对应于管电流的4%到8%的变化。令人惊讶的是，我们发现IR的auc略低于FBP的auc。虽然幻影是足够的这些实验，它包含小气泡和替代的制造方法将需要广泛应用。在具有数百个微珠的模体上使用搜索任务来测量机器LCD是可行的，并且只需一次扫描即可获得精确的误差条。我们的方法可以促进常规的质量保证或可能使不同的协议和扫描仪之间的比较。
Low contrast detectability (LCD) is a metric of fundamental importance in computed tomography (CT) imaging. In spite of this, its measurement is challenging in the context of nonlinear data processing. We introduce a new framework for objectively characterizing LCD with a single scan of a special-purpose phantom and automated analysis software. The output of the analysis software is a “machine LCD” metric which is more representative of LCD than contrast-noise ratio (CNR). It is not intended to replace human observer or model observer studies. Following preliminary simulations, we fabricated a phantom containing hundreds of low-contrast beads. These beads are acrylic spheres (1.6 mm, net contrast ~10 HU) suspended and randomly dispersed in a background matrix of nylon pellets and isoattenuating saline. The task was to search for and localize the beads. A modified matched filter was used to automatically scan the reconstruction and select candidate bead localizations of varying confidence. These were compared to bead locations as determined from a high-dose reference scan to produce free-response ROC curves. We compared iterative reconstruction (IR) and filtered backpropagation (FBP) at multiple dose levels between 40 and 240 mAs. The scans at 60, 120, and 180 mAs were performed three times each to estimate uncertainty. Experimental scans demonstrated the feasibility of our technique. Our metric for machine LCD was the area under the exponential transform of the FROC curve (AUC). AUC increased monotonically from 0.21 at 40 mAs to 0.84 at 240 mAs. The sample standard deviation of AUC was approximately 0.02. This measurement uncertainty in AUC corresponded to a change in tube current of 4% to 8%. Surprisingly, we found that AUCs for IR were slightly worse than AUCs for FBP. While the phantom was sufficient for these experiments, it contained small air bubbles and alternative fabrication methods will be necessary for widespread utilization. It is feasible to measure machine LCD using a search task on a phantom with hundreds of beads and to obtain tight error bars using only a single scan. Our method could facilitate routine quality assurance or possibly enable comparisons between different protocols and scanners.
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