Carl E. Ravin Advanced Imaging Labs, Duke University Health System, 2424 Erwin Road, Suite 302, Durham, NC, 27710, USA.
Clinical Imaging Physics Group, Duke University Health System, 2424 Erwin Road, Suite 302, Durham, NC, 27710, USA.
Med Phys. 2020 Apr;47(4):1633-1639. doi: 10.1002/mp.14089. Epub 2020 Mar 3.
Phantoms are useful tools in diagnostic CT, but practical limitations reduce phantoms to being only a limited patient surrogate. Furthermore, a phantom with a single cross sectional area cannot be used to evaluate scanner performance in modern CT scanners that use dose reduction techniques such as automated tube current modulation (ATCM) and iterative reconstruction (IR) algorithms to adapt x-ray flux to patient size, reduce radiation dose, and achieve uniform image noise. A new multisized phantom (Mercury Phantom, MP) has been introduced, representing multiple diameters. This work aimed to ascertain if measurements from MP can predict radiation dose and image noise in clinical CT images to prospectively inform protocol design.
The adult MP design included four different physical diameters (18.5, 23.0, 30.0, and 37.0 cm) representing a range of patient sizes. The study included 1457 examinations performed on two scanner models from two vendors, and two clinical protocols (abdominopelvic with and chest without contrast). Attenuating diameter, radiation dose, and noise magnitude (average pixel standard deviation in uniform image) was automatically estimated in patients and in the MP using a previously validated algorithm. An exponential fit of CTDI and noise as a function of size was applied to patients and MP data. Lastly, the fit equations from the phantom data were used to fit the patient data. In each patient distribution fit, the normalized root mean square error (nRMSE) values were calculated in the residuals' plots as a metric to indicate how well the phantom data can predict dose and noise in clinical operations as a function of size.
For dose across patient size distributions, the difference between nRMSE from patient fit and MP model data prediction ranged between 0.6% and 2.0% (mean 1.2%). For noise across patient size distributions, the nRMSE difference ranged between 0.1% and 4.7% (mean 1.4%).
The Mercury Phantom provided a close prediction of radiation dose and image noise in clinical patient images. By assessing dose and image quality in a phantom with multiple sizes, protocol parameters can be designed and optimized per patient size in a highly constrained setup to predict clinical scanner and ATCM system performance.
体模是诊断 CT 中的有用工具，但实际限制使体模仅成为有限的患者替代物。此外，具有单一横截面积的体模不能用于评估现代 CT 扫描仪的性能，这些扫描仪使用剂量减少技术，例如自动管电流调制（ATCM）和迭代重建（IR）算法，以适应患者大小的 X 射线通量，降低辐射剂量并实现均匀的图像噪声。已经引入了一种新的多尺寸体模（汞体模，MP），代表多个直径。这项工作旨在确定 MP 测量值是否可以预测临床 CT 图像中的辐射剂量和图像噪声，以便前瞻性地为协议设计提供信息。
成人 MP 设计包括四个不同的物理直径（18.5、23.0、30.0 和 37.0 厘米），代表一系列患者尺寸。该研究包括在两个供应商的两种扫描仪型号上进行的 1457 次检查，以及两种临床方案（腹部盆腔有对比剂和胸部无对比剂）。使用先前验证的算法自动估计患者和 MP 中的衰减直径、辐射剂量和噪声幅度（均匀图像中平均像素标准偏差）。将 CTDI 和噪声作为尺寸的函数的指数拟合应用于患者和 MP 数据。最后，使用体模数据的拟合方程来拟合患者数据。在每个患者分布拟合中，在残差图中计算归一化均方根误差（nRMSE）值作为指标，以指示体模数据在多大程度上可以预测临床操作中尺寸的剂量和噪声。
对于患者尺寸分布的剂量，患者拟合和 MP 模型数据预测之间的 nRMSE 差异在 0.6%到 2.0%之间（平均值为 1.2%）。对于患者尺寸分布的噪声，nRMSE 差异在 0.1%到 4.7%之间（平均值为 1.4%）。
汞体模提供了对临床患者图像中辐射剂量和图像噪声的准确预测。通过在具有多个尺寸的体模中评估剂量和图像质量，可以根据患者尺寸设计和优化协议参数，以在高度受限的设置中预测临床扫描仪和 ATCM 系统的性能。
