1 Department of Translational Medicine, Medical Radiology, Lund University, Skåne University Hospital, Inga Marie Nilssons Gata 49, Malmö 20502, Sweden.
2 Department of Translational Medicine, Medical Radiation Physics, Lund University, Skåne University Hospital, Malmö, Sweden.
AJR Am J Roentgenol. 2019 Jan;212(1):84-93. doi: 10.2214/AJR.17.19441. Epub 2018 Oct 9.
Previous studies have shown the possibility to reduce radiation dose in abdominal CT by 25-50% without negatively affecting detection of liver lesions. How radiation dose reduction affects characterization of liver metastases is not as well known. The objective of this study was to investigate how different levels of simulated dose reduction affect the detection and characterization of liver lesions, primarily hypovascular metastases. A secondary objective was to analyze the relationship between the lesion size and contrast-to-noise ratio (CNR) and the detection rate.
Thirty-nine patients (19 with metastases and 20 without) were retrospectively selected. The following radiation dose levels (DLs) were simulated: 100% (reference level), 75%, 50%, and 25%. Five readers were asked to mark liver lesions and rate the probability of malignancy on a 5-grade Likert scale. Noninferiority analysis using the jackknife free-response ROC (JAFROC) method was performed as well as direct comparison of detection rates and grades.
JAFROC analysis showed noninferior detection and characterization of metastases at DL75 as compared with DL100. However, the number of benign lesions and false-positive localizations rated as "suspected malignancy" was significantly higher at DL75.
Radiation dose can be reduced by 25% without negatively affecting diagnosis of hypovascular liver metastases. Characterization of benign lesions, however, is impaired at DL75, which may lead to unnecessary follow-up examinations. Finally, increased image noise seems to affect the detection of small lesions to a degree that cannot be explained solely by the reduction in CNR.
先前的研究表明，在不影响肝脏病变检测的情况下，腹部 CT 的辐射剂量可以降低 25%-50%。但辐射剂量降低对肝脏转移瘤特征的影响却并不明确。本研究旨在探讨不同程度的模拟剂量降低如何影响肝脏病变，尤其是乏血供转移瘤的检测和特征描述。次要目的是分析病变大小与对比噪声比（CNR）及检测率之间的关系。
回顾性选择了 39 名患者（19 名转移瘤患者和 20 名无转移瘤患者）。模拟以下辐射剂量水平（DL）：100%（参考水平）、75%、50%和 25%。5 名读者被要求标记肝脏病变并在 5 级 Likert 量表上对恶性肿瘤的可能性进行评分。使用刀切自由响应 ROC（JAFROC）法进行非劣效性分析，以及直接比较检测率和等级。
JAFROC 分析显示，与 DL100 相比，DL75 对转移瘤的检测和特征描述具有非劣效性。然而，在 DL75 时，良性病变的数量以及被评为“疑似恶性”的假阳性局部定位明显更高。
辐射剂量可降低 25%，而不会对低血供肝脏转移瘤的诊断产生负面影响。然而，在 DL75 时，对良性病变的特征描述会受到影响，这可能导致不必要的随访检查。最后，图像噪声的增加似乎会在一定程度上影响小病变的检测，而这种影响不能仅用 CNR 的降低来解释。
