Lin Michael F, Chang-Sen Lauren Q, Heiken Jay P, Pilgram Thomas K, Bae Kyongtae T
Mallinckrodt Institute of Radiology, Washington University in St. Louis, 510 South Kingshighway, Box 8131, St. Louis, MO, 63131, USA,
Abdom Imaging. 2015 Aug;40(6):1666-74. doi: 10.1007/s00261-014-0307-6.
To determine the effectiveness of the CT histogram method to characterize indeterminate adrenal nodules above 10 Hounsfield units (HU) on noncontrast CT.
Retrospective review of clinical CT data from January 2005 through 2008 identified 194 indeterminate adrenal nodules (>10 HU on noncontrast CT) in 175 patients. 20 nodules in 18 patients were excluded due to large standard deviation (SD > 30) of HU values. Of the remaining 174 nodules, 131 were classified as benign lipid-poor nodules based on size stability for ≥1 year (104), in- and opposed-phase MRI (17), adrenal washout CT (3), or biopsy (7). 43 were classified as malignant by size increase over a short time (30), avid FDG uptake on PET/CT (15), or biopsy (5). Histogram analysis was performed by drawing a circular region of interest on all adrenal nodules. Mean attenuation, total number of pixels, number of negative pixels, and percentage of negative pixels were recorded for each nodule.
At the threshold value of >10% negative pixels, 59/131 benign nodules were correctly characterized, but 1/43 malignant nodules was falsely characterized as benign (sensitivity 45%, specificity 98%, positive predictive value 98%). With a slightly higher threshold value of >15% negative pixels, there were no false benign judgments. 36 nodules had more than 15% negative pixels, all of which were benign (sensitivity 27%, specificity 100%, positive predictive value 100%). In the subgroup of benign nodules measuring 11-20 HU, 80% and 54% were identified with threshold values of >10% and >15% negative pixels, respectively.
The CT histogram method with a threshold value of >10% negative pixels can identify many benign adrenal nodules with attenuation values >10 HU on unenhanced CT with extremely high specificity. A threshold of >15% negative pixels can achieve 100% specificity. This method is highly robust provided very "noisy" CT examinations (SD > 30) are eliminated.
确定CT直方图法对非增强CT上10亨氏单位（HU）以上的肾上腺不确定结节进行特征性分析的有效性。
回顾性分析2005年1月至2008年的临床CT数据，共识别出175例患者的194个肾上腺不确定结节（非增强CT上>10 HU）。18例患者的20个结节因HU值标准差较大（SD>30）被排除。在其余174个结节中，131个基于以下标准被分类为良性低脂结节：大小稳定≥1年（104个）、正反相位MRI（17个）、肾上腺洗脱CT（3个）或活检（7个）。43个因短时间内大小增加（30个）、PET/CT上FDG摄取活跃（15个）或活检（5个）被分类为恶性。通过在所有肾上腺结节上绘制圆形感兴趣区进行直方图分析。记录每个结节的平均衰减、像素总数、负像素数和负像素百分比。
在负像素>10%的阈值下，131个良性结节中有59个被正确分类，但43个恶性结节中有1个被错误地分类为良性（敏感性45%，特异性98%，阳性预测值98%）。在稍高的负像素>15%的阈值下，没有假阳性判断。36个结节的负像素超过15%，均为良性（敏感性27%，特异性100%，阳性预测值100%）。在11 - 20 HU的良性结节亚组中，分别有80%和54%的结节在负像素>10%和>15%的阈值下被识别。
负像素>10%阈值的CT直方图法能够以极高的特异性识别许多非增强CT上衰减值>10 HU的良性肾上腺结节。负像素>15%的阈值可实现100%的特异性。如果排除非常“嘈杂”的CT检查（SD>30），该方法具有很高的稳健性。
