Manley J A, O'Neill W C
Renal Division, Emory University School of Medicine, Atlanta, GA 30322, USA.
Am J Kidney Dis. 2001 Apr;37(4):706-11. doi: 10.1016/s0272-6386(01)80118-9.
The echogenicity of the cortex is an important parameter in interpreting renal sonograms that suggest changes in cortical structure. Echogenicity is currently measured qualitatively, and no attempts have been made at quantification. We developed a method to quantify renal cortical echogenicity in reference to the liver and evaluated its reproducibility, dependence on scanning variables, and potential utility. Sonograms of the right kidney were digitized, and the mean pixel density of regions of the renal cortex and liver was measured and normalized to the gray scale. Echogenicity was expressed as the ratio of the brightness (inverse of mean pixel density) of the cortex to that of the liver. The mean coefficient of variation among measurements performed on multiple sonograms from the same study was 2.8%, and the coefficient of variation among multiple measurements performed on the same kidney over 1 year was 1.8%. The correlation between measurements obtained by two different individuals on identical images was 0.92, with a mean variation of 3.0%. Echogenicity was not significantly affected by type of scanner or probe frequency, but varied inversely with gain. However, the effect of gain was very small within the useful range. Water loading after an overnight fast increased echogenicity in all cases, with a mean increase of 6.4%. Echogenicity of normal kidneys was significantly less than that of the liver (range, 0.810 to 0.987), and in clinical sonograms analyzed retrospectively but blindly, echogenicity correlated with the qualitative gradations of echogenicity originally assigned. The most echogenic kidneys were 62% brighter than normal kidneys, many times greater than the variability of the measurement. We conclude that quantification of renal cortical echogenicity is feasible and reproducible and may be useful in detecting and following renal disease. Echogenicity of the renal cortex is less than that of the liver in healthy subjects and is influenced by the state of diuresis.
皮质的回声性是解读提示皮质结构改变的肾脏超声图的一个重要参数。目前回声性是通过定性测量的，尚未进行定量尝试。我们开发了一种参照肝脏对肾脏皮质回声性进行定量的方法，并评估了其可重复性、对扫描变量的依赖性以及潜在用途。对右肾的超声图进行数字化处理，测量肾皮质和肝脏区域的平均像素密度，并将其归一化到灰度。回声性表示为皮质亮度（平均像素密度的倒数）与肝脏亮度的比值。同一研究中对多张超声图进行测量的平均变异系数为2.8%，同一肾脏在1年期间多次测量的变异系数为1.8%。两名不同个体对相同图像测量结果的相关性为0.92，平均差异为3.0%。回声性不受扫描仪类型或探头频率的显著影响，但与增益呈反比。然而，在有用范围内增益的影响非常小。禁食过夜后饮水负荷在所有情况下均增加了回声性，平均增加6.4%。正常肾脏的回声性明显低于肝脏（范围为0.810至0.987），在回顾性且盲法分析的临床超声图中，回声性与最初指定的回声性定性分级相关。回声性最高的肾脏比正常肾脏亮62%，远大于测量的变异性。我们得出结论，肾脏皮质回声性的定量是可行且可重复的，可能有助于检测和跟踪肾脏疾病。在健康受试者中，肾皮质的回声性低于肝脏，且受利尿状态影响。
