Measurement of the kidney size by ultrasound. (A) We first select an image where the renal hilum is clearly observed and the area of longitudinal plane is at the maximum. In this image, the major axis (line "a") and minor axis (line "b") are measured. The line "b" should be vertical to the major axis and pass through the center of the renal hilum. (B) Next, we select the maximum transverse image, which is almost a circle, and passes through the center of the renal hilum. In this image, the transverse axis (line "c") is measured.