Shear wave velocity measurements.A Siemens ACUSON S2000 US system (Siemens, Germany) equipped with a 3.5–5.5 MHz linear array transducer (4C1) was used for the measurements. After measuring the cortex and medulla thicknesses in the lower pole of the kidney (the perpendicular distance from the apex of the pyramid to the capsule of the kidney), an acoustic push pulse was transmitted immediately in the region of interest (box with fixed dimensions of 1 cm × 0.5 cm). Three valid measurements were obtained for each kidney at the same portion of the mid-pole, as parallel as possible to the radically arranged tubular system. The results are expressed as meters per second (m/sec).