Ultrasound anatomy and normal ECD of the kidney.

The adult kidney is studied using convex-array probes with a frequency of 3.5 MHz, whereas in children higher frequencies are advisable (5 MHz). The study of the organ may be carried out with three possible approaches (access routes): abdominal (anterior), lumbar (lateral), dorsal (posterior). For a correct and complete study of the renal echostructure 5 fundamental parameters need to be evaluated: shape, size, parenchymal echotexture, renal sinus and renal hilum. The most common anatomical variants need to be identified and namely, dromedary humps, foetal lobation, hypertrophied column of Berten, hypertrophied renal tubercles and labia. The use of colour-Doppler ultrasound equipment permits assessment of the main renal arteries, the segmentary branches at the level of the hilum, the interlobar arteries, the arcuate arteries, and the interlobular arteries (inconsistently). Colour and duplex ultrasound enable identification of flow signals from arteries that are not directly visible at B-mode sonography, since frequency resolution (related to the Doppler-shift) is greater than spatial and contrast resolution. Power doppler provides a detailed visualisation of the distribution of vascular structures and blood circulation in the different regions of the kidney parenchyma, affording a perfusion study similar to angiographic parenchymography. Unlike colour Doppler, power Doppler allows identification of the cortical circulation. The Doppler pattern of the renal arteries is typical of arteries with parenchyma destination, which show a systolic peak and a well-depicted diastolic curve due to low peripheral resistance. The parameters to be analysed are peak systolic velocity, acceleration time, pulsatility index, and resistive index.