[Vascular pathology of urologic significance: Doppler and color Doppler].
The combined use of B-mode ultrasonography and doppler (p.w. and/or color doppler) provides a more accurate and detailed study of vascular pathology than B-mode ultrasonography alone. In fact, besides to document the presence of blood flow and to assess its direction, doppler US provides a quantitative evaluation of blood flow. Chromatic codification of blood flow (usually red if flowing towards the probe, blue if flowing away from the probe and yellow or green in the case of turbulence) permits to assess the presence of blood flow even in areas where a vessel cannot be depicted by B-mode ultrasonography. In fact in the study of blood flow to the kidney it's possible with color-doppler to visualize not only the main renal arteries but segmental-intraparenchymal arteries too; that is very useful in the detection of rejection of allograft. In renal artery, blood flow presents a pattern of low resistance: a brief systolic phase followed by a longer diastolic one, without inversion of flow. In renal vein, blood flow is, on the contrary, continuous. The main disorders of the kidney and urinary tract, which can be detected by color doppler are the following: renal-vascular hypertension, rejection of allograft, renal vein thrombosis, portal hypertension with spleno-renal collateral channels, disorders of ureteral motility, space occupying lesions, medical nephropathies and obstructive uropathies. Sophisticated analysis of the flow pattern to the kidney with color doppler, by some doppler sonographic parameters (resistance index RI, pulsatility index PI), in these disorders adds a functional element to the traditional ultrasonographic imaging with a better characterization of the disease.