*'''Scan''' through the renal volumes in two projections, looking for focal changes or hydronephrosis.
Normal adult kidney.jpg|thumb|Figure 1. Normal adult kidney. Measurement of kidney length on the US image is illustrated by ‘+’ and a dashed line. * Column of Bertin; ** pyramid; *** cortex; **** sinus.<ref name= "Hansen2015 " />]]
*Measure '''renal size''': The length of the adult kidney is normally 10–12 cm, and the right kidney is often slightly longer than the left kidney. The adult kidney size is variable due to the correlation with body height and age; however, normograms for pediatric kidney size are available.<ref name="Hansen2015" />
*Measure '''cortical thickness''': Cortical thickness should be estimated from the base of the pyramid and is generally 7–10 mm. If the pyramids are difficult to differentiate, the parenchymal thickness can be measured instead and should be 15–20 mm (Figure
3). The echogenicity of the cortex decreases with age and is less echogenic than or equal to the liver and spleen at the same depth in individuals older than six months. In neonates and children up to six months of age, the cortex is more echogenic than the liver and spleen when compared at the same depth.<ref name="Hansen2015" />
*Compare the '''echogenicity''' of the kidneys, comparing to the liver on the right side, and to the spleen on the left side if possible. A hyperechoic renal cortex indicates chronic kidney disease ([[#Chronic kidney disease|see section below]]).
*Have at least a quick glance at the '''bladder''' for excessive distension or obvious pathology.
==Findings in the normal kidney==
In the longitudinal scan plane, the kidney has the characteristic oval bean-shape. The right kidney is often found more caudally and is slimmer than the left kidney, which may have a so-called dromedary hump due to its proximity to the spleen. The kidney is surrounded by a capsule separating the kidney from the echogenic perirenal fat, which is seen as a thin linear structure.<ref name="Hansen2015" />
The kidney is divided into parenchyma and renal sinus. The renal sinus is hyperechoic and is composed of calyces, the renal pelvis, fat and the major intrarenal vessels. In the normal kidney, the urinary collecting system in the renal sinus is not visible, but it creates a heteroechoic appearance with the interposed fat and vessels. The parenchyma is more hypoechoic and homogenous and is divided into the outermost cortex and the innermost and slightly less echogenic medullary pyramids. Between the pyramids are the cortical infoldings, called columns of Bertin (Figure
1). In the pediatric patient, it is easier to differentiate the hypoechoic medullar pyramids from the more echogenic peripheral zone of the cortex in the parenchyma rim, as well as the columns of Bertin (Figure 2).<ref name="Hansen2015" />
[[File:Doppler ultrasound of systolic velocity (Vs), diastolic velocity (Vd), acceleration time (AoAT), systolic acceleration (Ao Accel) and resistive index (RI) of normal kidney.jpg|thumb|350px|Figure 4. Doppler ultrasound (US) of a normal adult kidney with the estimation of the systolic velocity (Vs), the diastolic velocity (Vd), acceleration time (AoAT), systolic acceleration (Ao Accel) and resistive index (RI). Red and blue colors in the color box represent flow towards and away from the transducer, respectively. The specrogram below the B-mode image shows flow velocity (m/s) against time (s) obtained within the range gate. The small flash icons on the spectrogram represent initiation of the flow measurement.<ref name="Hansen2015" />]]
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File:Normal pediatric kidney.jpg|Figure
2. Normal pediatric kidney. * Column of Bertin; ** pyramid; *** cortex; **** sinus .<ref name=Hansen2015/> File:Measures of the kidney.jpg|Figure 3. Measures of the kidney. L = length. P = parenchymal thickness. C = cortical thickness.<ref name=Hansen2015/>