Renal doppler is one of the most frustrating doppler study where struggle begins right from the moment you start looking for renal artery, especially in a poorly prepared obese patient. 12 hour fasting and taking them as first patient in morning is advised. Adjust color doppler parameters like color gain, pulse repitition frequency and wall filter, by setting it on larger vessel like aorta. Try first anterior abdominal approach to locate renal vessels. If it fails, try an oblique or decubitus position with liver serving as acoustic window. Begin at celiac axis or SMA as they are easier to locate, and move slightly caudad, you may easily find atleast the origin of right renal artery. Then, you may follow the right renal artery till the hilum. Left renal artery is harder to follow all the way, so one may make the patient turn in right lateral decubitus position and scan from left posterolateral aspect (using left kidney as acoustic window). Similar approach may be used for right renal artery by turning patient to left decubitus.
Checklist
a. Kidney echotexture, parenchymal thickness, any focal lesion.
b. Longitudinal survey of aorta from ceilac artery origin till bifurcation, to look for plaques.
c. Measure PSV (peak systolic velocity) in aorta at the level of origin of renal artery.
d. Origin of renal arteries (atleast PSV)
e. Proximal, mid and distal segments of each renal artery (PSV)
f. Segmental arteries at upper, mid and lower poles.
Thus, capture 7 waveforms on each sides (Measure PSV, RI, Acceleration time). Look for areas of color shift, aliasing or any turbulence. Make sure to look at origin and proximal segment in elderly patients, where plaques are more likely to occur. Similarly, look for entire renal artery and segmental branches in younger patients to rule out Fibromuscular Dysplasia.
Normal renal artery waveform is low resistance flow pattern with good diastolic forward flow, with no spectral window.
1. Raised Peak systolic velocities: Normal PSV in renal arteries is 74-127 cm/s. PSV >180 cm/s and renal artery:aorta ratio >3.5 signifies significant stenosis.
2. Damping of intrarenal vessels: Tardus parvus waveform in segmental arteries with slow rise peak and rounded contour signifies stenosis. (Acceleration time >0.07)
Resistivity index (RI) is usually less than 0.7 in renal arteries. Raised RI is seen in many medical renal diseases and is quite non-specific.
Checklist
a. Kidney echotexture, parenchymal thickness, any focal lesion.
b. Longitudinal survey of aorta from ceilac artery origin till bifurcation, to look for plaques.
c. Measure PSV (peak systolic velocity) in aorta at the level of origin of renal artery.
d. Origin of renal arteries (atleast PSV)
e. Proximal, mid and distal segments of each renal artery (PSV)
f. Segmental arteries at upper, mid and lower poles.
Thus, capture 7 waveforms on each sides (Measure PSV, RI, Acceleration time). Look for areas of color shift, aliasing or any turbulence. Make sure to look at origin and proximal segment in elderly patients, where plaques are more likely to occur. Similarly, look for entire renal artery and segmental branches in younger patients to rule out Fibromuscular Dysplasia.
Normal renal artery waveform is low resistance flow pattern with good diastolic forward flow, with no spectral window.
1. Raised Peak systolic velocities: Normal PSV in renal arteries is 74-127 cm/s. PSV >180 cm/s and renal artery:aorta ratio >3.5 signifies significant stenosis.
2. Damping of intrarenal vessels: Tardus parvus waveform in segmental arteries with slow rise peak and rounded contour signifies stenosis. (Acceleration time >0.07)
Resistivity index (RI) is usually less than 0.7 in renal arteries. Raised RI is seen in many medical renal diseases and is quite non-specific.
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