Investigation of the assessment of low degree (<50%) renal artery stenosis based on velocity flow profile analysis using Doppler ultrasound: An in-vitro study.

PURPOSE: Renal arterial stenosis can lead to disrupted renal function due to reduced blood flow to the kidneys and is largely thought to be caused by atherosclerosis. Current diagnostic strategies for renal arterial stenosis rely on detecting large degree stenoses (>50%). This study aimed to test the viability of using Doppler ultrasound to assess velocity profiles to detect the presence of low degree (<50%) stenoses. METHODS: A series of anatomically realistic renal artery flow phantoms were constructed exhibiting a range of low degree stenoses (symmetric and asymmetric). The behaviour of fluid flow in the phantoms was examined using Doppler ultrasound and analysed to calculate the clinical biomarker, wall shear stress. RESULTS: A number of fluid behaviours were observed in relation to stenosis degree: asymmetric stenoses tended to result in a skewing of peak velocities away from the centre of the vessel towards the outer wall, the magnitude of increase in velocity was observed to correlate with stenosis degree, and the wall shear stress curves observed large peaks in the presence of even the lowest degree stenosis (20%). CONCLUSIONS: Doppler ultrasound could potentially be utilised to diagnose low degree stenoses in a clinical setting. Doppler ultrasound in conjunction with wall shear stress analysis in particular has significant potential in the diagnosis of renal artery stenosis.

An investigation of the detection capability of pulsed wave duplex Doppler of low grade stenosis using ultrasound contrast agent microbubbles - An in-vitro study.

OBJECTIVE: The objective of the study was to investigate whether clinically used ultrasonic contrast agents improved the accuracy of spectral Doppler ultrasound in the detection of low grade (<50%) renal artery stenosis. Low grade stenoses in the renal artery are notoriously difficult to reliably detect using Doppler ultrasound due to difficulties such as overlying fat and bowel gas. METHODS: A range of anatomically-realistic renal artery phantoms with varying low degrees of stenosis (0, 30 and 50%) were constructed and peak velocity data was measured from within the pre-stenotic and mid-stenotic regions in each phantom, for both unenhanced and contrast-enhanced spectral Doppler data acquisitions. The effect of a 20 mm overlying fat layer on the ultrasound beam distortion and phase aberration, and hence on the measured peak velocity data, was also investigated. RESULTS: The overlying fat layer produced a statistically significant underestimation (p < 0.01) in both the peak velocity and peak velocity ratio [Stenotic Region(Vmax)/Pre-stenotic Region(Vmax)] for the 0% and 30% stenosis models, but not the 50% model. A statistically significant increase (p < 0.01) in the peak velocity was found in the contrast-enhanced Doppler spectra; however, no significant difference was found between the unenhanced and contrast enhanced peak velocity ratio data, which suggests that the ratio metric has better diagnostic accuracy. The peak velocity ratios determined for each of the contrast-enhanced phantoms correctly predicted if the phantom had a stenosis and furthermore correctly classified the degree of stenosis. CONCLUSION: Contrast-enhanced Doppler ultrasound could significantly assist in the early detection of renal artery disease.