Renal Artery

Renal Artery Velocity and Renal Aortic Ratio (RAR)

1. Normal flow

a. PSV < 180 cm/sec

b. RAR <3.5

2. Stenosis <60%

a. PSV ≥ 180 cm/sec

b. Post-stenotic turbulence

c. RAR < 3.5

3. Stenosis ≥ 60%

a. PSV ≥ 180 cm/sec

b. Post-stenotic turbulence

c. RAR ≥ 3.5

Note: The RAR is unreliable if aorta velocity used is <40 cm/sec or >100 cm/sec

Hilar Systolic Rise Time/Acceleration Time Analysis

1. Normal - Acceleration time < 100 msec

2. Abnormal - Acceleration time ≥ 100 msec, consistent with significant proximal stenosis

Parenchymal Resistive Index (RI) RI = [PSV-EDV]/PSV)

1. Normal: RI ≤ 0.70

2. Borderline Resistance: >= 0.70 to 0.80

3. Parenchymal disease: >= 0.80, consistent with medical renal disease

Parenchymal Diastolic/Systolic Ratio (DSR): if used in place of the more typical reporting of RI

1. Normal: DSR ≥ 0.3

2. Borderline Resistance: DSR = 0.2 to 0.3

3. Small vessel or parenchymal disease: DSR < 0.2

Kidney Measurements

1. Normal: 9-12 cm

2. High grade stenosis vs. occlusion: kidney ≤ 9 cm unilaterally

3. Cystic Disease or Mass: kidney length >12 cm

Note: Kidney size may vary by patient due to body habitus, therefore symmetry of kidney size is important. Discrepancies in size >2.0 cm should be mentioned when reporting findings.

Renal Stent stenosis ≥ 60%

1. PSV ≥  280 cm/s

2. RAR ≥ 4.5

Renal Transplant Arterial Stenosis

1. PSV ≥ 200 cm/sec with PST

2. Renal to Iliac artery velocity ratio ≥ 1.8