Basics of Renal Doppler

Renal Doppler

1. Renal Doppler (BASICS) OSR Dr. YASH KUMAR ACHANTANI

2. ANATOMY

3. The RAs originate from the lateral sides of the aorta, typically at the level of the superior border of the second lumbar vertebra, directed slightly anteriorly, usually 1-2 cm below the superior mesenteric artery origin. The right RA originates from the anterolateral aspect of the aorta and immediately turns posteriorly to course beneath the inferior vena cava (IVC). The proximal right RA is not only deep in the abdomen but it also lies perpendicular to the Doppler beam in the usual transverse scan plane. The left RA tends to originate from the posterolateral surface of the aorta and courses posteriorly the surface of the aorta and over the psoas muscle. Arterial anatomy

4. Upon reaching the renal hilum, the main renal arteries divide into anterior and posterior segmental arteries. These further divide to feed the multiple segments of the kidney. The segmental arteries, in turn, give rise to the interlobar arteries which course alongside the renal pyramids toward the periphery of the kidney. The interlobar arteries branch into arcuate arteries at the corticomedullary junction. The arcuate arteries travel across the top of the renal pyramids and give rise to the interlobular arteries

5. Variant anatomy is common in the renal vascular system. Approximately 30% of individuals have more than a single renal artery on each side. Supernumery arteries may occur unilaterally or bilaterally. Most accessory renal arteries arise from the abdominal aorta, but they may also originate from the common iliac, superior or inferior mesenteric, adrenal, and right hepatic arteries. Supernumary right renal arteries.

6. RENAL VEINS The right renal vein is located anterior to the right renal artery. The left renal vein lies between the superior mesenteric artery and the aorta (as opposed to the splenic vein, which lies anterior to the superior mesenteric artery). The left renal vein may normally be quite large in a supine individual.

7. The left renal vein may following a retroaortic course passing posterior to the aorta instead between the aorta and SMA. Anomalous left renal vein

8. Circum Aortic Left Renal Vein Alternatively, the renal vein may be circumaortic , dividing before reaching the aorta with one branch coursing anteriorly and another posteriorly

9. Normal Kidney Renal capsule : outer echogenic line Renal parenchyma: outer cortex and inner medulla Renal sinus: central, highly echogenic (fat , vessels, fibrous tissue)

10. Kidney parenchyma compared to liver parenchyma

11. RENAL DOPPLER INDICATIONS Hypertension , particularly when there is a moderate to high suspicion of renovascular hypertension, Uncontrolled hypertension despite optimal therapy , Hypertension with progressive decline in renal function , Progressive decline in renal function associated with ACE inhibition therapy or Abrupt onset of hypertension Follow-up of patients with known renovascular disease who have undergone: Renal artery stents placement, Renal artery intervention Or known unilateral stenosis concerning for stenosis in contralateral kidney.

12. 3. Suspected vascular abnormality Aneurysm Pseudoaneurysm Arteriovenous malformation Arteriovenous fistula 4. Renal insufficiency in patients at risk for renovascular disease 5. Evaluation of renal artery blood flow in patients with Known aortic dissection Trauma Other abnormalities that may compromise blood flow to the kidneys

13. 6. Evaluation of discrepant renal size 7. Concern for thrombus at aortic or renal artery orifice in infants who have or have had an aortic catheter, e.g., umbilical artery catheter 8. Abdominal or flank bruit

14. Doppler examination

15. ULTRASOUND OF THE RENAL ARTERIES

16. TECHNIQUE The procedure begins with the patient in the supine position and the head of the bed elevated about 30 degrees. A low-frequency scanhead (2.5-5.0 MHz) is used to depict the abdominal aorta and renal arteries (RAs).

17. ANTERIOR APPROACH The renal arteries are clearly imaged in B Mode from an anterior, subcostal approach however as it is perpendicular to the ultrasound beam it is not suitable for Doppler assessment. Supernumerary (duplicate) arteries can be seen looking posterior to the IVC in B Mode and Color in a sagittal plane. In most cases the anterior approach is used to evaluate the main RAs. APPROACH

18. Anterior Approach

19. OBLIQUE APPROACH By moving the probe to the left of midline and angling toward the patient's right, an acceptable Doppler angle of 60 degrees is achieved. To avoid aliasing set the colour scale high enough so it is minimized. If the scale is too low then it is difficult to determine which vessel is the vein and which vessel is the artery.

20. Anterior Approach Oblique Approach Transverse B-mode view of the abdominal aorta and right renal artery from an anterior approach. The ultrasound probe is oriented at midline and the Doppler cursor placed in the proximal right renal artery. The angle of incidence of the Doppler beam to the flow is unacceptable at approximately 89 degrees. By moving the probe to the left of midline and angling toward the patient’s right, an acceptable Doppler angle of 60 degrees is achieved

21. Flank/ Coronal Approach   Roll the patient into a decubitus position to avoid bowel gas and improve visibility of the renal artery, especially the mid to distal portion.

22. Flank Approach The flank approach may be used to image both the intrarenal vasculature and the main RAs.

23. Color-Doppler US image of the right kidney with the renal vessels. Good visualization of the entire renal vascular tree.

24. Flank approach showing the abdominal aorta and origin of both renal arteries.

25. COLOUR AND PULSED DOPPLER EXAMINATION

26. Color flow imaging is an integral component of renal artery ultrasound examination. Color flow imaging is used to locate the renal arteries and detect flow disturbances that indicate stenosis. However, when used alone, this modality may give a false impression of renal artery stenosis, because atherosclerotic plaques can cause flow disturbances in vessels that are not significantly stenotic. Pulsed Doppler spectral analysis must be used in conjunction with color flow imaging, as it provides quantitative information through the measurement of blood flow velocity in areas of stenosis

27. The spectral Doppler examination is performed with a small sample volume so as to obtain flow information from only the vessel of interest. Pulsed Doppler sampling is performed with angles of 60 degrees or less. We never use angles of greater than 60 degrees, because this artifactually increases the peak systolic velocity measurement.

28. Axial section of the midepigastric region showing the origin of both RAs.

29. Color image of the ostium (arrows) in both RAs arising from the aorta using the ‘‘banana peel’’ technique. The Doppler beam angle is optimized and close to zero. The right RA is depicted in red, the left RA in blue. Abdominal aorta (AA), left RA (LRA), right RA (RRA), inferior vena cava (IVC).

30. The Basic waveforms The three basic waveforms are  Triphasic :  triphasic waveform forward flow in systole reverse flow in late systole / early diastole forward flow in late diastole Biphasic :  biphasic waveform forward flow in systole reverse flow in diastole Monophasic : monophasic waveform - single phase with slow acceleration/deceleration high velocity low velocity Triphasic flow is considered normal, and monophasic flow is considered abnormal. Most authors consider biphasic flow abnormal, although some authors classify it as a normal waveform 

31. Parameters to be measured in pulsed Doppler Peak Systolic Velocity (PSV) Resistivity Index (RI) Renal Aortic Ratio (RAR) Acceleration time (AT) Acceleration index (AI)

32. Normal values Peak Systolic Velocity (PSV)- < 150 cm/sec Resistivity Index (RI)- < 0.7 Renal Aortic Ratio (RAR)- <3 Acceleration time (AT)- <0.07 sec Acceleration index (AI)- > 3.5 m/sec2

33. The Doppler sample volume is placed within the proximal right renal artery. In this view, an acceptable Doppler angle of 60 degrees or less is easily obtained. Flank approach showing the abdominal aorta and origin of both renal arteries. The Doppler reading of the abdominal aorta is taken near the level of the renal arteries. This value is applied to the RAR .

34. Spectral Doppler US image of the right RA in a normal subject. Note the small spike occurring at the end of the systolic rise. This feature is seen only in a normal main RA.

35. A low resistance waveform with sharp systolic upstroke is expected in the normal main renal artery (A). The early systolic peak (ESP) (arrow) is seen as a small notch in systole in the normal intrarenal arterial waveform(segmental and arcuate artries ). The systolic upstroke is rapid with an acceleration time of 0.07 seconds or less. Normal Doppler waveforms obtained from the main renal artery and segmental renal artery

36. Bilateral Renal Doppler Clinical information Findings Kidney length for age Mean +/- Standard deviation: cm +/- cm Right kidney Size: -------cm Morphology: Location, contour,length . Focal parenchymal thinning: Mild/Moderate/ Severe Hydronephrosis : Mild/Moderate/ Severe Main renal artery peak systolic velocity: Ostium: cm/s Proximal: cm/s Mid: cm/s Distal: cm/s Resistance index: Main renal vein: Patency and waveform (normal or abnormal)

37. Left kidney Size: -------cm Morphology: Location, contour,length . Focal parenchymal thinning: Mild/Moderate/ Severe Hydronephrosis : Mild/Moderate/ Severe Main renal artery peak systolic velocity: Ostium: --- cm/s Proximal: --- cm/s Mid: ---cm/s Distal:--- cm/s Resistance index: Main renal vein : Patency and waveform (normal or abnormal) Ureters Urinary bladder Abdominal aorta and IVC Impression

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