US RENAL DOPPLER

The US Renal Doppler is a type of ultrasound imaging that employs Doppler technology to assess the blood supply into and from the kidneys. It is a non-invasive imaging technique that is frequently performed for evaluation of renal artery stenosis, renal perfusion as well as to monitor pathological processes that alter renal blood flow. Unlike traditional ultrasound machines that generate still images, Doppler studies permit dynamic imaging of blood coursing through vessels, aiding diagnosis of the vascular components of renal disorders. 

What is a Renal Doppler Ultrasound Test? 

The US Renal Doppler integrates ultrasound imaging with Doppler flow analysis to assess the anatomy of the kidney and how blood is supplied and drained from the kidney via renal arteries and veins.

Types of Renal Doppler Ultrasound Techniques Used in Radiology 

1. Colour Doppler Ultrasound 
2. Depicts blood flow direction and velocity as overlays in colorful representations. 
3. Spectral Doppler 
4. It provides and analyses the waveform of the blood flow with respect to time which is helpful in finding the peak systolic velocity (PSV) and resistance index (RI). 
5. Power Dopler 
6. This type of Doppler ultrasound is used more for detecting the flow of blood through vessels by its sensitivity compared to color Doppler, which has little flow velocity. This is especially helpful in some transplant cases. 
7. Duplex Ultrasound 
8. This merge uses traditional B mode ultrasound alongside Doppler to provide both the structure and flow information of the region being scanned. 

• Peak Systolic Velocity (PSV): Measures maximum blood flow within a vessel which occurs during systole 
• Resistive Index (RI): Measures resistance to blood flow within a renal artery 
• Renal Aortic Ratio (RAR): PSV of renal artery against PSV of aorta 
• Acceleration Time (AT): Time taken to reach a certain level of velocity 
• Turbulence or changes in the form of the wave: Indicate stenosis or obstruction 
• Kidney size and cortical thickness: Evaluate scarring or atrophy 
• Parenchymal flow patterns: Shows the level of perfusion adequacy 

Adjustment Factors: 

• Changes in RI due to age factors 
• Changes in heart rate and blood pressure 
• Factors related to transplanted kidney or native one 

• Determine secondary hypertension due to stenosis renal arteries 
• Follow-up of renal allograft function 
• Study renal vein thrombosis 
• Check kidney perfusion in patients with chronic kidney disease 
• Examine fibromuscular dysplasia 
• Diagnose renal infarction 

When is a Renal Doppler Ultrasound Radiology Test Needed? 

This is Recommended for: 

• A case of unrelieved hypertension for a longer period, especially in older or younger individuals. 
• Renal artery stenosis is suspected. 
• To monitor the perfusing blood of renal transplant. 
• To assess renal vein thrombosis. 
• For diagnostic work on abrupt or progressive kidney failure. 
• Elevated creatinine levels. 

Who Typically Needs a Renal Doppler Ultrasound? 

• Patients with difficult to manage hypertension. 
• Patients suffering from atherosclerotic disease and individuals with a family member suffering from the disease. 
• Transplanted kidney patients. 
• Individuals with a family history of vascular diseases. 
• Patients who have renal bruits. 

Advantages of Renal Doppler Ultrasound in Clinical Radiology

• Non-invasive and no ionizing radiation involved 
• Lower cost when compared to CT or MR angiography 
• Repeated with no adverse consequences 
• Real-time update of blood flow activity 
• Detection of issues early in vascular conditions 
• Well Suited for renal transplant monitoring 

Conditions Diagnosed with Renal Doppler Ultrasound Scan

• Fibromuscular dysplasia 
• Atherosclerosis of renal vessels 
• Kidney transplant rejection or failure 
• Renal infarction 
• Renal vein thrombosis 
• Renal artery stenosis 
• Renovascular hypertension 
• Renal aneurysms (in select cases) 

• Fasting for 6–8 hours before the test to reduce bowel gas 
• Wear loose fitting clothing 
• Avoid gas producing foods the day before 
• Should encouraged drink hydrated fluids unless outlined otherwise 
• Advise the technician of any prior abdominal surgical procedures or any renal malformations 

Pre-Test Requirements for Renal Doppler Ultrasound Radiology 

• Most recent creatinine levels (if follow up imaging with contrast is anticipated) 
• No heavy meals prior to the test Travelled by car 
• Beta blockers and ACE inhibitors has suggested restriction at some centres but physician discretion only 
• If accessible, present prior imaging documents for comparison 

Best Time to Undergo a Renal Doppler Ultrasound Scan 

• Accomplished any time of the day 
• Required preferred during morning hours if fasting is expected 
• Might be completed for acute cases (ex. assume renal thrombosis) immediately 

Eligibility for Renal Doppler Ultrasound Testing 

Generally Eligible: 

• Adults and children with suspected renal vascular disease 
• Women who are pregnant (does not involve radiation) 
• Individuals who have undergone renal transplant 
• Individuals with abnormal renal function tests 

Exceptions: 

None are absolute; However, in cases where patients are morbidly obese, suffering from excessive bowel gas, or are non-cooperative, imange quality may be impaired. 

Step-by-Step Process of a Renal Doppler Ultrasound Examination 

1. Patient is positioned as to lie on the examination table usually supine or in a lateral semi-prone position. 
2. Ultrasound Gel is applied on the patient's abdomen. 
3. A transducer is moved over the region of interest. 
4. Blood flow within the structure being examined is determined using Color Doppler Imaging. 
5. Waveform analysis using spectral Doppler is performed on the renal arteries and aorta. 
6. Evaluation of both kidneys along been their respective vascular structures. 
7. The procedure takes approximately 30 to 60 minutes. 

Important Precautions Before a Renal Doppler Ultrasound Test 

• Discuss with your doctor or the attending technologist if you: 
• Have had surgical interventions in the abdominal cavity 
• Use antihypertensive medications. 
• Have had renal arteries stents in the past. 
• Are pregnant (for the sake of positioning). 
• As instructed do not eat or drink anything other than clear fluids. 
• Do not smoke prior to the examination (as it impairs blood flow).