What are DOPPLER RENAL ARTERIES ?
Ultrasound is a diagnostic tool that is used to assess the structural and functional characteristics of the main artery supplying the kidney. Renal artery disease correlates with the degree of kidney dysfunction. As the end-organ, the kidney depends on a normal flow through its artery to supply oxygen and nutrients to its cells, as well as to serve as the source of waste products and electrolytes for active and passive filtration, elimination, or re-absorption.
Renal artery Doppler duplex ultrasound uses the combined approach of B mode ultrasound, which renders an image based on the differences of reflected sound waves from differing tissue densities; and Doppler technology that uses to advantage reflections from red blood cells that render actual flow imagery.
Renal artery disease, i.e., renal artery stenosis, is caused via two mechanisms:
- Atherosclerosis involves the branching point of the renal artery from the aorta or the proximal renal artery.
- Fibromuscular dysplasia involves the distal renal artery or its intrarenal branches.
Renal artery stenosis presents the untoward dynamic of obstruction into the kidney’s physiology, with its resulting hypoperfusion of tissue and impairment of waste elimination. Duplex Doppler ultrasonography can assess function via information gleaned from the renal arteries; it also can provide information on the structure and anatomy. B-mode imaging combined with Doppler measurements can identify both stenotic lesions and arterial flow, and make comparisons to the blood flow of the aorta.
Duplex Doppler ultrasonography can detect both unilateral and bilateral disease and can be used for serial evaluations to observe for progression of the disease. It provides a convenient method to follow those who have had surgical angioplasty or other vascular surgery.
Since the kidney is also an important regulator of electrolyte balance and part of the Renin-Angiotensin-Aldosterone system that regulates blood pressure, balanced homeostasis is at risk with renal artery stenosis and other problems. Doppler ultrasonography can evaluate renal vascular flow to evaluate renal artery stenosis, renal vein thrombosis, and renal infarction. CT and magnetic resonance (MR) are required for confirmation, but a screen can be performed using the less expensive ultrasonography.
Renal Artery Ultrasound Diagnosis
The kidneys not only eliminate waste, but are integral to electrolyte balance, homeostatic hydration, and blood pressure control. Renal artery ultrasound is indicated in
- Hypertension: when secondary causes are suspected (i.e., not “essential” hypertension): suspected renovascular hypertension.
- Elevated serum creatinine levels: when stenosis threatens the entire kidney.
- Atherosclerosis: 70-80% occlusions can lead to renal tissue hypoxia.
- Back pain attributable to renal disease
- Electrolyte disturbances: Such as hyperkalemia, hyperphosphatemia, hypocalcemia, etc., and associated metabolic acidosis.
- Computations of renal “resistive index”: A pre-operative measurement comparing systolic blood flow velocity with end-diastolic velocity, which correlates well with a predicted benefit of planned revascularization surgery.
Renal artery ultrasound is also part of a global assessment of kidney anatomy, which can distinguish differences in size between the pair when the unilateral kidney disease is present. A perusal for calcifications and obstruction of the urinary tract is easily included when renal artery ultrasound is performed. Because renal artery ultrasound is not as sensitive as confirmatory imaging methods, such as CT and MRI, a negative result is not necessarily reassuring but indicative of the necessity for the more involved imaging that uses contrast.