user: How to diagnose Renal Artery Stenosis ?

assistant: A health care provider can diagnose RAS by listening to the abdomen with a stethoscope and performing imaging tests. When blood flows through a narrow artery, it sometimes makes a whooshing sound, called a bruit. The health care provider may place a stethoscope on the front or the side of the abdomen to listen for this sound. The absence of this sound, however, does not exclude the possibility of RAS.
                
In some cases, RAS is found when a person has a test for another reason. For example, a health care provider may find RAS during a coronary angiogram for diagnosis of heart problems. A coronary angiogram is a procedure that uses a special dye, called contrast medium, and x rays to see how blood flows through the heart.
                
The following imaging tests are used to diagnose RAS:
                
- Duplex ultrasound. Duplex ultrasound combines traditional ultrasound with Doppler ultrasonography. Traditional ultrasound uses a device, called a transducer, that bounces safe, painless sound waves off organs to create an image of their structure. Doppler ultrasonography records sound waves reflected off of moving objects, such as blood, to measure their speed and other aspects of how they flow. The procedure is performed in a health care providers office, outpatient center, or hospital by a specially trained technician, and the images are interpreted by a radiologista doctor who specializes in medical imaging. Anesthesia is not needed. The images can show blockage in the renal artery or blood moving through nearby arteries at a lower-than-normal speed. Ultrasound is noninvasive and low cost.  - Catheter angiogram. A catheter angiogram, also called a traditional angiogram, is a special kind of x ray in which a thin, flexible tube called a catheter is threaded through the large arteries, often from the groin, to the artery of interestin this case, the renal artery. The procedure is performed in a hospital or outpatient center by a radiologist. Anesthesia is not needed though a sedative may be given to lessen anxiety during the procedure. Contrast medium is injected through the catheter so the renal artery shows up more clearly on the x ray. Catheter angiogram is the gold standard for diagnosing RAS due to the high quality of the image produced. In addition, severe RAS can be treated during the same visit. However, a catheter angiogram is an invasive procedure, and a person may have side effects from the sedative or contrast medium or may have bleeding or injury to the artery from the catheter. The procedure is also more expensive than other imaging tests.  - Computerized tomographic angiography (CTA) scan. CTA scans use a combination of x rays and computer technology to create images. The procedure is performed in an outpatient center or hospital by an x-ray technician, and the images are interpreted by a radiologist. Anesthesia is not needed. Contrast medium is injected into a vein in the persons arm to better see the structure of the arteries. CTA scans require the person to lie on a table that slides into a tunnel-shaped device where the x rays are taken. CTA scans are less invasive than catheter angiograms and take less time. However, the risks from the x-ray radiation still exist, and the test often requires more contrast medium than a catheter angiogram, so it may not be recommended for a person with poor kidney function.  - Magnetic resonance angiogram (MRA). MRA uses radio waves and magnets to produce detailed pictures of the bodys internal organs and soft tissues without using x rays. The procedure is performed in an outpatient center or hospital by an x-ray technician, and the images are interpreted by a radiologist. Anesthesia is not needed though light sedation may be used for people with a fear of confined spaces. Contrast medium may be injected into a vein in the persons arm to better see the structure of the arteries. With most MRA scans, the person lies on a table that slides into a tunnel-shaped device that may be open ended or closed at one end; some newer machines are designed to allow the person to lie in a more open space. In addition to providing high-quality images noninvasively, MRA can provide a functional assessment of blood flow and organ function. However, the use of contrast medium for an MRA is not advised for people with poor kidney function because of the risk of complications to the skin and other organs if the kidneys do not remove the contrast medium well enough.