The use of a magnetic resonance angiogram is often more accurate than a CT scan or an ultrasound in certain diagnostic tests, according to WebMD. MRA testing is done to detect problems in the blood vessels that lead to the brain, issues with the aorta and narrowing of other blood vessels.
A computed tomography scan is fairly accurate and is often used to evaluate problems or injuries to the abdomen, notes John Hopkins. A CT scan may be used to detect medical issues in any part of the body as well. CT scans are often used to determine the correct placement of needles during biopsies. They are much more detailed than a standard x-ray, giving health care professionals a 2-D image of organs and blood vessels. Contrast is often used with an MRA and a CT scan to provide a better image.
The accuracy of an ultrasound is limited, especially in relation to dense bone or areas of the body such as the intestines, according to WebMD. This is because ultrasounds use sound waves to record the dimension and consistency of organs. Ultrasounds are useful for pregnancy, diagnosing medical conditions in many organs of the body and conducting needle biopsies.