About the Program: X-rays and Scans

Angiogram (Arteriogram)

For detecting disease of the arteries resulting from atherosclerosis (and occasionally other conditions), the angiogram is the gold standard. It is performed by inserting a catheter (long plastic tube) directly into the artery and then injecting dye (iodine containing liquid that is opaque to x-rays), which makes the blood in the artery show up when an x-ray picture is taken. If there is no disease causing obstruction, the pictures look like a road map of the arteries. If there is atheromatous plaque blocking the artery, the narrowing is clearly visible.

The down sides of angiograms are that the catheter needs to be put in under local anesthetic (usually through the femoral artery in the groin) and that the dye that is injected can occasionally harm the kidneys if given in large amounts (this latter is not usually a problem these days). You experience a hot feeling when the dye is injected. It used to be necessary to stay in the hospital for an angiogram, but nowadays it can be done as an outpatient procedure.

Angiograms are used for evaluating the coronary arteries (supplying the heart), renal arteries (supplying the kidneys), and carotid arteries (supplying the head).

CT (Computerized Tomography) Scan

CT scans are used to diagnose all sorts of diseases. They may be regarded as three-dimensional x-rays because they show the size and location of all the organs in the body. They're also very good at showing tumors. In the evaluation of hypertension their main use is the detection of adrenal gland tumors, which raise blood pressure by secreting hormones into the bloodstream. There are two main kinds: one is the pheochromocytoma, which secretes catecholamines, and the other is an aldosterone -secreting tumor or adenoma. Aldosterone is another hormone that raises blood pressure. Both of these tumors are usually benign (not cancerous) and are often quite small, sometimes no bigger than a pea.

Renal Scan (Renogram)

This test is performed to show the size and function of each kidney. It works on the principle that radioactive substances (called radioisotopes ) injected into the bloodstream can be detected by a special camera (a gamma camera ), which is rather like an x-ray machine. The amount of radiation used is very small. For a renal (kidney) scan an isotope that is rapidly excreted by the kidneys is used. The procedure is carried out by injecting a small dose of the isotope into an arm vein while the gamma camera takes pictures of the kidney region. As the isotope passes through the kidneys and into the urine the two kidneys "light up" on the camera images. If one kidney is not working properly (because of a blocked artery, for example) it will excrete less of the isotope than the normal kidney and also take longer to do so. Like many other diagnostic tests, however, this test is not 100 percent reliable; it may occasionally indicate an abnormality that isn't truly there and also at times may miss an abnormality that does exist. Its main use is for diagnosing renovascular hypertension.

MRI (Magnetic Resonance Imaging) Scan

These scans provide similar information to that of CT scans, but they work on a somewhat different principle. MRI involves placing the body in an intense magnetic field and then taking x-rays. You lie inside a large metal tube while the pictures are taken. Because of the magnetic field, it may not be possible to perform this test if you have metal implanted in your body (such as a heart pacemaker or artificial hip). Traditional x-rays mainly show the bones, whereas MRIs can show the details of the soft tissue as well. They are thus used for all sorts of explorations and can help provide diagnoses ranging from a torn cartilage in the knee to a brain tumor.

For evaluating hypertension, the main MRI targets are the head, for detecting strokes, and the abdomen, for finding tumors of the adrenal glands that may be causing high blood pressure.

MRA (Magnetic Resonance Angiogram)

The MRA is related to the MRI, but it uses a slightly different technique designed to show blood flowing in the arteries and veins of the body. It is usually done by injecting a substance called gadolinium into a vein, which makes the arteries show up better when the pictures are taken. (Gadolinium is an inert substance and can be given even if you have damaged kidneys). MRAs are increasingly used for diagnosing renal artery stenosis ( stenosis means a narrowing). They can provide pictures that are nearly as good as conventional angiograms without requiring a catheter in an artery. They are also commonly used for looking at the arteries in the neck ( carotid arteries).

Chest X-Ray
This is a traditional medical test, but for the evaluation of high blood pressure it is rarely of value. It does show enlargement of the heart, but only when it's very severe.