Patient Evaluation

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Intimal-Medial Thickness (IMT) Test

The identification of patients at risk for heart attack and stroke is of great concern for a physician. There are now several "imaging" tests that can supplement our ability to detect the presence of atherosclerotic plaque in the carotid and coronary arteries.

Many patients have been sent for Electron Beam Cat Scans (EBCT) of their hearts. This technique has several notable weaknesses. It does not identify early plaques, which are non-calcified, and cannot be used to track a patient's progress on therapy. Hence, it is probably better to think of this as a marker for risk, rather than a modifiable risk factor.

The measurement of Intimal-Medial Thickness (IMT) in the carotid arteries is a painless test that utilizes High Frequency M-Mode ultrasound scanning to detect and quantify the amount of thickening just below the inner lining of the carotid artery; i.e., the place in the artery where atherosclerotic plaques develop and enlarge.

There have been several large studies that have evaluated this finding in patients of all ages, revealing that increased IMT can predict risk for stroke and MI. In addition, treatment with cholesterol lowering medications (such as statins) or Angiotensin Converting Enzyme (ACE) inhibitors can slow an increase in or actually partially reverse the IMT.

The presence of carotid plaque appears to correlate very well with coronary plaque. These show that when carotid IMT has been reduced coronary artery plaque may behave in a similar manner. The sequence of slides below explains the basics of IMT and the rationale for its use.

The faculty of the Lipid Treatment and Research Center have been performing this procedure for several years. In our experience, the data are highly reproducible, correlate well with underlying risk factors, and have been useful for diagnostic and treatment purposes.

B-mode carotid ultrasound is extremely effective at delineating anatomic divisions of the carotid arterial walls, including boundaries between the periadventitia, adventitia, media, intima, and lumen in both the near and far walls.

Consequently, such a modality can accurately estimate wall thickness, lumen size, and the presence, size, and location of atheromatous lesions.

This set of ultrasound scans shows varying degrees of thickening in the wall of a carotid artery. An extreme level of detail is visible, to the level of hundredths of a millimeter.

This is a brief summary of some of the numerous studies during the last 8-10 years as to the effectiveness of various medical therapies in reducing progression of carotid IMT.

This large study of older patients demonstrates the prognostic capability of advanced levels of Carotid IMT in predicting heart attack and stroke. Back to Physician Referral