MRI technique reveals fat in the hearts of prediabetics

Nancy D. Lamontagne

Studies have shown that fat accumulates in the hearts of people who experience heart failure or who have noninsulin-dependent diabetes (type 2). Researchers from the University of Texas Southwestern Medical Center, from Veterans Affairs Medical Center and from Presbyterian Hospital, all in Dallas, wanted to find out whether this buildup of fat occurs before or after the diabetic conditions develop because such information could help screen for early signs of heart disease in diabetic patients.

The challenge was that magnetic resonance spectroscopy is sensitive to motion, and the investigators wanted to use the technique to quantitatively assess the fat content in myocardium. Thus they needed a way to freeze cardiac and respiratory motion. They developed a method that can convert the signals from a moving heart recorded with a clinical MRI system into a single spectrum.

Led by Lidia S. Szczepaniak, the researchers used the software that they developed with ¹H magnetic resonance spectroscopy and cardiac MRI to examine 134 participants in the Dallas Heart Study — a multiethnic-population-based study of more than 6000 patients in Dallas County that was designed to examine cardiovascular disease. Each person was assigned to one of four groups representing progressive stages in the development of type 2 diabetes: lean with normal blood sugar, obese with normal blood sugar, obese and beginning to show abnormal sugar metabolism, and obese with full-blown type 2 diabetes.

The imaging showed that, compared with lean subjects, myocardial triglyceride content was 2.3 times higher in those with impaired glucose tolerance and 2.1 times higher in those with type 2 diabetes mellitus (P<0.05). This was important because it showed that fat buildup begins before the onset of diabetes.

The researchers are continuing to study how the accumulating fat affects the heart. The magnetic resonance spectroscopy and imaging method not only could reveal more information about this process but also could provide a noninvasive way to screen for early signs of heart disease in diabetic patients; the method possibly also could provide a way to measure the effectiveness of medical treatments targeted toward lowering fat in the heart.

Circulation, Sept. 4, 2007, pp. 1170-1175.