High-fat diet makes cardiac images more clear

Cardiac sarcoidosis is a tough diagnosis requiring the analysis of several testing techniques. New research from the University of Illinois at Chicago (UIC) suggests that a high-fat diet before imaging may improve diagnostic results of cardiac sarcoidosis.

"Up until now, diagnosis is made by expert opinion based on the results of several testing techniques including imaging," Yang Lu, MD, PhD, assistant professor of radiology in the UIC College of Medicine, said. "But what these scans show is often ambiguous, and so using them to definitively diagnose cardiac sarcoidosis is problematic. There is really currently no gold standard for diagnosing cardiac sarcoidosis."

Positron emission tomography (PET) scans and computed tomography (CT) scans are typically used to diagnose cardiac sarcoidosis, but the results are hard to interpret.

Because these scans require patients to be injected with fludeoxyglucose (FDG), doctors have typically had patients consume a high-fat, low-sugar diet for 24 hours prior to imaging. Unfortunately, results have been unsatisfactory, according to Lu.

"The unpredictable uptake of FDG by healthy heart cells makes the scans hard to read," Lu said. A little under half of the scans preceded by 24 hours of the special diet were not useful for diagnosis.

Then one day a sarcoidosis patient scheduled for a scan came in a day late for their scheduled appointment.

"The patient had been following the high-fat, low-sugar diet for two days at that point instead of the usual 24 hours," Lu said. When they scanned the patient, the areas where the heart picked up the FDG were much clearer, and showed active cardiac sarcoidosis.

More importantly, the abnormal areas were in the same location as abnormal findings from the patient’s cardiac MRI.

Lu and his colleagues set out to determine how 72 hours of the high-fat, low-sugar diet in advance of scans would affect the images. They looked at 215 tests from 207 patients at the University of Illinois Hospital in 2014 and 2015.

The patients consumed a high-fat, low-sugar diet for either 24 or 72 hours before their scans.

In the 24-hour diet group, 42 percent of patients had indeterminate results. In contrast, only 4 percent of patients in the 72-hour group had indeterminate results.

"By following the diet for three days instead of one, the unpredictable but normal uptake of sugar by healthy heart cells was suppressed, so we could be more confident that areas that picked up the FDG had a very high likelihood of being affected by sarcoidosis, and this minimized the number of indeterminate findings where we can't make a diagnosis," Lu said. The technique will also allow clinicians to better-follow their patients' progress under treatment for sarcoidosis, he said.