MR-compatible treadmill eases cardiac stress imaging

October 6, 2008

While treadmill exercise stress testing is an essential tool for detecting and treating cardiovascular disease, it is often difficult for physicians to obtain clear images of the heart when a patient's heart is at peak stress. This is changing at the Ohio State University Medical Center, where researchers have designed equipment that allows for quick transfer of patients between treadmill and scanner.

Clinicians have been hampered by the time lapse between the completion of exercise and image capture. But now they could be able to exercise patients to peak stress and obtain high-definition images of their hearts within a minute, said Orlando "Lon" Simonetti, Ph.D., an associate professor of internal medicine and radiology at OSUMC.

"This is made possible by positioning the treadmill next to the MRI machine," Simonetti told Diagnostic Imaging.

The standard design of treadmills has made exercise stress testing a challenge near the intense magnetic field generated by MRI equipment. Treadmill stress testing is usually conducted in a separate area, after which the patient is moved into the MR room.

"It's not safe to walk a patient any distance after they're at peak stress on the treadmill," Simonetti said. "Also, any time delay between completion of the treadmill stress test and entering the MRI machine affects the imaging results."

To address these issues, Simonetti and a group of graduate students in mechanical and biomedical engineering modified a treadmill to be totally nonferromagnetic, making it MRI-compatible. All components, including the motor, are made of aluminum and nonferromagnetic stainless steel. Placing the treadmill in the room with the scanner minimizes the time needed for patients to get off the treadmill and into the scanner for stress function and perfusion imaging.

"We are able to exercise patients to peak stress and obtain high-definition MR images of their heart within 60 seconds," Simonetti said. "We do real-time cine imaging, and then first-pass perfusion imaging back-to-back."

According to Dr. Raymond Kim, codirector of the cardiovascular MRI center at Duke University Medical Center, treadmill stress testing with MRI provides much more information than pharmacological stress testing, in which dobutamine is administered to accelerate heart rate, or the vasodilator adenosine is given to detect the presence of coronary stenoses.

"The symptoms from which the patient is suffering can actually be reproduced with exercise stress testing, revealing the presence and extent of coronary artery disease, the cause of angina, and ECG changes, or confirmation of myocardial infarction," Kim said.The situation is different with treadmill exercise because ischemia is induced, according to Simonetti.

"What we're imaging now is really a state of ischemia rather than a state of vasodilated flow with adenosine," he said.

-By Gerald W. Keister