MR-compatible treadmill for exercise stress cardiac magnetic resonance imaging.

This article describes an MR-safe treadmill that enables cardiovascular exercise stress testing adjacent to the MRI system, facilitating cardiac MR imaging immediately following exercise stress. The treadmill was constructed of nonferromagnetic components utilizing a hydraulic power system. Computer control ensured precise execution of the standard Bruce treadmill protocol commonly used for cardiovascular exercise stress testing. The treadmill demonstrated no evidence of ferromagnetic attraction and did not affect image quality. Treadmill performance met design specifications both inside and outside the MRI environment. Ten healthy volunteers performed the Bruce protocol with the treadmill positioned adjacent to the MRI table. Upon reaching peak stress (98 ± 8% of age-predicted maximum heart rate), the subjects lay down directly on the MRI table, a cardiac array coil was placed, an intravenous line connected, and stress cine and perfusion imaging performed. Cine imaging commenced on average within 24 ± 4 s and was completed within 40 ± 7 s of the end of exercise. Subject heart rates were 86 ± 9% of age-predicted maximum heart rate at the start of imaging and 81 ± 9% of age-predicted maximum heart rate upon completion of cine imaging. The MRI-compatible treadmill was shown to operate safely and effectively in the MRI environment.

Diagnostic Performance of Treadmill Exercise Cardiac Magnetic Resonance: The Prospective, Multicenter Exercise CMR's Accuracy for Cardiovascular Stress Testing (EXACT) Trial.

BACKGROUND: Stress cardiac magnetic resonance (CMR) has typically involved pharmacologic agents. Treadmill CMR has shown utility in single-center studies but has not undergone multicenter evaluation. METHODS AND RESULTS: Patients referred for treadmill stress nuclear imaging (SPECT) were prospectively enrolled across 4 centers. After rest (99m)Tc SPECT, patients underwent resting cine CMR. In-room stress was then performed using an MR-compatible treadmill with continuous 12-lead electrocardiogram monitoring. At peak stress, (99m)Tc was injected, and patients rapidly returned to the MR scanner isocenter for real-time, free-breathing stress cine and perfusion imaging. After recovery, cine and rest perfusion followed by late gadolinium enhancement acquisitions concluded CMR imaging. Stress SPECT was then acquired in adjacent nuclear laboratories. A subset of patients not referred for invasive coronary angiography within 2 weeks of stress underwent coronary computed tomography angiography. Angiographic data available in 94 patients showed sensitivity of 79%, specificity of 99% for exercise CMR with positive predictive value of 92% and negative predictive value of 96%. Agreement between treadmill stress CMR and angiography was strong (κ=0.82), and moderate between SPECT and angiography (κ=0.46) and CMR versus SPECT (κ=0.48). CONCLUSIONS: The multicenter EXACT trial indicates excellent diagnostic value of treadmill stress CMR in typical patients referred for exercise SPECT.