Exercise Cardiac MR Techniques
Oliver Wieben1
1University of Wisconsin, Madison, United States

Synopsis

Exercise cardiovascular magnetic resonance (CMR) is an emerging technique with great clinical potential. Advances in device design and availability and image acquisition and reconstruction and MR methodology continue to improve the image quality and robustness and enable novel research approaches such as realtime MRI or complex quantitative hemodynamic analysis with 4D Flow MRI under exercise conditions.

Motivation and Background

Exercise stress tests are a useful tool for discerning differences in cardiac physiology and function that may not be apparent at rest. The current clinical standard for such stress tests is echocardiography which is highly efficient but has some notable limitations, including (1) Echo is less reliable for RV imaging than LV imaging, (2) Echo cannot accurately quantify complex flow, (3) Echo is not acquired during exercise. Exercise cardiovascular magnetic resonance (CMR) is an emerging technique with great clinical potential. CMR is uniquely positioned to assess cardiac health through various measuring techniques that can quantify global and local cardiac function, wall motion, hemodynamics, valve function, and more. Challenges for CMR studies in connection with exercise include added complexity for device setup, imaging at higher temporal resolution because of increased heart rates, and more challenging cardiac gating. When imaging during exercise, the space constraints of the bore and increased chest motion pose additional problems. For these reasons, clinical MRI stress tests are conducted with pharmacological agents such as adenosine, dobutamine instead of exercise stress.

Exercise CMR as a Research Tool

Previous studies have used exercise either adjacent to or inside the bore of the MRI scanner to measure ventricular volumes [1,2], myocardial perfusion [3], and cardiac output [4–6] immediately after or during exercise. Exercise-induced wall motion abnormalities and changes to myocardial perfusion with exercise CMR have shown similar diagnostic capabilities to the clinical standards of stress echocardiography [7] and stress nuclear imaging [8]. Several setups have been used in such studies, including MR compatible treadmills placed adjacent to the scanner as well as custom built and commercially available devices that enable exercising in the bore with MR data acquisition either quickly after exercise completion or for imaging under exercise conditions [9]. These devices typically use stepper or recumbent bike setups and allow for high exercise loads of up to 400W and more. Realtime cardiac imaging has compelling properties for exercise studies [10] which have less reliable cardiac gating due to motion and compromised electrode contact from sweat as well as increased short term variability in the RR intervals [11]. However, spatial and temporal resolution are typically compromised compared to standard clinical cine imaging that stretches the acquisition over multiple heart beats. Recent advances in data acquisition and reconstruction have improved realtime cardiac imaging in these regards [12] . The interrogation of hemodynamic changes in response to exercise can be explored with 4D Flow MRI in an unprecedented fashion [12, 13]. Of note, 4D Flow MRI [13] and realtime cardiac imaging [14] were able to unravel differences between patients and controls not observed under resting conditions.

Summary

Exercise cardiovascular magnetic resonance (CMR) is an emerging technique with great clinical potential. Advances in device design and image acquisition and reconstruction continue to improve the image quality and robustness but widespread application continues to be hampered by the challenge of introducing additional equipment to the scanner setup.

Acknowledgements

We thank GE Healthcare for Research Support.

References

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Proc. Intl. Soc. Mag. Reson. Med. 30 (2022)