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Biomedical Imaging and Instrumentation

Biomedical Imaging and Instrumentation - Poster Session B

Poster F10 - Development of a Low-Cost Magnetic Resonance Imaging-Compatible Cycle Ergometer

Thursday, October 24, 2024
2:45 PM - 3:45 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Magnetic resonance imaging (MRI) is a powerful, non-invasive imaging technique capable of capturing detailed anatomic and physiologic information. Accordingly, MRI has become indispensable in clinical and research arenas. Currently, MRI is primarily constrained to imaging of flow in blood vessels at rest. This has some limitations as certain disease states, and their clinical sequalae, are often altered and amplified under physiological stress, including exercise. Thus, a system that allows patients to exercise during dynamic MRI scanning offers several potential clinical benefits. Nonetheless, development of an MRI-compatible exercise device is challenging due to the unique safety and compatibility requirements, including the need to use solely non-ferromagnetic materials, allowing for supine exercise in the MRI tube with minimal upper body movement and providing adjustability for different patient sizes and exercise conditions. Currently, only a limited number of MRI-compatible cycle ergometers are commercially available. However, current models have difficulty with imaging during exercise and are extremely costly (approx. $100,000), thus hindering widespread clinical adoption. To address this unmet need, we developed a portable, low-cost MRI-compatible cycle ergometer with adjustable resistance. The ergometer is easily mountable on the MRI table and can be customized for different body sizes. The device allows patients to lie supine in the MRI machine, and pedal to prescribed cadences via audio-visual guide instruction. Herein, we present the design of our custom-built MRI-compatible cycle ergometer, along with proof-of-concept data from a pilot study conducted with healthy volunteers.

Materials and

Methods:  The ergometer was constructed from non-ferromagnetic materials. At its core, is a large aluminum rod inside a plastic ball bearing spanning two acrylic plates. Aluminum discs at both ends of the rod serve as a platform for radial fixation of aluminum cranks, on which the plastic pedals attach. At the center of the ergometer, two acrylic brakes with felt pads press against the central rod, providing resistance. Resistance can be adjusted by turning acrylic handles on either side of the rod. The resistance torque was measured with a digital torque wrench. Two aluminum bars were attached to the ergometer base, which contain custom fixation devices that slide into the railings of the MRI table, securing the ergometer.
A pilot study was conducted in a simulated MRI environment to validate the exercise mechanism. The ergometer was placed on a table with a plastic hoop fastened to it - replicating the MRI width and height. The resistance torque was set to 1.2Nm. The volunteers laid supine on the table, holding handle straps and securing their feet into the pedals. A chest belt was attached to track respiratory effort (ApneaLink Air, ResMed) and a pulse oximeter monitored heart rate. During exercise, an audio-visual guide instructed participants to pedal at 51 (level 1), 69 (level 2), and 87 (level 3) revolutions per minute (RPM) for 3 minutes each, producing power outputs of 6.4, 8.7 and 10.9 W, respectively. The RPM was recorded using video tracking , allowing computation of actual cadence and power output.

Results, Conclusions, and Discussions: The pilot study was conducted with 9 healthy participants (7 male and 2 female, 26.0 ± 5.2 years old). The measured power output for levels 1, 2 and 3 was 6.6 ± 0.2 W, 8.8 ± 0.1 W and 11.3 ± 0.4 W, respectively, and thus in close agreement with target output values. Compared to baseline, the increasing power output due to increased cadence resulted in a mean increase in respiratory effort of 10.6 ± 28%, 15.9 ± 27.5% and 25.1 ± 34.8%, respectively, and an increase in heart rate of 20.7 ± 8.6%, 29.5 ± 15.1% and 32.7 ± 19.3%, respectively.
Here we present a novel portable, low-cost, MRI-compatible cycle ergometer with adjustable pedaling resistance. This device offers the capability of assessing the effect of exercise on hemodynamic conditions. Due to its streamlined design and portability, this ergometer can be easily installed and removed from MRI machines . Additionally, the crank length enables ease of clinical use and mitigates the risk of unwanted contact with the MRI machine during exercise. Individuals can successfully pedal the ergometer at various cadences causing an increase in heart rate and producing various power outputs.
This ergometer manages to overcome the significant limitation of commercial ergometers, which are highly expensive and often have limited capability for simultaneous exercise and imaging. Given these advantages, the custom ergometer design presented here shows potential for diverse clinical applications. Having demonstrated proof of concept, the ergometer is currently being utilized in a pilot clinical study to assess blood flow characteristics using 2-D phase contrast (PC-MRI) to acquire real-time flow measurements in patients with congenital heart disease under various exercise conditions. Sensitivity and velocity encoding were applied during image acquisition. To date, three patients have been enrolled and successfully completed the exercise study within the MRI. Previously, such data was challenging to obtain in this patient population. This low-cost MRI-compatible ergometer shows promise to facilitate detailed real-time analysis of the physiological response to exercise in patients impacted by a variety of disease states.

Acknowledgements (Optional):