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Design Innovation Paper

Low Cost Magnetic Resonance Imaging-Compatible Stepper Exercise Device for Use in Cardiac Stress Tests

[+] Author and Article Information
Omid Forouzan

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: forouzan@wisc.edu

Evan Flink

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: ewflink@gmail.com

Jared Warczytowa

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: jaredwarczytowa@gmail.com

Nick Thate

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: nthate@gmail.com

Andrew Hanske

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: ahanske@epic.com

Tongkeun Lee

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: leto@seas.upenn.edu

Alejandro Roldan-Alzate

Department of Medical Physics,
Wisconsin Institutes for Medical Research,
1111 Highland Avenue,
Madison, WI 53705-2275;
Department of Radiology,
University of Wisconsin,
School of Medicine and Public Health,
E3/366 Clinical Science Center,
600 Highland Avenue,
Madison, WI 53792-3252
e-mail: aroldan@uwhealth.org

Chris François

Department of Radiology,
University of Wisconsin,
School of Medicine and Public Health,
E3/366 Clinical Science Center,
600 Highland Avenue,
Madison, WI 53792-3252
e-mail: cfrancois@uwhealth.org

Oliver Wieben

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706;
Department of Medical Physics,
Wisconsin Institutes for Medical Research,
1111 Highland Avenue,
Madison, WI 53705-2275;
Department of Radiology,
University of Wisconsin,
School of Medicine and Public Health,
E3/366 Clinical Science Center,
600 Highland Avenue,
Madison, WI 53792-3252
e-mail: owieben@wisc.edu

Naomi C. Chesler

Department of Biomedical Engineering,
University of Wisconsin-Madison,
Engineering Centers Building,
1550 Engineering Drive,
Madison, WI 53706
e-mail: chesler@engr.wisc.edu

Manuscript received October 11, 2013; final manuscript received March 26, 2014; published online August 19, 2014. Assoc. Editor: Carl Nelson.

J. Med. Devices 8(4), 045002 (Aug 19, 2014) (8 pages) Paper No: MED-13-1255; doi: 10.1115/1.4027343 History: Received October 11, 2013; Revised March 26, 2014

Cardiovascular disease is the leading cause of death worldwide. Many cardiovascular diseases are better diagnosed during a cardiac stress test. Current approaches include either exercise or pharmacological stress echocardiography and pharmacological stress magnetic resonance imaging (MRI). MRI is the most accurate noninvasive method of assessing cardiac function. Currently there are very few exercise devices that allow collection of cardiovascular MRI data during exercise. We developed a low-cost exercise device that utilizes adjustable weight resistance and is compatible with magnetic resonance (MR) imaging. It is equipped with electronics that measure power output. Our device allows subjects to exercise with a leg-stepping motion while their torso is in the MR imager. The device is easy to mount on the MRI table and can be adjusted for different body sizes. Pilot tests were conducted with 5 healthy subjects (3 male and 2 female, 29.2 ± 3.9 yr old) showing significant exercise-induced changes in heart rate (+42%), cardiac output (+40%) and mean pulmonary artery (PA) flow (+%49) post exercise. These data demonstrate that our MR compatible stepper exercise device successfully generated a hemodynamically stressed state while allowing for high quality imaging. The adjustable weight resistance allows exercise stress testing of subjects with variable exercise capacities. This low-cost device has the potential to be used in a variety of pathologies that require a cardiac stress test for diagnosis and assessment of disease progression.

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Figures

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Fig. 1

MRI-compatible stepper exercise device in the initial position and a subject ready to begin exercising. The L-shaped lever arms have enclosures for weights at the end of the long arms (which are horizontal in orientation shown) and foot pedals for the subject’s feet at the end of the short arms (which are vertical in the orientation shown). The moving parts are fixed on a platform designed to sit securely on the MRI bed. A backpack-type shoulder harness and hand straps are used to enhance stability and decrease torso motion during exercise. A shielded electronic box with a motion sensor that transmits information regarding stepping cadence is installed on the platform.

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Fig. 2

MRI-compatible stepper exercise device shown in use in an MR imaging system. The exercise device is placed on the MR table while the subject is on his/her back (supine position); the subject’s torso, which is being imaged, must be inside the cylindrical cavity (the MR bore). As the subject extends and then flexes alternating knees, the L-shaped lever arms are raised and then lowered in a dynamic stepping motion. The subject is prompted to maintain cadence using a metronome; the actual stepping cadence is measured by the built-in motion sensor which is connected to a computer in the monitoring room.

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Fig. 3

A single L-shaped lever arm in a midstep position and angle θ from the initial position. Note, the initial position is marked by the dotted lines in the X and Y directions and the position of the pivot bar is denoted by (0,0). Gravity (g) acts in the Y direction.

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Fig. 4

Sections of the L-shaped lever arm. For power calculations, three sections of each L-shaped lever arm were considered: the long arm (L), short arm (S), and WE. See Table 1 for the mass and location of center of mass of each of these three sections.

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Fig. 5

Screenshot of matlab GUI displayed in control room during exercise stress. The graph shows the distance of the lever arm from the optical sensor. “Power” indicates real-time calculation of the workload based on Eqs. (1)(3).

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Fig. 6

Ascending and descending aorta slice locations. Flows in the ascending and descending aorta were measured at rest and during a brief cessation in physical exercise stress. (a) Sagittal image displaying the location of the 2D PC slices that include the ascending and descending aorta. (b) The cross sections of both the AA and DA at rest.

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Fig. 7

Magnitude and phase MR images of the MPA. Flow in the MPA was measured at rest and during a brief cessation from physical exercise stress from the phase contrast-derived velocity maps integrated over the magnitude-derived area. Grayscale magnitude (a) and phase contrast (b) images of MPA cross section at rest. Grayscale image (c) and phase contrast image (d) of MPA during a brief cessation from physical exercise stress. Both image sets represent peak systole. Color-bar represents flow velocity in the phase images (ranges from −100 cm/s to 100 cm/s) ((b) and (d)).

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Fig. 8

Ensemble-averaged blood flow rates (over 10 heartbeats) in the AA (a) and DA (b) of a representative female subject, at rest and during a brief cessation from physical exercise stress. The time component was normalized with respect to the total period of the cardiac cycle for each curve. Panel (c) shows mean flow rates for 5 subjects at rest and during a brief cessation from exercise. Both AA and DA mean flow rates significantly increased due to exercise. Statistical significance (P < 0.05) was detected with Student’s t-test.

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Fig. 9

Ensemble-averaged blood flow rate (over 10 heartbeats) in the MPA (a) and cross-sectional area of the MPA (b) of a representative female subject, showing both rest and a brief cessation from exercise stress. The time component was normalized with respect to the total period of the cardiac cycle for each curve. Panel (c) shows the average MPA flow rate of 5 subjects at rest and during brief cessation from exercise (*P < 0.05). Panel (d) shows the minimum and maximum MPA cross-sectional area at rest and during a brief cessation from exercise stress (+P < 0.05).

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