Feasibility of Cardiovascular Four-dimensional Flow MRI during Exercise in Healthy Participants

Abstract

Purpose: To explore the feasibility of using four-dimensional (4D) flow MRI to quantify blood flow and kinetic energy (KE) in the heart during strenuous exercise.

Materials and methods: For this prospective study, cardiac 4D flow MRI was performed in 11 healthy young adult participants (eight men, three women; mean age, 26 years ± 1 [standard deviation]) at rest and during exercise with an MRI-compatible exercise stepper between March 2016 and July 2017. Flow was measured in the ascending aorta (AAo) and main pulmonary artery (MPA). KE was quantified in the left and right ventricle. Significant changes in flow and KE during exercise were identified by using t tests. Repeatability was assessed with inter- and intraobserver comparisons and an analysis of internal flow consistency.

Results: Nine participants successfully completed both rest and exercise imaging. Internal flow consistency analysis in systemic and pulmonary circulation showed average relative differences of 10% at rest and 16% during exercise. For flow measurements in the AAo and MPA, relative differences between observers never exceeded 6% in any vessel and showed excellent correlation, even during exercise. Relative differences were increased for KE, typically on the order of 30%, with poor interobserver correlation between measurements.

Conclusion: Four-dimensional flow MRI can quantify increases in flow in the AAo and MPA during strenuous exercise and is highly repeatable. KE had reduced repeatability because of suboptimal segmentation methods and requires further development before clinical implementation. Supplemental material is available for this article. © RSNA, 2020See also the commentary by Markl and Lee in this issue.

Conflict of interest statement

Disclosures of Conflicts of Interest: J.A.M. disclosed no relevant relationships. A.G.B. disclosed no relevant relationships. P.A.C. Activities related to the present article: supported by two National Institutes of Health awards (UL1TR000427 and TL1TR000429) as a predoctoral trainee. Activities not related to the present article: disclosed no relevant relationships. Other relationships: disclosed no relevant relationships. G.P.B. Activities related to the present article: employed by University of Wisconsin-Madison. Activities not related to the present article: disclosed no relevant relationships. Other relationships: disclosed no relevant relationships. K.N.G. disclosed no relevant relationships. M.W.E. Activities related to the present article: institution received a grant from the National Institutes of Health. Activities not related to the present article: disclosed no relevant relationships. Other relationships: disclosed no relevant relationships. C.J.F. Activities related to the present article: institution received grant from the National Institutes of Health. Activities not related to the present article: grant to institution from GE Healthcare. Other relationships: disclosed no relevant relationships. O.W. Activities related to the present article: disclosed no relevant relationships. Activities not related to the present article: institution received research support from GE Healthcare. Other relationships: disclosed no relevant relationships.

2020 by the Radiological Society of North America, Inc.

Figures

Figure 1:

A, Photograph shows the participant set-up for the MRI-compatible exercise stepper. The participant is attached to the stepper with boots with hook and loop fastener straps. A chest harness connected to the stepper minimizes bulk motion during exercise. The strap lengths can be altered to adjust the participant’s positioning on the table. B, Photograph shows the participant exercising in MRI bore. C, Photograph of the frontal view of the stepper shows the dynamic range of stepper pedals. D, Screenshot of monitoring software shows the real-time measurements of step frequency and power during exercise.

Figure 2:

Composite Poincaré plots generated from normalized R-R interval length data in each participant at rest (left) and during exercise (right). Variation along the x1 axis represents short-term variability in heart rate, whereas variation along the x2 axis represents long-term variability. The different colored dots represent measurements from different participants.

Figure 3:

A–D, Representative images obtained at rest include an A, axial magnitude image, B, sagittal PC angiogram, C, segmented volume-rendered PC angiogram reconstructed from a 4D flow MRI acquisition, and D, pathline visualization image in the RV and MPA. Images E–H show corresponding images obtained during exercise. Increased blurring and decreased conspicuity of regions with slow or complex flow are observed in the axial magnitude image (E, green arrows) and sagittal PC angiogram (F, yellow arrows). G, The volume-rendered angiogram obtained during exercise shows loss of fine vessel detail (blue arrows). H, The pathline visualization image shows increased velocities in the RV and MPA at peak systole. MPA = main pulmonary artery, PC = phase-contrast, RV = right ventricle.

Figure 4:

Comparison of segmented masks in the RV and LV between two observers. One observer (blue mask) was consistently more conservative in segmentation than the other observer (purple mask) owing to the poor contrast between the blood pool and myocardial wall. LV = left ventricle, RV = right ventricle.

Figure 5:

Bland-Altman plots for interobserver and intraobserver variability in mean flow in the AAo (blue dots) and MPA (orange dots) at rest and during exercise. The solid blue line indicates the mean difference (d), while the dashed red lines indicate the upper and lower bounds of the 95% limits of agreement. AAo = ascending aorta, MPA = main pulmonary artery.

Figure 6:

Bland-Altman plots for interobserver and intraobserver variability of total KE in the LV (blue dots) and RV (orange dots) at rest and during exercise. The solid blue line indicates the mean difference (d), while the dashed red lines indicate the upper and lower bounds of the 95% limits of agreement. KE = kinetic energy, LV = left ventricle, RV = right ventricle.