Application of BOLD Magnetic Resonance Imaging for Evaluating Regional Volumetric Foot Tissue Oxygenation: A Feasibility Study in Healthy Volunteers

Abstract

Objective/background: To evaluate the feasibility and repeatability of applying blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) in the feet to quantify regional dynamic changes in tissue oxygenation during proximal cuff occlusion and reactive hyperemia.

Methods: Ten healthy male subjects underwent BOLD and T1-weighted imaging of the feet on two separate occasions, using a 3-T scanner. Dynamic changes in BOLD signal intensity were assessed before and during proximal cuff occlusion of the thigh and during reactive hyperemia, and BOLD time course data were evaluated for the time-to-half ischemic minimum, minimum ischemic value, peak hyperemic value, time-to-peak hyperemia, time-to-half peak hyperemia, and end value. T1-weighted images were used for segmentation of volumes of interest (VOI) in anatomical regions of the foot (heel, toes, dorsal foot, medial and lateral plantar foot). Repeatability of vascular responses was assessed for each foot VOI using semiautomated image registration and quantification of serial BOLD images.

Results: The heel VOI demonstrated a significantly higher peak hyperemic response, expressed as percent change from baseline BOLD signal intensity, compared with all other VOIs of the foot (heel, 7.4 ± 1.2%; toes, 5.6 ± 0.8%; dorsal foot, 5.7 ± 1.6%; medial plantar, 5.6 ± 1.7%; lateral plantar, 5.6 ± 1.5% [p < .05]). Additionally, the lateral plantar VOI had a significantly lower terminal signal intensity value (i.e., end value) when compared with all foot VOIs (p < .05). BOLD MRI was repeatable between visits in all foot VOIs, with no significant differences between study visits for any of the evaluated functional indices.

Conclusion: BOLD MRI offers a repeatable technique for volumetric assessment of regional foot tissue oxygenation. Future application of BOLD imaging in the feet of patients with peripheral vascular disease may permit serial evaluation of regional tissue oxygenation and allow for improved assessment of therapeutic interventions targeting specific sites of the foot.

Keywords: Diabetes; Magnetic resonance imaging; Peripheral vascular disease; Reactive hyperemia; Skeletal muscle.

Figure 1

Experimental set-up for creating transient ischemia and reactive hyperemia. The foot was firmly secured within a phased array head coil with blood pressure cuff positioned over the mid-thigh. Contralateral foot was supported and secured alongside head coil.

Figure 2

Serial image registration of the foot. Registration was performed using points sampled from outer skin surfaces. Shown are the rendered surfaces from T1-weighted MR images from two separate study visits (red=visit 1; green=visit 2) at the (A) starting position before registration, (B) after global rigid alignment, and (C) after non-rigid registration.

Figure 3

Foot volumes of interest (VOIs). Lateral (A) and medial (B) views of a three-dimensional representation of regional foot segmentation generated from T1-weighted MR images. VOIs for the heel (orange), dorsal foot (green), lateral plantar (red), medial plantar (blue), and toes (yellow) are displayed.

Figure 4

A) Axial, (B) sagittal, and (C) coronal views of T1-weighted and BOLD MR images of the foot.

Figure 5

A) Average BOLD time course curves for each foot VOI demonstrate regional variability during occlusion and reactive hyperemia while individual response curves for the (B) heel, (C) toes, (D) dorsal foot, (E) medial plantar, and (F) lateral plantar VOI demonstrate inter subject variability. Arrows indicate time of cuff inflation (initialization of ischemia) and deflation (start of reactive hyperemia phase). Values represent average ± SD. N=10 subjects.