BOLD MRI mapping of transient hyperemia in skeletal muscle after single contractions

Abstract

Transient increases in signal intensity (DeltaSI, peak 2.6 +/- 0.6 %, mean +/- SE, n = 14) were observed in axial, gradient-echo, echo-planar magnetic resonance images acquired at 1.5 T from human anterior tibialis muscle following single, 1 s duration, isometric ankle dorsiflexion contractions. The magnitude of the MRI-measured DeltaSI was not significantly different using TR of 2000 vs 500 ms, or using spin-echo vs gradient-echo echo-planar pulse sequences. However, DeltaSI measured by gradient-echo sequences was significantly greater at 3 vs 1.5 T (3.8 +/- 0.8 vs 1.6 +/- 0.2 %, n = 5). The time course of the transient DeltaSI (peak at 7.9 +/- 0.4 s after each contraction, decay with half-time of 4.6 +/- 0.6 s) was comparable to the time course of the transient increase in relative heme saturation (13 +/- 2 %, n = 5) measured after single contractions in another group of subjects by near-infrared spectroscopy (peak at 9.3 +/- 0.5 s, decay with half-time 6.2 +/- 0.8 s, n = 8). Simulations of intravascular and extravascular blood-oxygenation level-dependent (BOLD) effects in muscle suggested that intravascular BOLD makes a major contribution to the transient changes, although other factors such as increased vascular volume or increased muscle cell T2 may also contribute. The transients can be exploited for muscle functional imaging analogous to BOLD-based brain functional imaging, and might provide an index of peripheral vascular function.

Blood oxygenation level‐dependent (BOLD) MRI of human skeletal muscle at 1.5 and 3 T

“…Initial theoretical predictions and comparison between studies conducted at different field strengths led to the hypothesis that relative muscle BOLD signal changes vary as a function of B 1:5 0 (3). By using single 1-second ankle dorsiflexion contractions in five volunteers a previous muscle BOLD study (15) showed a significant increase in the muscle BOLD signal of the anterior tibialis muscle at 3.0 T when compared with 1.5 T (3.81% 6 0.82 vs. 1.58% 6 0.23, P < 0.05).…”

“…Activation-induced changes in the transverse relaxation rate R2* (¼1/T2*) were found to scale linearly to hyperlinearly with respect to B 0 (10)(11)(12)(13). Comparison of skeletal muscle BOLD studies conducted at different field strengths also implies a particular dependence of the muscle BOLD effect on B 0 (2,3,14,15).…”

Vasomodulation of skeletal muscle BOLD signal

“…Any change in deoxyhemoglobin content is manifested through T 2 * changes, and thus changes in blood flow, blood volume, hematocrit, and oxygenation have the potential to alter BOLD contrast (12)(13)(14). BOLD imaging has been used for exercise assessment and has been shown to be sensitive to even single muscle contractions at 1.5T and 3.0T (15,16). Studies have shown that muscle structure changes with age (17), sex (18), fitness (19), and peripheral circulation/cardiac disease (20).…”

Alterations of the proton‐T2 time in relaxed skeletal muscle induced by passive extremity flexions

“…In contrast, a single, active contraction of the biceps elevated the potential of the biceps significantly. Short-term changes in T 2 following a single con- traction have been reported to occur in the regime of the slow-relaxing T 2 -L component, and to decay within 20 seconds after stimulus (29,30). Such an effect was not measured in the described experiments, since the delay between position change and start of data acquisition exceeded this scale of seconds, and no activation occurred due to the passive operation used.…”