Exercise-stimulated arterial transit time in calf muscles measured by dynamic contrast-enhanced magnetic resonance imaging

Abstract

The primary goal of this study was to evaluate arterial transit time (ATT) in exercise‐stimulated calf muscles as a promising indicator of muscle function. Following plantar flexion, ATT was measured by dynamic contrast‐enhanced (DCE) MRI in young and elderly healthy subjects and patients with peripheral artery disease (PAD). In the young healthy subjects, gastrocnemius ATT decreased significantly (P < 0.01) from 4.3 ± 1.5 to 2.4 ± 0.4 sec when exercise load increased from 4 lbs to 16 lbs. For the same load of 4 lbs, gastrocnemius ATT was lower in the elderly healthy subjects (3.2 ± 1.1 sec; P = 0.08) and in the PAD patients (2.4 ± 1.2 sec; P = 0.02) than in the young healthy subjects. While the sensitivity of the exercise‐stimulated ATT is diagnostically useful, it poses a challenge for arterial spin labeling (ASL), a noncontrast MRI method for measuring muscle perfusion. As a secondary goal of this study, we assessed the impact of ATT on ASL‐measured perfusion with ASL data of multiple post labeling delays (PLDs) acquired from a healthy subject. Perfusion varied substantially with PLD in the activated gastrocnemius, which can be attributed to the ATT variability as verified by a simulation. In conclusion, muscle ATT is sensitive to exercise intensity, and it potentially reflects the functional impact of aging and PAD on calf muscles. For precise measurement of exercise‐stimulated muscle perfusion, it is recommended that ATT be considered when quantifying muscle ASL data.

Microvascular response to exercise varies along the length of the tibialis anterior muscle

“…Our data also enabled the assessment of ATT, which was shown to be shorter just after exercise, increasing over time thereafter, and was shorter in the proximal compared with the distal slice during the first 2 min of recovery. The shorter ATT just after exercise is in line with previous work using dynamic contrast‐enhanced imaging showing that ATT decreases with increasing workload 14 . More specifically, we found that the ATT was shorter just after exercise, meaning that the labeled blood travels faster to the imaged region.…”

“…The shorter ATT just after exercise is in line with previous work using dynamic contrast-enhanced imaging showing that ATT decreases with increasing workload. 14 More specifically, we found that the ATT was shorter just after exercise, meaning that the labeled blood travels faster to the imaged region. As a result, the peak ASL signal is reached F I G U R E 5 The average Buxton fit for each time window over all participants after exercise for the proximal and distal slice.…”

“…However, especially in postexercise muscle studies, ATT is most likely not constant over time and postexercise changes in ATT could also be different between participants and/or slices. This is important because Conlin et al 14 have shown that the measured perfusion values are highly dependent on the ATT. This can partly be overcome by the use of a “quantitative imaging of perfusion using a single subtraction” (QUIPSS) 15 module to achieve a sharp labeling bolus.…”