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Abstract

Purpose: To demonstrate the feasibility of simultaneous blood oxygen level-dependent (BOLD) magnetic resonance imaging of calf and foot muscles and investigate age-related changes of BOLD signal changes during ischemia and postocclusive hyperemia in healthy volunteers.
Material and Methods: In this study, 15 healthy elderly volunteers (mean age: 69.0 ± 7.4 years) and 15 healthy young volunteers (mean age: 26.1 ± 3.9 years) were enrolled. In both legs, simultaneous BOLD imaging of calf and foot muscles was performed at 1.5 Tesla. Short-term ischemia and consecutive reactive hyperemia were provoked by a cuff-compression paradigm. T2*-weighted signal time courses were obtained from foot and calf muscles simultaneously. Ischemia was assessed by T2* minimum ischemic value (MIV) and the time to half ischemic minimum (THIM). Reperfusion was assessed by the time to reach T2* half hyperemia peak (THHP). Reactive hyperemia was characterized by hyperemia peak value (HPV), time to peak (TTP), and relative T2* change from end of ischemia to HPV (δS). Parameter differences were assessed using a 2-sided Student t test.
Results: Dynamic BOLD measurement of foot and calf muscles was techniqually feasible and successful in all volunteers.
In comparison, THIM was significantly longer in elderly than in young volunteers for calf (P < 0.01) muscles (young: 28.9 ± 3.7 seconds; elderly: 57.8 ± 31.4 seconds) and foot (P = 0.01) muscles (young: 36.8 ± 25.5 seconds; elderly: 56.6 ± 31.7 seconds). MIV relative to baseline T2*-signal was significantly (P < 0.01) lower in the elderly for calf (young: 96.0 ± 2.6; elderly: 91.3 ± 4.4) and foot (young: 95.8 ± 2.5; elderly: 91.1 ± 8.2) muscles. TTP was significantly (calf: P = 0.01; foot: P = 0.02) delayed in the elderly (elderly calf: 103.0 ± 92.7 seconds and foot: 157.1 ± 109.9 seconds vs. young calf: 54.8 ± 42.1 seconds and foot: 95.1 ± 77.6 seconds). HPV was significantly (calf: P < 0.01 and foot: P = 0.03) higher in (young calf: 114.1 ± 7.2 and foot: 105.8 ± 3.3 vs. elderly calf: 104.0 ± 2.1 and foot: 103.9 ± 3.2 seconds) young volunteers.
In a muscle-group comparison, no significant differences in THIM and MIV were observed between calf and foot.
THHP was significantly (P = 0.02) longer in foot muscles (foot young: 32.5 ± 29.8 seconds and elderly: 34.1 ± 25.0 seconds vs. calf young: 16.8 ± 14.1 seconds and elderly: 23.6 ± 14.1 seconds) of both age groups. TTP was significantly (P = 0.01 and 0.02) longer in foot muscles (foot young: 95.1 ± 77.6 seconds and elderly: 157.1 ± 109.9 seconds vs. calf young: 54.8 ± 42.1 seconds and elderly: 103.0 ± 92.7 seconds) of both age groups. HPV was lower (P < 0.01) in foot muscles of the young (calf: 114.1 ± 7.2 vs. foot: 105.8 ± 3.3).
Conclusion: Simultaneous BOLD-imaging of calf and foot muscles is feasible and reveals statistically significant age-related differences during ischemia and postocclusive hyperemia in healthy volunteers.