Simultaneous R2, R2' and R2* measurement of skeletal muscle in a rabbit model of unilateral artery embolization.

PURPOSE

To demonstrate the feasibility of using a susceptibility-based MRI technique with multi-echo gradient and spin echo (MEGSE) sequence to achieve simultaneous R2, R2' and R2* measurement and assess skeletal muscle oxygenation alternations in a rabbit model of unilateral artery embolization.

MATERIALS AND METHODS

Approved by the local institutional review board for experimental animal studies, nine New Zealand White rabbits were included in this study. The MEGSE sequence consists of embedding a set of gradient echoes around the echo of a single spin-echo sequence using several gradient echoes to collect the magnetization intensity during the formation and attenuation of spin-echo simultaneously after 180° radio frequency pulse. Within-session and between-day tests were conducted to evaluate the reproducibility of this skeletal muscle oxygenation alternations measurement. Furthermore, all the MEGSE scans of skeletal muscle were conducted using a 3-T clinical MRI scanner during resting state (before unilateral artery embolization operation, pre), 1 h after unilateral artery embolization operation (post1) and 2 h after unilateral artery embolization operation (post2) model to verify the feasibility and sensitivity of this method.

RESULTS

The within-session coefficient of variations (CVs) of R2, R2' and R2* measurements were 1.57%, 3.33% and 2.57%, while the between-day CVs of were 1.42%, 5.85% and 2.85%. In all rabbits, the mean R2 decreased significantly from 36.46 ± 1.03 s (pre) to 30.58 ± 2.11 s (post1,**P < 0.01, relative to pre) and 28.62 ± 1.53 s (post2, **P < 0.01, relative to post1), and the mean R2' went up markedly from 9.88 ± 2.14 s (pre) to 16.10 ± 2.74 s (post1, **P < 0.01) and 17.33 ± 2.25 s (post2, *P < 0.05). The mean R2 increased from 43.27 ± 3.75 s (pre) to 47.90 ± 5.08 s (post1, *P < 0.05) and to 48.04 ± 4.42 s (post2, NS, P > 0.05).

CONCLUSION

This study demonstrates the feasibility of simultaneous R2, R2' and R2* measurement method for the evaluation of skeletal muscle ischemia. Besides, this study indicates the sensitivity of the R2 and R2' compared with R2* and especially the necessity of R2 and R2' measurement for the further evaluation of skeletal muscle ischemia which always causes both edema and hypoxia in a rabbit model of unilateral artery embolization.