3D 23Na MRI of human skeletal muscle at 7 Tesla: initial experience - PubMed (original) (raw)

3D 23Na MRI of human skeletal muscle at 7 Tesla: initial experience

Gregory Chang et al. Eur Radiol. 2010 Aug.

Abstract

Objective: To evaluate healthy skeletal muscle pre- and post-exercise via 7 T (23)Na MRI and muscle proton T(2) mapping, and to evaluate diabetic muscle pre- and post-exercise via 7 T (23)Na MRI.

Methods: The calves of seven healthy subjects underwent imaging pre- and post-exercise via 7 T (23)Na MRI (3D fast low angle shot, TR/TE = 80 ms/0.160 ms, 4 mm x 4 mm x 4 mm) and 1 week later by (1)H MRI (multiple spin-echo sequence, TR/TE = 3,000 ms/15-90 ms). Four type 2 diabetics also participated in the (23)Na MRI protocol. Pre- and post-exercise sodium signal intensity (SI) and proton T(2) relaxation values were measured/calculated for soleus (S), gastrocnemius (G), and a control, tibialis anterior (TA). Two-tailed t tests were performed.

Results: In S/G in healthy subjects post-exercise, sodium SI increased 8-13% (p < 0.03), then decreased (t(1/2) = 22 min), and (1)H T(2) values increased 12-17% (p < 0.03), then decreased (t(1/2 )= 12-15 min). In TA, no significant changes in sodium SI or (1)H T(2) values were seen (-2.4 to 1%, p > 0.17). In S/G in diabetics, sodium SI increased 10-11% (p < 0.04), then decreased (t(1/2) = 27-37 min) without significant change in the TA SI (-3.6%, p = 0.066).

Conclusion: It is feasible to evaluate skeletal muscle via 3D (23)Na MRI at 7 T. Post-exercise muscle (1)H T(2) values return to baseline more rapidly than sodium SI. Diabetics may demonstrate delayed muscle sodium SI recovery compared with healthy subjects.

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Figures

Fig. 1

Fig. 1

Plot of sodium signal intensity vs. phantom NaCl concentration (100–300 mM/L) with background signal intensity plotted as 0 mM/L NaCl. There is a linear relationship between sodium MR signal and NaCl concentration. The results of three experiments performed on different days are plotted

Fig. 2

Fig. 2

a Resting sodium MR image (TR=80 ms, TE=0.160 ms, 4 mm × 4 mm × 4 mm) from the calf of a healthy volunteer. The NaCl phantoms can be seen at the anterior aspect of the leg. b Immediate post-exercise sodium MR image from the same volunteer, showing subtle increase in sodium signal intensity within the posterior compartment muscles. c Corresponding proton 3D fast low angle shot (FLASH) MR image (TR=20 ms, TE=5 ms, 0.195 mm × 0.195 mm, 1-mm slice thickness) from the same volunteer, which was performed after the sodium MRI to delineate muscle anatomy. TA tibialis anterior, S soleus, G gastrocnemius. Coil inhomogeneity artefact is seen at the anterior and posterior aspects of the leg

Fig. 3

Fig. 3

Bar graph demonstrating the time course of recovery for sodium signal intensity after exercise in healthy subjects. Immediately after exercise, sodium signal intensity increased in S (8±4%, _p_=0.028) and G (13±8%, _p_=0.028), but not in the dorsiflexor control muscle TA (0.55%, _p_=0.92). Sodium signal intensity then decreased to near baseline in an exponential fashion with a _t_1/2 of approximately 22 min for both S and G

Fig. 4

Fig. 4

Bar graph demonstrating changes in proton T2 relaxation values before and after exercise. Baseline T2 relaxation values for tibialis anterior (TA), soleus (S) and gastrocnemius (G) were 33.9± 3.78 ms, 36.8±4.2 ms and 36.7±4.67 ms, respectively. Immediately after exercise, T2 relaxation values increased in S (12±3%, _p_=0.01) and G (17±8%, _p_=0.029), but not in TA (1±2%, _p_=0.18). T2 relaxation values in S and G then decreased in a logarithmic fashion with half-lives (_t_1/2) of approximately 15 and 12 min, respectively

Fig. 5

Fig. 5

Bar graph demonstrating the time course of recovery for sodium signal intensity after exercise in diabetics. Immediately after exercise, sodium signal intensity increased in S (10±6%, _p_=0.034) and G (11±4%, _p_=0.009), but not in TA (−3.6±4%, _p_=0.066). Over time, sodium SI in S and G gradually decreased with half-lives (_t_1/2) of approximately 37 and 27 min, respectively

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