Evaluation of healthy and diseased muscle with magnetic resonance elastography

To investigate whether a new tissue-imaging technique, magnetic resonance elastography (MRE), offers a viable, noninvasive way to study healthy and diseased muscle.

Convenience sample.

A magnetic resonance imaging (MRI) laboratory.

Eight control subjects (4 men, 4 women), between the ages of 24 and 41 years, with normal neuromuscular examinations and histories, and 6 subjects (3 men, 3 women), ages 17 to 63 years, with lower-extremity neuromuscular dysfunction (1 with childhood poliomyelitis, 2 with flaccid, 3 with spastic paraplegia).

Subjects lay supine with their legs within the coils of a 1.5T MRI machine, with their feet strapped to a footplate positioned so that the axes of rotation of their ankles coincided with the apparatus. All subjects were tested in a no-load (0 torque) condition. Control subjects were also evaluated as they isometrically resisted ankle dorsi- (20.2Nm, 40.5Nm) and plantar- (8.2Nm, 16.4Nm) flexion moments. Subjects with neuromuscular dysfunction were evaluated in the same manner, except 1 individual with residual lower-extremity strength who could only be tested in the resting and passive ankle dorsiflexion modes. Shear waves were induced with a 150-Hz electromechanic transducer located over the belly tibialis anterior. MRE images were collected with a gradient-echo technique gated to the transducer's motion. Wave-phase propagation was visualized with 8 equally offset images across 1 vibration-cycle.

Changes in shear-wave wavelength (lambda) and muscle stiffness (as expressed by the shear modulus [G]) in the tibialis anterior and gastrocnemius muscles.

Wavelength and G differed between the groups in all the muscles studied, and increased as the load increased. Moreover, lambda and G in the neuromuscular disease group at rest (eg, 3.88+/-0.48cm; range, 2.87-4.91cm; 38.40+/-00.77kPa; range, 22.35-59.67kPa) and in the lateral gastrocnemius were, respectively, more than 1.5 and 2.4 times larger than they were in the same muscle in the control group (2.56+/-0.28cm, 16.16+/-00.19kPa; P=.0002) (1Pa=1N/m(2)).

Shear-wave wavelength and muscle stiffness increased with load in healthy muscle. In addition, at least for our sample, these quantities differed significantly between muscles with and without neuromuscular disease. In summary, MRE appears to provide in vivo physiologic information about the mechanical properties of muscle at rest and during contraction that is not otherwise available. The potential of this technique for monitoring the effects of treatment and exercise on both healthy and diseased muscle merits further research.