Intramuscular distribution of botulinum toxin--visualized by MRI.

OBJECTIVE: A precise knowledge of the spread of botulinum toxin (BoNT) in muscle tissue is required to efficiently access endplate zones and increase BoNT's therapeutic efficacy. Here, we aimed to understand the spatiotemporal dynamics of BoNT distribution in skeletal muscle and its modulating factors, such as injected volume and exercise after injection. METHODS: To visualize distribution in muscle tissue, sagittal, dynamic, balanced fast field echo (BFFE) MRI imaging was performed during injection of 1 ml BoNT/NaCl bolus in spastic biceps brachii muscles (SBB, n=4), and 1 ml NaCl in the right and 2 ml NaCl in the left healthy biceps brachii (HBB, n=6), with or without successive muscle exercise. The pattern of extracellular fluid distribution was evaluated by T2-weighted and diffusion tensor imaging (DTI) sequences. RESULTS: BFFE indicated an immediate increase in hyperintensity, parallel to the muscle fibers, in the shape of a long (5.3±1.7 cm) and thin (0.52±1.3 cm) layer in HBB. The layer in SBB was shorter (3.25±0.6 cm, p=0.01) and tended to be thicker (0.74±2.9 cm, p=0.27). In HBB, an increase in volume (2 ml) resulted in an increase in thickness (0.95±0.2 cm, p=0.015), but a consistent length (5.67±1.3 cm, p=0.54). DTI visualized a change of diffusion, which exceeded the bolus region by approximately 0.5 cm. Redistribution occurred 10 min after injection and was more prominent in HBB, compared to SBB. Additional muscle activity did not alter the diffusion pattern or bolus distribution. CONCLUSION: Injecting BoNT at different depths perpendicular to the direction of the muscle fiber might optimize the efficacy of BoNT treatment. Additional sites along muscle fibers should be considered in SBB.

Dynamic interleaved 1H/31P STEAM MRS at 3 Tesla using a pneumatic force-controlled plantar flexion exercise rig.

OBJECTIVE: To develop a measurement method for interleaved acquisition of 1H and 31 STEAM localised spectra of exercising human calf muscle. MATERIALS AND METHODS: A non-magnetic exercise rig with a pneumatic piston and sensors for force and pedal angle was constructed to enable plantar flexion measured in the 3 T MR scanner, which holds the dual tuned (1H ,31P) surface coil used for signal transmission and reception. RESULTS: (31) spectra acquired in interleaved mode benefit from higher Signal to noise ratio (factor of 1.34 +/-0.06 for PCr) compared to standard acquisition due to the Nuclear Overhauser effect and substantial PCr/P(i) changes during exercise can be observed in 31P spectra. 1H spectral quality is equal to that in single mode experiments and allows Cr2 changes to be monitored. CONCLUSION: The feasibility of dynamic interleaved localised 1H and 31P spectroscopy during plantar flexion exercise has been demonstrated using a custom-built pneumatic system for muscle activation. This opens the possibility of studying the dynamics of metabolism with multi nuclear MRS in a single run.

1H NMR relaxation times of skeletal muscle metabolites at 3 T.

This study reports proton relaxation times of water and metabolites in soleus and tibialis anterior muscles of young healthy volunteers at 3 T. The results are in agreement with data reported for 1.5 and 4 T, showing a steady increase of spin-lattice relaxation times of water, creatine and lipids with B(0) and no effect of B(0) on spin-spin relaxation. Comparison between muscles revealed a longer spin-spin relaxation time of water in soleus than in tibialis anterior muscle (31+/-1 ms vs. 28+/-1 ms, p<0.05). These data can be applied to relaxation correction for the absolute quantification of skeletal muscle metabolite concentrations and further sequence optimization.