Significant Differences in Proton Trimethyl Ammonium Signals between Human Gastrocnemius and Soleus Muscle

Purpose: To study the apparent heterogeneous characteristics of trimethyl ammonium (TMA) in healthy human muscles at rest, and to illustrate the importance of establishing the baseline characteristics of proton metabolites in muscles with a West Nile patient, Materials and Methods: Point-resolved spectroscopy (PRESS) magnetic resonance spectroscopy imaging (MRSI) with lipid suppression and optional outer-volume presaturation were used to acquire ¹H spectra of human muscles at rest at 1.5 Tesla. A total of 28 subjects (27 normal volunteers and 1 patient with West Nile disease) between the ages of 22 and 76 participated in the study. Results: The apparent T ₂ values of TMA for soleus and gastrocnemius muscles in normal volunteers are 180 ± 50 and 80 ± 20 msec, respectively. This difference has profound effects on the apparent spectral pattern of ¹H metabolites. The TMA/total creatine (tCr) spectral pattern of the soleus muscle of a West Nile patient resembles that of gastrocnemius muscle of healthy volunteers. Conclusion: There are significant differences in the apparent T₂ values of TMA between healthy soleus and gastrocnemius muscles at rest. It is important to establish the baseline characteristics of proton metabolites before clinical or physiological studies can be performed.