Fast monitoring of T 1 , T 2 , and relative proton density (M 0 ) changes in skeletal muscles using an IR‐TrueFISP sequence

Purpose: To investigate the feasibility of fast and simultaneous assessment of T 1 , T 2 , and M 0 (relative proton density) changes in skeletal muscle studies using an inversion recovery true fast imaging with steady‐state precession (TrueFISP) sequence. Materials and Methods: NMR signal dynamics in calf muscles were analyzed under four different conditions: intravenous injection of a low‐molecular weight Gd contrast agent (CA), postarterial occlusion reactive hyperemia, local cooling, and an exercise bout. Experiments were conducted on a clinical 3T whole‐body scanner. Results: At rest, average muscle T 1 and T 2 values obtained from the IR‐TrueFISP experiments were 1.34 ± 0.13 seconds and 45 ± 5 msec, respectively (median ± standard deviation). 1) Noticeable T 1 decreases (ΔT 1 max ≈−30%) were measured in the calf muscles after CA injection, while no significant changes were observed for T 2 and M 0 . 2) T 2 increased rapidly during reactive hyperemia and reached a peak value (+6%) at about 1 minute postischemia. During ischemia, a significant decrease was observed only in the soleus muscle. No significant paradigm‐related changes in M 0 and T 1 were noted in all muscle groups, except in the m. soleus (ΔT 1 ≈+1% during reactive hyperemia). 3) Opposite variations in muscle T 1 (ΔT 1 max ≈−30%) and M 0 (ΔM 0 max ≈+25%) associated with local cooling were detected. 4) Concomitant changes in T 1 (ΔT 1 max ≈+15%), T 2 (ΔT 2 max ≈+35%), and M 0 (ΔM 0 max ≈+16%) were observed in the activated muscles following the exercise bout. Conclusion: IR‐TrueFISP was sufficiently fast and sensitive to detect small and transient T 1 , T 2 , and M 0 changes in the calf muscles under different experimental conditions. The sequence offers a time‐resolution adequate to track rapid physiological adaptations in skeletal muscle. J. Magn. Reson. Imaging 2011;33:921–930. © 2011 Wiley‐Liss, Inc.