A Pilot Study of Ratiometric Creatine CEST MRI Assessment of Rabbit Skeletal Muscle Energy Metabolism at 3 T.

BACKGROUND

pH MRI may provide useful information to evaluate metabolic disruption following ischemia. Radiofrequency amplitude-based creatine chemical exchange saturation transfer (CrCEST) ratiometric MRI is pH-sensitive, which could but has not been explored to examine muscle ischemia.

PURPOSE

To investigate skeletal muscle energy metabolism alterations with CrCEST ratiometric MRI.

STUDY TYPE

Prospective.

ANIMAL MODEL

Seven adult New Zealand rabbits with ipsilateral hindlimb muscle ischemia.

FIELD STRENGTH/SEQUENCE: 3 T/two MRI scans, including MRA and CEST imaging, were performed under two B amplitudes of 0.5 and 1.25 μT after 2 hours of hindlimb muscle ischemia and 1 hour of reperfusion recovery, respectively.

ASSESSMENT

CEST effects of two energy metabolites of creatine and phosphocreatine (PCrCEST) were resolved with the multipool Lorentzian fitting approach. The pixel-wise CrCEST ratio was quantified by calculating the ratio of the resolved CrCEST peaks under a B amplitude of 1.25 μT to those under 0.5 μT in the entire muscle.

STATISTICAL TESTS

One-way ANOVA and Pearson's correlation. P < 0.05 was considered statistically significant.

RESULTS

MRA images confirmed the blood flow loss and restoration in the ischemic hindlimb at the ischemia and recovery phases, respectively. Ischemic muscles exhibited a significant decrease of PCr at the ischemia (under both B amplitudes) and recovery phases (under B amplitude of 0.5 μT) and significantly increased CrCEST from normal tissues at both phases (under both B levels). Specifically, CrCEST decreased, and PCrCEST increased with the CrCEST ratio. Significantly strong correlations were observed among the CrCEST ratio, and CrCEST and PCrCEST under both B levels (r > 0.80).

DATA CONCLUSION

The CrCEST ratio altered substantially with muscle pathological states and was closely related to CEST effects of energy metabolites of Cr and PCr, suggesting that the pH-sensitive CrCEST ratiometric MRI is feasible to evaluate muscle injuries at the metabolic level.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY STAGE: 1.