A model-based framework for correcting inhomogeneity effects in magnetization transfer saturation and inhomogeneous magnetization transfer saturation maps.

PURPOSE

In this work, we propose that Δ -induced errors in magnetization transfer (MT) saturation (MT ) maps can be corrected with use of an R and map and through numerical simulations of the sequence.

THEORY AND METHODS

One healthy subject was scanned at 3.0T using a partial quantitative MT protocol to estimate the relationship between observed R (R ) and apparent bound pool size ( ) in the brain. MT values were simulated for a range of , R , and . An equation was fit to the simulated MT , then a linear relationship between R and was generated. These results were used to generate correction factor maps for the MT acquired from single-point data. The proposed correction was compared to an empirical correction factor with different MT-preparation schemes.

RESULTS

was highly correlated with R (r > 0.96), permitting the use of R to estimate for correction. All corrected MT maps displayed a decreased correlation with compared to uncorrected MT and MT corrected with an empirical factor in the corpus callosum. There was good agreement between the proposed approach and the empirical correction with radiofrequency saturation at 2 kHz, with larger deviations seen when using saturation pulses further off-resonance and in inhomogeneous (ih) MT maps.

CONCLUSION

The proposed correction decreases the dependence of MT on inhomogeneities. Furthermore, this flexible framework permits the use of different saturation protocols, making it useful for correcting inhomogeneities in ihMT.