Balanced spin‐lock preparation for B<sub>1</sub>‐insensitive and B<sub>0</sub>‐insensitive quantification of the rotating frame relaxation time T<sub>1ρ</sub>
Maximilian Gram, Michael Seethaler, Daniel Gensler, Johannes Oberberger, Peter M. Jakob, Peter Nordbeck
Abstract
Purpose Accurate and artifact‐free T 1ρ quantification is still a major challenge due to a susceptibility of the spin‐locking module to B 0 and/or B 1 field inhomogeneities. In this study, we present a novel spin‐lock preparation module (B‐SL) that enables an almost full compensation of both types of inhomogeneities. Methods The new B‐SL module contains a second 180° refocusing pulse to compensate each pulse in the preparation block by a corresponding pulse with opposite phase. For evaluation and validation of B‐SL, extensive simulations as well as phantom measurements were performed. Furthermore, the new module was compared to three common established compensation methods. Results Both simulations and measurements demonstrate a much lower susceptibility to artifacts for the B‐SL module, therefore providing an improved accuracy in T 1ρ quantification. In the presence of field inhomogeneities, measurements revealed an increased banding compensation by 79% compared with the frequently used composite module. The goodness of the mono‐exponential T 1ρ fitting procedure was improved by 58%. Conclusion The B‐SL preparation enables the generation of accurate relaxation maps with significantly reduced artifacts, even in the case of large field imperfections. Therefore, the B‐SL module is suggested to be highly beneficial for in vivo T 1ρ quantification.