Spiral MR fingerprinting at 7 T with simultaneous B1 estimation

Magnetic resonance fingerprinting is an efficient, new approach for quantitative imaging with MR. We aimed to extend this technique to cases with B1 + inhomogeneities within the imaging volume. Previous approaches have used abrupt changes in flip angles to estimate the B1 + field simultaneously with T1 and T2, using a Cartesian approach in a small-animal scanner at 4.7 T. Here, we evaluated whether a similar approach would be suitable for imaging human brains using spiral readouts with a 7 T scanner. We found that our modified scheme could significantly reduce the adverse effects of B1 + inhomogeneities even in extreme cases, reducing both the bias and the variance in T2 estimations by an order of magnitude when compared to literature methods. Acquisitions used less than 1.5 W/kg SAR and could be performed in 12 s per slice. In conclusion, our approach can be used to perform quantitative imaging of the brain at 7 T in a short time, simultaneously estimating the B1 + profile.