Efficient 3D FISP-MRF at 0.55 T using long spiral readouts and concomitant field effect mitigation

Abstract

Purpose

To demonstrate the feasibility of SNR-efficient 3D fast imaging with steady state precession MR fingerprinting (FISP-MRF) using long spiral readouts with mitigation of concomitant field effects at 0.55 T.

Methods

Fourteen FISP-MRF sequences with different spiral readout lengths (2.9 ms to 22.0 ms) were implemented with the open-source Pulseq framework. Datasets were reconstructed using a low-rank and subspace model-based reconstruction combined with MaxGIRF spatial encoding model. Concomitant field-induced blurring and MRF precision were evaluated using reconstructed images and quantitative maps acquired from an ACR phantom, an ISMRM/NIST system phantom, and 2 healthy volunteers.

Results

A simulation study shows that the SNR of time-series images would increase by ∼2× in white matter as a spiral readout increased from 2.9 ms to 22.0 ms. Empirically, MRF T₁ and T₂ standard deviations of in-vivo white matter were reduced by ∼50 %, and concomitant field mitigation was necessary. Residual spatial blurring was non-negligible for readouts ≥16.5 ms, suggesting an operating regime (2.9–16.5 ms) for 3D FISP-MRF at 0.55 T.

Conclusion

We demonstrate SNR-efficient 3D FISP-MRF using long spiral readouts in conjunction with concomitant field-induced blurring mitigation. A wide operating regime with improved precision is feasible only after concomitant field mitigation.