Simultaneous T1, T2, R2*, PDFF, and triglyceride quantification in the head and neck using magnetic resonance...

The extraction of quantitative biomarkers on the MR-Linac, which have been shown to be promising in the head and neck, remains a significant challenge due to the strict time constraints.

The purpose of this study was to assess the technical feasibility of magnetic resonance fingerprinting (MRF) to simultaneously extract quantitative T1, T2, R2*, PDFF, and triglyceride composition in the head and neck on the MR-Linac.

Inversion-prepared, multi-echo, golden angle radial, variable flip angle, MRF data were acquired on a 1.5T MR-Linac. The data were corrected for phase errors in the bipolar multi-echo acquisition followed by low rank reconstruction with total variation regularization. A dictionary of signals parameterized by T1/T2 was calculated with an extended phase graph algorithm. The singular images were constructed using a signal subspace from the dictionary and the first singular images were then jointly fit for R2* and PDFF using the off-resonance information from an independent B0 map. The complete set of B0/T2*-corrected fat-water separated water singular images were fitted for T1/T2. Triglyceride composition was computed using the multi-echo complex readout. Three phantoms and three healthy volunteers were assessed for accuracy, repeatability, and reproducibility against validated reference sequences across five days using a test-retest setup.

All coefficients of determination were at least 0.9 against reference sequences in standard phantoms across all quantitative parameters. The repeatability and reproducibility averaged under 5% in phantoms and under 10% in healthy volunteers.

The proposed MRF acquisition demonstrated the potential to replace the current time-intensive sequences on the 1.5T MR-Linac, thus increasing the adoption of specialized quantitative imaging biomarker approaches at high temporal density in the head and neck.