Ultrashort echo time magnetic resonance fingerprinting (UTE-MRF) for simultaneous quantification of long and ultrashort T tissues.

PURPOSE

To demonstrate an ultrashort echo time magnetic resonance fingerprinting (UTE-MRF) method that allows quantifying relaxation times for muscle and bone in the musculoskeletal system and generating bone enhanced images that mimic CT scans.

METHODS

A fast imaging steady-state free precession MRF sequence with half pulse excitation and half projection readout was designed to sample fast T decay signals. Varying echo time (TE) of a sinusoidal pattern was applied to enhance sensitivity for tissues with short and ultrashort T values. The performance of UTE-MRF was evaluated via simulations, phantom, and in vivo experiments.

RESULTS

A minimal TE of 0.05 ms was achieved. Simulations indicated the sinusoidal TE sampling increased T quantification accuracy in the cortical bone and tendon but had little impact on long T muscle quantifications. For the rubber phantom, the averaged relaxometries from UTE-MRF (T = 162 ms and T = 1.07 ms) compared well with the gold standard (T = 190 ms and = 1.03 ms). For the long T agarose phantom, the linear regression slope between UTE-MRF and gold standard was 1.07 (R = 0.991) for T and 1.04 (R = 0.994) for T . In vivo experiments showed the detection of the cortical bone (averaged T = 1.0 ms) and Achilles tendon (averaged T = 15 ms). Scalp structures from the bone enhanced image show high similarity with CT.

CONCLUSION

The UTE-MRF with sinusoidal TEs can simultaneously quantify T , T , proton density, and B in long, short, even ultrashort T musculoskeletal structures. Bone enhanced images can be achieved in the brain with UTE-MRF.