Initial experience of cardiac T1ρ mapping at 0.55 T: Continuous wave versus adiabatic spin-lock preparation pulses.

Purpose: To propose and validate a cardiac T₁ρ mapping sequence at 0.55 T comparing continuous-wave and adiabatic spin-lock (SL) preparation pulses.

Methods: The proposed 2D sequence acquires four single-shot balanced SSFP readout images with differing contrasts in a single breath-hold. The first three images are prepared with T₁ρ preparation pulses with different durations, while the last image uses a saturation pulse immediately before data acquisition. The T₁ρ map is calculated using a 3-parameter fitting method. Bloch equation simulations were performed to optimize the parameters of the adiabatic-SL pulses. Phantom studies and in vivo experiments in 10 healthy volunteers, a porcine myocardial infarction model, and a patient with suspected hypertrophic cardiomyopathy were performed to validate the performance of the proposed adiabatic T₁ρ (T₁ρ_Ad) mapping in comparison with conventional continuous-wave T₁ρ (T₁ρ_CW) mapping.

Results: The adiabatic-SL pulse with simulation-optimized parameters demonstrated robust performance despite B₀ and B₁ field inhomogeneities. Phantom T₁ρ_CW and T₁ρ_Ad mapping exhibited comparable precision. In vivo experiments on healthy volunteers showed that myocardial T₁ρ_Ad is higher than T₁ρ_CW (106.1 ± 7.1 vs. 47.0 ± 5.1 ms, p < 0.01) with better precision (11.4% ± 2.6% vs. 14.5% ± 2.1%, p < 0.01) and less spatial variation (10.9% ± 3.0% vs. 14.4% ± 3.4%, p < 0.01). Both T₁ρ_CW and T₁ρ_Ad mapping agreed with late gadolinium enhancement findings in the porcine model and the patient, and exhibited improved contrast compared to T₁ and T₂ mapping.

Conclusion: Both T₁ρ_CW and T₁ρ_Ad are promising for non-contrast detection of various cardiomyopathies at 0.55 T, but T₁ρ_Ad demonstrates better spatial uniformity than T₁ρ_CW.