External authors:

• Dongyue Si ( King's College London )
• Michael G. Crabb ( King's College London )
• Simon J. Littlewood ( King's College London )
• Karl Kunze ( King's College London , Siemens United Kingdom )

Abstract:

Background: Commercial 0.55T low-field magnetic resonance imaging (MRI) systems have recently become available, offering the potential to enhance global accessibility to MRI. T1 rho mapping is an emerging quantitative cardiac MR imaging technique capable of detecting myocardial disease without the need for contrast administration. However, experience with cardiac T1 rho mapping at low-field strength remains limited. This study aims to develop and validate an efficient, free-breathing three-dimensional (3D) high-resolution adiabatic T1 rho mapping sequence for non-contrast whole-heart tissue characterization at 0.55T. Methods: The proposed 3D T1 rho mapping research sequence acquires four interleaved volumes with different contrast weightings using saturation and adiabatic spin-lock preparation pulses, and a 3-parameter fitting method is used to calculate T1 rho maps. Two-dimensional (2D) image navigators are acquired for non-rigid motion-compensated image reconstruction, enabling 100% respiratory scan efficiency. Phantom and in-vivo experiments in 10 healthy volunteers were conducted to evaluate the accuracy and precision of the proposed 3D sequence in comparison with 2D T1 rho mapping sequences. Results: Phantom T1 rho values measured using the proposed 3D sequence showed strong agreement with the 2D reference (R-2 = 0.997), demonstrating high accuracy and reduced sensitivity to heart rate variations. In-vivo experiments in healthy subjects demonstrated that the proposed sequence is feasible for acquiring whole-heart T1 rho maps with 2 mm isotropic resolution in an efficient scan time of 6.6 +/- 0.5 min. The mean myocardial T1 rho value obtained with the 3D sequence was slightly higher than that of a conventional 2D breath-hold sequence (112.8 +/- 16.7 vs. 106.1 +/- 15.1%, p<0.01), while coefficient of variation (CV) was slightly lower (10.2 +/- 5.2 vs. 11.4 +/- 4.4%, p = 0.02). Conclusion: The proposed sequence enables 3D free-breathing high-resolution adiabatic T1 rho mapping and shows promising potential for non-contrast whole-heart tissue characterization at 0.55T.