# Free-breathing three-dimensional whole-heart adiabatic T1ρ mapping for non-contrast tissue characterization at 0.55T

## TL;DR

This paper introduces a new 3D MRI technique for non-contrast heart imaging at low-field strength, improving accessibility and efficiency.

## Contribution

A free-breathing 3D adiabatic T1ρ mapping sequence is developed for whole-heart tissue characterization at 0.55T.

## Key findings

- Phantom T1ρ values showed strong agreement with 2D reference (R2 = 0.997).
- In-vivo experiments achieved 2 mm isotropic resolution in 6.6 ± 0.5 minutes.
- 3D sequence had slightly higher T1ρ values but lower coefficient of variation than 2D.

## Abstract

Commercial 0.55T low-field magnetic resonance imaging (MRI) systems have recently become available, offering the potential to enhance global accessibility to MRI. T1ρ mapping is an emerging quantitative cardiac MR imaging technique capable of detecting myocardial disease without the need for contrast administration. However, experience with cardiac T1ρ mapping at low-field strength remains limited. This study aims to develop and validate an efficient, free-breathing three-dimensional (3D) high-resolution adiabatic T1ρ mapping sequence for non-contrast whole-heart tissue characterization at 0.55T.

The proposed 3D T1ρ 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 T1ρ 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 T1ρ mapping sequences.

Phantom T1ρ values measured using the proposed 3D sequence showed strong agreement with the 2D reference (R2 = 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 T1ρ maps with 2 mm isotropic resolution in an efficient scan time of 6.6 ± 0.5 min. The mean myocardial T1ρ 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).

The proposed sequence enables 3D free-breathing high-resolution adiabatic T1ρ mapping and shows promising potential for non-contrast whole-heart tissue characterization at 0.55T.

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