Simultaneous 3-D Adiabatic T_1ρ, T₂*, and Quantitative Susceptibility Mapping for Characterization of Myocardial...

To develop a T_1ρ-weighted quantitative susceptibility mapping (QSM) technique for simultaneous imaging of T_1ρ and T₂* relaxation and magnetic susceptibility in ex vivo mouse hearts after myocardial infarction (MI). MI was induced in C75Bl/6JOlaHsd mice, and their hearts (n_MI = 7, n_CTRL = 6) were imaged ex vivo by combining adiabatic T_1ρ preparation with a 3-D multi-echo gradient recalled echo (GRE) sequence for simultaneous T_1ρ-weighted QSM. As a reference, 2-D adiabatic T_1ρ mapping and QSM without preparation were used. T₂* and susceptibility maps were calculated for both T_1ρ-QSM and QSM measurements. Additionally, T_1ρ maps were calculated from T_1ρ-T₂*-QSM. Region of interest analysis was performed using American Heart Association (AHA) segments. Correlation and Bland-Altman bias between 2-D/3-D T_1ρ and T_1ρ-T₂*-QSM/QSM segments were assessed, respectively. Statistical significance between the segments was tested using Mann-Whitney U test. Histological validation was conducted using Picro Sirius red (SR), hematoxylin and eosin (HE), and Perls' Prussian Blue (PPB) stainings. T_1ρ relaxation times were elevated significantly in basal AHA segments 1, 2, and 6, compared to the corresponding control segments. T₂* relaxation times decreased significantly in basal and apical segments 4, 6, 13, and 14. QSM revealed visible heterogeneity within the same segments, and greater variance in basal, mid, and apical segments 6, 7, 11, 12, and 13 compared to controls. Histology confirmed the formation of myocardial fibrosis and hemosiderin-laden macrophages within the corresponding MRI segments with minimal residual blood in MI hearts. Quantitative analysis showed a moderate agreement between 2-D and 3-D T_1ρ mapping (Spearman's r = 0.71). Bland-Altman analysis between T_1ρ-T₂*-QSM and reference QSM showed minimal bias (-7.6 · 10^-4) and Pearson's correlation coefficient r_p = 0.69. For T₂* (T_1ρ-T₂*-QSM) and QSM, the Bland-Altman analysis bias was -0.84 and r_p = 0.77. The developed T_1ρ-weighted QSM technique enabled simultaneous acquisition of T_1ρ, T₂*, and susceptibility maps in ex vivo mouse hearts. All imaging contrasts showed good correlation with reference methods, and MI regions were visible using either T_1ρ, T₂*, or susceptibility mapping. The identified MI areas were in line with histological findings, supporting the accuracy of the proposed imaging approach.