Abstract
ABSTRACT
To develop a T
1ρ
‐weighted quantitative susceptibility mapping (QSM) technique for simultaneous imaging of T
1ρ
and T
2
* 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. T
2
* and susceptibility maps were calculated for both T
1ρ
–QSM and QSM measurements. Additionally, T
1ρ
maps were calculated from T
1ρ
–T
2
*–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
–T
2
*–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. T
2
* 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
–T
2
*–QSM and reference QSM showed minimal bias (−7.6 · 10
−4
) and Pearson's correlation coefficient
r
p
= 0.69. For T
2
* (T
1ρ
–T
2
*–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
, T
2
*, 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,
T
2
*, or susceptibility mapping. The identified MI areas were in line with histological findings, supporting the accuracy of the proposed imaging approach.