Dynamic tracking of manganese uptake in mouse hearts by rapid multi-slice T1 mapping
Journal of Cardiovascular Magnetic Resonance volume 16, Article number: W35 (2014)
Manganese (Mn2+)-enhanced MRI (MEMRI) has the potential for in vivo assessment of the voltage-gated L-type Ca2+ channel activity. Quantitative assessment of Mn2+ uptake via Ca2+ channels requires fast and accurate T1 mapping. In the current study, a multi-slice saturation recovery Look-Locker (MSRLL) method was developed for T1 mapping of the whole mouse heart in < 3 min.
A schematic diagram of the MSRLL pulse sequence is shown in Figure 1. An ECG-triggered saturation module was applied at the beginning of each phase-encoding step, followed by the acquisition of k-space lines along the magnetization recovery curve in multiple slices. ECG-triggered image acquisition was performed at late diastole.
All MRI studies were performed on a horizontal 7.0T Bruker scanner with a 35 mm volume coil. The MSRLL method was first validated in vitro using a multi-compartment phantom with MnCl2 solution ranging from 30 μM to 1000 μM. T1 maps of 5 slices were compared with those acquired with a previously validated single-slice method (SRLL). Imaging parameters were: flip angle, 10°; TE, 1.9 msec; slice thickness, 1 mm; number of average, 1; field of view, 3 × 3 cm2; matrix size, 128 × 64.
In Vivo Study
In vivo MEMRI studies were performed in 3-month-old FVB mice (n = 19). T1 maps of three adjacent short-axis slices at mid-ventricular levels were acquired with the same imaging parameters as those used in vitro. Continuous T1 mapping was performed during the 30 min of MnCl2 infusion through tail vein (0.2 mL/hr) and the 15 minutes washout. To investigate the Mn2+-induced relaxivity changes, two different MnCl2 solutions at 126 mM (n = 9) and 63 mM (n = 10) were used. Validation study was performed either at baseline (n = 10) or post-contrast (n = 10).
In vitro studies showed strong agreement between MSRLL and SRLL. Average imaging time in vivo was 140~166 s. Shown in Figure 2 are representative T1 maps acquired at baseline (Figure 2a-c) and after Mn2+ infusion (Figure 2d-f). All three slices showed significant reduction in T1 after Mn2+ infusion. The time courses of the R1 changes for all three slices are presented in Figure 2g. In general, higher Mn2+ dose induced larger increase in R1 during Mn2+ infusion.
An ECG-triggered, multi-slice saturation-recovery Look-Locker method was developed for fast and complete cardiac T1 mapping in mice. Validity and utility of this method was well demonstrated in the phantom and in vivo two-dose MEMRI studies.
This study was supported by NIH Grants HL73315 and HL86935 (Yu).
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Jiang, K., Yu, X. Dynamic tracking of manganese uptake in mouse hearts by rapid multi-slice T1 mapping. J Cardiovasc Magn Reson 16 (Suppl 1), W35 (2014). https://doi.org/10.1186/1532-429X-16-S1-W35