Dynamic tracking of manganese uptake in mouse hearts by rapid multi-slice T1 mapping

Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA Figure 1 MSRLL pulse sequence. After 90° non-slice selective saturation pulses, 10 sequential multi-slice FLASH acquisitions separated by an interval τ were applied. Each block on the relaxation curve represents a multi-slice acquisition module. Jiang and Yu Journal of Cardiovascular Magnetic Resonance 2014, 16(Suppl 1):W35 http://www.jcmr-online.com/content/16/S1/W35


Background
Manganese (Mn 2+ )-enhanced MRI (MEMRI) has the potential for in vivo assessment of the voltage-gated L-type Ca 2+ channel activity. Quantitative assessment of Mn 2+ uptake via Ca 2+ channels requires fast and accurate T 1 mapping. In the current study, a multi-slice saturation recovery Look-Locker (MSRLL) method was developed for T 1 mapping of the whole mouse heart in < 3 min.

MSRLL Sequence
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.

Phantom Study
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 multicompartment phantom with MnCl 2 solution ranging from 30 μM to 1000 μM. T 1 maps of 5 slices were compared with those acquired with a previously validated single-slice method (SRLL). Imaging parameters were: flip Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA Figure 1 MSRLL pulse sequence. After 90°non-slice selective saturation pulses, 10 sequential multi-slice FLASH acquisitions separated by an interval τ were applied. Each block on the relaxation curve represents a multi-slice acquisition module.

In Vivo Study
In vivo MEMRI studies were performed in 3-month-old FVB mice (n = 19). T 1 maps of three adjacent short-axis slices at mid-ventricular levels were acquired with the same imaging parameters as those used in vitro. Continuous T 1 mapping was performed during the 30 min of MnCl 2 infusion through tail vein (0.2 mL/hr) and the 15 minutes washout. To investigate the Mn 2+ -induced relaxivity changes, two different MnCl 2 solutions at Jiang and Yu Journal of Cardiovascular Magnetic Resonance 2014, 16(Suppl 1):W35 http://www.jcmr-online.com/content/16/S1/W35 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).

Results
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 T 1 maps acquired at baseline (Figure 2a-c) and after Mn 2+ infusion (Figure 2d-f). All three slices showed significant reduction in T 1 after Mn 2+ infusion. The time courses of the R 1 changes for all three slices are presented in Figure 2g. In general, higher Mn 2+ dose induced larger increase in R 1 during Mn 2+ infusion.

Conclusions
An ECG-triggered, multi-slice saturation-recovery Look-Locker method was developed for fast and complete cardiac T 1 mapping in mice. Validity and utility of this method was well demonstrated in the phantom and in vivo two-dose MEMRI studies.

Funding
This study was supported by NIH Grants HL73315 and HL86935 (Yu).