Abstract
ObjectTo develop and evaluate a 2D modified Look-Locker (MOLLI) for high-resolution T1 mapping in mice using a 3T MRI scanner.Materials and methodsTo allow high-resolution T1 mapping in mice at high heart rates a multi-shot ECG-triggered 2D MOLLI sequence was developed. In the proposed T1 mapping sequence the optimal number of sampling points and pause cardiac cycles following an initial adiabatic inversion pulse was investigated in a phantom. Seven native control and eight mice, 3 days post myocardial infarction (MI) after administration of gadolinium were scanned. Two experienced readers graded the visual T1 map quality.ResultsIn T1 phantoms, there were no significant differences (<0.4% error) between 12, 15 and 20 pause cardiac cycles (p = 0.1, 0.2 and 0.6 respectively) for 8 acquisition cardiac cycles for 600bpm in comparison to the conventional inversion recovery spin echo T1 mapping sequence for short T1’s (<600 ms). Subsequently, all in-vivo scans were performed with 8 data acquisitions and 12 pause cardiac cycles to minimize scan time. The mean native T1 value of myocardium in control animal was 820.5±52 ms. The post-contrast T1 measured 3 days after MI in scar was 264±59 ms and in healthy myocardium was 512±62 ms. The Bland-Altman analysis revealed mean difference of only -1.06% of infarct size percentage between T1 maps and LGE.ConclusionsA multi-shot 2D MOLLI sequence has been presented that allows reliable measurement of high spatial resolution T1 maps in mice for heart rates up to 600bpm.
Highlights
The mouse model of myocardial infarction (MI) has been increasingly used to investigate functional and molecular processes including metabolism, remodeling and energetics during the healing phase post MI in order to identify biomarkers that may predict the development of heart failure [1, 2]
Several previous studies have shown that T1 mapping in preclinical research can be used to detect the presence of edema in the myocardium [4, 5] and allow visualization and quantification of gadolinium labeled stem cells [6]
Several methods for measuring the T1 relaxation time in patients have been introduced mostly based on Look-Locker sequences with steady state free precession (SSFP) readout [7, 8] to acquire single shot images along the Mz relaxation curve after an initial saturation or inversion prepulse
Summary
The mouse model of myocardial infarction (MI) has been increasingly used to investigate functional and molecular processes including metabolism, remodeling and energetics during the healing phase post MI in order to identify biomarkers that may predict the development of heart failure [1, 2]. The small size of the heart and the high heart rates in mice create several challenges and impose limitations for mouse imaging using cardiac MR. The main challenges are the rapid heart rate in mice of 450– 600 bpm (RR interval: 100–150 ms) and the high-spatial resolution required (~200–300 microns) for reliable (accurate infarct size, functional parameters and tissue characterization) cardiac imaging in mice. The single shot 2D Modified Look-Locker (MOLLI) sequence is the most widely used T1 mapping technique in humans but not feasible in mice due to the high heart rates and requirements on spatial resolution. For high resolution imaging in small animals, which typically requires long repetition times the FLASH-based readout is more robust because it is less sensitive to field inhomogeneities as well as cardiac and respiratory motion [9, 10]
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