Real-time cardiac MRI in the mouse model

Abstract

Background: Cardiovascular magnetic resonance (CMR) imaging has proven valuable for the assessment of structural and functional cardiac abnormalities. Even though an established imaging method in small animals, the long acquisition times of gated or self-gated techniques still limit its widespread application. In this study, the application of tiny golden angle radial sparse MRI (tyGRASP) for real-time cardiac imaging in the mouse model was investigated for the quantification of cardiac functional parameters at rest and pharmacological stress, and first-pass perfusion. Methods: The technique was tested in 12 constitutive nexilin (Nexn) knock-out (KO) mice, heterozygous (Het, N=6) and wild-type (WT, N=6), and the resulting functional parameters compared with the well-established self-gating approach. Real-time images were reconstructed for different temporal resolutions between 16.8ms, 31.5ms and 48.3ms per image. All the mice were additionally scanned after an intraperitoneal injection of 1.5µg/g body weight dobutamine. One week later, first-pass perfusion imaging during intravenous injection of 0.1mmol/kg GD-DTPA was performed. The image quality was investigated between self-gating and real-time techniques. Further, three healthy mice were measured for the assessment of the reproducibility of real-time cardiac functional and dobutamine stress imaging. Results: In direct comparison with the high-quality self-gated technique, the real-time approach did not show any significant differences in global function parameters at rest or stress for acquisition times below 50ms. Compared with WT, the end-diastolic volume (EDV) and end-systolic volume (ESV) were markedly higher (p < 0.01) and the ejection fraction (EF) was significantly lower in the Het Nexn-KO mice at rest (p < 0.01). For the stress investigation, a clear decrease of EDV, ESV, and increase of EF but maintained stroke volume (SV) could be observed in both groups. Combined with ECG-triggering, tyGRASP provided first-pass perfusion data with a temporal resolution of one image per heartbeat, allowing the quantitative assessment of upslope curves in the blood-pool and myocardium. Compare with gated approach, the reduction of signal-to-noise ratio, contrast-to-noise ratio and image sharpness could be observed in real-time technique. Excellent reproducibility was achieved in all the functional parameters (CoV < 10%). Conclusions: The tyGRASP is a valuable real-time MRI technique for mice, which significantly reduces scan time in preclinical cardiac functional imaging, providing sufficient image quality for deriving accurate functional parameters, and has the potential to investigate real-time and beat to beat changes.