Electrocardiogram-less, free-breathing myocardial extracellular volume fraction mapping in small animals at high heart rates using motion-resolved cardiovascular magnetic resonance multitasking: a feasibility study in a heart failure with preserved ejection fraction rat model

Abstract

Background Extracellular volume fraction (ECV) quantification with cardiovascular magnetic resonance (CMR) T1 mapping is a powerful tool for the characterization of focal or diffuse myocardial fibrosis. However, it is technically challenging to acquire high-quality T1 and ECV maps in small animals for preclinical research because of high heart rates and high respiration rates. In this work, we developed an electrocardiogram (ECG)-less, free-breathing ECV mapping method using motion-resolved CMR Multitasking on a 9.4 T small animal CMR system. The feasibility of characterizing diffuse myocardial fibrosis was tested in a rat heart failure model with preserved ejection fraction (HFpEF). Methods High-salt fed rats diagnosed with HFpEF (n = 9) and control rats (n = 9) were imaged with the proposed ECV Multitasking technique. A 25-min exam, including two 4-min T1 Multitasking scans before and after gadolinium injection, were performed on each rat. It allows a cardiac temporal resolution of 20 ms for a heart rate of ~ 300 bpm. Myocardial ECV was calculated from the hematocrit (HCT) and fitted T1 values of the myocardium and the blood pool. Masson's trichrome stain was used to measure the extent of fibrosis. Welch’s t-test was performed between control and HFpEF groups. Results ECV was significantly higher in the HFpEF group (22.4% ± 2.5% vs. 18.0% ± 2.1%, P = 0.0010). A moderate correlation between the ECV and the extent of fibrosis was found (R = 0.59, P = 0.0098). Conclusions Motion-resolved ECV Multitasking CMR can quantify ECV in the rat myocardium at high heart rates without ECG triggering or respiratory gating. Elevated ECV found in the HFpEF group is consistent with previous human studies and well correlated with histological data. This technique has the potential to be a viable imaging tool for myocardial tissue characterization in small animal models.

Three‐dimensional simultaneous brain mapping of T1, T2, and magnetic susceptibility with MR Multitasking

“…In this study, we did not investigate the robustness of our sequence to motion, which can be important during a long scan or for the pediatric patient population 80,81 . However, we note that the Multitasking framework has been demonstrated to support several motion‐handling techniques to produce motion‐robust maps, 82 such as automatically identifying and removing motion‐corrupted data 83,84 or by modeling motion as a separate dimension in the tensor form 31,85,86 . Finally, clinical validations would be performed in the future to investigate the usefulness of the technique for diagnostic purposes.…”

Whole‐brain steady‐state CEST at 3 T using MR Multitasking

“…Image reconstruction was done similarly to previous MR Multitasking works, 28–31 in two steps. First, the components of the temporal factor tensor were estimated from the training data .…”

“…where × i denotes the tensor i-mode product; U x ∈ ℂ J×L 0 contains L 0 spatial basis functions with J voxels each; U Δ ∈ ℂ K×L 1 contains L 1 basis functions, which characterize the Z-spectra; U ∈ ℂ M×L 2 contains L 2 temporal basis functions, which characterize the signal evolution to reach steady state within each frequency offset; and ∈ ℂ L 0 ×L 1 ×L 2 denotes the core tensor. The core tensor and temporal bases can be combined into a temporal factor tensor Φ = × 2 U Δ × 3 U , in which case Equation (1) simplifies to Image reconstruction was done similarly to previous MR Multitasking works, [28][29][30][31] in two steps. First, the components of the temporal factor tensor Φ were estimated from the training data d tr .…”

T1 mapping of myocardium in rats using self‐gated golden‐angle acquisition

“…Because of the aforementioned problems in UHF MRI, methods using retrospective navigation with navigator extraction from the measured MR data have been proposed in this field. [4][5][6][7][8][9][10] While clinical T1 mapping of myocardium has become an established method, corresponding techniques for small animals are not well established. This is because of the very different respiratory and mainly cardiac rates which are much higher in mice and rats compared to humans (rats vs. humans: approx.…”

“…This makes small-animal T1 quantification of myocardium, the focus of this paper, a specific task on its own. Most of the known cardiac T1 quantification methods can be divided into two basic groups: variable flip angle 7 on one hand and Inversion Recovery (IR) prepared sequences 4,6,14,15 (or saturation recovery prepared sequences 16 ) on the other hand. Some more advanced techniques, such as MR fingerprinting, 17 stand aside of the mentioned groups.…”