3D magnetization transfer (MT) for the visualization of cardiac free-running Purkinje fibers: an ex vivo proof of concept

Abstract

Objectives We investigate the possibility to exploit high-field MRI to acquire 3D images of Purkinje network which plays a crucial role in cardiac function. Since Purkinje fibers (PF) have a distinct cellular structure and are surrounded by connective tissue, we investigated conventional contrast mechanisms along with the magnetization transfer (MT) imaging technique to improve image contrast between ventricular structures of differing macromolecular content. Methods Three fixed porcine ventricular samples were used with free-running PFs on the endocardium. T1, T2*, T2, and M0 were evaluated on 2D slices for each sample at 9.4 T. MT parameters were optimized using hard pulses with different amplitudes, offset frequencies and durations. The cardiac structure was assessed through 2D and 3D T1w images with isotropic resolutions of 150 µm. Histology, immunofluorescence, and qPCR were performed to analyze collagen contents of cardiac tissue and PF. Results An MT preparation module of 350 ms duration inserted into the sequence with a B1 = 10 µT and frequency offset = 3000 Hz showed the best contrast, approximately 0.4 between PFs and myocardium. Magnetization transfer ratio (MTR) appeared higher in the cardiac tissue (MTR = 44.7 ± 3.5%) than in the PFs (MTR = 25.2 ± 6.3%). Discussion MT significantly improves contrast between PFs and ventricular myocardium and appears promising for imaging the 3D architecture of the Purkinje network.

A 3D high resolution MRI method for the visualization of cardiac fibro-fatty infiltrations

“…Eliav et al 43 and Kim et al 44 demonstrated that the collagen matrix greatly contributes to the MT; moreover, there was a linear correlation between the MTR ratio and percentage of collagen in vitro. It was recently shown that MTR varies in the heart as a function of the collagen type (I vs. III) 45 . Indeed, the relative proportion of type I and type III collagen is expected to evolve with age and pathologies in the cardiac tissue.…”

Application of advanced magnetic resonance imaging in glaucoma: a narrative review

“…In addition, since MTI measures the MT between free water and water bound to macromolecules through chemical exchange and/or dipole-dipole interaction, it can Therefore, MTI can be used to more specifically detect how to organize the microstructure of collagen fibers, and how to reshape the extracellular matrix (92). Ho et al used freshly prepared amniotic eyes to evaluate the tissue magnetic resonance relaxation in response to dynamic IOP changes.…”