Myocardial Tissue Composition Mapping Based on Three‐Compartment Modeling: A Preliminary Study on Patients With Hypertrophic Cardiomyopathy for Detecting Myocardial Fibrosis Without Contrast Agents

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Noncontrast enhancement MRI is highly desired for tissue characterization, such as detecting myocardial fibrosis. The widely available MOdified Look-Locker Inversion Recovery (MOLLI) sequence with balanced Steady State Free Precession (bSSFP) acquisition is designed for mapping myocardial T1 values. Apart from T1 relaxation, the acquired data for fitting the T1 maps has inherent information of relaxation related to T2 decay and magnetization transfer. Using that information could allow more direct and reliable tracking of the underlying tissue composition. We developed a multicompartment model (MCM) method to quantify tissue composition from a single scan, to differentiate myocardial fibrosis from normal myocardium without the use of contrast agents, demonstrated in patients with hypertrophic cardiomyopathy (HCM). A three-compartment model (macromolecular proton, bound water, and free water) was built to generate instant signal evolution of the MOLLI acquisition, given scan parameters and pre-defined ranges of tissue parameters, forming a dictionary of signal evolution curves. An iterative matching algorithm was developed to derive a series of quantitative parameters, including the fractions of the three compartments, T1 and T2 of bound water and free water. The multicompartment mapping allowed the detection of myocardial fibrosis in 12 patients with HCM without the use of contrast agents. It demonstrated outstanding performance, with the area under the receiver operating characteristic curve (AUC) reaching 0.90 or higher: 0.94 for T1 of the bound water pool, 0.91 for T1, and 0.90 for T2 of the free water pool, compared to the gold standard method, late Gadolinium enhancement (LGE). This outperformed extracellular volume (ECV) mapping, which had an AUC of 0.77. Myocardial tissue composition quantification based on the three-compartment model is a promising noncontrast enhanced imaging tool for comprehensive and reliable evaluation of cardiac fibrosis. Myocardial tissue composition can be quantified using the widely accessible cardiac T1 mapping technique and a three-compartment model. This approach offers a promising noncontrast enhanced imaging tool for the comprehensive and reliable evaluation of cardiac fibrosis.

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