Accelerated MR parameter mapping with low-rank and sparsity constraints : Fast MR Parameter Mapping with Sparse Sampling

Summary Magnetic Resonance (MR) is an exceptionally powerful and versatile measurement technique. The basic structure of an MR experiment has remained nearly constant for almost 50 years. Here we introduce a novel paradigm, Magnetic Resonance Fingerprinting (MRF) that permits the non-invasive quantification of multiple important properties of a material or tissue simultaneously through a new approach to data acquisition, post-processing and visualization. MRF provides a new mechanism to quantitatively detect and analyze complex changes that can represent physical alterations of a substance or early indicators of disease. MRF can also be used to specifically identify the presence of a target material or tissue, which will increase the sensitivity, specificity, and speed of an MR study, and potentially lead to new diagnostic testing methodologies. When paired with an appropriate pattern recognition algorithm, MRF inherently suppresses measurement errors and thus can improve accuracy compared to previous approaches.

The purpose of this study was to investigate a noninvasive method for quantifying diffuse myocardial fibrosis with cardiac magnetic resonance imaging (CMRI). Diffuse myocardial fibrosis is a fundamental process in pathologic remodeling in cardiomyopathy and is postulated to cause increased cardiac stiffness and poor clinical outcomes. Although regional fibrosis is easily imaged with cardiac magnetic resonance, there is currently no noninvasive method for quantifying diffuse myocardial fibrosis. We performed CMRI on 45 subjects (25 patients with heart failure, 20 control patients), on a clinical 1.5-T CMRI scanner. A prototype T(1) mapping sequence was used to calculate the post-contrast myocardial T(1) time as an index of diffuse fibrosis; regional fibrosis was identified by delayed contrast enhancement. Regional and global systolic function was assessed by cine CMRI in standard short- and long-axis planes, with echocardiography used to evaluate diastology. An additional 9 subjects underwent CMRI and endomyocardial biopsy for histologic correlation. Post-contrast myocardial T(1) times correlated histologically with fibrosis (R = -0.7, p = 0.03) and were shorter in heart failure subjects than controls (383 +/- 17 ms vs. 564 +/- 23 ms, p < 0.0001). The T(1) time of heart failure myocardium was shorter than that in controls even when excluding areas of regional fibrosis (429 +/- 22 ms vs. 564 +/- 23 ms, p < 0.0001). The post-contrast myocardial T(1) time shortened as diastolic function worsened (562 +/- 24 ms in normal diastolic function vs. 423 +/- 33 ms in impaired diastolic function vs. 368 +/- 20 ms in restrictive function, p < 0.001). Contrast-enhanced CMRI T(1) mapping identifies changes in myocardial T(1) times in heart failure, which appear to reflect diffuse fibrosis.