Direct and Indirect Surface Coil Correction for Cardiac Perfusion MRI

Introduction Although the first-pass myocardial perfusion MRI has proven its effectiveness in the diagnosis of ischemic heart disease, this technique is still not routinely used. Certain technical difficulties prevent perfusion MRI from being added into the clinical workflow, including complex cardiac motion, limited imaging time, and B1-field inhomogeneity caused by non-uniform characteristics of the receiver coils. While the perfusion imaging sequences and motion correction has been thoroughly investigated by many researchers [1], the B1-field inhomogeneity correction still lacks intensive studies. Even as qualitative visual reading is often not compromised by the inhomogeneity [2], it causes the drifting of signal intensities and leads to errors of quantitative or semi-quantitative perfusion analysis [1]. We therefore propose algorithms to perform surface coil inhomogeneity correction (SCC) using proton density (PD) weighted images and B-Spline Free-Form Deformation (FFD) [3]. Two strategies were developed: one was to directly approximating the inhomogeneity field and the other interleaved the FFD approximation and PD image tissue classification using the Expectation-Maximization (EM) algorithm. The feasibility of the proposed techniques was verified on patient datasets.