Coil Combination Method for Peak-Combination HARP

A. K. Rutz, S. Ryf, G. Crelier, S. Kozerke, P. Boesiger Institute for Biomedical Engineering, University and ETH, Zurich, Switzerland Introduction: Myocardial tagging such as CSPAMM [1] combined with harmonic phase-analysis (HARP) [2] is a powerful method to quantify myocardial motion of healthy and diseased hearts. CSPAMM data are typically acquired using a phased array coil. In order to achieve optimal tracking results, combination of the signals from all coil elements is desirable. Using the root-mean-square (RMS) combination, images of different coil elements can easily be combined into modulus images, which can then be used in the HARP method. However, the modulus operation doubles the tag frequency and reduces the intensity of the displacement-encoded peaks in k-space by shifting parts of the signal to higher order harmonics and to an additional peak at zero spatial frequency. The increased number of phase-wraps and the resultant crowding in k-space may lead to errors in HARP evaluation. Another technique for combining the signals from different coil elements is the Roemer combination [3]. Taking into account a body-coil image, it produces images with constant signal amplitude across the field of view and phase contributions from different coil locations are removed. However, the Roemer combination requires an additional scan to calculate coil sensitivity maps. Especially in the presence of patient movement, e.g. in an exam with physiological stress conditions, misregistration of sensitivity information and actual data may occur, which results in errors of myocardial motion quantification. In this work, an efficient algorithm for combining signals from multiple coil elements using peak-combination HARP [4] is presented. Phase contributions originating from the different spatial locations of the coil elements are compensated for without requiring an additional coil calibration scan.