Emil K S Espe1, Lili Zhang, Ivar Sjaastad. 1. Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway; KG Jebsen Cardiac Research Center and Center for Heart Failure Research, University of Oslo, Oslo, Norway.
Abstract
PURPOSE: Phase-contrast MRI (PC-MRI) is a versatile tool allowing evaluation of in vivo motion, but is sensitive to eddy current induced phase offsets, causing errors in the measured velocities. In high-resolution PC-MRI, these offsets can be sufficiently large to cause wrapping in the baseline phase, rendering conventional eddy current compensation (ECC) inadequate. The purpose of this study was to develop an improved ECC technique (unwrapping ECC) able to handle baseline phase discontinuities. THEORY AND METHODS: Baseline phase discontinuities are unwrapped by minimizing the spatiotemporal standard deviation of the static-tissue phase. Computer simulations were used for demonstrating the theoretical foundation of the proposed technique. The presence of baseline wrapping was confirmed in high-resolution myocardial PC-MRI of a normal rat heart at 9.4 Tesla (T), and the performance of unwrapping ECC was compared with conventional ECC. RESULTS: Areas of phase wrapping in static regions were clearly evident in high-resolution PC-MRI. The proposed technique successfully eliminated discontinuities in the baseline, and resulted in significantly better ECC than the conventional approach. CONCLUSION: We report the occurrence of baseline phase wrapping in PC-MRI, and provide an improved ECC technique capable of handling its presence. Unwrapping ECC offers improved correction of eddy current induced baseline shifts in high-resolution PC-MRI.
PURPOSE: Phase-contrast MRI (PC-MRI) is a versatile tool allowing evaluation of in vivo motion, but is sensitive to eddy current induced phase offsets, causing errors in the measured velocities. In high-resolution PC-MRI, these offsets can be sufficiently large to cause wrapping in the baseline phase, rendering conventional eddy current compensation (ECC) inadequate. The purpose of this study was to develop an improved ECC technique (unwrapping ECC) able to handle baseline phase discontinuities. THEORY AND METHODS: Baseline phase discontinuities are unwrapped by minimizing the spatiotemporal standard deviation of the static-tissue phase. Computer simulations were used for demonstrating the theoretical foundation of the proposed technique. The presence of baseline wrapping was confirmed in high-resolution myocardial PC-MRI of a normal rat heart at 9.4 Tesla (T), and the performance of unwrapping ECC was compared with conventional ECC. RESULTS: Areas of phase wrapping in static regions were clearly evident in high-resolution PC-MRI. The proposed technique successfully eliminated discontinuities in the baseline, and resulted in significantly better ECC than the conventional approach. CONCLUSION: We report the occurrence of baseline phase wrapping in PC-MRI, and provide an improved ECC technique capable of handling its presence. Unwrapping ECC offers improved correction of eddy current induced baseline shifts in high-resolution PC-MRI.
Authors: Gary McGinley; Bård A Bendiksen; Lili Zhang; Jan Magnus Aronsen; Einar Sjaastad Nordén; Ivar Sjaastad; Emil K S Espe Journal: PLoS One Date: 2019-07-05 Impact factor: 3.240