Improved accuracy in susceptibility-based OEF measurements by mitigation of partial-volume effects via combined magnitude and phase reconstruction

Abstract

Regional quantitative Oxygen Extraction Fraction (OEF) values can only be reliable obtained from blood vessels larger than the acquisition voxel size. Blood vessels beyond this limit produce unreliable measurements due to partial-volume effects. We demonstrate a method for obtaining more reliable OEF measurements beyond this limit by performing a joint reconstruction using both the magnitude and phase of the complex-valued MRI signal. This method is validated both in numerical simulations and on in vivo data. The ability to perform high-quality fetal brain imaging is hampered by motion of the fetus, which can severely degrade image quality. Previously, low-resolution volumetric navigator (vNav) acquisitions have been shown to accurately track motion in human adults and prospectively correct for it. Here, a technique for using vNavs to measure fetal head motion in utero is developed and validated on in vivo data. Parallel Transmission (pTx) improves image quality and patient safety in high-field MRI. Unlike in single-channel MR excitation, an array of multiple excitation coils is used in pTx. However, coupling between these independent coils significantly degrades the power efficiency of the pTx array. Previously, it a decoupling matrix was proposed to solve this inefficiency. In this work, a physical realization of a 4-channel decoupling matrix was constructed and tested.