(A) high-resolution MR imaging method using phase signal of dynamic objects

Abstract

Using the magnetic resonance imaging (MRI), a high-resolution-tomographic image can be obtained. Unlike other imaging modalities, magnetic resonance (MR) signal has complex values so that phase information as well as magnitude information provides physiological characteristics in the body. In this work, the high-resolution MR-imaging methods using phase information of moving objects are proposed for cardiac and perfusion imaging.

In the CMR part, to obtain multi-phase cardiac cine images with high resolution, a novel self-gating method for both cardiac and respiratory motions is proposed. The proposed method uses the phase of projection data obtained from a separate axial slice to measure cardiac and respiratory motion, after the acquisition of every k-space line in the image plane. Cardiac motion is estimated from the phase of the projection data passing through the aorta, which is amplified by superior-inferior directional bi-polar gradients, whereas respiratory motion is estimated from the phase of the left-right directional projection data of the abdomen. Then, the proposed method can capture time-resolved cardiac and respiratory motion from the phase information of the projection data. To verify the proposed self-gating method, a simulation and the in-vivo SSFP cardiac imaging were performed.

In the PWI part, to obtain a high-resolution perfusion-weighted image with quantitative perfusion information, a novel perfusion-weighted imaging method and its signal model are proposed. The proposed method is based on the perfusion model of intravoxel inherent motion (IVIM), which assumes that perfusion is a microcirculation of blood in the capillary network. The proposed method introduces two-types of bi-polar gradients in a radial spin-echo sequence with a new ordering of bi-polar gradients for isotropic perfusion weighting. Then, the isotropic perfusion-weighting scheme can reduce imaging time by avoiding repetitive scans. To verify the proposed method, a computer simulation and the in-vivo imaging in 3 T MRI was performed to compare with the conventional echo-planar-imaging (EPI)-based arterial spin labeling (ASL) technique. The further works will be to apply the proposed PWI to the 7 T MRI system.