Purpose: Commonly used diffusion weighted (DW) imaging such as DW spin echo (SE) type echo planar imaging (DW-SE-EPI) is known to be a snapshot-like acquisition and to have a relatively high signal-to-noise ratio. Spi...Purpose: Commonly used diffusion weighted (DW) imaging such as DW spin echo (SE) type echo planar imaging (DW-SE-EPI) is known to be a snapshot-like acquisition and to have a relatively high signal-to-noise ratio. Spiral MRI sequence (SPIRAL) has characteristics similar to these of EPI, but it has rarely been used for diffusion-weighted imaging (DWI). In vivo DW-SPIRAL of the rat brain has almost never been reported. Our purpose in this study was to examine the potential of SE-type two-dimensional (2D) multi-shot spiral acquisition MRI for apparent diffusion coefficient (ADC) mapping of the rat brain in vivo. Materials and Methods: We made an SE-type DW-2D-spiral MRI sequence (DW-SPIRAL) which was prepared on a 2.0-T animal-experiment MR scanner. Comparing the phantom experimental result of DW-SPIRAL with the phantom experimental result of DW SE-type echo-planar imaging (DW-SE-EPI) and conventional DW spin echo imaging (DW-SE), we estimated the characteristics of DW-SPIRAL and assessed the clinical application of DW-SPIRAL in an animal experiment on the rat brain. Results: There was not much difference between the calculated water/glycerol phantom diffusion coefficient of DW-SPIRAL and the calculated diffusion coefficient of DW-SE. This result shows that the DW-SPIRAL sequence is appropriate for use in diffusion weighted imaging. There were fewer phantom image distortions and ghosting artifacts with DW-SPIRAL than with DW-SE-EPI, and this tendency was similar in the animal experiment on the rat brain. Conclusion: The DW-SPIRAL sequence had been successfully tested in phantom experiments and rat brain experiments. It has been demonstrated that the DW-SPIRAL sequence is capable of producing in vivo rat brain DWI.展开更多
Magnetic resonance elastography (MRE) allows the quantitative assessment of the stiffness of tissues based on the tissue response to oscillatory shear stress. Shear wave displacements of the tissues are encoded as pha...Magnetic resonance elastography (MRE) allows the quantitative assessment of the stiffness of tissues based on the tissue response to oscillatory shear stress. Shear wave displacements of the tissues are encoded as phase shifts and converted to stiffness (elastogram). Generally, a partial volume effect occurs when different materials are encompassed on the same voxel. In MRE, however, the partial volume effect occurs even if the voxel is filled with the same materials because wave displacements due to vibrations are spatially distributed. The purpose of this study was to investigate how the partial volume effect can affect the phase shift and the elastogram in MRE. We assumed that the partial volume effect appears only in the slice thickness direction and performed a simulation and MRE experiment with various slice thicknesses (1 - 19 mm), two types of imaging plane (coronal and axial) and two types of vibration frequency (100 and 200 Hz). The results of the simulation and the MRE experiment were similar, and indicated that the phase shift and the elastogram changed variously depending on the slice thickness, the wave pattern and the vibration frequency, even if the voxel was filled with the same material. To reduce the partial volume effect, it is necessary to perform the MRE under the following conditions: Use a wave pattern which barely causes this artefact, a smaller voxel size and a lower vibration frequency.展开更多
文摘Purpose: Commonly used diffusion weighted (DW) imaging such as DW spin echo (SE) type echo planar imaging (DW-SE-EPI) is known to be a snapshot-like acquisition and to have a relatively high signal-to-noise ratio. Spiral MRI sequence (SPIRAL) has characteristics similar to these of EPI, but it has rarely been used for diffusion-weighted imaging (DWI). In vivo DW-SPIRAL of the rat brain has almost never been reported. Our purpose in this study was to examine the potential of SE-type two-dimensional (2D) multi-shot spiral acquisition MRI for apparent diffusion coefficient (ADC) mapping of the rat brain in vivo. Materials and Methods: We made an SE-type DW-2D-spiral MRI sequence (DW-SPIRAL) which was prepared on a 2.0-T animal-experiment MR scanner. Comparing the phantom experimental result of DW-SPIRAL with the phantom experimental result of DW SE-type echo-planar imaging (DW-SE-EPI) and conventional DW spin echo imaging (DW-SE), we estimated the characteristics of DW-SPIRAL and assessed the clinical application of DW-SPIRAL in an animal experiment on the rat brain. Results: There was not much difference between the calculated water/glycerol phantom diffusion coefficient of DW-SPIRAL and the calculated diffusion coefficient of DW-SE. This result shows that the DW-SPIRAL sequence is appropriate for use in diffusion weighted imaging. There were fewer phantom image distortions and ghosting artifacts with DW-SPIRAL than with DW-SE-EPI, and this tendency was similar in the animal experiment on the rat brain. Conclusion: The DW-SPIRAL sequence had been successfully tested in phantom experiments and rat brain experiments. It has been demonstrated that the DW-SPIRAL sequence is capable of producing in vivo rat brain DWI.
文摘Magnetic resonance elastography (MRE) allows the quantitative assessment of the stiffness of tissues based on the tissue response to oscillatory shear stress. Shear wave displacements of the tissues are encoded as phase shifts and converted to stiffness (elastogram). Generally, a partial volume effect occurs when different materials are encompassed on the same voxel. In MRE, however, the partial volume effect occurs even if the voxel is filled with the same materials because wave displacements due to vibrations are spatially distributed. The purpose of this study was to investigate how the partial volume effect can affect the phase shift and the elastogram in MRE. We assumed that the partial volume effect appears only in the slice thickness direction and performed a simulation and MRE experiment with various slice thicknesses (1 - 19 mm), two types of imaging plane (coronal and axial) and two types of vibration frequency (100 and 200 Hz). The results of the simulation and the MRE experiment were similar, and indicated that the phase shift and the elastogram changed variously depending on the slice thickness, the wave pattern and the vibration frequency, even if the voxel was filled with the same material. To reduce the partial volume effect, it is necessary to perform the MRE under the following conditions: Use a wave pattern which barely causes this artefact, a smaller voxel size and a lower vibration frequency.
