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Research Summary

My DPhil research focused on the development of a readout-segmented EPI sequence (in collaboration with Dr David Porter, Siemens Healthcare) for high spatial resolution diffusion-weighted imaging of the brain. Diffusion imaging is widely used for diagnosis of acute stroke and to visualise the white matter pathways that form connections between brain regions. Typically multiple images are acquired, each with diffusion encoding along a different direction, to build up 3D information about water diffusion in the brain. The standard acquisition method (single-shot EPI) is fast and robust to motion artifacts, however, it has limited spatial resolution and the images are distorted and blurred in the phase-encode direction.

Readout-segmented EPI uses "navigator" techniques to measure and correct for cardiac-related brain motion between image segments and thereby generate high-resolution diffusion-weighted images of high quality. However, the acquisition time for each diffusion image is extended, making it difficult to acquire large numbers of diffusion directions in acceptable scan times. We have therefore implemented partial Fourier and simultaneous multi-slice acceleration strategies and have demonstrated them in clinical stroke and white matter tractography applications. We have also developed and implemented a novel 3D multi-slab extension of the original 2D multi-slice sequence. The 3D-encoded sequence reduces motion-induced phase artifacts by using real-time feedback to synchronise the k-space acquisition to the subject's cardiac cycle.

I am now working on prospective motion correction to mitigate problems caused by subject motion in clinical scanning. Individual images can suffer from blurring and ghosting when the patient moves during the acquisition and motion between images can be problematic for some specialised methods developed by the group, including techniques to visualise arterial blood flow and for measuring tissue pH. We aim to minimise motion artifacts by using information from navigator acquisitions to update the position and orientation of the imaging volume in real time.

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Robert Frost


Post-Doctoral MRI Physicist

Biography

My DPhil research focused on the development of a readout-segmented EPI sequence (in collaboration with Dr David Porter, Siemens Healthcare) for high spatial resolution diffusion-weighted imaging of the brain. Diffusion imaging is widely used for diagnosis of acute stroke and to visualise the white matter pathways that form connections between brain regions. Typically multiple images are acquired, each with diffusion encoding along a different direction, to build up 3D information about water diffusion in the brain. The standard acquisition method (single-shot EPI) is fast and robust to motion artifacts, however, it has limited spatial resolution and the images are distorted and blurred in the phase-encode direction.

Readout-segmented EPI uses "navigator" techniques to measure and correct for cardiac-related brain motion between image segments and thereby generate high-resolution diffusion-weighted images of high quality. However, the acquisition time for each diffusion image is extended, making it difficult to acquire large numbers of diffusion directions in acceptable scan times. We have therefore implemented partial Fourier and simultaneous multi-slice acceleration strategies and have demonstrated them in clinical stroke and white matter tractography applications. We have also developed and implemented a novel 3D multi-slab extension of the original 2D multi-slice sequence. The 3D-encoded sequence reduces motion-induced phase artifacts by using real-time feedback to synchronise the k-space acquisition to the subject's cardiac cycle.

I am now working on prospective motion correction to mitigate problems caused by subject motion in clinical scanning. Individual images can suffer from blurring and ghosting when the patient moves during the acquisition and motion between images can be problematic for some specialised methods developed by the group, including techniques to visualise arterial blood flow and for measuring tissue pH. We aim to minimise motion artifacts by using information from navigator acquisitions to update the position and orientation of the imaging volume in real time.

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Recent Publications

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