Highest Resolution In Vivo Human Brain MRI Using Prospective Motion Correction

Abstract

High field MRI systems, such as 7 Tesla (T) scanners, can deliver higher signal to noise ratio (SNR) than lower field scanners and thus allow for the acquisition of data with higher spatial resolution, which is often demanded by users in the fields of clinical and neuroscientific imaging. However, high resolution scans may require long acquisition times, which in turn increase the discomfort for the subject and the risk of subject motion. Even with a cooperative and trained subject, involuntary motion due to heartbeat, swallowing, respiration and changes in muscle tone can cause image artifacts that reduce the effective resolution. In addition, scanning with higher resolution leads to increased sensitivity to even very small movements. Prospective motion correction (PMC) at 3T and 7T has proven to increase image quality in case of subject motion. Although the application of prospective motion correction is becoming more popular, previous articles focused on proof of concept studies and technical descriptions, whereas this paper briefly describes the technical aspects of the optical tracking system, marker fixation and cross calibration and focuses on the application of PMC to very high resolution imaging without intentional motion. In this study we acquired in vivo MR images at 7T using prospective motion correction during long acquisitions. As a result, we present images among the highest, if not the highest resolution of in vivo human brain MRI ever acquired.

How to choose the right MR sequence for your research question at 7 T and above?

“…Currently some of the most robust results have been achieved with camera based systems that are able to dynamically update gradient coordinates in real time. Yet these still have some limitations regarding subject comfort (best results are obtained with oral fixation devices) and compatibility with the surface coil arrangements used to maximise SNR (Stucht et al, 2015). Image based navigators based on fat image can be used at different resolutions ) depending on the needed accuracy and time available in the host sequence.…”

Prospective motion correction in functional MRI

“…For traditional imaging, the tracking data precision must be greater than a fraction of the voxel size and is related to the contrast of the image. A general rule of thumb that 1/5 th to 1/10 th of the target voxel size is sufficient for the majority of applications (Maclaren et al, 2010; Stucht et al, 2015). Although as the typical fMRI voxel size is much larger than that of structural imaging, one can expect that more stringent specifications may apply.…”

7T MRI for neurodegenerative dementias in vivo: a systematic review of the literature

“…A navigator echo was used, in which physiological movement such as that caused by respiration and pulse is tracked using additional RF pulses, and a correction for this is factored in when the MRI signal is converted into k-space. Excessive motion artefact can also be corrected prospectively, for example, using an optical tracking system where a marker is attached to a dental plate, which is held in the subject’s mouth 45. However, such methods require an extremely cooperative participant and may be uncomfortable, and for patient participants in dementia studies, such methods may not be ideal.…”