Development of a real-time fetal brain tracking method to be applied to BOLD MRI and diffusion MRI aimed at monitoring cerebral development in-utero

Fetal brain MRI offers unique insights into life before birth. Fetal BOLD and diffusion MRI measurements are correlated with fetal health and growth, thus offering an opportunity to probe processes involved in human development noninvasively. One of the main challenges of fetal MR is unpredictable fetal motion. Typically multi-slice 2D acquisitions are chosen. Thereby, the rapid single-shot acquisitions allow freezing of the motion during the readout of each slice/volume. Post-processing techniques (SVR) allow reconstruction of a continuous 3D volume out of these slices. However, techniques that rely on the acquisition of multiple repetitions all combined in the following analysis, such as BOLD MRI and dMRI, are significantly affected by inter-volume motion and usually require post-processing to improve spatiotemporal analysis. Therefore, these MR techniques would highly benefit from brain tracking for motion robustness. Such methodology has been implemented in adults- 3D-EPI navigators are acquired and processed for scan-to-scan prospective motion correction. Its extension to fetal imaging is, however, challenging due to the surrounding uterine environment and maternal tissue. While examples of fetal 3D-EPI navigators have been shown, they are prone to motion artifacts and their processing involved manual intervention and slow conventional registration. We are therefore developing an intrinsically motion-robust fetal MRI method that uses a 3D U-Net for fetal head position and translational motion estimation. Our method thereby uses the acquisition volumes directly as navigators. This is possible due to the relatively high speed of such acquisitions (TR<5 s). A fast real-time feedback system, via Gadgetron, will provide the scanner with the brain position estimation to update the VOI position before each dynamic and maintain it irrespective of fetal motion. We aim for this method to monitor brain development in-utero and to be adopted in routine clinical evaluation.