823 Ultra-high field 7 Tesla Magnetic Resonance Brain Imaging in Neonates: feasibility studies

Objectives

Magnetic Resonance Imaging (MRI) can provide detailed information about the neonatal brain when it is rapidly developing and thus vulnerable to injuries. However, at standard MRI field strengths MRIs (1.5 and 3 Tesla (T)) there are limitations in tissue contrast and resolution. MRI imaging at ultra-high field (7T) provides significant gains in signal-to-noise-ratio and tissue contrast, which can markedly increase sensitivity to anatomy and pathology.¹ Experience of scanning neonates at 7T is limited and there are specific challenges due to differences in tissue composition and the ultra-high magnetic field environment. The aim of this study was to determine feasibility of 7T neonatal imaging and explore the potential gains in anatomical and pathological sensitivity.

Methods

17 neonatal scans (median corrected age 40+3 weeks) were acquired with ethical approval (19/LO/1384) using a 7T Siemens MAGNETOM Terra system. Scanner software was modified to mitigate potential risks of temperature instability in neonates.² Infants were scanned in natural sleep following feeding, swaddled using a vacuum-evacuated bag and hearing protection with lateral immobilisation. Pulse-oximetry, heart rate and axillary temperature were continuously monitored by neonatal staff throughout scanning using 7T compatible equipment. 15 infants also had MRI scans on a 3T Philips Achieva system for comparison. Sequences acquired included high-resolution T2-weighted images in three orthogonal planes, susceptibility-weighted images, T1 and T2 quantitative maps, fMRI and spectroscopy.

Results

Images were successful acquired in 16 neonates (1 infant was imaged on 2 occasions) (table 1). All infants tolerated scanning on the 7T system and vital sign monitoring was stable throughout scanning over 52 minutes (range 25–80). There was no significant difference in temperature before and after 7T scanning (p-value=0.2). Additional detail of anatomical or pathological features were seen in 7T images compared to 3T, with image quality classified as equivalent or superior following neuroradiology review. These included improved visualization of the hippocampus, cerebellar vermis and occipital cortical folding. 7T images also provided improved visualization of cystic septi in periventricular leukomalacia and the haemorrhagic origin of cystic lesions in preterm infants.

Conclusion

We provide evidence for feasibility of 7T scanning in neonates and highlight the potential benefits for clinical care and research through improving image quality by increasing resolution and tissue contrast. In addition to improving diagnostic sensitivity, this could have provided new insight into the pathophysiological processes underlying poorly understood conditions such as neurodevelopmental disorders.

References

Yamada K, Yoshimura J, Watanabe M, Suzuki K. Application of 7 tesla magnetic resonance imaging for pediatric neurological disorders: early clinical experience. Journal of Clinical Imaging Science 2021;11:65. https://doi.org/10.25259/JCIS_185_2021 Malik Malik SJ, Hand JW, Satnarine R, Price AN, Hajnal JV. Specific absorption rate and temperature in neonate models resulting from exposure to a 7T head coil. Magn Reson Med. 2021;86:1299– 1313. https://doi.org/10.1002/mrm.28784