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MRI scan quantity and quality in childhood
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in line with other research that also recommends a scanning time of 30-40 minutes for young children (Raschle et al., 2012), whereas a longer scanning protocol of 60 minutes is only recommended for an older population ((Fassbender et al., 2017b). If more scanning time is required to collect all data, a way to ensure scan quality would be to conduct two separate MRI sessions divided over different days (Fassbender et al., 2017b). Moreover, as the field of (developmental) neuroimaging is rapidly evolving, the technology of MRI is progressing. New methods such as simultaneous multi-slice imaging (SMS or ‘Multiband’, Feinberg and Yacoub (2012); Demetriou et al. (2018)) and real-time monitoring of head motion (Framewise Real-time Integrated MRI Motion Monitoring (FIRMM; Dosenbach et al. (2017)) have the potential to drastically shorten acquisition time without compromising on the number of scans. The effects on these methods on MRI scan quality should be examined in more detail in future studies. For example, a pioneering study of Greene et al. (2018b) reported that real time feedback about motion (using FIRMM) reduced head displacement in 5-10 year old children, but not in children older than 10.
Limitations
The study had several limitations, which should be addressed in future research. First, the current study examined one general aspect of scan quality (head motion), nevertheless, several other factors can influence scan quality, amongst others: thermal noise, respiratory signals, and scanner drifts (Kotsoni et al., 2006; Liu, 2017; Power, 2017). Future studies should also investigate the effects of these other factors, for example by investigating fMRI signal variability in regions of interest. Second, due to ethical considerations all participating children in the current study received the MRI simulation, therefore we were unable to directly test the effects of the MRI simulation and can only conclude that scanner related distress changed over time. Third, we report that children displayed the most head motion in the RS fMRI run, but this might be influenced by different definitions of sufficient quality, as the threshold for RS fMRI data was more conservative than the criteria for task-based fMRI. Nevertheless, Engelhardt et al. (2017) also report that their sample of 7-8-year-olds showed the most movement during rest and the least movement during an inhibition task and they suggested that the inhibition task was more engaging and therefore might have resulted in less head motion than the RS fMRI run. The sequence of MRI runs in our MR session was fixed, hindering direct comparison of task engagement, as the differences in head motion between task-based and RS fMRI might reflect a time effect. Studies in adults have indeed reported less head motion under engaging task conditions than during rest, irrespective of acquisition order (Huijbers et al., 2017) and future studies should investigate the effects of task demands versus time on scan quality in children. Relatedly, we instructed participants to lie still with eyes closed for the RS-fMRI. During the piloting phase of the scan protocol
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