# Reliability of Automated Intracranial Volume Measurements by Synthetic Brain MRI in Children
## 4 Discussion  
The assessment of the presence or absence of hydrocephalus in cerebral MRIs is a difficult and highly subjective endeavour for radiologists. SyMRI provides experts with an interesting tool to reliably and quickly assess the presence of hydrocephalus or other intracranial volume disorders [3; 16]. Our retrospective data analysis focused on the reliability of SyMRI in the clinical-radiological routine of a tertiary center and demonstrated its suitability for its application in children. In the literature, the image quality of SyMRI is repeatedly described as equivalent or at least not inferior to that of conventional MRI. While this may well be the case for some image parameters such as contrast, in our opinion the subjective image quality is generally inferior to correspondingly weighted turbo spin echo sequences. A SyMRI is therefore never performed as the only sequence in our center, but the method is primarily used as an add-on in cases in which parameters such as cerebrospinal fluid volume, intracranial volume, and brain parenchyma volume are important. This is where SyMRI demonstrates  
Figure 8: Box plots displaying relative differences in CSF volume measurements (manual vs. SyMRI) for gender and age. Figure 9: A bar chart showing the normalized slice position in the x-axis, meaning 0 is the most caudal slice and 1 is the most cranial slice in comparison to the probability of the presence of segmentation errors by SyMRI. its strengths, which are also reflected in the results presented. For example, it was difficult for human experts to distinguish incipient cases of hydrocephalus from normal cases (see the Cohen's Kappa of human ratings vs. SyMRI, k = 0.47). Our data demonstrated a small systematic error between manual and SyMRI volume measurements which has been described in accordance with previous studies [15, 17]. In our case, the SyMRI method produced higher values compared to the alternative method [18]. Our assumption is based on the marginally lower volumes in the manual volume assessments, which had been meticulously corrected for masking errors. Overall, the extent of these masking issues in the SyMRI was limited. Severe masking errors were isolated cases. Minor masking errors were more common and repeatedly observed in the boundary layers (the cranial sections and skull base, see Figure 10), while the middle layers rarely showed problems. Masking problems in the central parts of the slice were primarily due to areas of clearly pathologically altered signaling or image distortions due to metal artifacts (Figure 11). The results of our work indicate that the SyMRI measurements show imperfections in younger children (compare Figure 8b). These are probably methodological in nature and apply in part in the same way to alternative measurement variants. For example, we observed a decrease in the fluctuation range of the measurements with increasing patient age. In particular, in the group of newborns and infants, i.e., children up to the age of one, considerable ranges of manual and SyMRI measurements were recognisable. It should also be noted that measurement inaccuracies also affected the reference measurements. In our patient cohort, we observed a failure rate of approximately 5% (7 out of 131 studies, Figure 4) in the automated SyMRI analysis of the MDME sequence. This was attributed to inaccurately or incompletely archived MDME data (n = 4) and motion artifacts (n = 3). Due to the acquisition time of about 6 min, the MDME sequence may have been impaired by motion artefacts (Figure 12). This hardly applies to patients under anesthesia, but is regularly observed during \"feed and wrap\" examinations. Older children of school age and above may also be affected depending on their daily condition or compliance capability. In  
Figure 10: Errors in automatic masking (marked by white arrows) were commonly observed in the most cranial parts of the head and were mostly insignificant to the final result.