# Ultrasound and Magnetic Resonance Imaging of the Tongue in Obstructive Sleep Apnoea
## 4 Discussion
Based on our results, a significant correlation was detected between male and female patients concerning BMI and US tongue parameters, with a stronger correlation in the case of females. AHI and BMI values also showed a stronger correlation in women. However, it can also be concluded that the correlation between AHI and BMI parameters was significant in all cases. A strong correlation was detected between men's and women's MRI and AHI parameters. Although fewer womenwere enrolled, the correlation was defined as significant. Finally, it can be concluded that female patients had significantly lower values of tongue parameters, and these parameters were stronger correlated with AHI and BMI parameters, as in the case of male subjects. Therefore, in addition to the parameters of the tongue and BMI, other factors, for example age and central type of obesity, are also essential in the pathogenesis of OSA in men, in contrast to women. In the present investigation, the US parameters were not influenced by the participants' age, but in the MRI examinations, most of the parameters showed significantly higher values in the group of patients under 40 years of age. This finding can be explained by the younger OSA patients' (i.e., under 40 years) higher BMI and AHI values. No influence of nutritional status on US parameters was detected, BMI and tongue volume were not strongly correlated since the inaccuracy for US measurements is well known, and according to Gauss's law of error propagation [26], multiple inaccuracies of measurements can be observed in the case of tongue volume, determined by tongue parameters. However, significantly higher anteroposterior sagittal diameters, tongue volume, and midsagittal area parameters were shown in obese patients using MRI. Similar to our results, [PERSON] et al. have also found a significant correlation between tongue volume and BMI [12]. However, our results have shown significant differences between BMI, US, and most MRI parameters in the OSA and control groups. In the OSA group, obese patients had significantly higher tongue volumes by MRI, although the Tongue Fat % and Tongue Fat midsagittal parameters did not differ significantly. Although obesity is a significant risk factor for OSA, no correlation was observed between tongue fat tissue and OSA. This contrasts with previous results, which have indicated correlations between tongue fat and sleep-related breathing disorders [27; 28]. In the current study, our objective was to analyse the presence of OSA and tongue-based obstruction, using US and MRI and machine learning methods for data processing. The sensitivity and specificity of the applied algorithm, which included some anthropometric parameters in addition to the values of the US and MRI values, were different in the case of the two medical imaging methods. In the prognosis of OSA, a US sensitivity of 94% was detected, preceding the MRI sensitivity (56%). However, a similar specificity for the two methods was observed (89% for US and 92% for MRI). The US could detect tongue-based obstruction with an 84% sensitivity, and so was MRI with 79%. In the location of tongue-based obstruction, US and MRI showed similar results in specificity (91%). The algorithm based on quadratic discriminant analysis was correct in the prognosis of the presence of OSA in 91% using US and 82% applying MRI. We correctly detected tongue-based obstruction in 89% and by MRI in 87%. Tongue-based obstruction severity (i.e., no, partial or total obstruction) could be observed using US in 71%. To our knowledge, it is the first study that has analysed the role of US and MRI examinations in the prognosis of OSA and tongue-based obstruction and the effects of age, sex, and BMI on the tongue parameters in patients with OSA. US examinations can detect the possible background of OSA using a relatively inexpensive and safe method, which can be easily applied even in an outpatient setting.