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Automatic Segmentation and Quantification of Upper Airway Anatomic Risk Factors for Obstructive Sleep Apnea on Unprocessed Magnetic Resonance Images

      Rationale and Objectives

      Accurate segmentation of the upper airway lumen and surrounding soft tissue anatomy, especially tongue fat, using magnetic resonance images is crucial for evaluating the role of anatomic risk factors in the pathogenesis of obstructive sleep apnea (OSA). We present a convolutional neural network to automatically segment and quantify upper airway structures that are known OSA risk factors from unprocessed magnetic resonance images.

      Materials and Methods

      Four datasets (n = [31, 35, 64, 76]) with T1-weighted scans and manually delineated labels of 10 regions of interest were used for model training and validations. We investigated a modified U-Net architecture that uses multiple convolution filter sizes to achieve multi-scale feature extraction. Validations included four-fold cross-validation and leave-study-out validations to measure generalization ability of the trained models. Automatic segmentations were also used to calculate the tongue fat ratio, a biomarker of OSA. Dice coefficient, Pearson's correlation, agreement analyses, and expert-derived clinical parameters were used to evaluate segmentations and tongue fat ratio values.

      Results

      Cross-validated mean Dice coefficient across all regions of interests and scans was 0.70 ± 0.10 with highest mean Dice coefficient in the tongue (0.89) and mandible (0.81). The accuracy was consistent across all four folds. Also, leave-study-out validations obtained comparable accuracy across uniquely acquired datasets. Segmented volumes and the derived tongue fat ratio values showed high correlation with manual measurements, with differences that were not statistically significant (p < 0.05).

      Conclusion

      High accuracy of automated segmentations indicate translational potential of the proposed method to replace time consuming manual segmentation tasks in clinical settings and large-scale research studies.

      Key Words

      Abbreviations:

      OSA (obstructive sleep apnea), MRI (magnetic resonance imaging), MR (magnetic resonance), DL (deep learning), CNN (convolutional neural network), ROI (region of interest), V1 (voxel-weighted at max fat pad intensity), V2 (voxel-weighted at 99th percentile fat pad intensity)
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