# Automatic Detection of Airway Invasion from Videofluoroscopy via Deep Learning Technology
## 4 Discussion
The distance and relative position between the larynx and the cervical spine usually remain constant even when an individual moves his or her head and neck. From the dynamic ROI obtained using the proposed method, more stable images can be obtained, with minimal movement of background objects, even when patients move their head and neck. Consequently, the task of airway invasion detection is considerably simplified, as the images can be classified based only on the position of the bolus. Consequently, with the consideration of a dynamic ROI, the accuracy of airway invasion detection is dramatically improved compared with the results of a pilot test, although these results are not shown in this article. The performance of the model was tested in two ways: per frame and per swallow. The performance per frame was defined as the accuracy of classifying image frames with airway invasion among all 76,797 image frames in the test set only, regardless of the individual patient from whom each image frame was taken. Meanwhile, the performance per swallow was defined as the ability to classify the video clips containing the image frames showing airway invasion. The present model demonstrated an overall accuracy of 97.2% in classifying image frames. However, its recall, or sensitivity, was rather unsatisfactory (74.2%), and its precision was 59.1%. By contrast, the specificity and NPV were 98.0% and 99.0%, respectively, indicating that negative results are more reliable. The present model showed \"more balanced\" results in terms of the performance per swallow, with a slightly lower accuracy (93.2%), specificity (94.2%), and NPV (95.8%), but much higher recall (91.2%) and precision (88.1%). The performance per swallow can be considered more crucial for clinical applications because the occurrence of airway invasion in every swallowing event is one of the primary concerns in the analysis of VFSS data. The observed agreement of 93.2% can be recalculated to an inter-rater reliability (Cohen's k coefficient) of 0.86 between the computer and the human raters. Given that the inter-observer reliability among human observers has been reported to be in the range of 0.3\(\sim\)0.8 for judging the presence of penetration or aspiration, it can be considered that the present model shows very good agreement with the human raters, although the dataset was labeled based on agreement between only two human observers. The present model is valuable for clinical practice in many respects. It can provide screening information to clinicians to allow them to identify the airway invasion more accurately and efficiently. Errors from human fatigue will be reduced because human observers only need to confirm the results provided by the machine. This model could be developed into a more comprehensive analysis program by combining with models to be developed for the analysis of other parameters of VFSS in the future. Incorporating the present model into the recording software of the VFSS may increase safety by generating real-time warnings to the medical personnel for the presence of airway invasion. The VFSS procedure would be paused to prevent further airway invasion. In the present study, more effort was made to reduce false negatives than false positives in the present study, as the goal of this study was to develop a basis for screening or assistance tools for human analysts. If the number of false negatives is negligible, only positive results need to be reviewed by human observers. Although this result was not presented in the previous section, the false negative rate in swallow classification was 0.9%. Specifically, the model failed to classify five out of 57 swallowing events with airway invasion. When all images missed by the model were reviewed, no aspiration was found to be misinterpreted as normal, and all false negative images showed penetration corresponding to a PAS (penetration aspiration score) of two, in which the bolus invades the laryngeal vestibule, but does not cross the true vocal folds and is expelled immediately after swallowing [35].