Table 1.

Definitions for key events and timing measures.

Event or parameter	Definition
Bolus passing mandible (BPM)	The first frame where the leading edge of the bolus touches or crosses the shadow of the ramus of mandible. In cases where the bolus was considered to have escaped prematurely from the mouth into the pharynx, the first frame showing bolus material at or below the ramus of mandible was counted as the BPM frame. When a double mandible shadow was seen on the lateral view image, the lower edge of the more superior ramus was used as the landmark.
Hyoid burst onset (HYB)	The first anterior–superior “jump” of the hyoid that is associated with a swallow. This event has previously been referred to using the terminology “onset of maximal hyoid excursion” or “onset of the pharyngeal response” (Robbins et al., 1992).
Upper esophageal sphincter opening (UESO)	The first frame where the leading edge of the bolus (or, in rare cases, air) passes through the upper esophageal sphincter (UES). The UES is a narrow segment or region that typically lies between C4 and C6; the narrowest opening seen between C4 and C6 during a swallow is marked as the location of the sphincter (Leonard et al., 2004). In addition, recognizing that the UES moves superiorly during the swallow (Kahrilas et al., 1992), the narrowest portion may be located above C4. The superior boundary of the tracheal air column can be used as a guide to decide where the location of the UES is during pharyngeal shortening.
First frame of most-complete laryngeal vestibule closure (LVC)	The first frame where there is maximum approximation of the arytenoids to the laryngeal surface of the epiglottis. Complete closure of the laryngeal vestibule (i.e., a seal between epiglottis and arytenoids leaving no visible airspace) may or may not be present.
Laryngeal vestibule closure offset (LVCOff)	The first frame where there is visible opening (white space) of the laryngeal vestibule. This requires some separation of the tissues or of the arytenoids from the inferior surface of the epiglottis, but complete opening is not required. The leaf of the epiglottis may still be in a downward position. This event cannot be identified in cases of incomplete LVC.
Upper esophageal sphincter closure (UESC)	The first frame where the UES achieves closure behind the bolus tail. This does not require closure of the entire UES segment, simply closure at a single point along the segment.
Maximum UES opening (UESmax)	The frame where the distention of the upper esophageal sphincter has the widest width (i.e., widest lumen width and/or bolus column). This frame is not used in any timing measures but is used for measuring the diameter of UES opening.
Maximum pharyngeal constriction (MPC)	The first frame showing maximum obliteration of the pharynx (i.e., the smallest bolus area and/or airspace in the pharynx). This event typically occurs between UESO and LVCOff, before the upper pharynx begins to relax, and before the laryngeal air column begins to descend. This frame is not used in any timing measures but is used for measuring pharyngeal area at maximum pharyngeal constriction (PhAMPC).
Swallow rest	The terminal event of each swallow, identified as the first frame showing the pyriform sinuses at their lowest position, relative to the spine, prior to any hyoid burst or laryngeal elevation for a subsequent clearing or piecemeal swallow. For the terminal swallow of a bolus, this event is further defined as occurring within 30 frames (approximately 1 s) of UESC, prior to any nonswallow events such as coughing, talking, or UES reopening. This frame is not used in any timing measures but is used for measuring postswallow pharyngeal residue and pharyngeal area at rest.
Peak XY hyoid position	The first frame showing the hyoid at peak position, i.e., the greatest distance measured along the XY hypotenuse from the anterior inferior corner of the C4 vertebra (Smaoui et al., 2021).
Swallow reaction time	The interval between BPM and HYB. This parameter has gone under a variety of different names in previous literature including “pharyngeal delay time” (Logemann et al., 2000, 2002), “duration of stage transition” (Robbins et al., 1992), and “swallow response time” (Power et al., 2007).
Hyoid burst–to–UES opening	The interval between HYB and UESO. This parameter has previously gone under the name “pharyngeal swallow duration” (Palmer, 1998) and “pharyngeal response time” (Rademaker et al., 1994).
UES opening duration	The interval between UESO and UESC.
Time–to–most complete LVC	The interval between HYB and LVC. This parameter has gone under the name LVC Reaction Time in previous literature (Guedes et al., 2017; Humbert et al., 2018; Steele et al., 2019).
LVC duration	The interval between LVC and LVCOff.