Sonographic examination of the oral phase of swallowing: bolus image enhancement

PURPOSE: The purpose of this study was to evaluate the ability of 4 liquid boluses to enhance pixel brightness and the ease with which the boluses could be identified during the sonographic evaluation of oral swallowing in healthy young adults. METHODS: Ten healthy adult volunteers (5 men and 5 women), ranging in age from 21 to 31 years, underwent sonographic evaluation of the oral phase of swallowing while sitting in their usual feeding position. We compared the ability of the 4 following liquids to improve sonographic visualization of swallowing with that of water: a carbonated cola beverage, 5.0 ml of Thick-It in 120 ml of water, 2.5 ml of Thick-It in 120 ml of water, and 7.5 ml of confectioners' sugar in 120 ml of water. Water was used as a control. In each case, 5 ml of the liquid was introduced into the subject's oral cavity using a syringe, and the subject was instructed to swallow. Digitized still images and recorded video sequences of sonographic examinations of the swallowing were analyzed. The brightness of the bolus image on selected digitized video frames was measured digitally using Image Analyst software. Pixel brightness within selected regions of interest for each of the test liquids was statistically compared with that for water. Seven clinicians rated the visualization of each test liquid and water on paired sonographic videotape sequences. These ratings and the level of agreement between them were statistically tested. RESULTS: Only the carbonated cola beverage demonstrated statistically greater pixel brightness than that of water on digitized video frames (p = 0.01), whereas both cola (with a moderate inter-rater agreement, kappa = 0.50) and 5.0 ml Thick-It mixed with 120 ml of water (with a fair inter-rater agreement, kappa = 0.24) were significantly better visualized on sonographic video sequences. CONCLUSIONS: The digital still-frame analysis confirmed the clinicians' ratings of bolus visualization on real-time sonography, but dynamic sonography is more important than still frames in assessing sonographic swallow media because the dynamic images more closely parallel what is seen in clinical practice. Future investigations of sonographic contrast agents for use in the examination of the oral phase of swallowing should use both static digital (still-frame) and dynamic (real-time) assessment methods, as well as expert reviewers.