1 2 3 4 5 99m 99m 6 7 8 9 10 11 12 Methods Volunteers Eleven healthy volunteers (9 female, 2 male, mean age = 29.1 years, standard deviation [SD] = 8.9), recruited by public advertisement, were invited to participate. All volunteers reported no history of swallowing problems. All volunteers gave written informed consent to participate in the study, which was approved by the Medical Ethics Committee of the Academic Medical Center of the University of Amsterdam. Bolus Characteristics + 99m 99m Data Collection For this study a gamma camera (Orbiter, Siemens Medical Systems, Germany) was fitted with a low-energy all-purpose collimator. A dynamic acquisition using 0.25-s frames was performed for 30 s. Data were acquired and processed on a Hermes workstation (Nuclear Diagnostics, Sweden). Volunteers were asked to sit in front of the gamma camera and hold their right cheek against the collimator. The oral cavity was placed in the middle of the field-of-view. When the volunteer was placed in the right position, 10 ml of one of the solutions was emptied in the mouth of the volunteer with a syringe. Volunteers were instructed to hold the bolus in their mouth and swallow on command. They were specifically instructed to swallow the whole bolus in one swallow and to breath through the mouth to inhibit a second swallow. Three cobalt markers were placed on the skin of the volunteers using a pen pointer: one on the mastoid bone, one on the hyoid bone, and one underneath the thyroid cartilage. The exact placement for the marker was found by palpation of the head and neck. 99m 10 11 1 Fig. 1. Scintigraphic evaluation with three regions of interest (ROI). 1= oral cavity, 2 = pharynx, 3 = background radiation, a = mastoid marker, b = hyoid marker, 3 = thyroid marker.  Statistical Analysis The calculated percentages of pharyngeal residue were transferred to SPSS v12.0 (SPSS Inc., Chicago, IL) for further analysis. Distribution of the percentages was formally tested with the Kolmogorov–Smirnoff test for normality and was not found to be normally distributed. To explore differences in median percentages of pharyngeal residues of the three xanthan solutions to the reference (tap water) on a group level, a nonparametric (Friedman) test was used. All statistical tests were two-tailed and differences were evaluated at the 5% level of significance. Results The mean pharyngeal residue after swallowing tap water was 2.3% (SD = 1.2; range = 1.1%–4.5%) of the initial volume in the oral cavity. The percentage of pharyngeal residue after swallowing the 0.5% xanthan solution was 1.8% (SD = 0.8; range = 0.9%–2.8%), after swallowing the 0.75% xanthan solution the residue was 2.6% (SD = 2.2; range = 0.7%–8.1%), and after swallowing the 1.00% xanthan solution the pharyngeal residue was 2.8% (SD = 1.7; range = 1.2%–6.4%). 2 2 p . Fig. 2. Distribution of percentages residue on group level.  post hoc n 1 Table 1. Pharyngeal residue in percentages with 10ml boluses No. Water 0.5% Xanthan 0.75% Xanthan 1.00% Xanthan 1 1.1 1.2 0.7 1.2 2 1.8 1.2 1.0 1.7 3 1.3 0.7 8.1 3.4 4 1.4 1.5 1.7 1.3 5 4.1 2.3 2.6 6.4 6 2.9 1.5 1.5 1.2 7 1.2 0.9 1.2 2.4 8 2.4 2.5 5.3 5.4 9 3.1 2.5 2.4 2.4 10 2.0 2.5 2.1 2.7 11 4.5 2.8 2.1 2.4 Mean a a a a a p Discussion Our study attempted to investigate the correlations between viscosity and pharyngeal residue in healthy volunteers; we did not find evidence for a positive correlation between an increase of viscosity and an increase in pharyngeal residue. 12 Only one bolus per viscosity was used, therefore no data on intrasubject differences could be provided. If multiple boluses per viscosity had been used in this study, the radiation exposure for our volunteers would have been much higher. Because none of the volunteers had swallowing disorders and all were used to swallowing tap water and yogurt, any adaptation in swallowing during the study to the circumstances during data collection or intrasubject differences can be considered negligible. 13 11 99m 11 11 3 4 14 11 1 12 Conclusion In 11 healthy volunteers, mean pharyngeal residue after swallowing tap water was 2.3% (SD = 1.2) of the initial volume in the oral cavity. The percentage of pharyngeal residue after swallowing 0.5% xanthan solution was 1.8% (SD = 0.8), after swallowing 0.75% xanthan solution the residue was 2.6% (SD = 2.2), and after swallowing 1.00% xanthan solution the residue was 2.8% (SD = 1.7). Our data do not show a significant increase in pharyngeal residue in healthy volunteers as a result of an increasing viscosity of viscous solutions, ranging from tap water to full-fat yogurt. Although some trends may be seen, (confounding) factors other than viscosity may play a role in the build up of pharyngeal residue.