Image-based measurement of post-swallow residue: the normalized residue ratio scale

Abstract

Post-swallow residue is considered a sign of swallowing impairment. Existing methods for capturing post-swallow residue (perceptual and quantitative) have inherent limitations. We employed several different perceptual and quantitative (ratio) methods for measuring post-swallow residue on the same 40 swallows and addressed the following questions: (1) Do perceptual and quantitative methods demonstrate good agreement? (2) What differences in precision are apparent by measurement method (one-dimensional, two-dimensional, and circumscribed area ratios)? (3) Do residue ratios agree strongly with residue area measures that are anatomically normalized? Based on the findings of this series of questions, a new method for capturing residue is proposed: the Normalized Residue Ratio Scale (NRRS). The NRRS is a continuous measurement that incorporates both the ratio of residue relative to the available pharyngeal space and the residue proportionate to the size of the individual. A demonstration of this method is presented to illustrate the added precision of the NRRS measurement in comparison to other approaches for measuring residue severity.

Conflict of interest statement

Conflict of interest The authors have no conflicts of interest to disclose.

Figures

Fig. 1

Example demonstrating that multiplying the same width (X) by height (Y) may not capture individual differences in vallecular area (a vs. b)

Fig. 2

Summary of research questions for development of the NRRS

Fig. 3

a The “freehand” tool is used to outline the residue in the valleculae. b The “freehand” tool or “selection brush” tool (shown here) is used to outline the vallecular space. c The “line” tool is used to measure the length of the anterior inferior corner of C2 to the anterior inferior corner of C4

Fig. 4

aScatter plot shows that the most precise measurement of residue-to-pharyngeal space ratio is not predictive of the amount of residue in the valleculae sinuses as characterized by the normalized residue proportion (r2 < 0.80). bScatter plot shows that the most precise measurement of residue-to-pharyngeal space ratio is not predictive of the amount of residue in the piriform sinuses as characterized by the normalized residue proportion (r2 < 0.80)