QUANTIFYING ASPIRATION IN SCINTIGRAPHIC DEGLUTITION TESTING - TISSUE ATTENUATION EFFECTS

Scintigraphic studies for determining aspiration associated with swall owing have ignored error due to differential gamma attenuation in the patient by the various regions of the body. This study sought to estim ate the magnitude of that error, and to assess the feasibility of prov iding individual attenuation corrections based on clinical data. Metho ds: Relative attenuation for the pharynx, thorax and abdomen were dete rmined from physical measurements employing an anthropomorphic phantom and 45 adult human subjects. A small sealed radioactive source of 2.5 mCi of Tc-99m was placed inside the phantom at various locations with in the upper digestive tract and respiratory system, and relative coun t rates determined via static scans with a gamma camera. Similar data for human subjects was obtained from clinical swallowing testing using a bolus of 2.5 mCi of (TC)-T-99m in 10 cc of water. Results: The rati os representing relative counts were highly similar between the phanto m and average human data. Test-retest replication of results was good for the abdominal reference and pharynx ratios-less so for the thorax. A procedure is described for estimating accuracy of percent aspiratio n calculation based on group data, using normalization coefficients de rived for separate anatomical regions in the subglottic respiratory sy stem. Conclusions: Error in percent aspiration calculation will depend on the amount and location of aspirate. Individual subject correction s based on the type of clinical data studied should be attempted with caution.