Quantifying aspiration in scintigraphic deglutition testing: tissue attenuation effects.

Abstract

Scintigraphic studies for determining aspiration associated with swallowing have ignored error due to differential gamma attenuation in the patient by the various regions of the body. This study sought to estimate the magnitude of that error, and to assess the feasibility of providing individual attenuation corrections based on clinical data. Relative attenuation for the pharynx, thorax and abdomen were determined from physical measurements employing an anthropomorphic phantom and 45 adult human subjects. A small sealed radioactive source of 2.5 mCi of 99mTc was placed inside the phantom at various locations within the upper digestive tract and respiratory system, and relative count 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 99mTc in 10 cc of water. The ratios representing relative counts were highly similar between the phantom 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 aspiration calculation based on group data, using normalization coefficients derived for separate anatomical regions in the subglottic respiratory system. Error in percent aspiration calculation will depend on the amount and location of aspirate. Individual subject corrections based on the type of clinical data studied should be attempted with caution.