Tissue Attenuation Corrections in Gamma Scintigraphy

Abstract

Gamma scintigraphy may be used to quantify deposition patterns from aerosol inhalers provided that appropriate corrections are made for the attenuation of gamma rays by different body tissues. Tissue attenuation correction factors (ACFs) were determined in a group of 10 healthy volunteers, using four different techniques: measurement of body thickness, transmission scans, a sealed radioactive source, and a perfusion scan. Different combinations of these ACFs were then used to calculate deposition values from data obtained in the same volunteers in a previous study in which the deposition pattern of a drug inhaled from two different asthma inhalers was investigated. In addition, deposition patterns were determined from data that had not been corrected for tissue attenuation. Lung and stomach ACFs were relatively independent of the correction method (means, 1.84–2.16 for the lungs and 3.42–3.81 for the stomach), although ACFs for the oropharynx were more variable (means, 1.41–2.29). There were significant differences (P < 0.05) between the deposition patterns calculated using five different combinations of ACFs, although the actual magnitudes of the differences were small. Lung deposition was significantly underestimated (P < 0.05) by not correcting for tissue attenuation. It is therefore suggested that corrections for tissue attenuation must be made when quantifying aerosol deposition and that a simple approach based on the measurement of body thickness offers a convenient means of doing this without exposing subjects to an additional radiation dose.