EFFECTS OF NONLINEAR FLOW AND SPATIAL ORIENTATION ON TC-99M HEXAMETHYLPROPYLENE AMINE OXIME SINGLE-PHOTON EMISSION TOMOGRAPHY

The effects of two post-acquisition corrections on the visual and quan titative analysis of technetium-99m hexamethylpropylene amine oxime (H MPAO) single-photon emission tomography (SPET) were determined. The co rrections were for: (1) the improper spatial orientation of the patien t data sets, and (2) the non-linear uptake of HMPAO across the blood-b rain barrier. Reorienting the SPET image data sets removed observers' uncertainty in assessment caused by suspected head tilt; however, it i ncreased their uncertainty due to perceived subtle perfusion deficits. Applying the correction to compensate for the decrease in uptake of H MPAO in high-flow regions resulted in an increase in the number of pos itive assessments. In a study involving 30 patient studies, intra-obse rver reliability increased from 62% to 83% (average of two observers) after applying both of the corrections, while inter-observer reliabili ty improved from 62% to 81%. Quantitative methods of analysing the ima ges are also affected by the corrections. In an ROI-based classificati on scheme, the quantitative assessments of more than one-half of the i mages are affected by the two corrections. These results need to be co nsidered when comparing both quantitative and visual results from diff erent studies in which the corrections may or may not have been applie d.