A basic study on lesion detectability for hot spot imaging of positron emitters with dedicated PET and positron coincidence gamma camera

The aim of this study was to explore the correlations of detectability and the semi-quantification for hot spot imaging with positron emitters in posi tron emission tomography (PET) and with a positron coincidence detection sy stem (PCD). Phantom study results for the measurement of the lesion-to-back ground (WB) ratio ranged from 2.0 to 30.3, and detectability for hot spot l esion of PET and PCD were performed to correspond to clinical conditions. T he detectability and semi-quantitative evaluation of hot spots from 4.4 mm to 36.9 mm in diameter were performed from the PET and PCD images. There we re strong correlations between the L/B ratios derived from PET and PCD hot spot images and actual L/B ratios; but the L/B ratio derived from PET was h igher than that from PCD with a significant difference of 10% to 54.8%. The detectability of hot spot imaging of PCD was lower than that of PET at 64. 8% (PCD) versus 77.8% (PET). Even the actual L/B ratio was 8.0, hot spots m ore than 10.6 mm in diameter could be clearly identified with PCD imaging. The same identification could be achieved with PET imaging even when the ac tual L/B ratio was 4.0, This detailed investigation indicated that FDG PCD yielded results comparable to FDG PET on visual analysis and semi-quantitat ive analysis in detecting hot spots in phantoms, hut semi-quantitative anal ysis of the L/B ratio with FDG PCD was inferior to that with FDG PET and th e detectability of PCD in smaller hot spots was significantly poor.