Quantification of [123I]FP-CIT SPECT brain images:: an accurate technique for measurement of the specific binding ratio

Purpose: A technique is described for accurate quantification of the specific binding ratio (SBR) in [I-123] FP-CIT SPECT brain images. Methods: Using a region of interest (ROI) approach, the SBR is derived from a measure of total striatal counts that takes into account the partial volume effect. Operator intervention is limited to the placement of the striatal ROIs, a task facilitated by the use of geometrical template regions. The definition of the image for the analysis is automated and includes transaxial slices within a slab approximately 44 mm thick centred on the highest striatal signal. The reference region is automatically defined from the non-specific uptake in the whole brain enclosed in the slab, with exclusion of the striatal region. A retrospective study consisting of 25 normal and 30 abnormal scans classified by the clinical diagnosis reached with the scan support - was carried out to assess intra-and interoperator variability of the technique and its clinical usefulness. Three operators repeated the quantification twice and the variability was measured by the coefficient of variation (COV). Results: The COVs for intra-and inter-operator variability were 3% and 4% respectively. A cutoff similar to 4.5 was identified that separated normal and abnormal groups with a sensitivity, specificity and diagnostic concordance of 97%, 92% and 95% respectively. Conclusion: The proposed technique provides a reproducible and sensitive index. It is hoped that its independence from the partial volume effect will improve consistency in quantitative measurements between centres with different imaging devices and analysis software.