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 [(123)I]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 inter-operator 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 approximately 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.