Standardization of the specific binding ratio in [123I]FP-CIT SPECT: study by striatum phantom.

The quantitative values of the specific binding ratio (SBR) in [I]FP-CIT have been reported to change because of differences in apparatus, collection conditions, and image reconstruction. The aim of this study was to clarify the distribution of calculated SBR values by performing [I]FP-CIT single-photon emission computed tomography in a multicenter collaborative study using a phantom. A simple correction method was also devised that enables direct comparison of the SBR value calculated at one facility with those calculated at other facilities. Data were acquired at 14 facilities using the phantom adjusted to right striatum : left striatum : cerebral parenchyma (back ground)=8 : 4 : 1, and the SBR values were calculated.We devised a method to correct the SBR using the results of experiments with a known ratio phantom. The SBR values considerably differed between facilities. The average SBR with a theoretical value of 7 and with a theoretical value of 3 in all facilities was 6.48±0.89 and 2.58±0.51, respectively. The range of SBRs with a theoretical value of 7 and a theoretical value of 3 was 3.18 and 1.59, respectively. We devised a simple method for calibrating the SBR value at the clinical examination of each facility to a directly comparable value. Direct comparison of the SBR with those of other facilities and sharing other facilities normal values is clinically difficult. We devised countermeasures that do not affect the diagnosis and developed a simple tool to calculate the standardized SBR.