Effect of brain atrophy in quantitative analysis of ¹²³I-ioflupane SPECT

Dopamine transporter (DAT) imaging such as ¹²³I-ioflupane (¹²³I-FP-CIT) SPECT is a useful tool for the diagnosis of parkinsonism and dementia. The Southampton method is the quantitative method for evaluating ¹²³I-FP-CIT SPECT and is less affected by the partial volume effect of the striatum. The method may be vulnerable to contamination by low-uptake areas of cerebrospinal fluid in whole brain, and the threshold of voxel value (threshold method, TM) was developed to correct the contamination. The purpose of this study is to evaluate the TM in the patients with neurological disease.

We studied 99 subjects, including 39 patients with Alzheimer's disease (AD), 15 patients with Parkinson's disease (PD) and 10 patients with dementia with Lewy bodies (DLB). Each subject had undergone ¹²³I-FP-CIT SPECT. We calculated the SBR with and without the TM. The SBR laterality was assessed using the asymmetry index (AI). We investigated the relationship between the SBR change with TM and brain atrophy, which were assessed using Evans index (EI), sylvian index (SI) and cerebral atrophy index (CAI). Cutoff value for EI was 0.3, and cutoff values for SI and CAI were the first quartile, respectively.

The SBR with TM was 0.53 percentage points lower than the SBR without TM overall (p < 0.01). Positive and negative reversal of AI increased with age. The rate of the SBR change with TM was tended to be lower in groups with brain atrophy. The number of voxels excluded by TM in striatal volumes of interest (VOIs) was larger with high groups for EI, SI and CAI than in low groups. The number of voxels excluded using TM in reference VOIs was related to SI.

The SBR was decreased using TM. The effect of TM on the SBR tended to be small in the subjects with severe brain atrophy. The effect of brain atrophy in the TM is larger in the striatal VOIs than in the reference VOIs. Even if quantitative analyses are available, visual assessment of ¹²³I-FP-CIT SPECT is essential for diagnosis.