Improved accuracy of brain MRI/SPECT registration using a two-cluster SPECT normalization algorithm and a combinative similarity measure: application to the evaluation of Parkinson's disease

Optimization of Parameters for Quantitative Analysis of 123I-Ioflupane SPECT Images for Monitoring Progression of Parkinson Disease

Quantitative assessment of dopamine transporter imaging can aid in diagnosing Parkinson disease (PD) and assessing disease progression in the context of therapeutic trials. Previously, the software program SBRquant was applied to ¹²³I-ioflupane SPECT images acquired on healthy controls and subjects with PD. Earlier work on optimization of the parameters for differentiating between controls and subjects with dopaminergic deficits is extended here for maximizing change measurements associated with disease progression on longitudinally acquired scans. Methods: Serial ¹²³I-ioflupane SPECT imaging for 51 subjects with PD (conducted approximately 1 y apart) were downloaded from the Parkinson Progression Markers Initiative database. The software program SBRquant calculates the striatal binding ratio (SBR) separately for the left and right caudates and putamen regions of interest (ROIs). Parameters were varied to evaluate the number of summed transverse slices and the positioning of the striatal ROIs for determining the signal-to-noise ratio associated with their annual rate of change in SBR. The parameters yielding the largest change in the lowest putamen's SBR from scan 1 to scan 2 were determined. Results: From scan 1 to scan 2 in the 51 subjects, the largest annual change was observed when the putamen ROI was placed 3 pixels away from the caudate and by summing 5 central striatal slices. This resulted in an 11.2% ± 4.3% annual decrease in the lowest putamen SBR for the group. Conclusion: Quantitative assessment of dopamine transporter imaging for assessing progression of PD requires specific, optimal parameters different from those for diagnostic accuracy.

Semiquantitative Analysis of Dopamine Transporter Scans in Patients With Parkinson Disease

PURPOSE

Dopamine transporter (DaT) imaging is an adjunct diagnostic tool in parkinsonian disorders. Interpretation of DaT scans is based on visual reads. SBRquant is an automated method that measures the striatal binding ratio (SBR) in DaT scans, but has yet to be optimized. We aimed to (1) optimize SBRquant parameters to distinguish between patients with Parkinson disease (PD) and healthy controls using the Parkinson's Progression Markers Initiative (PPMI) database and (2) test the validity of these parameters in an outpatient cohort.

METHODS

For optimization, 336 DaT scans (215 PD patients and 121 healthy controls) from the PPMI database were used. Striatal binding ratio was calculated varying the number of summed transverse slices (N) and positions of the striatal regions of interest (d). The resulting SBRs were evaluated using area under the receiver operating characteristic curve. The optimized parameters were then applied to 77 test patients (35 PD and 42 non-PD patients). Striatal binding ratios were also correlated with clinical measures in the PPMI-PD group.

RESULTS

The optimal parameters discriminated the training groups in the PPMI cohort with 95.8% sensitivity and 98.3% specificity (lowest putamen SBR threshold, 1.037). The same parameters discriminated the groups in the test cohort with 97.1% sensitivity and 100% specificity (lowest putamen SBR threshold, 0.875). A significant negative correlation (r = -0.24, P = 0.0004) was found between putamen SBRs and motor severity in the PPMI-PD group.

CONCLUSIONS

SBRquant discriminates DaT scans with high sensitivity and specificity. It has a high potential for use as a quantitative diagnostic aid in clinical and research settings.