Evaluation of an Objective Striatal Analysis Program for Determining Laterality in Uptake of ¹²³I-Ioflupane SPECT Images: Comparison to Clinical Symptoms and to Visual Reads

An automated objective striatal analysis (OSA) software program was applied to dopamine transporter (123)I-ioflupane images acquired on subjects with varying severities of parkinsonism. The striatal binding ratios (SBR) of the left and right putamina (relative to the occipital lobe) were computed, and the laterality of that measure was compared with clinical symptoms and visual reads. The objective over-read of OSA was evaluated as an aid in confirming the laterality of disease onset.

Methods: One hundred one (123)I-ioflupane scans were acquired on clinically referred subjects. SPECT images were analyzed using the OSA software, which locates the slices containing the striatal and background (occipital) structures, positions regions over the left and right caudate nuclei and putamina, and calculates the background-subtracted SBR. Seven images were uninterpretable because of patient motion or lack of visualization of the striatum. The remaining 94 scans were analyzed with OSA. Differences between left and right putaminal SBR ranged from 0% to 36.6%, with a mean of 11.4%. When the difference between the SBR of the left and right putamina was greater than 6%, the lower side was taken as the side of onset. Left-to-right differences less than 6% were considered to be nonlateralizing (symmetric). The 94 scans were reviewed independently by 3 masked expert readers. By majority consensus, abnormal findings were seen on 67 of the 94 scans, of which 46 had available clinical findings.

Results: Clinically, 34 subjects presented with lateralized tremors and 12 with symmetric or no tremors. Of the 34 cases of clinically lateralized tremors, 26 (76%) were concordant with the OSA findings, 5 were disparate with OSA (15%), and in 3 the OSA results were symmetric (9%). For the same 34 patients, the visual reads were concurrent with clinical tremor findings in 24 cases (71%), 1 was disparate (3%), and 9 visual reads were symmetric (26%). Of the 9 scans deemed symmetric by readers, 4 were correctly lateralized by OSA, and of the 3 symmetric OSA results, 2 were correctly lateralized visually.

Conclusion: The OSA program may be a helpful aid in the interpretation of (123)I-ioflupane SPECT images for determining laterality representing the asymmetric loss of dopamine transporters in the striata. OSA offers an objective, reproducible over-read evaluation for the laterality of onset in Parkinson disease.