Dopamine transporter quantification by [123I]-SPECT – A future paraclinical tool?

Abstract

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Objectives: [123I]-PE2I is a high-affinity and selective cocaine analogue, used for imaging the dopamine transporter (DAT) with SPECT. The in vivo quantification of the dopamine transporters using [123I]-PE2I SPECT and the bolus/infusion (B/I) approach has been described in detail [1]. In addition the test-retest variability of in vivo quantification of PE2I in healthy subjects is low [2]. In this study we assess the usefulness of DAT quantification in daily clinical practise for early diagnosis of patients with movement disorders. Larger studies suggest that revision is required in up to 30% of patients with an initial diagnosis of Parkinson’s disease.

Methods: Forty-eight patients with a mean age of 65 (range 36-86 yrs) with one ore more of the following symptoms: tremor, bradykinesia, or rigidity were admitted for a diagnostic SPECT scan with [123I]-PE2I. Thirteen healthy volunteers with a mean age of 56 (range 41-69 yrs) were included in order to determine an age-related DAT density range of variation. [123I]-PE2I was given as an iv. bolus injection followed by a constant infusion (B/I ratio of 2.7 hours) to obtain steady-state concentrations of [123I]-PE2I in brain and plasma. Two hours after bolus injection SPECT scanning was conducted. Total scanning time was 60 minutes. DAT binding was quantified as BP2 = (CROI/CPlasma)-1. A clinical diagnosis was settled in all cases by a trained neurologists blinded to the SPECT results reviewing the medical records from 4 to 30 months post scan time.

Results: Fifteen patients had striatal BP2 within the normal range, defined as <2 SD’s of the age matched control value. The remaining patients had lower BP2 values (uni- or bilateral) than expected according to age in striatum. Out of the 48 patients a diagnosis was established in 31 patients, see table.

Conclusions: These preliminary results indicate that [123I]-PE2I with a bolus/infusion approach is a valuable paraclinical tool for studies in patients with symptoms indicative of a movement disorders. To further determine the usefulness of [123I]-PE2I SPECT for early diagnosis clinical follow-up ensues.

Research Support (if any): 1. Pinborg L et al: Quantification of 123I-PE2I binding to dopamine transporter with SPECT after bolus and bolus/infusion. J Nucl Med. 2005 Jul;46(7):1119-27. 2. Ziebell M et al: Reproducibility of [123I]PE2I Binding to Dopamine Transporters with SPET. E J Nucl Med (Submitted dec 2005).