TY - JOUR T1 - Reproducibility of <sup>11</sup>C-Raclopride Binding in the Rat Brain Measured with the MicroPET R4: Effects of Scatter Correction and Tracer Specific Activity JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 815 LP - 822 VL - 44 IS - 5 AU - David L. Alexoff AU - Paul Vaska AU - Douglas Marsteller AU - Timofei Gerasimov AU - Juan Li AU - Jean Logan AU - Joanna S. Fowler AU - Nicholas B. Taintor AU - Panayotis K. Thanos AU - Nora D. Volkow Y1 - 2003/05/01 UR - http://jnm.snmjournals.org/content/44/5/815.abstract N2 - A new generation of commercial animal PET cameras may accelerate drug development by streamlining preclinical testing in laboratory animals. However, little information on the feasibility of using these machines for quantitative PET in small animals is available. Here we investigate the reproducibility of microPET imaging of 11C-raclopride in the rat brain and the effects of tracer-specific activity and photon scatter correction on measures of D2 receptor (D2R) availability. Methods: Sprague-Dawley rats (422 ± 29 g; n = 7) were anesthetized with ketamine/xylazine and catheterized for tail vein injection of 11C-raclopride. Each animal was positioned prone in the microPET, centering the head in the field of view. MicroPET data was collected for 60 min—starting at 11C-raclopride injection—and binned into 24 time frames (6 × 10 s, 3 × 20 s, 8 × 60 s, 4 × 200 s, 3 × 600 s). In 3 studies, 11C-raclopride was administered a second time in the same animal, with 2–4 h between injections. In a fourth animal, raclopride (1 mg/kg) was coinjected with 11C-raclopride for the second injection. Three rats received a single dose of 11C-raclopride. The range of doses for all studies was 6.11–18.54 MBq (165–501 μCi). The specific activity at injection was 4.07–48.1 GBq/μmol (0.11–1.3 Ci/μmol). Region-of-interest analysis was performed and the distribution volume ratio (DVR) was computed for striatum/cerebellum using sinograms uncorrected and corrected for scatter using a tail-fit method. Results: Test-retest results showed that the 11C-raclopride microPET DVR was reproducible (change in DVR = −8.3% ± 4.4%). The average DVR from 6 rats injected with high specific activity (&lt;4 nmol/kg) was 2.43 ± 0.19 (coefficient of variation = 8%). The DVR for the blocking study was 1.23. The DVR depended on the mass of tracer 11C-raclopride injected for doses &gt;1.5 nmol/kg. Scatter fractions within the rat head were ∼25%–45% resulting in an average increase of DVR of 3.5% (range, 0%–10%) after correction. Conclusion: This study shows that the 11C-raclopride microPET-derived DVR is reproducible and suitable for studying D2R availability in the rat brain. MicroPET sensitivity was sufficient to determine reproducible DVRs from 11C-raclopride injections of 9.25 MBq (∼250 μCi). However, the effect of tracer mass on the DVR should be considered for studies using more than ∼1–2 nmol/kg raclopride, and scatter correction has a measurable impact on the results. ER -