In vivo measurement of brain monoamine oxidase B occupancy by rasagiline, using (11)C-l-deprenyl and PET.

UNLABELLED: In recent years, monoamine oxidase B (MAO-B) inhibitors have become widely used in the treatment of early-stage Parkinson's disease. (11)C-l-deprenyl PET has been used by others to characterize MAO-B ligands in terms of their in vivo potency toward MAO-B and duration of action. In this study, we used (11)C-l-deprenyl PET to demonstrate the specific binding characteristics of the new irreversible selective MAO-B inhibitor rasagiline in 3 healthy volunteers. METHODS: The healthy volunteers received 1 mg of rasagiline daily for 10 d. Dynamic (11)C-l-deprenyl PET brain scans were acquired before the first treatment (scan 1) and immediately (scan 2), 2-3 wk (scan 3), and 4-6 wk (scan 4) after the final treatment. RESULTS: On scan 1, all subjects showed the highest l-deprenyl uptake in the thalamus and basal ganglia, with fairly high activity also in the cortex and cerebellum and much lower activity in the white matter. The areas of high uptake were absent from scan 2, on which activity throughout the brain was comparable to that in white matter, presumably because of blocking of MAO-B binding sites by rasagiline. Gradual recovery toward the baseline state was observed in the weeks after termination of treatment (scans 3 and 4). CONCLUSION: (11)C-l-deprenyl PET showed binding of rasagiline to MAO-B, confirming blocking of MAO-B sites after 10 d of treatment with 1 mg of rasagiline per day, with immediate post-rasagiline treatment tracer uptake and metabolism in the basal ganglia compatible only with nonspecific binding. Subsequent gradual recovery was also seen, with return to near-baseline uptake. This finding is compatible with the known rate of de novo synthesis of MAO-B, confirming the irreversible binding of rasagiline.

Measurements of occupational exposure for a technologist performing 18F FDG PET scans.

Radiation doses to one PET technologist performing 100 18F FDG (18F fluorodeoxyglucose) imaging procedures were measured in a clinical setting using two types of thermoluminescent dosimeter (TLD) badges, one finger-ring TLD and one electronic pocket dosimeter (EPD). 18F FDG was handled either with unshielded or with viewing window tungsten shielded syringes. The resulting doses using unshielded syringes were 13.8 +/- 0.8 microSv/370 MBq and 14.3 +/- 0.4 microSv/370 MBq, measured with TLD 100 and with TLD 700H/600H, respectively. For the same series of measurements, the doses obtained using shielded syringes were 10.7 +/- 0.4 microSv/370 MBq and 7.2 +/- 2.1 microSv/370 MBq with TLD700H/600H and with EPD, respectively. The dose to the right hand from shielded syringes was 69.3 +/- 5.5 microSv/370 MBq. All these values are within the ICRP recommended dose limits. Extrapolated to 725 examinations per year, the resulting effective dose measured with TLD would be 10 mSv with unshielded and 7.5 mSv with shielded syringes, respectively (25% dose reduction). The doses measured by TLD were consistently higher than those measured by EPD, suggesting that EPD measurements might underestimate occupational doses.