Yoshio Homma

In vivo evaluation of [11C]SA4503 as a PET ligand for mapping CNS sigma1 receptors

Abstract The potential of the 11 C-labeled selective sigma 1 receptor ligand 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine ([ 11 C]SA4503) was evaluated in vivo as a positron emission tomography (PET) ligand for mapping sigma 1 receptors in rats. SA4503 is known to have a high affinity (IC 50 = 17.4 nM) and a higher selectivity (sigma 1 /sigma 2 = 103) for the sigma 1 receptor. A high and increasing brain uptake of [ 11 C]SA4503 was found. Pre-, co- and postinjection of cold SA4503 significantly decreased uptake of [ 11 C]SA4503 in the brain, spleen, heart, lung, and kidney in which sigma receptors are present as well as in the skeletal muscle. In the blocking study with one of four sigma receptor ligands including haloperidol, (+)-pentazocine, SA4503, and (−)-pentazocine (in the order of their affinity for sigma 1 receptor subtype), SA4503 and haloperidol significantly reduced the brain uptake of [ 11 C]SA4503 to approximately 30% of the control, but the other two benzomorphans did not. A high specific uptake of [ 11 C]SA4503 by the brain was also confirmed by ex vivo autoradiography (ARG) and PET. Ex vivo ARG showed a higher uptake in the vestibular nucleus, temporal cortex, cingulate cortex, inferior colliculus, thalamus, and frontal cortex, and a moderate uptake in the parietal cortex and caudate putamen. Peripherally, the blocking effects of the four ligands depended on their affinity for sigma 1 receptors. No 11 C-labeled metabolite was detected in the brain 30 min postinjection, whereas approximately 20% of the radioactivity was found as 11 C-labeled metabolites in plasma. These results have demonstrated that the 11 C-labeled sigma 1 receptor ligand [ 11 C]SA4503 has a potential for mapping sigma 1 receptors in the central nervous system and peripheral organs.

Reliability of the activity determined by the quenching correction method for two groups of emulsion scintillators

Abstract The reliability of the activity, determined using conventional quenching correction methods, has been studied for two groups of emulsion scintillators: (1) scintillators with three distinct water dilution criteria; and (2) scintillators forming a miscible solution with up to 50% water content. Whilst for the first group of scintillators the error of the activity measured very often becomes larger with increased water content, the measurements with the second group of scintillators fit the quenching correction curve.

The zero detection threshold of a liquid scintillation spectrometer and its application to liquid scintillation counting

Abstract The zero detectin threshold of a liquid scintillation spectrometer is found to be 2.4 ± 0.10 keV below zero pulse-height by measuring standardized 3H samples with a commercially-available liquid-scintillation spectrometer. Based on the results, a high accuracy modified integral counting method which extrapolates the integral pulse-height spectrum to the zero detection threshold is proposed.

Determination of air luminescence spectra for alpha-emitters with liquid scintillation spectrometers

Abstract Air luminescence spectra have been measured for 210 Po, 238 U and 241 Am with two commercially available liquid scintillation spectrometers. Since the measured end-point of the air luminescence spectra is approx. 18 keV, they can be determined by liquid scintillation counting in the 3 H detection region. The average counting efficiencies measured with the two counting systems were found to be 33.3 and 33.7%, respectively. The air luminescence effect on liquid scintillation counting of gaseous α-emitters is mentioned.

A modified integral counting method and efficiency tracing method for measuring 222Rn by liquid-scintillation counting

Abstract The integral counting method of liquid scintillation counting has been modified by extrapolating the integral pulse-height spectrum to the zero detection threshold of the liquid-scintillation system rather than to the zero pulse-height, and applied to the determination of 222 Rn samples. The results have been compared with those obtained by the conventional integral counting method and the efficiency tracing method. The modified integral counting method gives more accurate results than the conventional integral counting method and the efficiency tracing method. The possibilities and limitation of the efficiency tracing method has been discussed.

Assay of 222Rn in water samples by a modified integral counting method

22Rn activity concentrations in water collected from 163 private wells and 14 springs in Tokyo were measured with a liquid scintillation spectrometer using a modified integral counting method. The activity concentrations of 222Rn range from 0.2 to 22.9 Bq/L and average 4.8 Bq/L. The errors due to the air luminescence counts and the interferences from 220Rn and 219Rn are discussed and evaluated. 222Rn samples of 0.2 Bq/L can be assayed within an overall uncertainty of 3.1%. The liquid scintillation method involving agitation of the sample water directly with a liquid scintillation cocktail was compared with the present method and evaluated.

Efficient HPLC separation of [11C]β-CFT or [11C]β-CIT from an N-desmethyl precursor on a semipreparative reversed phase ODS column

HPLC separation of either [11C]beta-CFT or [11C]beta-CIT from the N-desmethyl precursor greatly depended on the ODS column used and the pH of the phosphate buffer in the mobile phase. The separation was accomplished on the semipreparative reversed phase ODS column without end-capping treatment over a pH ranging from 6.4 to 9.2, but failed on the end-capped ODS column. This suggests that the presence of residual silanol groups on the ODS is an important factor for the separation.

Production of 123I by Bombarding a Natural Tellurium Target with α and 3He Particles

天然テルルの電着ターゲットに40MeVのα, 3He照射を行い, 123Xe, 123I, 125Xe, 130Iなどを生ずる核反応の励起曲線, 厚いターゲット収率曲線を測定して, 123Iをつくるための最適照射条件を決めた。天然テルルを用いるとき123Iの収率は低く実用には向かないが, 濃縮123Teを用いたときの収率は天然テルルの場合の結果より計算でき, 123Te (76.5%) 174mg/cm2に30MeVの3He照射を行えば約724μCi/μAhの123Iが得られると推定される。123Te中の130Teから130Iが生ずるが容易に除去できる。高エネルギー陽子, 重陽子が利用できるなら127I (p, 5n) 123Xe→123I, 127I (d, 6n) 123Xe→123Iにより高収率の123Iが得られるが, これに対し, 本法は比較的低エネルギーで, 放射化学的純度の高い実用量の123Iをつくり得る。

Radiochemical Purity of 123I for Medical Use

123I for use in clinical diagnostic procedures has been produced by bombarding antimony with 40 MeV 3He particles. The purity of 123I was measured with a Ge(Li)spectrometer and a low energy Ge(Li) detector. The 123I-product was followed for 1.5 months with a well-type NaI scintillation counter to establish the half-life and confirm the identity of the nuclides. In order to minimize the yield of 121I the optimum cooling time and chemical procedures are presented. After 20 h cooling, the 121I, 124I and 125I contaminants were about 1.8, 4.3 and 0.04% respectively. These values were in agreement with those calculated from the thick-target yield curves. The calculated absorbed dose to the thyroid by the 123I and by-product nuclides were only 4.3 and 7.3% of 131I. 123I could be measured at the window of 99mTc of a NaI scintillation camera and a curie-meter with an error of 10%.