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Biomedical subjects

R Weinreich

Publications and source records attributed to R Weinreich.

17 recordsLinked to original sources
PubMed1998

Radiosynthesis and quality assurance of 5-[124I]Iodo-2'-deoxyuridine for functional PET imaging of cell proliferation.

5-[124I]Iodo-2'-deoxyuridine ([124I]IUdR) was routinely produced by direct electrophilic labelling of 2'-deoxyuridine with 124I of high specific activity (12 Ci/micromol) in an Iodogen-coated ReactiVial, followed by purification on a Sep-Pak C-18 cartridge. The radiochemical purity was determined by TLC on a Silicagel-60 plate and by reverse-phase HPLC on a RP-18 column. Based upon 45 syntheses, the yield ranged from 45% to 65%. The radiochemical impurity of [124I]IUdR was determined at 2.9% by TLC (mainly iodate) and 4.3% by HPLC. The chemical stability of the solvated formulation allowed a time window of 2 days following end of synthesis (EOS) for chemical application, based upon the required 95% radiochemical purity grade of [124I]IUdR. The labelled compound was routinely used for the clinical determination of cell proliferation in glioma patients by positron emission tomography.

Cell Division↗
PubMed1996

Auger-electron spectra of radionuclides for therapy and diagnostics.

The present paper documents the calculation of radiation spectra and of radial dose distribution around a point source for 24 selected radionuclides. The radionuclides were ordered into three groups: Nuclides potentially useful for therapy by emission of Auger electrons: 51Cr, 64Cu, 67Ga, 73Se, 75Se, 77Br, 80mBr, 94Tc, 99mTc, 114mIn, 115mIn, 123I, 124I, 125I, 167Tm, 193mPt, and 195mPt, nuclides potentially useful for therapy by alpha-particles with additional emission of Auger electrons: 212Bi, 211At and 255Fm, and nuclides potentially useful for electron Auger-therapy with simultaneous PET diagnosis: 73Se, 94Tc and 124I. The calculations imply strongly the development of labelled DNA-seeking compounds useful as carrier for the Auger- and Coster-Kronig electron-emitting radionuclides.

Half-Life↗
PubMed1993

COMT inhibitors and metabolism of fluorodopa enantiomers in aggregating cell cultures.

Organotypic primary cell cultures of fetal rat brain were used as a model system to study the effect of COMT inhibitors on the cerebral metabolic conversions of fluoro-DOPA enantiomers. The selective COMT inhibitors OR 486 and CGP 28014 were used in conjunction with 5F-L-DOPA, 6F-L-DOPA and 6F-D-DOPA as substrates. Methylation can be clearly reduced by application of OR 486 at nanomolar level, without inhibition of AADC and MAO. The uptake of the substrate is unchanged. CGP 28014, already known to be active only in vivo, has no influence on the metabolic conversion rates of the fluoro-DOPA isomers. These results show that use of this culture system allows statement concerning the in vitro activity of COMT inhibitors. It has not been possible to show an increase of absolute levels of decarboxylation products due to inhibition of COMT, however, but the reduction in levels of methylated product itself may have significance for PET studies of the human brain.

Amidines↗
PubMed1993

Savoxepine: striatal dopamine-D2 receptor occupancy in human volunteers measured using positron emission tomography (PET).

The extent and duration of striatal dopamine-D2 receptor occupancy by savoxepine in humans has been studied using positron emission tomography with [11C]-raclopride, in order to investigate why the anticipated favourable ratio between its extrapyramidal and antipsychotic effects was not achieved in practice. After 0.25 mg savoxepine, striatal D2 receptor occupancy peaked at 50-60% after 24-36 h and disappeared within 6 days. After doses of 0.1 mg to 0.5 mg, D2 receptor occupancy in the putamen and caudate nucleus increased from 20 to 70% 3-7 h after administration and amounted to 40 to 75% at the peak time (20-29 h). This suggests that cumulative D2 receptor blockade would occur if equal or increasing doses of savoxepine were given repeatedly. Extrapyramidal adverse-effects would be likely to occur under such circumstances. An adequate test of the theory that preference for hippocampal dopamine D2 receptors with afford a good therapeutic ratio requires an alternative dosing regimen.

Adult↗
PubMed1992

Metabolism of 5-fluoro-dopa and 6-fluoro-dopa enantiomers in aggregating cell cultures of fetal rat brain.

The cerebral metabolism of enantiomers of 5-fluoro-DOPA (5F-DOPA) and 6-fluoro-DOPA (6F-DOPA) was characterized in organotypic cell cultures of fetal rat brain. This system permits the investigation of metabolic processes in brain tissue exclusively, without the effects of peripheral metabolism and transport. Metabolic profiles for each substrate were determined in comparison with those of L-DOPA and D-DOPA. The uptake of DOPA and fluoro-DOPA in aggregating brain cell cultures is strongly preferential for L-enantiomers. Decarboxylation by aromatic L-amino acid decarboxylase is an active step: the major products are dopamine (DA) or 6F-DA and their corresponding products of oxidative deamination, i.e. dihydroxyphenylacetic acid (DOPAC) or 6F-DOPAC, respectively. Decarboxylation products of D-enantiomers occur in lower amounts, and 5F-D-DOPA is not decarboxylated. However, 5F-DOPA is O-methylated to a great extent, and levels of 3-O-methyl-5F-DOPA are higher after incubation with 5F-D-DOPA than with 5F-L-DOPA. These data may serve as a support for more detailed modeling of [18F]F-DOPA metabolism than can be applied to the evaluation of the cerebral biochemistry of the DA system with positron emission tomography in vivo.

Animals↗
PubMed1992

Comparative metabolism of fluorinated 3,4-dihydroxyphenylalanine isomers in aggregating brain cell cultures.

Fluorinated analogues of 3,4-dihydroxyphenylalanine (DOPA) were tested for intracellular metabolic conversion in aggregating cell cultures prepared from fetal rat brain. 5-Fluoro-D/L-DOPA was methylated almost exclusively to 3-O-methyl-5-fluoro-D/L-DOPA. Metabolism of 6-fluoro-D/L-DOPA resulted in 6-fluorodopamine, 6-fluoro-3,4-dihydroxyphenylacetic acid, and 3-O-methyl-6-fluoro-D/L-DOPA, but with a qualitatively and quantitatively different metabolite pattern compared with that of L-DOPA and D/L-DOPA, respectively. Homovanillic acid and fluorohomovanillic acid have not been found intracellularly in the cultures. On the basis of these data, the model development of the cerebral metabolism of tracers used in positron emission tomography can be improved.

Animals↗
PubMed1989

Routine 18F-2-deoxy-2-fluoro-D-glucose (18F-FDG) myocardial tomography using a normal large field of view gamma-camera.

There is a recent need to study glucose metabolism of the heart in ischemic, as well as in "hibernating or stunned" myocardium, and compare it with that in perfusion studies. In non-positron emission tomography centers, positron imaging is possible with a standard Anger-type camera if proper collimation and adequate shielding of the camera crystal can be achieved. For the study with fast-decaying isotopes, seven-pinhole tomography (7PHT), a limited-angle method designed for transaxial tomography of the left ventricle using a nonrotating camera, is well suited, because projections are acquired simultaneously. Individual adjustment (patient supine) of the camera's view axis (CAx) with the left ventricular axis (LVAx) gives excellent results: sensitivity for CHD 82%, specificity 72% in a prospective 201TI study (48 patients, x-ray coronarography as reference). Good alignment of CAx with LVAx is also achieved with the patient prone in LAO in a hammock above the camera surface. In this setting additional lead shielding of the camera is possible using a table reinforced with 5 cm of lead with a central hole for the 7PH-collimator, which has a special lead inlay. This allows utilization of the 511 KeV emitter 18F-FDG, which with a half-life of 109 minutes, can be transported a reasonable distance from the production site. System sensitivity and resolution for 18F was found comparable to 201Tl, 99mTc, and 123I using a phantom. First clinical examinations after 201Tl stress/redistribution studies showed increased 18F-FDG uptake in ischemic heart segments, as well as in "hibernating" nonperfused or "stunned" myocardium.

Deoxy Sugars↗
PubMed1983

Production of 77Kr and 79Kr for medical applications via proton irradiation of bromine: excitation functions, yields and separation procedure.

Excitation functions were measured for the formation of both 77Kr and 79Kr by interaction of protons with bromine of natural isotopic composition. The theoretical yields are 62.8 mCi/muAh for 77Kr in the energy range from 45 to 32 MeV, with 1.5% 76Kr and 11.7% 79Kr impurities, and 14.9 mCi/muAh for 79Kr in the energy range of 45 to 0 MeV, respectively. The experimental yield after dry distillation separation of the krypton isotopes from irradiated NaBr targets, lies between 40 and 60% of the theoretical ones. Below the melting point of NaBr, krypton is released by diffusion, caused by lattice defects in the target material.

Bromine↗
PubMed1975

Fixation, retention and exhalation of carrier-free 11C-labeled carbon monoxide by man.

Carrier-free 11C-labeled carbon monoxide was produced by proton irradiation of a nitrogen gas flow target via the 14N(p, alpha)11C process followed by on-line reduction of the predominantly formed 11C-carbon dioxide with a yield of 0.4 mCi/muAmin. After appropriate quality control about 2 mCi of carrier-free 11C-carbon monoxide in 500 ml on nitrogen gas were inhaled by test subjects in one breath. The 11C-activity distribution was then followed in vivo by scanning above thorax, head, liver, thigh and os sacrum; simultaneously the 11c-activity of the blood was also followed by batch measurement. The data indicate that part of the 11C-activity migrates from the blood into the intercellular space, while another part is exhaled. The 11C-activity leaves the individual organs with a biological half-life ranging from about 120 to 200 min, a time which is short as compared to the one observed for 51Cr-labeled erythrocytes. A radio gas chromatographic analysis of the exhaled air showed that the 11C-activity leaves the body exculsively in the form of 11C-labeled carbon monoxide. Consequently, metabolism of the 11CO into 11CO2 or other compounds can be excluded.

Carbon Monoxide↗
PubMed1975

Production of short-lived radioisotopes for medical applications using high-energy reactions at JULIC.

The advantages of high energy nuclear reactions for the production of some special short-lived carrier-free radionuclides for allication in nuclear medicine are outlined. The routine production of 11C (T = 20.3 min), 123I (T = 13.3 h) and 28Mg (T = 21.1 h) at the Julich Isochronous Cyclotron JULIC via the 12C(p,pn) 11C-, 127I(d,6n) 123Xe(beta+, EC) 123I- and 27Al(alpha,3p) 28Mg-reaction, respectively, is described. Some areas of fast labelling and its applications are given.

Nuclear Medicine↗