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The aim of this study is to investigate the possibility of measuring ornithine decarboxylase (ODC) activity in tissues such as prostate and tumor, by PET. The ODC activity in vitro and the distribution of L-[1-14C]- and L-[5-14C]ornithine were studied in prostate, tumor, liver and kidney. For the animal models, rats bearing Walker 256 carcinosarcoma, were used. Our results indicate that the ODC activity in prostate is correlated with the difference in uptake between L-[1-14C]- and L-[5-14C]ornithine. Measurement of ODC activity in tumor by PET demands a tumor with an ODC activity comparable to that of prostate. Such a tumor will show a sufficient difference in uptake, which can be detected by PET.

Using 11C-ACAC, 11C-TYR, and 18FDG as tracers, brain uptake of these substrates was studied in cat brain with a freezing lesion, by PET, at 1 day to 3 weeks after injury. Also MRI was conducted. Although the MRI scans depicted the morphological changes, such as edema formation, the PET studies of the brain uptake of substrates visualized the pattern of changes, which in the fresh lesion was largely governed by impairment of the BBB, but in the chronic lesion they were indicative of the proliferation of reactive cells in the process of tissue repair and edema resolution.

Carbon-11 labeled d-oxyphenonium iodide, a cholinergic antagonist is synthesized for in vivo visualization of muscarinic receptor-sites on airway tissue by positron emission tomography (PET). Methylation with [11C]CH3I of d-demethyloxyphenonium, followed by HPLC purification affords the desired radiopharmaceutical with a radiochemical yield of 66% (based on [11C]CH3I, and corrected for decay) and with a specific activity of 110-300 Ci/mmol. The biologically active labeled d-enantiomer is prepared within 40 min after EOB. Optical and chemical purity proved to be better than 99.9%. Radiochemical purity was determined to be higher than 99%.

1-11C-acetoacetic acid was synthesized by carboxylation of the acetone carbanion. Purification was carried out using HPLC. The product was obtained with a radiochemical yield of up to 58%, corrected for decay, in a total preparation time of 30 min. The distribution of 1-11C-acetoacetic acid after injection into adult Wistar rats and cats was investigated by PET. When the tracer was injected into cats, 3 weeks after inflicting a unilateral freezing lesion upon the brain, accumulation of 1-11C-acetoacetic acid in the ipsilateral brain hemisphere was observed.

A method for the rapid production and purification of 11C-labelled N-alkylated derivatives of the dopamine agonist 2-amino-6,7-dihydroxytetralin (ADTN) is described. The label is introduced by N-methylation with no-carrier-added 11CH3I of the corresponding secondary amines via their lithium salts. Following systemic injection in rats a uniform distribution of radioactivity in the brain was found for both the labelled 2-(N-methyl-N-n-propylamino)- and 2-(N,N-dimethylamino)-6,7-dihydroxytetralin.

14C-Formocresol and 14C-glutaraldehyde were placed in the root canals of freshly extracted human teeth. The outward diffusion of labeled aldehydes was then measured and autoradiograms of cross-sections taken. No diffusion of glutaraldehyde was detectable within 72 hours, whereas there was a rapidly increasing outflow of formocresol during the same period. In a separate group normal root canal treatment was completed until 2 mm. short of the roentgenologic apex with glutaraldehyde as an irrigant. The walls of the root canals of some of the specimens were examined with electron microscopy and the outflow of 14C-formocresol which was later placed in some specimens was counted. The use of glutaraldehyde as an irrigant resulted in closure of the apical third of the root canal as indicated by the absence of 14C-formocresol diffusion.

Tritiated 17 alpha-methylestradiol was synthesized to investigate the potential of the carbon-11-labeled analog as an estrogen-receptor-binding radiopharmaceutical. In vitro, 17 alpha-methylestradiol is bound with high affinity to the cytoplasmic estrogen receptor from rabbit uterus (Kd = 1.96 x 10(-10)M), and it sediments as an 8S hormone-receptor complex in sucrose gradients. The compound shows specific uptake in the uterus of the adult rat, within 1 hr after injection. After 30 min the uterine uptake was 1.73% dose/g. In female rats bearing DMBA-induced tumors, specific uterine and tumor uptakes were observed, although at 30 min the tumor uptake was only 23-30% of the uptake in the uterus. Tritiated 17 alpha-methylestradiol with a specific activity of 6 Ci/mmole showed a similar tissue distribution. Our results indicate that 17 alpha-methylestradiol is promising as an estrogen-receptor-binding radiopharmaceutical.

DL-[1-11C]Proline has been synthesized by carboxylation of alpha-lithiopyrrolidyl-N-tert-butyl-formamidine with a radiochemical yield of up to 18% without correction for decay. The total synthesis time is 45 min. Accumulation of DL-[1-11C]proline has been shown in Walker 256 carcinosarcoma transplanted in rats. A tumor/non-tumor ratio of 5.9 was found at 45 min after i.v. injection.

Using positron emission tomography (PET) in combination with compounds labelled with positron-emitting radionuclides like 11C, 13N and 15O, it is possible to study metabolism in vivo in a non-invasive way. Nuclear magnetic resonance (NMR) imaging takes advantage of the spin of protons in water molecules to measure both their number and relaxation times in vivo, but is, in principle, not limited to protons and can also be used for other nuclei with a non-zero spin, e.g. 13C and 31P. The use of 13C opens the possibility of studying the metabolism of a large number of compounds. In order to choose the appropriate methodology for metabolic imaging, i.e. PET or NMR, it is important to know the sensitivity of each modality. The present study outlines the sensitivity of both techniques.

The presence of D-enantiomer in L-[methyl-11C]methionine prepared from [11C]CH3I and L-homocysteine thiolactone, was measured by high performance liquid chromatography using a reverse-phase column with an eluent containing L-proline and cupric acetate. The amount of D-enantiomer increased with concentration of NaOH used. The reaction time, 2-10 min, and the reaction temperature, 40 degrees-80 degrees C, have only minor effect on the formation of D-enantiomer. No significant difference was found for three different lots of L-homocysteine thiolactone. At the highest concentration investigated, 1.0 M NaOH in 50% aqueous acetone, the percentage of D-enantiomer was found to be 7.7%. With 0.025 M NaOH used only 2.1% was measured. When L-[methyl-11C]methionine was incubated in 1.0 M NaOH, no conversion of L- into D-enantiomer was observed.

No-carrier-added DL-[1-11C]-DOPA has been synthesized by carboxylation of an alpha-lithioisocyanide with a radiochemical yield of up to 15% without correction for decay. The total synthesis time is 30 min. The resolution of the D- and L-isomers was accomplished within 16 min by HPLC using a chiral stationary phase and a phosphate buffer of pH 4.5 as eluent.

By external detection, the influence of arterial blood pressure (BP), osmolarity, and cold-induced blood-brain barrier damage was assessed on the extraction of water labeled with oxygen 15 during single-capillary transit in the rat. There was an inverse relation between arterial BP and extraction that was attributable to the influence of arterial BP on cerebral blood flow (CBF) and the relation between CBF and extraction. Neither arterial BP nor osmolarity of the injected bolus had any direct effect on extraction of water 15O, signifying that the diffusional exchange component (determined by blood flow) of extraction greatly surpasses the convection flow contribution by hydrostatic or osmotic forces. Damage to the blood-brain barrier did not change its permeability to water.

In 13 hemiparkinson patients possible changes in dopamine receptors were investigated in vivo with PET, using [11C]methylspiperone as the receptor labeling ligand. Though in individual patients the specific binding of the tracer differed between both striata, no consistent difference was found. However, the specific binding in the striatum of patients with longterm dopaminergic medication was significantly higher than in non-medicated patients, and close to normal. No correlation with the predominantly unilateral clinical pathology was found. Since the postsynaptic receptor changes in hemiparkinson patients appear not to be uniform, these results suggest that the clinical asymmetry is not only caused by a dysfunction of nigral dopaminergic cells, but by pathology in other cells and probably in other neurotransmitter systems as well. The observed bilateral increase in receptor binding during dopaminergic therapy most likely results from a symmetrical change in local pharmacokinetics or from alteration of the receptor binding. Further studies with PET are needed to determine the exact nature of this change.

To evaluate the feasibility of using either L-[1-11C]-methionine or L-[methyl-11C]methionine for measuring protein synthesis rates by positron emission tomography (PET) in normal and neoplastic tissues, distribution and metabolic studies with 14C- and 11C-labeled methionines were carried out in rats bearing Walker 256 carcinosarcoma. The tissue distributions of the two 14C-labeled methionines were similar except for liver tissue. Similar distribution patterns were observed in vivo by PET using 11C-labeled methionines. The highest 14C incorporation rate into the protein-bound fraction was found in the liver followed by tumor, brain, and pancreas. The incorporation rates in liver and pancreas were different for the two methionines. By chloroform-methanol fractionation of these four tissues, in liver significantly different amounts of 14C were observed in macromolecules. Also in brain tissue slight differences were found. By HPLC analyses of the protein-free fractions of plasma, tumor, and brain tissue at 60 min after injection, for both methionines several 14C-labeled metabolites in different amounts, were detected. About half of the 14C-labeled material in the protein-free fraction was found to be methionine. In these three tissues the amount of nonprotein metabolites and [14C]bicarbonate amount ranged from 10% to 17% and 12% to 15% for L-[1-14C]methionine and L-[methyl-14C]methionine, respectively. From these results it can be concluded that the minor metabolic pathways have to be investigated in order to quantitatively model the protein synthesis by PET.

To measure the rate of protein synthesis in human neoplasms by positron emission tomography, we prepared no carrier added DL-(1-11C)-tyrosine by 11C-carboxylation of the appropriate alpha-lithioisocyanide followed by hydrolysis of the isocyanide function and removal of the protecting methoxy group. The purification, resolution and solvent switch to saline was performed by high performance liquid chromatography (HPLC). DL-(1-11C)-Tyrosine in 0.1 N NaH2PO4 buffer was prepared with a radiochemical yield of 8%-16% (EOS, 35 min). The enantiomeric separation and solvent switch to saline were achieved in 5 min and 10 min respectively. Consequently L-(1-11C)-tyrosine in physiological saline was obtained in 2%-4% radiochemical yield. Tumor accumulation in rats with the experimental WALKER 256 carcinosarcoma was observed for both the L- and D-isomer. Using positron emission tomography a tumor/muscle ratio of two was observed for the L-isomer 15 min after injection. The corresponding figure for the D-isomer was 2.5. The first clinical results with DL-(1-11C)-tyrosine show accumulation of radioactivity in meningioma, a primary breast carcinoma and in liver metastases of a colonic carcinoma.

To evaluate a kinetic model for measuring protein synthesis rates by positron emission tomography (PET) in neoplastic and normal tissue, metabolic studies with L-[1-14C]tyrosine were carried out. As an animal model, rats bearing Walker 256 carcinosarcoma were used. Within 60 min after injection, several metabolic parameters were measured. The highest radioactivity uptake, expressed as the differential absorption ratio, was found in pancreas, followed by liver, tumor, and brain. A rapid decarboxylation was observed during the first 15 min. After 60 min, 7.4% of the total injected 14C was expired as 14CO2. In plasma a significant amount of [14C]bicarbonate was detected, but in tissue the amount was negligible. Protein incorporation increased with time. The incorporation rate was the highest in the liver followed by pancreas, tumor, and brain tissues. At 60 min after injection, more than approximately 80% of the 14C in tissue was protein bound. In plasma after a rapid clearance during the first 15 min, the total 14C level increased rapidly and paralleled the increase of protein-bound 14C. As nonprotein [14C]metabolites, in plasma, tumor and brain tissues, p-hydroxyphenylpyruvic acid, p-hydroxyphenyllactic acid, and unidentified metabolites were observed by high performance liquid chromatography. The formation of 14C-labeled 3,4-dihydroxyphenylalanine was found to be negligible. The total amount of these nonprotein metabolites increased with time. At 60 min after injection the percentages of the total nonprotein metabolites and [14C]bicarbonate were only 5.0%, 1.9%, and 3.7% in plasma, tumor and brain tissue, respectively. From our data it is concluded that [11C]carboxylic-labeled tyrosine would be a suitable radiopharmaceutical for measuring protein synthesis rates in neoplastic and normal tissue by PET.

Due to the solubility of xenon-133 in blood and tissues, errors are introduced in the determination of regional pulmonary ventilation. We investigated these errors by comparing the results from ventilation measurements with Xe-133 and N-13 in five normal subjects (both at rest and during exercise) and in seven patients after a pneumonectomy. In the normal subjects at rest, the upper lung fields showed no significant difference in the uptake rates of the two gases. In the middle and lower lung fields, however, the uptake rate for Xe-133 was higher than for N-13. During exercise a significant increase of the specific ventilation was found in the upper lung fields for N-13 compared with Xe-133. In the pneumonectomy patients the overall uptake rate for Xe-133 in the intact hemithorax was 25% larger than for N-13. Over the pneumonectomized hemithorax the uptake of the fastest component of Xe-133 was (8.5 +/- 1.3)% of the total. The total chest-wall contribution of Xe-133 was (27 +/- 8)% of the total count rate.

In order to investigate the possibility of using [1-11C] labelled 3,4-dihydroxyphenylalanine (DOPA) and tyrosine as radiopharmaceuticals for the detection of eye melanoma, the biodistributions of the same 1- and 3-14C-labelled compounds were investigated in Syrian golden hamsters with Greene melanoma. The results of these investigations were compared with positron emission tomography (PET) images of 11C labelled DOPA and tyrosine. The synthesis of these 11C labelled compounds procures of DL mixture, from which D and L forms can be separated. One h after intravenous injection, both 14C labelled DL-, L- and D-DOPA showed a high uptake in tumour tissue, that of DL- and D-DOPA being the highest. These high uptakes, together with relatively low uptake in bone, skin and eye resulted in high tumour/non tumour ratio (for DL-DOPA 5.9, 4.5 and 6.6 respectively). Extraction of the tumour tissue with trichloroacetic acid showed that L-DOPA was mainly incorporated into melanin, whereas D-DOPA was not. Also, the uptake 1 h after intravenous injection of 1-14C-L- and DL-tyrosine into the tumour were high, but L- and DL- were less different; tumour/non tumour ratios were favorable. PET images of the tumour obtained 40-80 min after injection of the [1-11C] labelled DOPA and tyrosine confirmed that melanoma detection was promising and that D-DOPA produced a better melanoma image than L-DOPA.

In cat brain with a freezing injury, the uptake of 1-11C-acetoacetate (11C-ACAC), 2-18F-fluorodeoxy-D-glucose (18FDG), and L-1-11C-tyrosine (11C-TYR) was monitored by positron emission tomography following intravenous administration of the tracers, at 1 day, and 1-3 weeks after the injury. The development and further course of the cold-induced oedema was monitored by magnetic resonance imaging. In the fresh (1 day old) lesion there was increased uptake of 11C-ACAC, probably due to release of the restrictive influence of the blood-brain barrier upon passage of the substance into brain. The uptake of 18FDG, which normally occurs by carrier-mediated transport at the barrier, was decreased in the fresh lesion, probably as a result of damage of the carrier mechanism. In the 3 week old lesion 18FDG uptake was still reduced, and 11C-ACAC uptake was still increased, although barrier function to Evans blue had recovered. It is suggested, that the increased 11C-ACAC uptake in the chronic lesion bears upon the proliferation of macrophages and reactive glial cells in the lesion. This is supported by the increased uptake of 11C-TYR in the 2 weeks old lesion, while in the fresh lesion 11C-TYR uptake was unchanged.

The accumulation and retention of radioactivity in rat brain were studied after intravenous injection of the dopamine (DA) agonist [3H]N-n-propylnorapomorphine ( [3H]NPA). Dose-dependent saturable accumulation of label was found in the striatum, nucleus accumbens and olfactory tubercle. DA agonists (apomorphine, N,N-dipropyl-5,6-ADTN) and antagonists (haloperidol, cis-flupenthixol) prevented this accumulation. Enhanced accumulation of radioactivity in the striatum was found after 6-OHDA lesions and short- and long-term treatment with reserpine. These results are an indication of specific NPA binding to presumably postsynaptically situated DA receptors. One hour after administration of the drug, the effect of NPA on striatal DA metabolism was not correlated with receptor saturation. Maximal numbers of in vivo NPA binding sites (about 30 and 22 pmol . g-1) in striatal tissue were calculated from independent measurements at 15 and 60 min after NPA injection. Regional distribution of radioactivity after a tracer dose of [3H]NPA was assessed in 35 brain areas and parts of the spinal cord. In addition to the already mentioned DA-rich areas receptor-specific NPA binding was also found in several other brain parts.

13N-ammonia, applied rectally, after absorption and transportation visualises the liver. After release of 13N-aminoacids and 13N-urea by the liver, 13N-activity can be measured over other organs. In patients with porta-systemic shunts, 13N-ammonia will appear in the systemic circulation as well. In 16 controls and 26 patients with cirrhosis, activities were measured for 20 minutes over liver, spleen, heart, lungs and forearm. In all subjects, the liver was visualised within a minute, in some patients with cirrhosis faintly, however. Release by the liver of 13N-ammonia metabolites started within a few minutes. Liver/heart activity ratios proved to be more discriminating between the control- and the cirrhosis group than liver/lung and liver/spleen ratios. In the control group, the 20 minutes' liver/heart ratio was most suitable for determining the normal range. The lower normal level was found to be 2.25. Fourteen of the 26 patients with cirrhosis had a normal, 12 an abnormally low 20 minutes' liver/heart ratio.

Carbon-11 (t1/2 equals 20.4 min, beta-+) labelled DL-alpha-phenylalanine and DL-alpha-phenylglycine were administered intravenously to rats and the distribution of the radioactive amino acids over pancreas, liver, spleen, kidneys and blood was measured after several time intervals. From these results the ratios of the concentration in pancreas and liver were calculated and compared with the corresponding ratios from the literature for some 18-F-labelled aromatic amino acids and L-selenomethionine-75-Se. On the basis of this study it appears that DL-alpha-phenylglycine-1-11-C, in spite of a small percentage of the administered dose reaching the pancreas, and DL-alpha-phenylalanine-1-11-C are better suited to pancreas scintigraphy than L-selenomethionine-75-Se.

DL-[1-11C]ornithine and lysine have been synthesized by carboxylation of the corresponding alpha-lithioisocyanide with a radiochemical yield of up to 14% without correction for decay. The total preparation time is 50 min. Accumulation of both DL-[1-11C]ornithine and lysine in Walker 256 carcinosarcoma is observed, with a tumor/non-tumor ratio of 4.9 and 4.5 respectively, at 45 min after intravenous injection.

The possibility of using radiolabeled divalent cations to visualize nerve cell degeneration in the brain was investigated after intoxication with neurotoxins. At different survival times after the intracerebral injection of kainic acid or 6-hydroxydopamine, autoradiographs were made from brain sections of rats that had received 45CaCl2 intravenously 24 h before death. Brain sections, adjacent to those used for autoradiography, of the 6-hydroxydopamine-treated rats were used for histofluorescence of catecholamines to check the neurochemical effect of the treatment. These experiments show that radioactive Ca accumulates in brain tissue during a particular phase of degeneration. Not only could degenerating cell bodies be traced by 45Ca autoradiography, but also degenerating nerve terminals in the striato-nigral and nigro-striatal projection systems. In positron emission tomography (PET) studies, 55CoCl2 was used as a marker for Ca2+. Unilateral lesions of the cat forebrain, produced by kainic acid, could be imaged in vivo by PET with 55CoCl2. PET with this radiolabel may provide diagnostic potentials for human neurodegenerative disorders.

The cerebral distribution of the positron-emitting agent [1-11C]beta-(3,4-dihydroxyphenyl)-D,L-alpha-alanine ([11C]DOPA) was studied after intravenous injection in rats pretreated with the peripheral decarboxylase inhibitor, carbidopa. Within 15 min of injection the accumulation of carbon-11 was almost twice as high in cortical areas and cerebellum as in the striatum and the brain stem. After destruction of catecholamine-containing nerve endings with 6-hydroxydopamine, the level of carbon-11 in the striatum was higher than in rats not treated with this neurotoxin. Pretreatment of rats with haloperidol or L-DOPA did not change the distribution pattern of carbon-11. Without pretreatment with carbidopa a uniform distribution of the label in the brain was observed. We suggest that [11C]DOPA is a potentially useful agent for external detection with positron imaging systems in patients and large animals of brain regions rich in the enzyme dopa-decarboxylase. (EC 4.1.1.26).

57-Co-bleomycin is useful in the detection and staging of lung cancer, but the long half-life of 57Co (270 days) has discouraged its widespread acceptance. We investigated the shorter living positron emitting 55Co (half-life 18.2 h) as a level for bleomycin. In eleven patients with proven lung cancer scintigraphy with 55Co-bleomycin, using a positron camera, demonstrated the tumor in ten cases. Tumor to lung ratios were calculated. The results were superior to those obtained with 55Co-bleomycin single photon imaging but inferior to those obtained with 57Co-bleomycin scintigraphy.

Based on a double-headed rotating uncollimated scintillation camera system, a positron imaging device was developed. After a rotating data acquisition in coincidence mode, 16 transverse section images are reconstructed by back projection. To obtain a uniform response, a limited angle reconstruction option is incorporated in this process. After correction for the system response by a three-dimensional deconvolution technique, the 16 transverse section images are stored on disk as a standard patient study for further analysis. The system can also be operated in a stationary mode. In this mode longitudinal tomographic images are obtained. Return to single photon scintigraphy is possible by remounting the collimators and by switching off the coincidence electronics.

Ethynylestradiol and moxestrol can be labeled with carbon-11 by introducing this positron emitter in the 17 alpha-ethynyl group. To investigate their potential as radiotracers binding to estrogen receptors, we studied the tissue distribution of tritiated ethynylestradiol and moxestrol, with specific activities of 57 Ci/mmol and 77-90 Ci/mmol, respectively, in the adult female rat. At 30 min after injection, both compounds showed specific uptake in the uterus (% dose/g): 2.52 for ethynylestradiol and of 2.43 for moxestrol. A decrease of the specific activity to 6-9 Ci/mmol resulted in uterine uptakes of 1.60 and 2.10 respectively, for ethynylestradiol and moxestrol, at 30 min. In the female rat bearing DMBA-induced mammary tumors, specific uptake was also measured in the tumors, although the values were only 25-30% of the uterine uptake. Moxestrol showed a greater uptake selectivity in the tumors compared with ethynylestradiol. From this study we conclude that ethynylestradiol and moxestrol have good potential as tracers binding to mammary tumors that contain estrogen receptors.

Carbon-11 labelled glycine has been prepared in 30 min by carboxylation of alpha-lithiomethylisocyanide with a radiochemical yield of 10-15%. After coupling with L-phenylalanine-N-carboxyanhydride and L-leucine-N-carboxyanhydride followed by HPLC purification, the corresponding dipeptides were obtained in 20 min with a radiochemical yield of 30-40%. Consequently, starting with 11CO2, non carrier added L-phenylalanyl[1-(11)C]glycine and L-leucyl-[1-(11)C]glycine in 0.1 N NaH2PO4 were obtained in 50 min with a radiochemical yield of 3-6%. The radiochemical yield figures are not corrected for decay.