Short Half-life Isotopes Research Articles

Generation of synthetic PET images of synaptic density and amyloid from 18 F-FDG images using deep learning.

Positron emission tomography (PET) imaging with various tracers is increasingly used in Alzheimer's disease (AD) studies. However, access to PET scans using new or less-available tracers with sophisticated synthesis and short half-life isotopes may be very limited. Therefore, it is of great significance and interest in AD research to assess the feasibility of generating synthetic PET images of less-available tracers from the PET image of another common tracer, in particular 18 F-FDG. We implemented advanced deep learning methods using the U-Net model to predict 11 C-UCB-J PET images of synaptic vesicle protein 2A (SV2A), a surrogate of synaptic density, from 18 F-FDG PET data. Dynamic 18 F-FDG and 11 C-UCB-J scans were performed in 21 participants with normal cognition (CN) and 33 participants with Alzheimer's disease (AD). Cerebellum was used as the reference region for both tracers. For 11 C-UCB-J image prediction, four network models were trained and tested, which included 1) 18 F-FDG SUV ratio (SUVR) to 11 C-UCB-J SUVR, 2) 18 F-FDG Ki ratio to 11 C-UCB-J SUVR, 3) 18 F-FDG SUVR to 11 C-UCB-J distribution volume ratio (DVR), and 4) 18 F-FDG Ki ratio to 11 C-UCB-J DVR. The normalized root mean square error (NRMSE), structure similarity index (SSIM), and Pearson's correlation coefficient were calculated for evaluating the overall image prediction accuracy. Mean bias of various ROIs in the brain and correlation plots between predicted images and true images were calculated for ROI-based prediction accuracy. Following a similar training and evaluation strategy, 18 F-FDG SUVR to 11 C-PiB SUVR network was also trained and tested for 11 C-PiB static image prediction. The results showed that all four network models obtained satisfactory 11 C-UCB-J static and parametric images. For 11 C-UCB-J SUVR prediction, the mean ROI bias was -0.3%±7.4% for the AD group and -0.5%±7.3% for the CN group with 18 F-FDG SUVR as the input, -0.7%±8.1% for the AD group, and -1.3%±7.0% for the CN group with 18 F-FDG Ki ratio as the input. For 11 C-UCB-J DVR prediction, the mean ROI bias was -1.3%±7.5% for the AD group and -2.0%±6.9% for the CN group with 18 F-FDG SUVR as the input, -0.7%±9.0% for the AD group, and -1.7%±7.8% for the CN group with 18 F-FDG Ki ratio as the input. For 11 C-PiB SUVR image prediction, which appears to be a more challenging task, the incorporation of additional diagnostic information into the network is needed to control the bias below 5% for most ROIs. It is feasible to use 3D U-Net-based methods to generate synthetic 11 C-UCB-J PET images from 18 F-FDG images with reasonable prediction accuracy. It is also possible to predict 11 C-PiB SUVR images from 18 F-FDG images, though the incorporation of additional non-imaging information is needed.

THE RADIOACTIVITY ESTIMATION OF THE IRRADIATED 13 MEV CYCLOTRON’S CONCRETE SHIELD

The Center for Accelerator Science and Technology (PSTA) planned to install K500 concrete shield in its 13 MeV cyclotron facility (DECY-13). However, fast neutrons that are generated by this cyclotron could activate materials of the concrete. It may harm the radiation workers. In this work, we conducted simulations using ORIGEN2 and PHITS computer code to estimate the formed radioactivity and the neutron flux distribution in the DECY-13 cyclotron's concrete shield. Based on the simulation, the induced radioactivity is 2.3478 × 109 Bq, while its gamma dose rate is 22.09 µSv/m2h. The most contributed isotopes are Th-233, Ho-166, Al-28, Mn-56 and Si-31. This dose is quite high. Neutron fluxes in the rear of the simulated concrete shield are also still prominent. Accordingly, it is necessary to attach neutron shielding materials which do not generate high-intensity gamma-ray. The formed radioactivity is high; but it appears from the short half-life isotopes such as Th-233, Ho-166, Al-28, Mn-56 and Si-31. Its activity will diminish quickly after the cyclotron is off. Hence, it will be safe for radiation workers.Keywords: Radioactivity, Concrete Shield, 13 MeV Cyclotron, Neutron Irradiation, DECY-13, PHITS

Synthesis and evaluation of 18F-PTTCO-Cys40-Exendin-4 for PET imaging of ectopic insulinomas in rodents.

A major limitation in the development of radiolabeled Exendin-4 analogues (short half-life isotopes) is an inability to efficiently and rapidly separate final products from precursors. This is important as lack of purity in the final product decreases probe efficiency. The purpose of this study was to develop a method to prepare the high-purity imaging reagent [18F] PTTCO-Cys40-Exendin-4. To accomplish this, magnetic TCO-beads were incubated with the crude product to remove unlabeled Exendin-4. In rodents pre-treatment with purified [18F] PTTCO-Cys40-Exendin-4 (~1.85MBq) allowed precise microPET imaging of ectopic insulinomas. Moreover, analogue uptake was successfully blocked by administering non-labelled "cold" Exendin-4. Biodistribution data revealed that [18F] PTTCO-Cys40-Exendin-4 accumulated specifically in GLP-1R-enriched insulinomas in mice, confirming results obtained using miroPET. Investigation of [18F] PTTCO-Cys40-Exendin-4 as a tracer to image portal vein-transplanted pancreatic islets is proceeding in animals.

Electromagnetic wave propagation in a fast pulse line ion accelerator.

The pulse line ion accelerator (PLIA) is a low-cost accelerator concept originally designed to accelerate heavy ions. Our group has been investigating the use of PLIA to accelerate light ions and believe a multi-stage PLIA could be useful for short half-life PET isotope production. The goal of this work was to develop a single prototype fast PLIA structure and demonstrate electromagnetic wave propagation using a high-voltage pulser. A 1.6m fast PLIA structure (wave speed>107 m/s) was constructed along with a high-voltage, sinusoidal pulse generator. The latter uses capacitive voltage doubling and spark gap switching. A step-up transformer couples voltage from the pulser to the PLIA coil. Voltage measurements on the coil were made in air using a high-voltage resistive probe, while capacitive probes placed along the length of the PLIA were used to measure wave propagation with the PLIA structure filled with transformer oil. Voltage measurements acquired on the primary and secondary coils of the transformer coupler in air demonstrated a peak-to-peak voltage step-up of 4.2 relative to the pulser DC charging voltage. The maximum voltage time-rate-of-change on the PLIA coil was 0.76×1013 V/s. Capacitive probe measurements indicated voltage oscillations on the PLIA coil with half-period equal to 43±0.9ns and wave speed (with oil) of 1.2×107 m/s. Average and peak accelerating gradients were conservatively estimated to be 0.44 and 0.60MV/m, respectively, with a charging voltage of 55kV. Wave propagation was demonstrated at these gradients without flashover at a vacuum pressure of 9×10-6 Torr. Submerging the pulser in oil would allow for charging voltages up to 150kV and produce accelerating gradients >1.2MV/m. Use of a multi-stage, fast PLIA for light ion acceleration could provide a low-cost complement to cyclotrons for the production of short half-life isotopes used for PET imaging, including carbon-11, nitrogen-13, oxygen-15, and fluorine-18.

PET radiometals for antibody labeling.

Recent advances in molecular characterization of tumors have made possible the emergence of new types of cancer therapies where traditional cytotoxic drugs and nonspecific chemotherapy can be complemented with targeted molecular therapies. One of the main revolutionary treatments is the use of monoclonal antibodies (mAbs) that selectively target the disseminated tumor cells while sparing normal tissues. mAbs and related therapeutics can be efficiently radiolabeled with a wide range of radionuclides to facilitate preclinical and clinical studies. Non-invasive molecular imaging techniques, such as Positron Emission Tomography (PET), using radiolabeled mAbs provide useful information on the whole-body distribution of the biomolecules, which may enable patient stratification, diagnosis, selection of targeted therapies, evaluation of treatment response, and prediction of dose limiting tissue and adverse effects. In addition, when mAbs are labeled with therapeutic radionuclides, the combination of immunological and radiobiological cytotoxicity may result in enhanced treatment efficacy. The pharmacokinetic profile of antibodies demands the use of long half-life isotopes for longitudinal scrutiny of mAb biodistribution and precludes the use of well-stablished short half-life isotopes. Herein, we review the most promising PET radiometals with chemical and physical characteristics that make the appealing for mAb labeling, highlighting those with theranostic radioisotopes.

The Nuclear Astrophysics program at n_TOF (CERN)

An important experimental program on Nuclear Astrophysics is being carried out at the n_TOF since several years, in order to address the still open issues in stellar and primordial nucleosynthesis. Several neutron capture reactions relevant to s-process nucleosynthesis have been measured so far, some of which on important branching point radioisotopes. Furthermore, the construction of a second experimental area has recently opened the way to challenging measurements of (n, charged particle) reactions on isotopes of short half-life. The Nuclear Astrophysics program of the n_TOF Collaboration is here described, with emphasis on recent results relevant for stellar nucleosynthesis, stellar neutron sources and primordial nucleosynthesis.

Clinical Applications of Choline PET/CT in Brain Tumors

Malignant gliomas and metastatic tumors are the most common forms of brain tumors. From a clinical perspective, neuroimaging plays a significant role, in diagnosis, treatment planning, and follow-up. To date MRI is considered the current clinical gold standard for imaging, however, despite providing superior structural detail it features poor specificity in identifying viable tumors in brain treated with surgery, radiation, or chemotherapy. In the last years functional neuroimaging has become largely widespread thanks to the use of molecular tracers employed in cellular metabolism which has significantly improved the management of patients with brain tumors, especially in the post-treatment phase. Despite the considerable progress of molecular imaging in oncology its use in the diagnosis of brain tumors is still limited by a few wellknown technical problems. Because 18F-FDG, the most common radiotracer used in oncology, is avidly accumulated by normal cortex, the low tumor/background signal ratio makes it difficult to distinguish the tumor from normal surrounding tissues. By contrast, radiotracers with higher specificity for the tumor are labeled with a short half-life isotopes which restricts their use to those centers equipped with a cyclotron and radiopharmacy facility. 11C-choline has been reported as a suitable tracer for neuroimaging application. The recent availability of choline labeled with a long half-life radioisotope as 18F increases the possibility of studying this tracer's potential role in the staging of brain tumors. The present review focuses on the possible clinical applications of PET/CT with choline tracers in malignant brain tumors and brain metastases, with a special focus on malignant gliomas.

Prediction of True Dosimetric Parameters Over the Life of the Implant in Prostate Brachytherapy

Dosimetric parameters for prostate brachytherapy have been correlated with cancer control rate as well as toxicity. D90 has the most data correlating it with cancer control. The ABS recommends post-implant quality assurance (QA) computed tomographic (CT) scans approximately one month after the procedure to verify proper dosimetry. With short half-life isotopes such as Cesium-131 (9.7 days), this one month CT may not account for volume changes from temporary prostatic edema during the majority of the dose deposition.

Radiopharmaceutical and Chemotherapy Combinations in Metastatic Castrate-Resistant Prostate Cancer: A New Beginning?

Two manuscripts in this issue of Journal of Clinical Oncology are focused on patients with bone-metastatic castrate-resistant prostate cancer (CRPC) treated with a combination of docetaxel and samarium-ethylenediaminetetramethylenephosphonic acid (Sm-EDTMP). These data are significant from a variety of perspectives, not only because they involve novel combinations of therapy, but also because they potentially lay a foundation for new approaches to treat this common and too often fatal disease. The propensity for prostate cancer to metastasize to bone is well delineated, though debate continues on why this is so. Two recent trials indicate that 84% to 92% of patients with metastatic CRPC have radiographic evidence of bone metastases. By contrast, measureable soft tissue disease (mostly nodal) was present in 39% to 44% of patients. Given the bone-tropic nature of prostate cancer metastases, and the number of men affected by this disease each year, a variety of bone-targeted agents are currently under development. The first bone-targeted agents to gain US Food and Drug Administration approval in the United States for treatment of prostate cancer were two bone-seeking beta particle-emitting radiopharmaceuticals. One of these agents (Strontium [Sr]), is a calcium homolog with a long half-life (50.5 days) and relatively high-energy average beta emission (0.58 MeV). The other is Sm-EDTMP, which binds to the hydroxyapetite crystals in blastic bone lesions and emits a low-energy beta (0.22 MeV) with a relatively short half-life (46 hours). The physical half-life of the isotopes in part determines their toxicity profile. The longer half-life of Sr translates into less reversible myelosuppression than Sm-EDTMP (which is the only notable toxicity encountered with these agents). These agents are approved for the palliative treatment of advanced prostate cancer but have had a relatively limited use. The reasons for limited use are multifactorial. Palliative agents (other than analgesics) have had relatively limited acceptance in the broad oncologic community. Systemic radiopharmaceuticals, even those quite effective in controlling cancer progression, have not been widely adopted by oncologists because of a variety of market forces. Additionally, despite some evidence to the contrary, concerns that systemic radio-isotopes may interfere with subsequent chemotherapy dosing has potentially limited use of these agents. The mechanism of action whereby bone-seeking radiopharmaceuticals exert favorable effects is currently debated. Sr and Sm-EDTMP both target the bone stroma and, as such, may be viewed as part of a new class of oncotherapies termed stromal-targeted therapies. Of note, antiangiogenic agents such as bevacizumab and thalidomide also target stromal rather than cancerous elements. Stromal-targeted agents have the advantage of targeting a relatively homogeneous stroma as compared with genetically heterogeneous cancer cells. Though direct tumoricidal effects are clearly plausible for the bone-targeted radiopharmaceuticals, effects on tumor stromal cells may be equally important. Given the vicious cycle that is hypothesized to occur between epithelial tumors and bone stroma, any effect on one cellular compartment may reverberate in another. For bone-metastatic CRPC, combinations of bone-seeking radiopharmaceuticals and chemotherapy have engendered considerable prior interest. Synergy between these two classes of agents was initially suggested in a small randomized phase II trial published by Tu et al in 2001. This trial used an innovative design in which all patients with bone-predominant metastatic disease were treated with a multi-agent chemotherapy before random assignment between Sr and doxorubicin or doxorubicin alone. Patients intolerant of, or having progression after, two to three cycles of the initial chemotherapy were randomly assigned. This design had the benefit of excluding patients with a poor prognosis, thereby enriching the randomly assigned population in patients more likely to benefit from therapy. The results were impressive in patients treated with combined-modality therapy. Overall survival was nearly 11 months longer (27.7 months) in the Sr plus doxorubicin arm as compared with the doxorubicin-alone arm (16.8 months). By comparison, the enrolled but non–randomly assigned patients (nearly one third of patients in this trial) had an 11.1 month survival, suggesting that rapid progression or intolerance of the multi-agent chemotherapy was a poor prognostic marker. Despite the initial promise of the combining a relatively noneffective chemotherapy (doxorubicin) with an US Food and Drug Administration–approved bone-seeking isotope (Sr), these results have neither been replicated nor expanded to date. The current reports by Morris et al and Fizazi et al provide another attempt to move these concepts forward. The designs of these studies are distinct. The Morris et al study makes the assumption that the docetaxel at 75 mg/m every 3 weeks is the standard of care for patients with bonemetastatic CRPC and attempts to improve on that regimen by adding dose escalated Sm-EDTMP in a repetitive fashion. Repetitive doses of this short–half-life isotope have previously been demonstrated to be well tolerated, but studies in combination with docetaxel at this JOURNAL OF CLINICAL ONCOLOGY E D I T O R I A L VOLUME 27 NUMBER 15 MAY 2

Fission Cross-Section Measurements of the Odd-Odd Isotopes 232Pa, 238Np, and 236Np

Transmutation of actinide waste into fission products could be enhanced by using resonance fission of odd-odd target materials; those of interest are 232Pa, 238Np, and 242Am. Fission cross-section measurements of two of these short-lived materials were performed at Los Alamos National Laboratory. Samples were produced by the (d,2n) reaction in the Los Alamos Ion Beam Facility followed by fast radiochemistry to separate the odd-odd target of interest. The fission cross section of the nanogram samples was measured in a high intensity pulsed neutron beam produced by 800-MeV proton spallation. Using this procedure, the fission cross sections of the 1.3-day 232Pa and 2.1-day 238Np were successfully measured in the energy range from 0.01 eV to 50 keV. The fission cross section of the relatively long-life isotope 236Np was also measured in the same system while the short half-life isotopes were being prepared. The results and resonance analysis are presented.

PILIS: Post-ISOCELE Laser Isobar Separation — a high efficiency apparatus for laser spectroscopy

A new experimental setup PILIS II has been installed on line with the ISOCELE isotope separator (IPN, Orsay). The mass-separated ions are slowed from 30 kV to 500 V and implanted on a graphite collecting disk. The atoms are then thermally desorbed at the implantation region by Nd-YAG laser pulses and selectively ionised by three laser beams. The ions created are mass identified by a time-of-flight (TOF) system. Two versions of the TOP system with accelerating voltage of 1.5 and 30 kV were used to carry out hyperfine structure measurements. With the 30 kV system we obtained an overall detection efficiency of 8.4 × 10 −5. First measurements were performed on very light gold isotopes. It has been shown that PILIS II is well adapted to study very short half-life isotopes ( T 1 2 ∼ 1 s ).

PILIS: post-ISOCELE laser isobar separation; a high efficiency apparatus for laser spectroscopy

A new experimental setup PILIS II has been installed on-line with the ISOCELE isotope separator (IPN, Orsay). The mass-separated ions are slowed from 30 kV to 500 V and implanted on a graphite collecting disk. The atoms are then thermally desorbed at the implantation region by Nd: YAG laser pulses and selectively ionized by three laser beams. The ions created are mass identified by a time-of-flight (TOF) system. Two versions of the TOF system with accelerating voltages of 1.5 and 30 kV were used to carry out hyperfine structure measurements. With the 30 kV system we obtained an overall detection efficiency of 1.4 × 10 −5. First measurements were performed on very light gold and platinum isotopes. It has been shown that PILIS II is well adapted to study very short half-life isotopes ( T 1 2 ∼ 1 s ).

The Use of the 11 C Technique to Measure Plant Responses to Herbivorous Soil Nematodes

An advantage of the short half-life (20_3 min) isotope method is the simultaneous measurement of several crucial plant processes without hindering or destroying whole-plant function. The technique was used to examine the effects of the herbivorous soil nematode, Meloidogyne javanica (Treub) Chitwood, on carbon assimilation and redistribution in tomato (Lycopersicum esculentum L.) and in two ecotypes [grazing adapted (GA) and non-grazing adapted (NGA)], of an African C4 grass, Panicum coloratum L. Preliminary tests, based on nematode eggs and galls, showed that M. javanica reproduced differentially on both P. coloratum ecotypes and suppressed GA shoot growth (weight), but had little effect on fresh root weight. In tomatoes, control plants had a higher pool of labile C in the roots than the nematode-infected plants. With P. coloratum, there were no differences in parameters between ecotypes. Plants with herbivorous nematodes had a lower stem sink activity, root activity and root transport speed than control plants. The technique proved valuable for measuring instantaneous changes in photosynthate accumulation and movement induced by herbivorous soil nematodes. Key-words: Carbon allocation, phytophages, root herbivory, soil nematodes

Design Considerations for Positron Transmission Tomograph Used for Non-Medical Applications

Design considerations for a positron transmission tomograph to be used for the crosssectional density distribution and dimensions measurements of metal or plastic sheets is described. A low cost piece of equipment constructed for performance studies of the transmission tomography is also described. The camera design consists of a small detector ring with a fixed positron active source in the middle of it. This transmission camera is independent of short half-life isotopes and a nearby cyclotron. It is possible to determine the type of an interaction between a photon and the object material and also the geometric line where the first interaction has taken place using positron annihilation coincidence detection. One of the photons in every annihilation pair escapes from the source into a known direction. A photon will scatter once or more in the object, penetrate it or become totally absorbed by it. The density distribution or the dimensions of the object material can be reconstructed from the count rates of interactions correponding to different projection angles. The detector array with a 10 cm (inner) and 40 cm (outer) diameter consisting of 34 crystals is capable of detecting an annihilation count rate of 1500 events/sμCi. Thie calculated maximum cross-sectional area of the photon beam is from 3×3 mm2 to 8.4×9.2 mm2 in the middle and 16×18 mm2 at each end of the view.

Operation and reliability characteristics of radiation loop

The radiation loop (RL-L) was first constructed at the research nuclear reactor of the Institute of Physics, Latvian SSR Academy of Sciences, in 1963, the total activity of gamma radiation source being 25 kCi (1). The radiation loop was reconstructed simultaneously with the reactor, and in 1976 its activity was 80 kCi (2). In the loop, the alloy circulates from the activity generator located in the reflector of the reactor, to the irradiators which are placed in the working chamber. Liquid metal In-Ga-Sn alloy serves as gamma carrier. Two types of irradiators are installed in the radiation loop. The irradiators of various designs might be installed and used for carrying out specific chemical, physical and biological radiation processes. A working chamber of an appropriate space is available for the irradiation of samples (2). An original hydraulic circuit with a single circulation of gamma-carrier within the activity generator and irradiators have been used in the radiation loop RL-LM (3, 4). The circuit contains no mechanical valves. A number of radiation-proof MHD devices, such as electromagnetic pumps, flowmeters, a level gauge and others have been developed and tested in order to provide maintenance. The main contribution (96%) from the total gamma radiation power is due to gamma radiation from the short half-life (54.12 min) isotope In 116m. The total activity of gamma-carrier is 80 kCi, whereas the total gamma radiation power is 1.22 kW and mean gamma quantum energy is 1.15 MeV. The maximum dose rate is 21 Mrad h .

A new assay for cytotoxic lymphocytes, based on a radioautographic readout of 111In release, suitable for rapid, semi-automated assessment of limit-dilution cultures

A new assay for cytotoxic T lymphocytes is described, of general application, but particularly suitable for rapid, semi-automated assessment of multiple microculture tests. Target cells are labelled with high efficiency and to high specific activity with the oxine chelate of 111indium. After a 3–4 h incubation of test cells with 5 × 10 3 labelled target cells in V wells of microtitre trays, samples of the supernatant are spotted on paper (5 μl) or transferred to soft-plastic U wells (25–50 μl) and the 111In release assessed by radio-autography. Overnight exposure of X-ray film with intensifying screens at −70°C gives an image which is an intense dark spot for maximum release, a barely visible darkening with the low spontaneous release, and a definite positive with 10% specific lysis. The degree of film darkening, which can be quantitated by microdensitometry, shows a linear relationship with cytotoxic T lymphocyte dose up to the 40% lysis level. The labelling intensity and sensitivity can be adjusted over a wide range, allowing a single batch of the short half-life isotope to serve for 2 weeks. The 96 assays from a single tray are developed simultaneously on a single small sheet of film. Many trays can be processed together, and handling is rapid if 96-channel automatic pipettors are used. The method allows rapid visual scanning for positive and negative limit dilution cultures in cytotoxic T cell precursor frequency and specificity studies. In addition, in conjunction with an automated densitometer designed to scan microtitre trays, the method provides an efficient alternative to isotope counting in routine cytotoxic assays.

Transintegumental Uptake of Metabolic Substrates in Male and Female Schistosoma mansoni

A new method for measuring transintegumental uptake in living schistosomes in vitro has been applied to the study of individual males and females. Uptake of a 14-C labeled test metabolite was compared to that of tritiated water (a highly diffusible reference substance). Use of the short half-life (T 1/2 = 100 min) isotope 113m-Indium, bound to EDTA (ethylene diamine tetra-acetic acid, a nondiffusible reference substance) permitted quantification of the relative amount of 14-C test substance passively adhering to the schistosoma surface. Substraction of this amount provided an estimate of net uptake. D-glucose uptake, as measured by this method, increased with time, approaching equilibrium by two min; a positive correlation between temperature and glucose uptake was also observed. Nondialyzable components in rat, human, horse and fetal calf sera did not enhance glucose uptake. In both male and female schistosomes, minimal uptakes were seen for the nonmetabolizable sugar alcohol mannitol (MW = 182). L-glucose uptake was similarly low, but high uptakes were observed in both sexes for D-glucose. In addition to confirming the stereospecificity of hexose uptake, these studies suggested our technique provides a sensitive method for measurement of both high and low uptake compounds. The uptakes of D-glucose and the L-amino acids--arginine, ornithine, lysine, histidine, phenylalanine and serine--were comparatively higher in female than male schistosomes. Slight elevations in uptake by females were observed for threonine, valine and glycine, but aspartate uptake was slightly higher in males. No dramatic male-female differences were immediately apparent for the uptakes of proline, leucine, isoleucine, tyrosine and glutamate. Schistosomal uptake of L-amino acids that are essential for vertebrates was generally higher than uptake of the nonessential amino acids.

Regional distribution of VA/Q in man at rest and with exercise measured with krypton-81m.

The regional distribution of ventilation-perfusion ratio (VA/Q) in the lung was obtained from the continuous inhalation and infusion of 81mKr. With this short half-life isotope (13 s) serial measurements were made in six young normal subjects during spontaneous breathing, with minimal radiation exposure. At rest in the upright position the apical zone had a high VA/Q, but over the lower two thirds VA/Q distribution was relatively homogeneous. There was a slight increase towards the base. During exercise at 50 and 100 W the distribution became more uniform but there was more obvious than at rest. These distributions are consistent with a zone of reduced basal blood flow (zone IV) which becomes more marked on exercise. Apical blood flow was followed during the transition from rest to exercise and recovery. There was a large (40-150%) increase within 30 s of starting to pedal at 50 W, but little change thereafter.

Clinical myocardial imaging with nitrogen-13 ammonia.

Myocardial infarcts may be clearly imaged using intravenous nitrogen-13 as carrier-free ammonia in doses of 10–30 mCi. This positron emitter is well imaged with the Nuclear Chicago HP Anger Camera with heavy collimation. The rapid blood disappearance of the agent gives good image contrast, and the short half-life and high isotope dosage give high-count density images with little radiation absorbed dose (5 mrad∕mCi total body).

Rapid Synthesis of π-Phenylglycine by Carboxylation of π-Lithiobenzylisocyanide

Abstract An expanding field of interest in nuclear medicine is the preparation of radiopharmaceuticals labelled with cyclorrn produced isotopes of short half life.1–3 In an investigation to prepare 11C-labelled amino acids we developed a new and repid synthesis for the preparation of a-phenylglycine. The preparation of other amino acids by this route is under investigation. α-Lithiobenzylisocyande4 was treated with carbondioxyde and the intermediate was hydrolysed to the amino acid. The overall yield (75–808) was accomplished in 50–70 minutes.+