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At least 19 recordsLinked to original sources
PubMed1979

A selected bibliography of biomedical and environmental applications of stable isotopes. V-2H, 13C, 15N, 18O and 34 S, 1977-1978.

The first biennial updated compilation, for the period 1977-1978, of selected references to the use of 2H, 13C, 15N, 18 O and 34S in biochemical, pharmacological, clinical and environmental applications is presented. Author and subject indices for this information are compiled to enable the reader to make further use of these references.

Bibliographies as Topic↗
PubMed1990

Direct simultaneous production of [15O]water and [13N]ammonia or [18F]fluoride ion by 26 MeV proton irradiation of a double chamber water target.

A simple double liquid chamber target was developed to provide the option for simultaneous production of [15O]H2O and either 13N or 18F using a single proton beam. Irradiation of natural water in a thin aluminium front chamber produced [15O]H2O by the 16O(p, pn)15O reaction directly. Large (0.5-1.0 Ci) doses of sterile [15O]H2O (greater than 99.95% radionuclide purity) were routinely prepared in 1 min from end of 20 microA bombardments using this target and an in-line mixed bed ion exchange column purification. Water in the thin front chamber degraded proton energies on exit to 20-18 MeV. The rear silver liquid chamber was threefold thick to 17 MeV protons in water and it efficiently produced either 13N by the 16O(p, alpha)13N reaction or [18F]fluoride ion by the 18O(p, n)18F reaction. Both target chambers were overpressurized with at least 6 atm of gas to minimize boiling/cavitation of water at high beam currents. Using hydrogen as the overpressure gas on the back chamber and an in-line anion exchange column radionuclidic cleanup process, high yields of sterile, aqueous [13N]NH3 (40-200 mCi; 20 microA) were produced directly from the back chamber at the same time that [15O]H2O was being produced from the front chamber. The combination of this target system with a cyclotron capable of generating 26-30 MeV protons provides great flexibility and simplicity for rapid, high volume production of the three best validated and most widely used radiopharmaceuticals at the present time in clinical positron emission tomography: [15O]H2O, [13N]NH3 and [18F]FDG.

Ammonia↗
PubMed1988

Radionuclide production and partial radiochemical characterization following fast neutron irradiation of mouse spleens.

When radiotherapy patients are irradiated with fast neutron beams (energies greater than 20 MeV), positron emitting radionuclides (15O, 13N, 11C) are created in their tissues. Capillary blood flow can be determined in the irradiated tissue by measuring the washout of the 15O. The chemical form of these positron emitting nuclides is important when assumptions about their transport in the development of a blood flow model are being made. In the present work, normal mouse spleen tissue was used as a model system for these studies. The mouse spleen was activated by whole mouse irradiation using the M.D. Anderson Hospital neutron beam produced by 42 MeV protons impinging on a beryllium target. Results of cellular studies and large molecule precipitation measurements (1) show that at least 65% of 15O created in situ in mouse spleen is capable of being transported out of the spleen by the blood supply, (2) suggest that 13N may be 100% biologically mobile, and (3) indicate that 11C appears to be evenly divided between a population associated with small biologically mobile molecules and a population associated with larger, biologically trapped or immobile molecules.

Animals↗
PubMed1993

Quantification and parametric imaging of renal cortical blood flow in vivo based on Patlak graphical analysis.

Patlak graphical analysis was applied to quantify renal cortical blood flow with N-13 ammonia and dynamic positron emission tomography. Measurements were made in a swine model of kidney transplantation with a wide range of normal and abnormal renal blood flows (N = 57 studies) and in 20 healthy human volunteers (N = 45 studies). Estimates of renal cortical blood flow by the Patlak method were compared to those from a two-compartment model for N-13 ammonia. In addition, estimates of renal cortical blood flow by the N-13 ammonia PET approach were compared in 10 normal human volunteers to estimates by the metabolically inert, freely diffusible O-15 water and a one-compartment model. Patlak graphical analysis estimates of renal cortical blood flow correlated linearly with the standard two-compartment model in pigs (y = -0.05 + 1.01x, r = 0.99) and in humans (y = 0.57 + 0.88x, r = 0.93). Estimates of renal cortical blood flow by O-15 water in human volunteers were also linearly correlated with those by N-13 ammonia and the Patlak graphical analysis (y = 0.71 + 0.84x, r = 0.86). Renal cortical blood flow estimates were highly reproducible both with N-13 ammonia and O-15 water measurements in humans. It is concluded that the Patlak graphical analysis with N-13 ammonia dynamic positron emission tomograpic imaging renders accurate and reproducible estimates of renal cortical blood flow. Moreover, the graphical analysis approach is 1,000 times faster than the standard model fitting approach and suitable for generating parametric images of renal blood flow in the clinical setting.

Adolescent↗
PubMed1996

Proton dose monitoring with PET: quantitative studies in Lucite.

The feasibility of using PET for proton dose monitoring is examined here in detail. First experimental studies in a Lucite phantom have been performed at the medical TRIUMF proton beamline for proton energies of 62 MeV and 110 MeV. The proton dose delivered to the phantom ranged from 16 Gy up to 317 Gy. The induced activity was analysed 20-40 min after the irradiation with a PET scanner. The obtained depth activity profiles were compared to our calculation based on a model using available isotope production cross-section data. Both the observed absolute count rates and the activity profiles were found to agree very well with this model. Effects such as proton range straggling, inelastic nuclear interactions and the energy spectrum of the emitted positrons were studied in detail and found to change the activities by 5-10%. The lateral deposition of dose in the phantom could be very well localized by the induced activity. However, the spatial correlation between dose depth profiles and depth activity profiles was found to be poor, hence the extraction of isodose profiles from activity profiles seems to be very difficult.

Carbon↗
PubMed1999

Calculation of positron range and its effect on the fundamental limit of positron emission tomography system spatial resolution.

Developments in positron emission tomography (PET) technology have resulted in systems with finer detector elements designed to further improve spatial resolution. However, there is a limit to what extent reducing detector element size will improve spatial resolution in PET. The spatial resolution of PET imaging is limited by several other factors, such as annihilation photon non-collinearity, positron range, off-axis detector penetration, detector Compton scatter, undersampling of the signal in the linear or angular directions for the image reconstruction process, and patient motion. The overall spatial resolution of the systems is a convolution of these components. Of these other factors that contribute to resolution broadening, perhaps the most uncertain, poorly understood, and, for certain isotopes, the most dominant effect is from positron range. To study this latter effect we have developed a Monte Carlo simulation code that models positron trajectories and calculates the distribution of the end point coordinates in water for the most common PET isotopes used: 18F, 13N, 11C and 15O. In this work we present some results from these positron trajectory studies and calculate what effect positron range has on the overall PET system spatial resolution, and how this influences the choice of PET system design parameters such as detector element size and system diameter. We found that the fundamental PET system spatial resolution limit set from detector size, photon non-collinearity and positron range alone varied from nearly 1 mm FWHM (2 mm FWTM) for a 10-20 cm diameter system typical for animal studies with 18F to roughly 4 mm FWHM (7 mm FWTM) for an 80 cm diameter system typical for human imaging using 15O.

Animals↗
PubMed1982

Air activation by an electron synchrotron.

The activation of 13N and 15O in air of the room housing the INS electron synchrotron was estimated. The total induced activity of 13N and 15O in the room was measured with an NaI(T1) scintillator to be 119.7 and 47.0 muCi, respectively, immediately after the operation of the electron synchrotron at 725-MeV electron energy and 176 W beam power. The operation was long enough for the steady-state concentrations of 13N and 15O to be reached. The generation of 13N and 15O was also evaluated, with only about 20% underestimation using a model calculation. In this calculation the emitted photon flux and distribution were calculated by the Monte-Carlo code, EGS, for electromagnetic cascade showers, and these photon distributions were multiplied by the (gamma, n) photoneutron reaction cross sections to calculate the production of 13N and 15O. From this analysis, it is clear that the usual method of estimating the photon spectrum at an electron accelerator, by using the forward bremsstrahlung spectrum of a thin target, is quite inaccurate when electrons are incident on a bulk structure or impinge on a magnet at a small angle of incidence. In such a case, one must consider that the photons are emitted mainly by backscattering, and have a considerably softer spectrum than the thin-target bremsstrahlung.

Air↗
PubMed1985

An evaluation of the external radiation exposure dosimetry and calculation of maximum permissible concentration values for airborne materials containing 18F, 15O, 13N, 11C and 133Xe.

To better understand the dose equivalent (D.E.) rates produced by airborne releases of gaseous positron-emitting radionuclides under various conditions of cloud size, a study of the external radiation exposure dosimetry of these radionuclides, as well as negatron, gamma and x-ray emitting 133Xe, was undertaken. This included a calculation of the contributions to D.E. as a function of cloud radii, at tissue depths of 0.07 mm (skin), 3 mm (lens of eye) and 10 mm (whole body) from both the particulate and photon radiations emitted by these radionuclides. Estimates of maximum permissible concentration (MPC) values were also calculated based on the calculated D.E. rates and current regulations for personnel radiation protection (CFR84). Three continuous air monitors, designed for use with 133Xe, were evaluated for applications in monitoring air concentrations of the selected positron emitters. The results indicate that for a given radionuclide and for a cloud greater than a certain radius, personnel radiation dosimeters must respond acceptably to only the photon radiations emitted by the radionuclide to provide acceptable personnel dosimetry. For clouds under that radius, personnel radiation dosimeters must also respond acceptably to the positron or negatron radiations to provide acceptable personnel dosimetry. It was found that two out of the three air concentration monitors may be useful for monitoring air concentrations of the selected positron emitters.

Air Pollutants↗
PubMed1995

Characteristics of the chemical forms of 11C, 13N, and 15O induced in air by the operation of a 100 MeV electron linear accelerator.

To characterize airborne radioactivity induced by the operation of high-energy accelerators, the fractions of aerosol and gaseous components, and the chemical forms of 11C, 13N, and 15O produced in the air of a target room of a 100 MeV electron linear accelerator were studied. Measurements of radioactivity using a particulate air sampling filter and a gas flow-through ionization chamber showed that more than 98% of 11C, 13N, and 15O were present as gaseous forms. Their chemical forms, detected by means of radio-gas chromatography, were 11C as CO2; 13N as N2 and NO; and 15O as O2 and NO. Machine operating conditions, which affect the compositions of the induced radionuclides and of their chemical forms, and the resulting effect on the estimation of internal doses are discussed.

Aerosols↗
PubMedDate not supplied

Absorbed dose comparison: positron emitters 11C, 13N, and 15O versus gamma-ray emitters.

Absorbed doses were calculated or taken from the literature for various compounds of 11C, 13N, and 15O, and compared to those of presently gamma-ray-emitting nuclear medicine radiopharmaceuticals. As a rule of thumb, the doses per millicurie of the injectable positron-emitting compounds are of the same order of magnitude as the dose per millicurie of 99mTc compounds. The absorbed doses from the injectable positron emitters are nearly one or more orders of magnitude lower on a per millicurie basis than those from the other injectable gamma emitters that were investigated.

Carbon Radioisotopes↗