Correlation of bioscintigraphy, contrast venography, and iodine-125 fibrinogen uptake test.

In 40 patients believed to have deep venous thrombosis, bioscintigrams performed with I-123 fibrinogen were available for comparison with either contrast venograms or I-125 fibrinogen uptake tests. If either contrast venography or the fibrinogen uptake test was accepted as a standard for comparison, the accuracy of bioscintigraphic imaging was 90%. Most discrepancies between the procedures could be interpreted as due to heparin treatment, although bioscintigrams often were positive in patients treated with heparin for a short interval of time. Additionally, bioscintigrams provided information to distinguish venous thrombosis from other sources for local accumulation of radioactivity. Bioscintigraphy seems to be a promising noninvasive method for the detection of deep venous thrombosis of the lower extremities.

Nitrogen-13-labeled nitrite and nitrate: distribution and metabolism after intratracheal administration.

Radioactive nitrogen-13 from nitrite (NO2-) or nitrate (NO3-) administered intratracheally or intravenously without added carrier to mice or rabbits was distributed evenly throughout most organs and tissues regardless of the entry route or the anion administered. Nitrogen-13 from both anions was distributed uniformly between plasma and blood cells. We found rapid in vivo oxidation of NO2- to NO3- at concentrations of 2 to 3 nanomoles per liter in blood. Over 50 percent oxidation within 10 minutes accounted for the similar nitrogen-13 distributions from both parent ions. The oxidation rates were animal species-dependent. No reduction of 13NO3- to 13NO2- was observed. A mechanistic hypothesis invoking oxidation of 13NO2- by a catalase-hydrogen peroxide complex accounts for the results. These results imply a concentration dependence for the in vivo fate of NO2- or nitrogen dioxide.

Neutron energy spectra and dose-distribution spectra of cyclotron-produced neutron beams.

Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques and the dose distribution was measured using a 1/2 in. spherical "tissue-equivalent" proportional counter filled with "tissue-equivalent" gas.

Fate and distribution of inhaled nitrogen dioxide in rhesus monkeys.

The intra- and extrapulmonary distributions of inspired nitrogen dioxide (NO2) were studied by exposing rhesus monkeys to air mixtures containing concentrations slightly greater than ambient (0.56 to 1.71 mg per m3, or 0.30 to 0.91 ppm) of NO2 labeled with tracer quantities of NO2 containing nitrogen-13 dioxide (13NO2). The 13NO2 (half-time, 10 min) was synthesized by the oxygen-16 (P, alpha)13N nuclear reaction in an isochronous cyclotron. The intrapulmonary location and concentration of the inspired 13NO2 was detected continuously by external monitoring of the annihilation radiation consequent to positron emissions from disintegrating 13N. The 13N concentration of arterial blood was also measured at intervals, and the blood values were correlated with those from the lung. Chemical measurements of NO2 concentration in inspired and expired air were performed by the Saltman method. Control studies were performed with xenon-125 (125Xe) (halftime, 17 hours). The results demonstrated that 50 to 60% of the inspired pollutant was retained by the primate during quiet respiration; the gas was distributed throughout the lungs. Once absorbed, NO2 or chemical intermediates remained within the lungs for prolonged periods after cessation of exposure, and dissemination of the pollutant or its derivatives to extrapulmonary sites occurred via the blood stream. Indirect evidence indicated the probable reaction of NO2 with water in the nasopharynx and lungs to form nitric and nitrous acids. The reaction of these acids with pulmonary and extrapulmonary tissues probably accounts for the biologic toxicity of NO2.

Production and characteristics of 125Xe: a new noble gas for in vivo studies.

Radionuclides of the noble gases are extensively used to assess ventilation and blood flow in clinical and investigative studies. Xenon-133 is most commonly used but is not optimal for these in vivo studies. Xenon-125 has better physical characteristics and can be produced with a cyclotron by a 127I(p,3n)125Xe reaction; this reaction results in a maximum of 25 mCi/gm/cm2/muA-hr for 31-MeV protons. Under actual production conditions, 11 mCi/muA-hr were collected. Xenon-125 decays by electron capture with a 17.2-hr half-life and contributes less radiation per dose of radioactivity than 133Xe. The radiation dose to the lungs from 133Xe and 125Xe is 5.0 and 1.8 mrads/mCi-min, respectively. The radiation dose per usable photon for 125Xe is only 0.3 of 133Xe. The principal photons of 125Xe, 188 keV (55%) and 243 keV (29%), are more intense and are in an energy range that is more advantageous for imaging than the 81 keV (35%) of 133Xe. These physical properties of 125Xe result in better spatial resolution at the same information density and with less radioactivity administered to the patient. Phantom studies showed that 12.7-, 9.5-, and 6.4-mm lead bars were resolved with 125Xe using a 410- keV diverging collimator wheras only the 12.7- and 9.k-mm lead bars were resolved using 133Xe and either a 410-keV or 140keV diverging collimator.