A simple method has been developed for the production of13NN and15OO by proton irradiation of aqueous solutions. 90 mCi of13NN was obtained in a 200 ml of He by using 1.0M NH4Cl solution at pH 11 as the target with 10 min irradiation of 15 MeV, 10 μA protons. 80 mCi/min of15OO was continuously obtained in a 200 ml of O2by using pure water as the target with 40 MeV, 2μA protons. The radiochemical purity of these short-lived radioactive gases obtained by this method was >99.9% by passing through a single absorber.
Below the critical concentration of polyvinyl alcohol, the effect of inorganic acids or alkalis on gelation of polyvinyl alcohol aqueous solution was investigated by color development with iodine after γ-ray irradiation. The absorbances of the polyvinyl alcohol-iodine complex decreased remarkably in the presence of nitric or perchloric acid. These acids decompose and form oxygen or hydrogen peroxide which oxidize the polymer and leads to a fading of the color. On addition of sulfuric, phosphoric and hydrochloric acids, the absorbances decrease in the order that agrees with that of the acidity of these acids at the same molarity. In the alkaline solution the absorbances decrease by the addition of sodium hydroxide and aqueous ammonia in the order that agrees with that of the basicity of these alkalis. These results indicate that the gel formation is caused by. the radiolysis of water. As a result of chemical analysis, these additives are considered not to be attached to the polymer.
A large area multi-crystal positron camera has been constructed for diagnostic investigations with cyclotron-produced short-lived positron emitters. The camera has two identical opposing detectors each consisting of a square array of 14×14 small NaI (Tl) crystals (20 mmφ×38 mm) viewed by an array of 112 photomultiplier tubes (38 mmφ) . The detectors have a useful area of 39×39 cm2. The electronic system is simplified by grouping the photomultiplier timing signals into each row and each column in the tube array. The fast coincidence operation between the detectors is performed with the grouped signals in row-row and column-column mode, and finally each crystal is in coincidence with 25 crystals in the opposite detector to form 4096 coincidence crystal pairs in total. The system processes the coincidence data which are stored in one of two 4K word-18 bit IC memories, and offers a 64×64 digital image focused on a plane between the detectors on a CRT monitor during and after the data acquisition. The camera has the spatial resolution of 8 mm (FWHM) at the midplane and the uniformity of the sensitive field is ±7%. The variation of sensitivity in the direction perpendicular to the detector plane is less than 1%. The efficiency of the camera is about 18 cps/μCi for a 15×15 cm2 plane source in air with a detector separation of 50 cm. The data rate of the system reaches about 120 kcps at the maximum, but image distortion is observed at the coincidence rate more than about 30 kcps. An estimation indicates that only a few percent increase in accidental coincidence rate is resulted from the coincidence operation in the row-row and column-column mode.
A new method for the quantification of shunting is discussed experimentally and clinically. Following quantitative injection of99mTc-MAA to a patient in a supine position, whole body counting was obtained by summing up the counts of linear scanning with our Medical Universal Human Counter. For linear scanning, two detectors with a slit-field collimator are placed symmetrically above and two below the table. The table of the scanning bed was moved automatically along the longitudinal axis at the speed of 40 cm/min. Isoresponse curves of this system in air and chest phantom were made with a window of 140 keV±2%. Whole body linear scanning was performed with the same window in the patients with cyanotic heart diseases. Mean transmission rate (MTR) of99mTc-MAA from the lung was calculated in healthy subjects. Good correlation was obtained between ln (MTR) and chest thickness (X) of the subjects (γ=-0.95, p<0.001) . Linear regression was ln (MTR) =-0.035X+0.024 Absorption of γ-rays in the chest was corrected by multiplying 1/MTR Right to left shunt rate was calculated as follows: R to L shunt rate=N0-Na/MTR/N0×100 (%) N0: Counts of the administered dose in air Na: Counts of the lung in the whole body linear scan MTR: Mean transmission rate in the patient Good correlation between linear scan method and cardiac catheterization was noted. This method is safe and can be simply performed at rest and even though on exertion.
As81mKr is a radioactive noble gas which has a very short half-life of 13 seconds, it leads no environmental contamination in a laboratory room. Because of its low radiation dose in the human body, it had many merits in routine tests of the inhalation and perfusion scintigraphy, which were very useful extremely in infants, old men and severe patients in need of cooperation. The studies with81mKr were, either, useful as a load test, since these could repeatedly readily, evaluate the ventilation and perfusion dynamics before and after administration of drugs and show the distribution of the ventilation and perfusion correspond to the various lung volume level.