[en] Emission computed tomograph wherein a pluralty of detectors surround an object to be examined so as to detect x- or gamma radiation emitted by said object. In front of each of said detectors there is provided a collimator which comprises a pair of main plates and a subsidiary plate interposed therebetween. The plates are made of a material capable of blocking penetration of the radiation therethrough and so supported as to be swingable over an angle sufficient to cover the whole of said object. The plates of all the collimators are simultaneously swung to the same side and at the same angular speed thereby to change the direction of incidence of said radiation on each of said detectors

[en] The morphological diagnosis of brain diseases has been advanced greatly by the development of X rays, computed tomography (CT) and magnetic resonance imaging. However, in the analysis of neurological disorders, it is important to know not only the structural abnormality of the brain but also regional changes in brain functions. Emission tomography (positron emission tomography (PET) and single photon emission computed tomography (SPECT)) is an analogue to autoradiography for animal experiments. The method gives regional functional parameters of the brain in vivo, such as regional cerebral blood flow, cerebral metabolism and neuroreceptor function. Through PET is an expensive and complicated procedure, it is the best method to quantify regional functions of the brain, with its excellent physical performance and with the ideal biological labels of ¹¹C, ¹⁵O, ¹³N and ¹⁸F. On the other, SPECT is far more economical than PET, though it cannot measure the metabolism of oxygen and glucose and has some physical limitations. However, it is now possible to image regional cerebral blood flow, i.e. basic examination for a functional brain study. Recently, several excellent radiopharmaceuticals for cerebral blood flow study by SPECT have become available. These are ⁹⁹Tc^m-HMPAO (hexamethylpropylene amine oxime), ⁹⁹Tc^m-ECD (ethyl cysteinate dimer) and ¹²³I-N-IMP (isopropyl-p-iodoamphetamine). Using these new radiopharmaceuticals, it is possible to study not only relative cerebral blood flow image, but also to quantify the absolute value of cerebral blood flow. Using PET and SPECT, various kinds of physiological and pathophysiological studies have been carried out and most of these have contributed to clinical medicine. These are: pathophysiological analysis of cerebrovascular diseases, identification of epileptic focus, diagnosis of dementia, and the detection and biological analysis of brain tumours. The paper presents basic issues of brain PET and SPECT, and the clinical applications for functional brain studies. (author). 59 refs, 9 figs

[en] Electron beams with high current density present a great interest for industrial and medical application because of its capacity to transport stored energy through rather long distance to the target objects without any noticeable losses. Besides, it is possible to control the beam parameters by means of external transporting conditions. In this work, the theoretical and experimental results due to additional external systems transporting investigation and focusing of electron beam propagation in the drift tube filled with plasma discharged at low pressure argon 10^-2 ∼ 10^-4 Torr were determined. The electrons movement equations in general case of nonuniform external field were analytically and numerically solved. It was obtained that the nonuniform of external magnetic field have noticeable role in transporting of electron beam. The experiments were conducted on several machines to determine the configuration influence of the magnetic field on compression (defocusing) of the beam. The experiments were realized also with application of two or three solenoids. The location of solenoids had been calculated theoretically. Experiments show possibility of compression of the beam, and increase in stability of the distribution of energy density on the irradiation area. The focusing of electron beam with initial angle speed spread tgΘ = v(perpendicular)/ v(parallel) = 0.26 (Θ ∼ 16^o) is shown. The radius of beam transporting envelope and longitudinal velocity of electrons essentially depends on the level of magnetic field gradient and the distance ratio between focuses and beam parameters. Changing of magnetic field can be governed by the energy density transferred to the beam collector. (author)

[en] The purpose of this paper is to evaluate the efficacy of PET and (C-11)-L-methionine (methionine-PET) to determine the grade of malignancy and the extent of the glioma. We examined 46 patients with cerebral glioma by using methionine-PET. Methionine-PET showed increased accumulation of (C-11)-L-methionine in the glioma regardless of the grade of malignancy. The (C-11)-L-methionine accumulated more widely than the area of abnormalities on CT scans in most cases, which were surgically confirmed that methionine-PET better delineated the extent of the glioma than CT. Methionine-PET has a great ability to assess the extent rather than the grade of malignancy of glioma

[en] We measured changes in the regional cerebral metabolic rate of glucose (rCMRGlu) using ¹⁸F-fluorodeoxyglucose and positron emission tomography for the assessment of neurotoxicity in childhood acute lymphocytic leukemia treated with high-dose methotrexate (HD-MTX) therapy. We studied 8 children with acute lymphocytic leukemia (mean age: 9.6 years) treated with HD-MTX (200 mg/kg or 2,000 mg/M2) therapy. CMRGlu after HD-MTX therapy was most reduced (40%) in the patient who had central nervous system leukemia and was treated with the largest total doses of both intrathecal MTX (IT-MTX) and HD-MTX. CMRGlu in the whole brain after HD-MTX therapy was reduced by an average of 21% (P less than 0.05). The reductions of CMRGlu in 8 patients were correlated with total doses of both IT-MTX (r = 0.717; P less than 0.05) and systemic HD-MTX (r = 0.784; P less than 0.05). CMRGlu of the cerebral cortex, especially the frontal and occipital cortex, was reduced more noticeably than that of the basal ganglia and white matter. We suggest that the measurement of changes in rCMRGlu after HD-MTX therapy is useful for detecting accumulated MTX neurotoxicity

[en] A digital model study has been developed for quantitative assessment of experimental errors in the analysis of ¹³³Xe clearance curve from the brain. A small computer synthesized a model of the clearance curve, varying combinations of fast and slow components. The curves were convoluted with Poisson random digits to simulate statistical fluctuations. Identical curves were overlapped with varying intervals to study the influence of remaining activity. The height over area method to ten minutes was confirmed to overestimate CBF by 10% to 15% with a slow component of 20 ml/100 gm per minute, and the overestimation was increased with a lower slow component. The initial slope value was shown to have a close relationship with the fast flow component when the latter was less than 100 ml/100 gm per minute. Errors due to statistical fluctuations were determined only by the initial height (H₀ cps), as the percent standard deviation was ΔH₀/H₀ in the height over area method and 2ΔH₀/H₀logH₀ in the initial slope method, where ΔH₀ = √H₀. Remaining activity caused errors of 1% to 3% in the initial slope method with an injection interval of 15 minutes. The influence of remaining activity can be eliminated with an injection interval of more than 25 to 30 minutes in the initial slope method and more than 40 minutes in the height over area method

[en] Regional cerebral blood flow (rCBF) and oxygen metabolism (rCMRO/sub 2/) were measured with a high resolution positron CT (HEADTOME-III) and 0-15 labeled CO/sub 2/, O/sub 2/ and CO gases. Seven normal volunteers and 13 cases with MCA territory ischemic infarction were performed on positron CT measurement. Remote effects from MCA territory infarction were noted in the following areas without structural damages by X-ray CT and cerebral angiography: (1) contralateral MCA territory, (2) ipsilateral thalamus, (3) contralateral cerebellar hemisphere, and (4) brainstem. Areas shown as remote effects had normal regional oxygen extraction fraction (rOEF), slightly depressed rCBF and rCMRO/sub 2/. These remote effects were demonstrated typically between 1 and 4 weeks after onset. The morphological damages were assessed as low density are with X-ray CT, and threshold levels of rCBF and rCMRo/sub 2/ were determined. Threshold of rCBF was about 12 ml/100 ml/min, and rCMRO/sub 2/ threshold was about 1.4 ml/100 ml/min in acute stroke within 1 day after onset. The areas of remote effects were indicated above these threshold values. These results suggest that (1) remote effects were not ischemic changes, (2) almost cases with MCA territory infarct showed in this effect, (3) these effects very frequently appeared in 1-4 weeks after onsets, (4) these remote effects may have connection of neural tracts, and the areas shown in remote effects may be a ''resting state''

[en] The transport and focusing of low-energy electron beams with effective transfer of stored energy in low-pressure ionized argon are investigated under the conditions of a high degree of charge neutralization in an external longitudinal magnetic field. It is shown that a nonuniform magnetic field provides the range of parameters, where it proved possible to tightly stabilize the position of the maximum of the beam on the target and, if necessary, compress the beam. It is demonstrated that the parameters of the electron beam can be controlled by selecting the configuration of the magnetic field appropriately matched to self-fields

[en] Simulation and experimental study to evaluate improvement of image quality by using time of flight (TOF) information in positron emission tomography(PET) were carried out. In computer simulation, the uniform pool phantoms of 20 cm in diameter were reconstructed through various activity by employing conventional PET algorithm and TOF-assisted PET algorithm with time of flight resolution of 0.5 ns (or 7.5 cm in spatial resolution) and 0.2 ns (3 cm) FWHM. The gains in signal to noise ratio of the TOF-assisted PET reconstruction images over the conventional PET were a factor of about 2 for 0.5 ns FWHM and 4 for 0.2 ns FWHM. The experiments were performed using a pair of CsF detectors with 0.56 ns time resolution. We prepared two phantoms, one for hot pattern and one for cold pattern. Reconstructed images were shown as follows

[en] We developed a new technique of weighted integration for the measurement of local cerebral blood flow (LCBF) and the blood-tissue partition coefficient (p) using dynamic positron emission tomography (PET) and H2(15)O. The weighted integration in the new technique is carried out on the equation of the first time integration of the Kety-Schmidt differential equation. Practically, serially accumulated images with sequentially prolonged accumulation times are weighted by two arbitrary functions. The weighting functions do not have to be differentiated because of the exclusion of the differential term in the starting equation. Consequently, the method does not require data at the end of the scan. The technique was applied to H2(15)O dynamic PET performed on four normal subjects, and was verified to provide a better signal-to-noise ratio than the previously developed integrated projection (IP) technique. Computer simulations were carried out to investigate the effects of statistical noise, tissue heterogeneity, and time delay and dispersion in arterial input function. The simulation showed that the new technique provided about a 1.4 times lower statistical error in both LCBF and p at 50 ml 100 g-1 min-1 compared to the IP technique, and it should be noted that the new technique was less sensitive to the shape of the weighting functions. The new technique provides a new strategy with respect to the statistical error for estimation of LCBF and p