Biomedical subjects
Publications and source records attributed to S Tanada.
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A whole-body, multislice positron emission tomograph, Positologica III, has been constructed based on a sampling method "positology." The scanner consists of four continuously rotating detector rings with 192 bismuth germanate (BGO) crystals (12 X 24 X 24 mm) arranged at irregular intervals along each ring, providing seven tomographic images at 16 mm intervals simultaneously, for a total axial coverage of 12 cm. The patient aperture is 54 cm in diameter, and the field of view is 40 cm in diameter and 12 cm in depth. Newly developed dual photomultiplier tubes are used with 12 mm wide BGO crystals to provide a packing ratio of 0.894. The spatial resolution at the center of the field is 7.6 mm full width at half maximum, and 2.5 mm hot spots were delineated in the Derenzo phantom. The sensitivity for a 20 cm diameter cylindrical phantom is 34.2 and 52.2 kcps/muCi/ml for true planes and cross planes, respectively. In clinical studies the posterior papillary muscle of the heart was visualized in the myocardial scan, and the lung behind the pulmonary artery was also visualized in the pulmonary ventilation scan. These results suggest that our machine has sufficient resolution for most of the clinical studies of the body.
A microsphere model is sometimes used when calculating cerebral blood flow (CBF) using N-isopropyl-p-[I-123]iodoamphetamine (IMP), and is based on the assumption that there is essentially no washout of IMP. The validity of a microsphere model was investigated by comparison with the values of CBF obtained by means of a model which takes into consideration the diffusion of IMP from brain tissue to blood (nonmicrosphere model). When calculating CBF by the latter model, the look-up table method was used with expression of the double integral in the model equation by the recursion relations, a method which is useful for obtaining pixel-by-pixel values. The average rate constants for diffusion from brain to blood of gray and white matter were 0.021 and 0.0016 min-1, respectively. The values of CBF obtained by applying a microsphere model to the data acquired from 0 to 3.2 min after IMP injection were overestimated by approximately 23% compared with those values obtained using a nonmicrosphere model. This is considered to be due to the effect of the IMP activity in the vascular space. Values obtained using the data acquired from 3.2 to 6.4 min were underestimated by approximately 15%. When the values of CBF obtained by a microsphere model were interpolated, they became nearly equal to those obtained using a nonmicrosphere model at about 4 to 5 min after injection. This is suggested to be the reason why the underestimation due to diffusion from brain to blood is cancelled out by the overestimation due to the IMP in the vascular space. Our preliminary results suggest that it is necessary to take the diffusion of IMP from brain tissue to blood into account for the quantification of CBF using IMP.
Though unilateral blood distribution of the vertebral artery has not been studied in humans, it is significant when considering the ischemic events especially embolic occlusion in vertebrobasilar system. To clarify the blood distribution, Krypton-81m was continuously infused into the vertebral arteries of 10 patients. Radioactivity was recorded by a rotating gamma camera. The perfusion images, reconstructed by computer in the transaxial plane, were classified according to whether the distribution was equal, or predominantly unilateral. Overlapping of blood supply from each vertebral artery was studied. In addition, the perfusion from one of the vertebral arteries revealed four distribution patterns with respect to laterality. A) ipsilateral; B) contralateral; C) bilateral; D) mosaic. Images obtained following perfusion of the vertebral artery show less uniformity compared to that of the internal carotid artery, suggesting a complicated vascular supply of the vertebral basilar territory. This complex distribution can be classified by the use of continuous infusion of Krypton-81m.
Fourier phase analysis has generally been used to investigate asynchronous emptying and filling in various heart diseases. A potential limitation of this form of analysis is curve fitting error, since a truncated Fourier series may not adequately describe the shape of a time-volume curve (TVC) and thus may produce errors in indices calculated from the fit. To overcome this problem, we developed a new method using Hilbert transform. Using Hilbert transform, the instantaneous phase (IP) curve was calculated directly from the TVC obtained from multigated cardiac blood pool images. Four parameters [time to maximum IP [T(max)], time to 0 in IP[T(0)], time to minimum IP[T(min)], and time from 0 to minimum IP [T(min-0)]] were extracted from the IP curves for each pixel, and functional images were constructed in 40 patients with ischemic heart disease (IHD), 16 with hypertrophic cardiomyopathy (HCM), 3 with dilated cardiomyopathy (DCM), and 7 normal controls (N). The standard deviations (SD) of these parameters were then calculated for the left ventricle. In IHD patients with a left ventricle ejection fraction (LVEF) of less than 50% and in DCM, the SDs of all parameters were significantly higher than in group N. In IHD patients with an LVEF of greater than 50%, the SDs of T(min), T(0), and T(min-0) were significantly higher than in group N, but there was no significant difference in the SD of T(max). In HCM patients, the SDs of T(min) and T(min-0) were significantly higher than in group N, suggesting the presence of asynchronous filling. In conclusion, this method appears to be promising for the quantitative analysis of asynchronous emptying and filling in various heart diseases.
A tomographic study of regional cerebral blood flow and hemodynamics was performed on 25 patients with cerebrovascular diseases by selective continuous infusion of krypton-81m (Kr-81m). Kr-81m single photon emission computed tomograms were superimposed on X-ray computed tomograms to assess topographically the perfusion of the entire brain. Study of cerebrovascular diseases using this method showed: (1) regional cerebral blood flow change; (2) perfusion distribution change; (3) the route by which blood reached the brain or the obstructed artery proximal to the circle of Willis; (4) development of a collateral system and its actual function; and (5) efficacy of surgical bypass after extracranial-intracranial anastomosis. This method is especially useful in hemodynamic assessment in patients with ischemic cerebrovascular disease.