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Biomedical subjects

S Kan

Publications and source records attributed to S Kan.

At least 19 recordsLinked to original sources
PubMed1992

Q optimization of RF inductors for use in NMR probes.

Radiofrequency inductors are important components of many NMR probe circuits, and a high quality factor Q of these inductors is necessary to achieve good signal-to-noise ratios. We have designed high Q inductors using an optimum coil diameter to coil length ratio of the order of 2.54. The latter was calculated from Lorenz's inductance formula for a solenoid and checked experimentally using a series of inductors of various diameters and lengths. The results show good agreement between theory and practice.

Humans↗
PubMed1992

Single-input double-tuned Foster-type probe circuit.

Synthesizing two different values of inductance from a given sample coil for use in a single-input double-tuned circuit is possible by means of three extra LC elements. A detailed analysis with derived equations shows how to calculate the circuit component values and what to expect from this kind of probe. It also derives the upper limit of the trap coil/sample coil inductance ratio beyond which no solution exists to double-tune the 31P-1H probe. The general expression for the channel efficiency shows that the latter is a function not only of the inductance of the coils, but also of their quality factor and of the operating frequencies. A numerical example is given illustrating good agreement between experiment and theory provided high quality rf capacitors are used.

Humans↗
PubMed1992

[Primary intracranial melanoma: a case report].

A rare case of primary intracranial melanoma is presented in a 34-year-old man with initial symptoms of persistent headache. In magnetic resonance imaging(MRI), this case had all the characteristic findings of intracranial melanoma which had been reported previously. In 123I-iodoamphetamine-single photon emission CT (123I-IMP-SPECT), abnormal accumulation of 123I-IMP was recognized in early and late phase imaging, which was very specific to the lesion. This is the first report of 123I-IMP-SPECT performed on a primary intracranial melanoma. Tumor mass originated from pia mater was surgically resected, but the dissemination of tumor cells was recognized macroscopically. Pathological examination of the specimen showed very little malignant changes of melanoma cells, which was in contrast to the previous reports. Although, no standard chemotherapy of the primary intracranial melanoma has been established, DAV therapy to the dissemination of tumor cells into the subarachnoid space, and intravenous administration of interferon-beta were performed in this case. Methods of differential diagnosis and treatments of primary intracranial melanoma are reviewed and discussed.

Adult↗
PubMed1992

[Experience with BALT magic catheter (PURSIL catheter); especially investigation about advantage, disadvantage and the applications].

BALT magic catheter (PURSIL catheter) is a new catheter which is more flexible and plaint than the TRACKER-18 catheter because its mid-section and distal portion are made from polyurethane and silicon rather than polyethylene. Because the PURSIL catheter is flexible, it cannot be inserted with a guide wire, although it can be inserted into circulation during injection of contrast medium. Its inner diameter, 3.5mm, is smaller than that (5mm) of the TRACKER. There are few reports of embolization with the PURSIL catheter, and these describe only embolization using adhesive liquid embolus material. Embolization using small particles through the PURSIL catheter has never been reported. We report the catheterization using the PURSIL catheter of 26 arteries in 15 patients. The catheter was used for superselective angiography to clarify feeder and amytal tests in 5 patients with AVM, and embolization using PVA particles (150-250 microns) was performed in 1 patient with AVM, 3 patients with dural AVM, 4 cases with meningioma and 1 patient with vertebral aneurysm. Small PVA particles were easily injected without resistance through this catheter. In only one patient with dural AVM, was catheterization with this catheter not successful, and that was because the distal portion of the internal maxillar artery was extremely tortuous because of severe atherosclerosis. No complications associated with the use of this catheter were observed. We think that the greatest advantage of this catheter is the safety afforded by not using a guide wire. A disadvantage of this catheter is that, because of its small inner diameter, only small particles, or liquid embolus material can be injected through it.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

[Preoperative embolization for meningiomas using PVA particles].

Preoperative embolization for highly vascularized and large meningiomas is an indispensable technique for facilitating their surgical removal by decreasing blood loss during the operation. This is a report of 4 large and highly vascularized meningiomas in the skull base, on which embolization of feeders was performed preoperatively by PVA (Polyvinyl alcohol foam) particles (150-250 micron produced by INGENOR CO, Paris) and small strips of gelfoam (0.5 x 0.5 x 3-5mm). Under EEG monitoring, Isosorbide dinitrate was used for prevention and relief of vascular spasm. Lidocaine injection tests (Xylocaine 2%: 50mg mixed in equal volumes with Iopamiron 300) were performed for checking before embolization. In the intracranial portion, standard taper steerable guide wire was changed to seeker flexible soft-tip guide wire. In two cases, the meningioma was located in the medial part of the sphenoidal ridge. In the other two cases, one meningioma was in the lateral part of the sphenoidal ridge and the other was in the olfactory groove. In all 4 cases, we successfully performed embolization without complication. In one case, we had to perform embolization twice, because of revascularization detected by angiography 3 weeks after the first embolization. In this latter case, we had performed central embolization only, by using PVA particles, having left feeder without occlusion (peripheral embolization) using gelfoam. The result suggested that it was also necessary to perform peripheral embolization especially if the tumor is fed by large tortuous and irregular abnormal vessels. Peripheral embolization may prevent PVA particles from washing out and causing progressive thrombosis by PVA particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Effect of vitamin E on the accumulation of fluorescent material in cultured cerebral cortical cells of mice.

The effect of vitamin E on the accumulation of lipofuscin-containing fluorescent material in the mouse cerebral cortical cells in primary culture was studied. Fluorescent material was extracted in ethanol:diethylether (3:1) and autofluorescence intensity of the extracts was measured by a spectrofluorophotometer. Although vitamin E at the concentration of 0.005 IU/ml was not effective, 0.01 IU/ml vitamin E inhibited the accumulation of fluorescent material. Fluorescent material accumulation was reduced to 76.3-86.4% of the control level in 6-, 12-, or 18-day treatment of 0.01 IU/ml vitamin E. High doses of vitamin E (0.05 or 0.1 IU/ml) were toxic for cultured cells. Ethanol, the vehicle of vitamin E, at the final concentration of 0.005% was also effective on the reduction of fluorescent material accumulation (81.0% of the control level at 18 days). The inhibitory effects of vitamin E as well as ethanol on the accumulation of fluorescent material in cultured cells are explained by their nature as free radical scavengers.

Animals↗
PubMed1991

Magnetic resonance imaging of the brain in patients with migraine.

Magnetic resonance imaging (MRI) was studied in 91 patients with migraine and in 98 controls. Risk factors known to cause MRI lesions were carefully examined. In 36 patients with migraine (39.6%), small foci of high intensity on T2-weighted and proton-density-weighted images were seen in the white matter. Of patients with migraine who were less than 40 years old and without any risk factor, 29.4% showed lesions on MRI; this was significantly higher than the 11.2% for the group of age-matched controls (n = 98). The lesions were distributed predominantly in the centrum semiovale and frontal white matter in young patients, but extended to the deeper white matter at the level of basal ganglia in the older age group. The side of the MRI lesions did not always correspond to the side of usual aura or headache. Migraine-related variables such as type of migraine, frequency, duration or intensity of headache or consumption of ergotamine showed no significant correlation with the incidence of MRI abnormalities. Our data indicated that migraine may be associated with early pathologic changes in the brain.

Adult↗
PubMed1990

Multicentric intracranial fibrous xanthoma--case report.

Intracranial fibrous xanthoma is extremely rare; only 11 cases have been reported so far. The authors report a case of multicentric intracranial fibrous xanthoma. Precontrast computed tomographic (CT) scans revealed a left frontal subdural mass, which had previously been diagnosed as a chronic subdural hematoma at another hospital. However, operation disclosed no hematoma but a granulomatous tumor. The biopsied specimen was histologically diagnosed as fibrous xanthoma. Postoperative postcontrast CT scans showed intense homogeneous enhancement at the clival and the left frontal regions, both of which appeared as iso- to low-intensity areas on T1-weighted magnetic resonance (MR) images and as low-intensity areas on T2-weighted MR images. She gradually recovered by conservative treatment but suddenly died of cerebral infarction. Autopsy revealed fibrous xanthomas in the left frontal and the clival regions. This is the first report of the use of MR imaging for intracranial fibrous xanthoma, and its features differ from those of common intracranial parenchymal tumors, MR imaging can be helpful in the diagnosis of this tumor.

Aged↗
PubMed1988

Parallel-plate split-conductor surface coil: analysis and design.

A split-conductor circular parallel-plate resonator with one end shorted to ground can be used to one's advantage as a surface coil for NMR imaging experiments. It can be easily constructed by a printed-circuit method and possesses a relatively high loaded Q with negligible frequency detuning. From the proposed equivalent circuit, an equation was derived that relates the self-resonance frequency of the resonator to the split distance measured from a reference point. An example of a 101-mm-diameter surface coil operating at 26 MHz for 31P in vivo spectroscopy is given to illustrate the concordance between calculated and experimental results. Complementary equations and formulas are also included to assist researchers in designing their own antennas to meet specific requirements.

Magnetic Resonance Imaging↗
PubMed1988

Transmission dynamics and estimates of malaria vectorial capacity for Anopheles balabacensis and An. flavirostris (Diptera: Culicidae) on Banggi island, Sabah, Malaysia.

Holoendemic malaria transmission in two small isolated forest communities and a coastal village was studied by (1) all night human bait collections of Anopheles species from inside and outside houses and (2) buffalo-biting and CDC light-trapping catches during March and November 1984. During the same period thick and thin blood films were collected from the human population, and spleen rates were determined in children from two to nine years of age. Using both the immunoradiometric assay (IRMA) and the dissection technique, more sporozoite-positive infections were detected in An. balabacensis and An. flavirostris in November than in March. IRMA confirmed the presence of Plasmodium falciparum sporozoites. An average of 76.2% of the An. balabacensis population lived long enough to have reached a point where infectivity with P. falciparum was possible in November. Although fewer than five adult females bit humans per night at any time, a resident could theoretically have received more than 160 infective bites in one year. A high frequency of feeding on humans, coupled with increased anopheline life expectancy, contributed to high estimates of falciparum malaria vectorial capacity (number of infections distributed per case per day); for An. balabacensis (1.44-7.44 in March and 9.97-19.7 in November) and for An. flavirostris (0.19-5.14 in March and 6.27-15.8 in November). These high values may explain the increased malaria parasite rates obtained from at least two forest communities. Correlation between actual and calculated rates of gametocytaemia was poorest in Kapitangan due to inadequate sampling of the human population. In Banggi island, malaria is stable and holoendemic, and the population enjoys a high degree of immunity.

Animals↗
PubMed1988

Minute esophageal granular cell tumor: a case report with immunohistochemical and ultrastructural examination.

A small granular cell tumor (GCT) of the esophagus, which developed in a 44-year-old Japanese man and was removed by endoscopic polypectomy, is presented. Histopathologically, the tumor, located in the submucosa, was composed of uniform neoplastic cells with nuclei and abundant round or oval cytoplasm containing eosinophilic granules. An immunohistochemical examination showed positive reactions with S-100 protein, especially the beta subunit, and neuron specific enolase in the neoplastic cells. Electron microscopic observation revealed abundant electron-dense or light granules and myelin-like structures in the cytoplasm. These findings support the concept that esophageal GCT is derived from Schwann cells.

Adult↗