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Biomedical subjects

K Doi

Publications and source records attributed to K Doi.

At least 775 records · Page 43Linked to original sources
PubMed1982

Investigation of the performance of antiscatter grids: Monte Carlo simulation studies.

Monte Carlo methods have been applied to the study of the performance of antiscatter grids in radiography. Photon histories for imaging with a 20 cm thick water phantom irradiated with an 80 kV x-ray spectrum were generated by Monte Carlo simulation. The scattering and absorption of the photons transmitted from the phantom were traced in the grid. Grids were evaluated with strip densities ranging from 10 to 67 lines/cm, grid ratios from 6 to 15, and lead-to-interspace ratios from 1/9 to 1/2. The contrast improvement factor and the Bucky factor were used as the benefit and cost indicators, respectively, for evaluation of the grids. The dependence of these factors on the grid ratio, lead-to-interspace ratio, strip density, lead content, and interspace material was investigated. The results indicate that high-strip-density grids with thin lead strips and high grid ratios can provide higher contrast improvement factors than are achieved with low-strip-density grids, without an increase in patient exposure. This theoretical approach is useful for the prediction and development of optimal antiscatter grids for radiographic procedures.

Radiography↗
PubMed1982

X-ray tube focal spot sizes: comprehensive studies of their measurement and effect of measured size in angiography.

Thirty-two focal spot sizes of four x-ray tubes were measured by the pinhole, star pattern, slit, and root-mean-square (RMS) methods under various exposure conditions. The modulation transfer functions (MTFs) and line spread functions (LSFs) were also determined. The star pattern focal spot sizes agreed with the effective sizes calculated from the frequencies at the first minimum of the MTF within 0.04 mm for large focal spots and within 0.01 mm for small focal spots. The focal spot size determined by the slit method was approximately equal to the width of the LSF at the cutoff level of 0.15 +/- 0.06 of the peak value. The RMS method provided the best correlation between the measured focal spot sizes and the corresponding image distributions of blood vessels. The pinhole and slit methods tended to overestimate the focal spot size, but the star pattern method tended to underestimate it. For approximately 90% of the focal spots, the average of the star and slit (or pinhole) focal spot sizes agreed with the RMS focal spot size within +/- 0.1 mm.

Angiography↗
PubMed1982

The energy-dependent behavior of noise Wiener spectra in their low-frequency limits: comparison with simple theory.

The Wiener spectra of five screen-film systems were studied as a function of monoenergetic x-ray energy. These spectra, in their low-frequency limits, were seen to depend linearly on x-ray energy. The Wiener spectra also decreased in magnitude as the incident x-ray energy exceeded that of the screen phosphor K absorption edge. The agreement of these experimental findings with simple theoretical predictions is discussed.

Models, Theoretical↗
PubMed1982

Thermogenic response to glucagon in cold-acclimated mice.

Heat production after injection of glucagon and norepinephrine was measured in warm- and cold-acclimated mice. Glucagon and norepinephrine in a dose of 100 microgram/100 g caused a marked increase in oxygen consumption. Heat production after administration of glucagon and norepinephrine was significantly potentiated by cold acclimation. A significant positive correlation was observed between the increase in oxygen consumption after injection of glucagon or norepinephrine and the weight of brown adipose tissue in warm- and cold-acclimated mice. These findings indicate that glucagon is a calorigenic hormone in mice and its effect is potentiated by cold acclimation possibly due to an activation of thermogenic mechanism(s) in brown adipose tissue.

Acclimatization↗
PubMed1982

Thermal and metabolic responses of temperature-acclimated rats during cold and heat exposures.

Some endocrine and metabolic responses to acute cold and heat exposures were observed in rats acclimated to cold, heat, or both cold and heat. Rats exposed to both cold (12 hr, 5 degrees C) and heat (12 hr, 34 degrees C) for 4 to 5 weeks (CHA) showed less fall of colonic temperature (Tc) in the cold (-5 degrees C) than heat-acclimated rats (34 degrees C, 4 to 5 weeks) (HA) and warm controls (WC), but a greater fall than cold-acclimated rats (5 degrees C, 4 to 5 weeks) (CA). CHA possessed a larger quantity of interscapular brown adipose tissue and showed greater cold-induced oxygen consumption (VO2) than WC and HA but less than CA. Blood glycerol levels rose similarly in all groups in the cold, while the increase in blood free fatty acids (FFA) levels was significantly greater in HA and smaller in CA than in WC and CHA. Acute cold exposure caused the elevation of plasma glucagon level in WC and HA, but not in CA and CHA. It lowered plasma insulin levels in HA, and the insulin/glucagon molar ratio (I/G) in WC, HA, and CHA. All groups showed the same increases in Tc during acute heat exposure (34 degrees C). However, the heat-induced increase in VO2 was greater in WC than in HA, CA, and CHA. Blood metabolite levels were not affected by acute heat exposure in all groups. Plasma glucagon levels decreased in CHA, while plasma insulin levels increased in WC and CA. I/G increased in WC and CHA. These results indicate that thermal and metabolic responses would be modified by previous exposures to cold, heat, and cold-heat.

Acclimatization↗
PubMed1982

Microsurgical thumb reconstruction--report of six cases with a wrap-around free flap from the big toe and an iliac bone graft.

Six patients with amputated thumb had reconstruction of the thumb using a free wrap-around flap from the big toe with a free autologous iliac bone graft. The wrap-around flap was based on the dorsalis pedis and the first dorsal metatarsal arteries and included the skin of the lateral two-thirds of the hallux with the nail and the nail-bed of the toe and the lateral digital nerve. This method reconstructed in one stage a thumb that closely resembled a normal thumb in girth, length and appearance without having to sacrifice a whole toe. Compared to a toe to thumb transfer, the appearance of the reconstructed thumb was superior. Although the reconstructed part did not have any joint, the sensibility was superior and the functional result was excellent. The donor toe defect however required a skin flap cover from a adjacent toe and split skin grafts. Some degree of graft resorption occurred in all cases. It is therefore advisable to harvest as big a graft in diameter as could possibly be accommodated within the width of the wrap-around flap without tension.

Adult↗