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Biomedical subjects

Yukio Yamada

Publications and source records attributed to Yukio Yamada.

14 recordsLinked to original sources
PubMed2003

Simulation study of in vitro glucose measurement by NIR spectroscopy and a method of error reduction.

The effects of some important factors on the blood glucose measurements by NIR spectroscopy are investigated by numerical simulation, and a method is proposed to significantly reduce the prediction errors induced by these effects. The changes in the absorbance spectra with the changes in the glucose concentration, temperature and scattering characteristics of background tissue are obtained by a Monte Carlo simulation of light propagation for the wavelength range from 1200 nm to 1800 nm. The glucose concentration is predicted by applying a multivariate analysis to the numerically simulated spectra. This process estimates the errors in the prediction of the glucose concentration induced by the temperature and scattering changes. It has been found that only 1 C change in the temperature or only 1% change in the scattering coefficient induces about 500 mg dl(-1) or 300 mg dl(-1) errors, respectively, in the prediction of the glucose concentration. These errors can be significantly reduced to less than 20 mg dl(-1) of the glucose concentration by incorporating the effects of the temperature and scattering characteristics on the spectra to the multivariate analysis.

Algorithms↗
PubMed2003

Induction of intestinal ATP-binding cassette transporters by a phytosterol-derived liver X receptor agonist.

The nuclear receptors liver X receptor (LXR) alpha and LXRbeta serve as oxysterol receptors and regulate the expression of genes involved in lipid metabolism. LXR activation induces the expression of ATP-binding cassette (ABC) transporters, such as ABCG5 and ABCG8, which inhibit intestinal absorption of cholesterol and phytosterols. Although several synthetic LXR agonists have been generated, these compounds have limited clinical application, because they cause hypertriglycemia by inducing the expression of lipogenic genes in the liver. We synthesized derivatives of phytosterols and found some of them to act as LXR agonists. Among them, YT-32 [(22E)-ergost-22-ene-1alpha,3beta-diol], which is related to ergosterol and brassicasterol, is the most potent LXR agonist. YT-32 directly bound to LXRalpha and LXRbeta and induced the interaction of LXRalpha with cofactors, such as steroid receptor coactivator-1, as effectively as the natural ligands, 22(R)-hydroxycholesterol and 24(S),25-epoxycholesterol. Although the nonsteroidal synthetic LXR agonist T0901317 induced the expression of intestinal ABC transporters and liver lipogenic genes, oral administration of YT-32 selectively activated intestinal ABC transporters in mice. Unlike T0901317 treatment, YT-32 inhibited intestinal cholesterol absorption without increasing plasma triglyceride levels. The phytosterol-derived LXR agonist YT-32 might selectively modulate intestinal cholesterol metabolism.

ATP-Binding Cassette Transporters↗
PubMed2003

Solution of the time-dependent diffusion equation for layered diffusive media by the eigenfunction method.

An exact solution of the time-dependent diffusion equation for the case of a two- and a three-layered finite diffusive medium is proposed. The method is based on the decomposition of the fluence rate in a series of eigenfunctions and upon the solution of the consequent transcendental equation for the eigenvalues obtained from the boundary conditions. Comparisons among the solution of the diffusion equation and the results of Monte Carlo simulations show the correctness of the proposed model.

Journal Article↗
PubMed2003

Treatment of nevus using medical tattooing.

Medical tattooing is used to color skin with a pigment loss. Currently, however, a trial-and-error scheme is employed to obtain the desired color appearance of tattooed skin because prediction of the color appearance is dependent on the experiences of medical doctors. We propose a method for predicting the color appearance of tattooed skin. Two trial dyes are first injected in the area of pigment loss, and the color appearance of a third dye to be injected can be predicted using measured spectrocolorimeter data and mathematical formula. The spectrocolorimeter measures the color appearances of the skin before and after tattooing using the first two dyes, and the mathematical formula calculates the color appearance of the tattooed skin using any third dye. In the derivation of the mathematical formula, light propagation in the skin has been modeled using the modified Lambert-Beer law considering the strong scattering of light by biological tissues. The proposed method was successfully validated by a preliminary tattooing of the skin to an area with pigment loss. Predicting the color appearance of tattooed skin significantly reduces the number of trial-and-error attempts required in the current methods. Medical tattooing using this method can also be applied to treat various skin color abnormalities such as leukoderma, intradermal nevi, and reconstructed nipples.

Colorimetry↗
PubMed2002

Semi-three-dimensional algorithm for time-resolved diffuse optical tomography by use of the generalized pulse spectrum technique.

Although a foil three-dimensional (3-D) reconstruction with both 3-D forward and inverse models provide, the optimal solution for diffuse optical tomography (DOT), because of the 3-D nature of photon diffusion in tissue, it is computationally costly for both memory requirement and execution time in a conventional computing environment. Thus in practice there is motivation to develop an image reconstruction algorithm with dimensional reduction based on some modeling approximations. Here we have implemented a semi-3-D modified generalized pulse spectrum technique for time-resolved DOT, where a two-dimensional (2-D) distribution of optical properties is approximately assumed, while we retain 3-D distribution of photon migration in tissue. We have validated the proposed algorithm by reconstructing 3-D structural test objects from both numerically simulated and experimental date. We demonstrate our algorithm by comparing it with the calibrated 2-D reconstruction that is in widespread use as a shortcut to 3-D imaging and proving that the semi-3-D algorithm outperforms the calibrated 2-D algorithm.

Algorithms↗
PubMed2002

Maps of optical differential pathlength factor of human adult forehead, somatosensory motor and occipital regions at multi-wavelengths in NIR.

The optical differential pathlength factor (DPF) is an important parameter for physiological measurement using near infrared spectroscopy, but for the human adult head it has been available only for the forehead. Here we report measured DPF results for the forehead, somatosensory motor and occipital regions from measurements on 11 adult volunteers using a time-resolved optical imaging system. The optode separation was about 30 mm and the wavelengths used were 759 nm, 799 nm and 834 nm. Measured DPFs were 7.25 for the central forehead and 6.25 for the temple region at 799 nm. For the central somatosensory and occipital areas (10 mm above the inion), DPFs at 799 nm are 7.5 and 8.75, respectively. Less than 10% decreases of DPF for all these regions were observed when the wavelength increased from 759 nm to 834 nm. To compare these DPF maps with the anatomical structure of the head, a Monte Carlo simulation was carried out to calculate DPF for these regions by using a two-layered semi-infinite model and assuming the thickness of the upper layer to be the sum of the thicknesses of scalp and skull, which was measured from MRI images of a subject's head. The DPF data will be useful for quantitative monitoring of the haemodynamic changes occurring in adult heads.

Brain↗
PubMed2002

Imaging of in vitro chicken leg using time-resolved near-infrared optical tomography.

Near-infrared optical imaging gains much attention because of its noninvasiveness and deep penetration depths into tissue. Here, we report near-infrared optical tomographic imaging of an in vitro chicken leg from time-resolved measurements. The in vitro chicken leg, dipped in a cylindrical container filled with diluted Intralipid-10% solution, was imaged with a multichannel time-resolved imaging system. A two-dimensional reconstruction algorithm based on a modified generalized pulse spectrum technique has been developed to reconstruct the images of both the absorption and reduced scattering coefficients simultaneously and quickly. The results demonstrate that a simultaneous reconstruction of absorption and reduced scattering coefficients from time-resolved measurement has a potential to reveal the changes in the optical properties associated with not only the physiological information but also the anatomical structure of the organ.

Algorithms↗
PubMed2002

Improvement of image quality in diffuse optical tomography by use of full time-resolved data.

In the field of diffuse optical tomography (DOT), it is widely accepted that time-resolved (TR) measurement can provide the richest information on photon migration in a turbid medium, such as biological tissue. However, the currently available image reconstruction algorithms for TR DOT are based mostly on the cw component or some featured data types of original temporal profiles, which are related to the solution of a time-independent diffusion equation. Although this methodology can greatly simplify the reconstruction process, it suffers from low spatial resolution and poor quantitativeness owing to the limitation of effectively applicable data types. To improve image quality, it has been argued that exploiting the full TR data is essential. We propose implementation of a DOT algorithm by using full TR data and furthermore a variant algorithm with time slices of TR data to alleviate the computational complexity and enhance noise robustness. Compared with those algorithms where the featured data types are used, our evaluations on the spatial resolution and quantitativeness show that a significant improvement in imaging quality can be achieved when full TR data are used, which convinces the DOT community of the potential advantage of the TR domain over cw and frequency domains.

Humans↗
PubMed2002

Power Doppler ultrasonography-directed prostate biopsy in men with elevated serum PSA levels: an evaluation of the clinical utility and limitations.

OBJECTIVES: To determine the utility and limitations of power Doppler ultrasonography (PDU)-directed prostate biopsy in patients with elevated serum prostate-specific antigen (PSA) levels. METHODS: A total of 108 men (mean age 67.7 years, range 50 to 86) with serum PSA levels of greater than 4.0 ng/mL were assessed using digital rectal examination (DRE), gray-scale transrectal ultrasonography (TRUS), and PDU. Prostate vasculature identified on PDU was judged using a grading system. Subsequently, these patients underwent systematic six-core transperineal biopsy and additional biopsies for positive sites on DRE, gray-scale TRUS, and PDU. RESULTS: A hypervascular site and prostate cancer on PDU was identified in 43 (40%) and 40 (37%) cases, respectively. PDU-directed and systematic six-core biopsies could independently detect 36 and 30 cancer cases, respectively. The sensitivity of PDU for cancer detection was 90%, specificity 90%, positive predictive value 84%, negative predictive value 94%, and accuracy 90%. High test performance was also observed in 53 cases with serum PSA levels of 4.1 to 10 ng/mL (sensitivity 77%, specificity 88%, positive predictive value 67%, negative predictive value 92%, and accuracy 85%). These values were superior or comparable to those of DRE and gray-scale TRUS. Inflammatory reactions and prostatic calculi were probable major causes of false-positive and false-negative results on PDU, respectively. CONCLUSIONS: PDU can identify appropriate sites for biopsy and improve the cancer detection rate. However, PDU-directed biopsy does not appear to identify prostate cancer with sufficient accuracy to omit the systematic biopsy, and combined use of these methods should be preferable.

Aged↗
PubMed2002

Effect of negative air ions on computer operation, anxiety and salivary chromogranin A-like immunoreactivity.

The effects of negative air ions on computer operation were examined using a biochemical index of the activity of the sympathetic/adrenomedullary system (i.e. salivary chromogranin A-like immunoreactivity (CgA-like IR)) and a self-report questionnaire (State-Trait Anxiety Inventory, Anxiety State--STAI-S). Twelve female students carried out a word processing task for 40 min. The salivary CgA-like IR increased more than three times on the task, but the salivary cortisol did not change. The increase in the CgA-like IR level was attenuated by the exposure to negative air ions during the task. The exposure to the ions during the recovery period following the task was effective for rapidly decreasing the CgA-like IR level that had increased after the task. These effects by negative air ions were also observed using STAI-S. Task performance was slightly but significantly improved by the presence of negative air ions. These results suggest that negative air ions are effective for the reduction of and the prompt recovery from stress caused by computer operation.

Adolescent↗
PubMed2002

LDL-cholesterol and HDL-cholesterol concentrations decrease during the day.

BACKGROUND: Homogenous assays for LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) are highly accurate, with little interference from triglyceride. Using these methods, we measured postprandial LDL-C and HDL-C. Earlier studies suggested a postprandial decrease in LDL-C. METHODS: To elucidate whether LDL-C and HDL-C decrease significantly during the day, we determined daily profiles of LDL-C and HDL-C using homogeneous assays in subjects with normal coronary arteries (N; n=10), and subjects with coronary artery disease (CAD; n=23). RESULTS: In both groups, LDL-C and HDL-C were significantly lower from after breakfast until midnight than they were before breakfast. The next morning, they returned to baseline levels. The mean reduction in LDL-C was 0.09-0.13 mmol/L in N and 0.05-0.20 mmol/L in CAD, while that in HDL-C was 0.02-0.06 mmol/L in N and 0.00-0.05 mmol/L in CAD. CONCLUSION: LDL-C and HDL-C decrease significantly over the course of the day.

Adult↗
PubMed2002

Analytical approximate solutions of the time-domain diffusion equation in layered slabs.

Time-domain analytical solutions of the diffusion equation for photon migration through highly scattering two- and three-layered slabs have been obtained. The effect of the refractive-index mismatch with the external medium is taken into account, and approximate boundary conditions at the interface between the diffusive layers have been considered. A Monte Carlo code for photon migration through a layered slab has also been developed. Comparisons with the results of Monte Carlo simulations showed that the analytical solutions correctly describe the mean path length followed by photons inside each diffusive layer and the shape of the temporal profile of received photons, while discrepancies are observed for the continuous-wave reflectance or transmittance.

Diagnostic Imaging↗
PubMed1996

Assessment of Mitotic Activity in Pituitary Adenomas and Carcinomas.

Assessment of mitotic activity represents one of the oldest and most routinely used histopathologic methods of evaluating the biological aggressiveness of human tumors. In the case of pituitary tumors, however, the relevance of this approach as a means of gauging tumor behavior remains ill-defined. In this article, the relationship between the mitotic index and biological aggressiveness of pituitary tumors was evaluated in a series of 54 pituitary adenomas and 6 primary pituitary carcinomas. All tumors were fully classified by immunohistochemistry and electron microscopy; adenomas were further stratified on the basis of their invasion status, the latter being defined as gross, operatively, or radiologically apparent infiltration of dura or bone. Mitotic figures were present in 11 tumors, 10 being either invasive adenomas or pituitary carcinomas. A significant association between the presence of mitotic figures and tumor behavior was noted, as evidenced by progressive increments in the proportion of cases expressing mitotic figures in the categories of noninvasive adenoma, invasive adenoma, and pituitary carcinoma (3.9, 21.4, and 66.7%, respectively; Fisher's exact test, two-tailed, p < 0.001). The mitotic index, however, appeared to be a less informative parameter, being extremely low in all cases (mean = 0.016% +/- 0.005 [+/- SEMI). Although the mean mitotic index in pituitary carcinomas (0.09% +/- 0.035) was significantly higher than the mean mitotic index of either noninvasive adenomas (0.002% +/- 0.002) or invasive adenomas (0.013% +/- 0.005), no practical threshold value capable of distinguishing these three groups was evident. Comparison of the mitotic index with Ki-67 derived growth fractions in these tumors revealed a significant but weak linear correlation (r = 0.41, p < 0.01). These data suggest that when, mitotic figures are present, they do provide some indication of the behavior and invasive potential of pituitary tumors. For routine diagnostic purposes, however, the discriminating power of this parameter is somewhat limited, being superseded by alternative and more informative methods of growth fraction determination such as that provided by the Ki-67 immunolabeling.

Journal Article↗