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Biomedical subjects

H Hirayama

Publications and source records attributed to H Hirayama.

At least 19 recordsLinked to original sources
PubMed2002

Response of GafChromic MD-55 radiochromic film to synchrotron radiation.

Synchrotron radiation has been increasingly and extensively used for materials science, biology and medical research. For measurement of high dose from the low energy photons, tissue-equivalent dosemeters having linearity in the Gy region are required. In this study, energy and dose responses of double-layer Gafchromic film MD-55 were measured using 10-40 keV monoenergetic photons from synchrotron radiation. The result showed that the energy responses normalised at 60Co gamma rays were 0.58-0.59 at 10-20 keV, 0.66 at 30 keV and 0.72 at 40 keV in air. The linearity was confirmed to extend from 2 Gy to 100 Gy.

Gamma Rays↗
PubMed2001

Troglitazone, an antidiabetic drug, improves left ventricular mass and diastolic function in normotensive diabetic patients.

AIMS: Patients with NIDDM have excessive cardiovascular morbidity and mortality, even in the absence of hypertension. Left ventricular hypertrophy (LVH), which is an ominous prognostic sign and an independent risk factor for cardiac events, is often present in NIDDM patients. METHODS AND RESULTS: NIDDM male patients with (n=10) and without (n=12) hypertension, all of whom had been diagnosed over 10 years ago, were examined in the present study. Normotensive NIDDM patients had not received any anti-hypertensive drugs. All patients were classified according to the left ventricular mass (LVM) index by using M-mode echocardiography and were assessed regarding their systolic (fractional shortening) and diastolic function, which included the maximal early flow velocity (MFV), the mitral valve deceleration time (DT), and the isovolumic relaxation time (IRT) as determined by Doppler indices. Troglitazone (TRO), an antidiabetic drug, was administered to both groups at a dose of 400 mg/day for 6 months. After TRO treatment, a reduction in the LVM index and an improvement in the diastolic function were observed in the normotensive but not in the hypertensive patients. CONCLUSION: The TRO treatment was sensitive for cardiac regression in those normotensive patients. These results suggest that LVH and the diastolic function in NIDDM patients without hypertension may be associated with elevated insulin resistance because TRO has a pharmacological function to increase the insulin sensitivity and to decrease insulin resistance.

Blood Flow Velocity↗
PubMed2001

Arterial remodeling influences the development of intimal hyperplasia after stent implantation.

OBJECTIVES: We examined whether preinterventional arterial remodeling influenced the interventional results after stenting. BACKGROUND: Arterial remodeling is seen in atherosclerotic lesions, and it may play an important role in the early stage of atherosclerosis. METHODS: We examined 113 lesions that underwent elective stenting using tubular slotted stents under intravascular ultrasound guidance. The lesions were divided into three groups--adequate, intermediate and inadequate remodeling group--according to preinterventional arterial remodeling. The patients were subjected to coronary angiography and intravascular ultrasound evaluation on average 6.4 months after stenting. RESULTS: At baseline and immediately after stenting, there were no differences in quantitative angiographic analysis among remodeling groups. However, the plaque cross-sectional area (CSA) in the minimal lumen CSA at preintervention and intimal hyperplasia CSA at follow-up were significantly larger in the adequate remodeling group than in the inadequate remodeling group. The restenosis rate of stenting for the lesions with inadequate arterial remodeling was very low (9.4%). A significant positive correlation was found between preinterventional plaque CSA and intimal hyperplasia CSA at follow-up (r = 0.47, p < 0.0001). Moreover, remodeling index significantly correlated with relative intimal hyperplasia CSA (r = 0.28, p < 0.01). CONCLUSIONS: Preinterventional arterial remodeling influenced the development of intimal hyperplasia after stenting.

Aged↗
PubMed2001

Dose measurements in inhomogeneous bone/tissue and lung/tissue phantoms for angiography using synchrotron radiation.

For angiography using synchrotron radiation we measured the absorbed dose distribution in inhomogeneous phantoms with thin LiF:Mg, Cu, P, LiF:Mg, Ti thermoluminescent dosimeters (TLDs) in tissue and lung substitutes, and with Mg2SiO4:Tb TLDs in bone substitute for 33.32 keV monoenergetic photons from synchrotron radiation. The energy responses of the TLDs were measured in air for 10-40 keV monoenergetic photons. The values at 30 keV became smaller by 30% for LiF:Mg, Cu, P and larger by 22% for Mg2SiO4:Tb than the ratio of the mass energy absorption coefficients of the TLDs to that of air. These values were used to modify the calculated response of the TLDs in each phantom material. The absorbed dose distribution obtained was compared with that calculated using the Monte Carlo transport code EGS4 expanded to a low-energy region, and their agreement was confirmed taking linear polarization into account. In the bone substitute the dose increased by a factor of 3.9, while behind the bone the dose decreased drastically because of photon attenuation. In the lung substitute a slight dose difference from that in soft tissue was observed because of its different density. The LiF:Mg, Cu, P TLDs exhibited a better energy response, higher sensitivity and wider linear regions than did the other tissue-equivalent TLDs in the low-energy region.

Bone and Bones↗
PubMed2001

An experimental study on radiation streaming through a labyrinth in a proton accelerator facility of intermediate energy.

A radiation streaming experiment has been carried out at the Takasaki Ion Accelerator Facility for Advanced Radiation Application at the Japan Atomic Energy Research Institute in a room housing a Cu target irradiated with 68 MeV protons and in a labyrinth of three-legs having a total length of 29 m. In the experiment, neutron and gamma ray energy spectra, neutron reaction rates, and neutron and gamma ray dose equivalent rates were measured using various counters and dosimeters. The experimental data show the applicability of some empirical formulas for estimating the thermal neutron flux in a room and neutrons streaming in a labyrinth designed for a proton accelerator operating in the intermediate energy region. The data suggest that it is mandatory to estimate the gamma ray dose equivalent rate in a labyrinth, which is dominated by the secondary gamma rays due to the neutron capture reaction.

Academies and Institutes↗
PubMed2001

Comparison of in-phantom dose distributions for coronary angiography using an x-ray machine and synchrotron radiation.

Coronary cineangiography using synchrotron radiation is anticipated, owing to the high intensity and availability of monoenergy. To investigate allowable dose levels in clinical application, absorbed dose distribution in a tissue substitute phantom for a conventional x-ray machine was measured with thermoluminescent dosimeters at the University of Tsukuba under the practical conditions used for digital angiography. The dose rate at a 0.5-cm depth was 0.145 Gy/s, and the dose per frame was 0.725 mGy for the irradiation period of 5 ms per frame. For synchrotron radiation, the dose distribution measurement was made at a 5-GeV AR (Accumulation Ring) of the High Energy Accelerator Research Organization, in which a polymethylmethacrylate (PMMA) phantom was irradiated with the strongest beam available at the facility, which was 33.32 keV, 5.2 x 6.2 cm2 beam. Using this beam, a 1-mm-diameter coronary artery has been visualized at 1% iodine concentration at the AR. Nonhomogeneous strength distribution in the beam was observed in the vertical direction. The maximum dose rate was 0.556 Gy/s, and it attenuated to 1/3000 at a 30-cm depth in the beam center. At the deep positions, the doses were influenced by the high harmonics, which was confirmed with an EGS4 Monte Carlo calculation. Outside the beam, beam contamination on both sides of the main beam affected the doses. For comparison to the x-ray machine, the measured dose was analytically converted to that needed for a 5.2 x 16 cm2 beam that is used for clinical application. The dose rate at 0.5-cm depth was found to be 0.215 Gy/s, which is 1.48 times larger than that for x-rays. Moreover, the attenuation rate in the phantom was significantly greater than that of the x-ray machine, because of the difference of the energy spectra between the x-rays and synchrotron radiation used.

Biophysical Phenomena↗
PubMed2001

Histopathologic evaluation of coronary artery thrombi obtained by directional coronary atherectomy in patients with restenosis-induced unstable angina pectoris.

The pathogenesis of unstable angina pectoris (UAP) following percutaneous transluminal coronary angioplasty (PTCA) or directional coronary atherectomy (DCA) has not been adequately investigated, so the present study aimed to determine whether thrombi are present in restenotic lesions. The study group comprised 14 patients (16 arterial branches) with angina pectoris in whom either PTCA or DCA was performed and who had developed UAP associated with restenosis, and who then underwent DCA of the restenosed lesion (R-UAP group). The control groups comprised individuals with UAP undergoing DCA with no prior history of PTCA or DCA (P-UAP group; n=29, 29 branches), patients with acute myocardial infarction (AMI group; n=34, 34 branches), and patients with stable angina pectoris (SAP group; n=31, 33 branches). The presence of thrombi was determined by light microscopy of histologic specimens. Thrombus was present in only 1 of the 16 (6.3%) branches in the R-UAP group. 21 of the 29 (72.4%) branches in the P-UAP group, and in 25 of the 34 (73.5%) in the AMI group. In the SAP group, it was detected in only 2 of the 33 (7.1%) branches. The incidence of thrombus was significantly lower in the R-UAP group than in the P-UAP group. In conclusion, the role of thrombus is limited in causing post-interventional UAP at restenosed sites.

Aged↗
PubMed2001

Traumatic basilar artery occlusion caused by a fracture of the clivus--case report.

A 56-year-old man presented with a rare traumatic basilar artery occlusion caused by a fracture of the clivus. He fell from the height of 2 meters and immediately fell into a coma. Head computed tomography (CT) revealed an open depressed fracture, an acute epidural hematoma 1 cm thick in the left middle frontal fossa, and a longitudinal fracture of the clivus. Emergency removal of the hematoma was performed with cranioplasty. Head CT 8 hours 50 minutes after injury showed infarctions in the brain stem, cerebellum, and occipital lobes. Cerebral angiography revealed occlusion of the basilar artery in the middle part of the clivus. The patient died after 3 days. Autopsy revealed that the basilar artery was trapped in the clivus fracture site. Vertebrobasilar artery occlusion due to trapping in a clivus fracture has a very poor prognosis. Diagnosis is difficult and generally only confirmed at autopsy. Cerebral angiography is recommended in a patient in a deep coma without massive brain contusion at the early stage of head injury to identify the possibility of vertebrobasilar artery occlusion in a clivus fracture.

Accidental Falls↗
PubMed2001

[Usefulness of intravenous myocardial contrast echocardiography in rats].

OBJECTIVES: Few intravenous myocardial contrast echocardiography trials have evaluated myocardial perfusion in small animals. The feasibility of using intravenous myocardial contrast echocardiography to assess the ischemic area in rats was investigated. METHODS: Fourteen open chest Wister male rats were examined. Intravenous myocardial contrast echocardiography was performed by fundamental and intermittent mode using a high frequency (5-12 MHz) transducer (SONOS 5500) with injection of NC100100 (20% dilution) into the femoral vein. The mechanical index was set to 1.6. Baseline-subtracted video intensity (256 level) was measured in the anterior, posterior, septal and lateral walls of the left ventricle. The left anterior descending artery was ligated in 16 rats. The area at risk was evaluated by myocardial contrast echocardiography and compared to the area of defect by Evans Blue staining. RESULTS: All wall segments were clearly opacified (anterior 63.8 +/- 24.7, posterior 27.0 +/- 11.0, septal 44.5 +/- 11.6, lateral 52.3 +/- 19.1), although the baseline-subtracted video intensity of the posterior wall was low. The area at risk was clearly observed, and there was a good correlation with the nonperfused area by Evans Blue staining (y = 1.13x-3.54, r = 0.98). CONCLUSIONS: Intravenous myocardial contrast echocardiography can detect the perfusion defect even in rats using a high frequency transducer and suitable setup of equipment.

Animals↗
PubMed2001

Evaluation of left ventricular function using electrocardiographically gated myocardial SPECT with (123)I-labeled fatty acid analog.

UNLABELLED: Electrocardiographically (ECG) gated myocardial SPECT with (99m)Tc-tetrofosmin has been used widely to assess left ventricular (LV) function. However, the accuracy of variables using ECG gated myocardial SPECT with beta-methyl-p-(123)I-iodophenylpentadecanoic acid (BMIPP) has not been well defined. METHODS: Thirty-six patients (29 men, 7 women; mean age, 61.6 +/- 15.6 y) with ischemic heart disease underwent ECG gated myocardial SPECT with (123)I-BMIPP and with (99m)Tc-tetrofosmin and left ventriculography (LVG) within 1 wk. LV ejection fraction (LVEF), LV end-diastolic volume (LVEDV), and LV end-systolic volume (LVESV) were determined on gated SPECT using commercially available software for automatic data analysis. These volume-related items on LVG were calculated with an area-length method and were estimated by 2 independent observers to evaluate interobserver validity. The regional wall motion with these methods was assessed visually. RESULTS: LVEF was 41.1% +/- 12.5% on gated SPECT with (123)I-BMIPP, 44.5% +/- 13.1% on gated SPECT with (99m)Tc-tetrofosmin, and 46.0% +/- 12.7% on LVG. Global LV function and regional wall motion between both gated SPECT procedures had excellent correlation (LVEF, r = 0.943; LVEDV, r = 0.934; LVESV, r = 0.952; regional wall motion, kappa = 0.92). However, the correlations of global LV function and regional wall motion between each gated SPECT and LVG were significantly lower. Gated SPECT with (123)I-BMIPP showed the same interobserver validity as gated SPECT with (99m)Tc-tetrofosmin. CONCLUSION: Gated SPECT with (123)I-BMIPP provides high accuracy with regard to LV function and is sufficiently applicable for use in clinical SPECT. This technique can simultaneously reveal myocardial fatty acid metabolism and LV function, which may be useful to evaluate various cardiac diseases.

Electrocardiography↗
PubMed2000

Crystal structures of heptakis(2,6-di-O-ethyl)cyclomaltoheptaose.

Heptakis(2,6-di-O-ethyl)-beta-cyclodextrin (DE-beta-CD) was crystallized in two forms from hexane and 95% aqueous methanol, respectively: A form I crystal with the space group P2(1)2(1)2(1) and a form II crystal with the space group P3(1). In both crystals, DE-beta-CD molecules are in a round shape with intramolecular O-3-H...O-2 hydrogen bonds. In the form I crystal, the DE-beta-CD molecules are arranged along the twofold screw axis to form a helically extended polymeric chain by including the 6-O-ethyl groups of the adjacent molecule. One hexane molecule with twofold disorder is located in the intermolecular channel along the a-axis. In contrast, the DE-beta-CD molecules in the form II crystal form a helical arrangement along the threefold screw axis. One methanol and one water molecule are included on the O-6 side of the molecular cavity. The water molecule links the methanol molecule and two ethoxy groups of the adjacent DE-beta-CD molecule with hydrogen bonds. The result suggests the important role of solvent in the formation of helical arrangement of DE-beta-CD molecules.

Carbohydrate Conformation↗
PubMed2000

Antiarrhythmic efficacy of dipyridamole in treatment of reperfusion arrhythmias : evidence for cAMP-mediated triggered activity as a mechanism responsible for reperfusion arrhythmias.

BACKGROUND: Intracellular calcium overload is believed to play an important role in development of reperfusion arrhythmias. Dipyridamole, an inhibitor of cellular uptake of adenosine, may prevent or terminate reperfusion arrhythmias by reducing intracellular calcium overload. METHODS AND RESULTS: First, we tested for a preventive effect of dipyridamole. Sixty-one patients who underwent primary PTCA for treatment of acute anterior wall myocardial infarction were enrolled in this prospective study. Patients were divided into dipyridamole (DP) and nondipyridamole (non-DP) groups. The 2 groups had similar baseline characteristics. In the DP group, dipyridamole 0.5 mg/kg was infused intravenously for 3 minutes immediately before reperfusion during primary PTCA. Arrhythmias after reperfusion were analyzed from continuous ECG recordings. None of the patients in the DP group (n=23) had accelerated idioventricular rhythms (AIVR) or ventricular tachycardia (VT). In contrast, 7 (18.4%) had AIVR and 3 (7.9%) had VT in the non-DP group (n=38; P<0.01). Second, we tested for a termination effect of dipyridamole. Dipyridamole 0.5 mg/kg was infused intravenously while continuous ECG recordings were obtained in 9 patients who had either sustained AIVR (n=7) or sustained VT (n=2) after reperfusion of occluded coronary artery. Arrhythmias were terminated in all patients. CONCLUSIONS: These results indicate that administration of dipyridamole can prevent and terminate reperfusion arrhythmias such as AIVR and VT. cAMP-mediated triggered activity may, at least in part, be responsible for reperfusion-induced AIVR and VT.

Adenosine↗
PubMed2000

A mathematical method for investigating dynamic behavior of an idiotype network of the immune system. The time minimum optimal control theory.

We proposed a mathematical method to investigate an integrated property of an idiotype immune network under the time minimum optimal control. The transient changes of amounts of B cell receptor bound antibodies and immune complex in the network system were expressed by detailed differential equations. The rate constant for binding the second Fab arm of antibody was set as a function of coulombic repulsive force to express the influence of redistribution of electrical charges in the ligand-receptor molecular complex. We proposed time minimum optimal control strategy as an organizing principle for rapid reactions of the immune system. Based on the rigorous mathematical foundations of the optimal control theory, we determined the differential equations for co-state variables for the state variables to compute the time minimum transient changes in the amount of the species. Biological parameters in the immune reactions were utilized from the reported experimental data. Numerical computation disclosed that influence of changes in a rate constant extended to all the species of the network. Changes in a rate constant in a different B cell system reinforced the collaborations among the idiotypes and lead them to set in motion the ejection of the antigen. Simulation of reported experimental data by the present method was successful. There were, however, some inevitable dissociations between reported experimental data and computed results. The present method will be available for evaluating the time minimum reaction of the immune network system.

Journal Article↗
PubMed2000

Simultaneous STM and UHV electron microscope observation of silicon nanowires extracted from Si(111) surface

A miniaturized scanning tunnelling microscope (STM) was fitted in a side-entry holder of an ultra-high vacuum electron microscope. The clean Si(111)7 x 7 surface was observed by both STM and reflection electron microscopy (REM) at atomic resolution. The tungsten tips were often rounded off upon tip-approach with a constant current, through a gentle touch with the sample surface. The apices of such rounded tips had radii of several tens of granometre with widths of about 3 x 3 nm. Atomically resolved STM of the Si(111)7 x 7 surface was obtainable when an atom or an atomic cluster sits on the tip surface. The rounded tips were used for fabrication of Si nanowires by the touch-and-away operation of the tip. The nanowires grew longer at higher substrate temperature and they reached as long as several tens of nanometre at 700 degrees C. The nanowire had many twins and the (111) twin lamellae were stacked in the direction of the wire axis. In another case, the twin planes were oblique to the wire axis so that the (112) direction was nearly parallel to the wire axis.

Journal Article↗
PubMed2000

Novel toluene elimination system in a toluene-tolerant microorganism.

In studies of Pseudomonas putida IH-2000, a toluene-tolerant microorganism, membrane vesicles (MVs) were found to be released from the outer membrane when toluene was added to the culture. These MVs were found to be composed of phospholipids, lipopolysaccharides (LPS), and very low amounts of outer membrane proteins. The MVs also contained a higher concentration of toluene molecules (0.172 +/- 0. 012 mol/mol of lipid) than that found in the cell membrane. In contrast to the wild-type strain, the toluene-sensitive mutant strain 32, which differs from the parent strain in LPS and outer membrane proteins, did not release MVs from the outer membrane. The toluene molecules adhering to the outer membrane are eliminated by the shedding of MVs, and this system appears to serve as an important part of the toluene tolerance system of IH-2000.

Bacterial Outer Membrane Proteins↗
PubMed2000

Determination of left ventricular mass by echocardiography in normotensive diabetic patients.

Patients with Type 2 diabetes mellitus (DM) have excessive cardiovascular morbidity and mortality, even in the absence of hypertension. Left ventricular hypertrophy (LVH), which is an ominous prognostic sign and an independent risk factor for cardiac events, is often present in Type 2 DM patients. Forty-two Type 2 DM patients without hypertension, all of whom had been diagnosed more than 10 years ago, were examined in the present study. They had no evidence of renal dysfunction and had not received any anti-hypertensive drugs. Age-matched healthy normal subjects (n=47) were recruited as controls. All participants were classified according to the left ventricular mass index (LVMI) using M-mode echocardiography and their systolic function (fractional shortening) was examined. The systolic function was not significantly different between the Type 2 DM and control groups. LVH can be seen even in the normotensive Type 2 DM patients, with these patients still having a higher LVMI than the normal control subjects. Although the plasma insulin levels were not significantly increased in the Type 2 DM patients, the LVMI significantly correlated with plasma insulin levels. However, the LVMI did not significantly correlate with plasma fasting glucose and hemoglobin A1c in the Type 2 DM patients. These results suggest that LVH in Type 2 DM patients without hypertension may be associated with elevated plasma insulin levels.

Age Factors↗
PubMed2000

Comparison of vectorcardiographic and 12-lead electrocardiographic detections of abnormalities in repolarization properties due to preexcitation in patients with Wolff-Parkinson-White syndrome: proposal of a novel concept of a "remodeling gradient".

Repolarization abnormalities after radiofrequency ablation in patients with manifest Wolff-Parkinson-White syndrome (WPW) have been attributed to cardiac memory of pre-existing changes in repolarization properties. We compared spatial ventricular gradient (VG) from vectorcardiograms with QRST values of 12-lead ECG in 41 patients with WPW (group A, manifest WPW due to left-sided accessory pathway (n = 20); group B, manifest WPW due to right-sided accessory pathway (n = 12); group C, concealed WPW (n = 9)) before and after ablation. Group N (n = 607) served as control. In groups A and B, the abnormalities of spatial VG and QRST values of 12-lead ECG that existed before and 1 day after ablation significantly decreased 1 week after ablation. In group C, spatial VG and QRST values of 12-lead ECG showed no significant changes. The diagnostic ability of spatial VG is almost equivalent to that of the QRST value of ECG in detecting repolarization abnormalities in patients with WPW before and after ablation. We propose a new concept of a "remodeling gradient" directing from the preexcited area to the opposite side of the ventricle as a result of preexcitation-induced electrical remodeling.

Adolescent↗