Biomedical subjects

T Irifune

Publications and source records attributed to T Irifune.

At least 19 recordsLinked to original sources

PubMed2002

[Report on the 13th European Congress of Radiology (ECR): Comparison of primary proton beams and secondary charged-particles].

PURPOSE: In the proton radiotherapy, primary proton beams contribute to the absorbed dose and the share of secondary charged-particles is small. The purpose is to discuss about the ratio of average dose of primary proton beams and secondary charged-particles. METHODS: We performed the dosimetry of 70 MeV proton beams in water using ionization chamber. The ratio of average dose for secondary charged-particles in some range shifter was calculated by the dose ratio of primary and scatter. To exclude the influence of lateral secondary charged-particles, the ratio of average dose for secondary charged-particles was extrapolated to zero field size of each. RESULTS: The ratio of average dose for secondary charged-particles was extrapolated to zero field size by the bi-exponential fit. The ratio of average dose for longitudinal secondary charged-particles for zero fields at each depth is almost the same; the different at the shallow depth is decreased. CONCLUSIONS: The secondary charged-particles from collimator is affected by the dose of shallow depth. The influence of lateral secondary charged-particles in water phantom was excluded with the extrapolation method for zero field size in each depth.

Alpha Particles↗

PubMed2000

[Study on evaluation method of patient dose in diagnostic radiology required for introducing the guidance level: investigation of entrance surface dose of patient using direct measurement by TLD].

Using direct measurement, we investigated entrance surface doses of patients for routine radiographs in attempt to develop evaluation methods of patient dose in order to establish the guidance level in Japan. To date, patient doses have been evaluated by calculations based on radiographic conditions, or model experiments using phantoms. Their patient doses are then evaluated based on several assumptions. Direct measurement of patient dose is difficult to perform in many patients due to its time requirement, level of expertise required and difficulty in providing an explanation of the procedure to the patient. However, such direct measurement is essential since it incorporates all aspects of radiography from the radiographic equipment used, to the actual conditions of each patient without assumption. In this study, we examined the (1) need for introducing the guidance level, (2) controversial points in the calculation method for patient dose evaluation, (3) evaluation accuracy required for introducing the guidance level, and (4) necessity for a standardized method.

Guidelines as Topic↗

PubMed1999

Vascular and stromal changes in irradiated and recovering rat thymus.

To analyze the mechanisms responsible for thymocyte proliferation, maturation and migration in the thymus, the rat thymus just after, and recovering from irradiation was studied morphologically. The vascular structures of the rat thymus after a radiation dose of 6 Gy were found to be destroyed on day 3, but had recovered to almost normal by day 7, suggesting that the abrupt recovery of thymus structure after irradiation was due primarily to this change in vascular structure. Furthermore, the epithelial tissues in the thymic cortex appeared to contribute to this abrupt proliferation, and possibly to the abrupt maturation of thymocytes, while medullary epithelial tissues remained sparse and appeared inactive for a relatively long period. These findings are considered important for understanding the interrelationship between thymic epithelial cells and thymocytes with respect to thymocyte proliferation, maturation and migration.

Animals↗

PubMed1999

[Detection size dependence of field factor for narrow beam].

An absorbed dose in the narrow beam is calculated based on the depth dose distribution and a field factor. The field factor has to be measured with especially high accuracy because it is highly variable. The field factor was calculated when detection size was changed, by using Monte Carlo simulation, which had no energy dependency or geometrical error. Then the relation between field factor and detection size in the narrow beam was investigated. An absorbed dose in peak depth and reference depth according to detection size was calculated for each field size. Detection size dependency was recognized in the case of measuring a field factor, because the absorbed dose tended to decrease as detection size increased. The absorbed dose in the narrow beam has to be calculated within a change of +/- 2%. The change in peak depth according to detection size was eliminated, and then the relation between an absorbed dose at the ideal detection size of 0 mm phi by extrapolation and detection size which has a deference of 2% from it, were acquired. In addition, the maximum usable detection size was estimated in the case of measuring the field factor.

Models, Theoretical↗

PubMed1998

The postspinel phase boundary in Mg2SiO4 determined by in situ X-ray diffraction

The phase boundary between spinel (gamma phase) and MgSiO3 perovskite + MgO periclase in Mg2SiO4 was determined by in situ x-ray measurements by a combination of the synchrotron radiation source (SPring-8) and a large multianvil high-pressure apparatus. The boundary was determined at temperatures between 1400 degrees to 1800 degreesC, demonstrating that the postspinel phase boundary has a negative Clapeyron slope as estimated by quench experiments and thermodynamic analyses. The boundary was located at 21.1 (+/-0.2) gigapascals, at 1600 degreesC, which is approximately 2 gigapascals lower than earlier estimates based on other high-pressure studies.

Journal Article↗

PubMed1996

Amorphization of Serpentine at High Pressure and High Temperature

Pressure-induced amorphization of serpentine was observed at temperatures of 200° to 300°C and pressures of 14 to 27 gigapascals with a combination of a multianvil apparatus and synchrotron radiation. High-pressure phases then crystallized rapidly when the temperature was increased to 400°C. These results suggest that amorphization of serpentine is an unlikely mechanism for generating deep-focus earthquakes, as the temperatures of subducting slabs are significantly higher than those of the rapid crystallization regime.

Journal Article↗

PubMed1995

[Determination of source position for four radiography systems with orthogonal projections in brachytherapy].

Four configurations of two X-ray tube positions are available for determining the position of a point using two orthogonal films. For each configuration, there are many formulas for calculating the coordinate of a point: the least squares methods with and without physical meaning, such as six sets of geometrical solutions, an approximation method with constant magnifications and so on. It is troublesome for a person in charge of treatment planning to directly derive a formula or select an appropriate formula from numerous ones for the four configurations. Thus, a method to easily apply the published formula for a configuration to the other three configurations is described in simulations and a clinical case using rotation matrixes of the right-handed coordinate system. Each diagonal element of the rotation matrixes is 1 or -1, and the other elements are 0.

Brachytherapy↗

PubMed1995

[Techniques for determining position from more than two radiographs intersecting at arbitrary angles in brachytherapy].

The least squares method and geometrical solution for calculating position were used in the two-projection method. Five coordinate systems were defined as a normal system, image system on film intersecting the beam central axes at an arbitrary angle and the projection, virtual coordinate and virtual image coordinate systems with beam central axis as one of the three coordinate axes to determine the geometrical relationship between a point and image on the film. Normal coordinates of the point were calculated by six geometrical solution sets and two forms of the least squares method using the rotation matrixes of the coordinate systems. One least squares method solves simultaneous nonlinear equations, and the other derives a strict solution from simultaneous linear equations. The latter least squares method has little physical meaning and is not as useful as the former. Although the former has physical meaning, the iterative approximation method should be used to determine position since a strict solution cannot be obtained directly. By these least squares methods, position is determined with less error using the projections at more than two focal spots.

Brachytherapy↗

PubMed1993

[Determination of the point position for brachytherapy from the shift-projection method using the least squares method and geometrical solutions].

We have derived formulas by the least squares method and six sets of geometrical solutions for calculating the position for brachytherapy from shift-projection images on one or two films. There are four types of expression for each coordinate in both methods, the shift-film technique with double exposures on a film and the stereo-shift technique with two films. Some geometrical solutions for the shift-film technique are equal to well-known conventional formulas. In the case of the stereo-shift technique, each conventional formula for the two coordinates is equal to the mean of the two geometrical solutions of each coordinate, and the one for the other coordinate is equal to one of the geometrical solutions. Formulas for the shift-film technique can be easily reduced to those for the stereo-shift technique. The error of the position calculated by the least squares method was the smallest among all the formulas for the shift-film technique in simulation.

Brachytherapy↗

PubMed1993

[Crosstalks onto photopeak windows of 99mTc and other radionuclide (201Tl, 123I or 111In) in simultaneous acquisitions using a scinticamera--a fundamental study through phantom experiments].

In simultaneous acquisitions of both 99mTc and other radionuclide, there are crosstalks onto those photopeak windows. Therefore, to quantify the organ uptake in scintigraphic imaging, it is important to correct the crosstalk counts. The purpose of this study is to estimate the crosstalk fractions onto each photopeak window from other radionuclide. Those crosstalk fractions were determined from pulse height spectra, which were measured by inputting signals from a scinticamera into a multi-channel (2048 ch) pulse height analyzer. Four types of collimators, which are HR (high resolution), AP (all purpose) for low energy, ME (medium energy) and HE (high energy), as well as cuboid phantoms (10 x 10 x 10 cm3) were used in this experiment. The crosstalk fractions have a tendency to show small increases at the window width of 10 to 20%, excepting at 30%, a small change for the source thickness from 1 to 7 cm, and the least with the ME-collimator. The crosstalk fractions using the ME-collimator were obtained as follows, when the source thickness and the window width were 5 cm and 15%, respectively. 99mTc and 201Tl: 9.4% onto 201Tl window and 7.3% onto 99mTc window, 99mTc and 123I: 36.1% onto 99mTc window and 14.8% onto 123I window, 99mTc and 111In: 32.6% onto 99mTc window and 6.1% onto 111In window.

Gamma Cameras↗

PubMed1990

[Determination of the point position from two orthogonal X-ray photographs using least squares method and geometrical solutions].

Six sets of solutions for calculating the position of an interest point were obtained geometrically using four measured image coordinates on two X-ray photographs orthogonally projected. When the image coordinates had no error, all the solutions gave the same position without error. When an error occurred, the calculated positions differed from each other due to the propagation of error. Some solutions could not be used for this determination owing to a large propagation of error. Under conditions similar to those of clinical practice, the ratio of maximum error of position calculated by the six geometrical solutions to minimum error was about 426. The least squares method that we proposed gave results with less error. When one of the image coordinates could not be measured for some reason, the least squares method became automatically equivalent to one of the six geometrical solutions.

Image Processing, Computer-Assisted↗

PubMed1990

Biosynthesis of Phytosiderophores : In Vitro Biosynthesis of 2'-Deoxymugineic Acid from l-Methionine and Nicotianamine.

2' -Deoxymugineic acid (DMA), one of mugineic acid-family phytosiderophores (MAs), was synthesized in vitro both from l-methionine and from nicotianamine (NA) with a cell-free system derived from root tips of iron-deficient barley (Hordeum vulgare L.). The reactions producing DMA from NA needed an amino group acceptor (i.e. 2-oxoglutarate, pyruvate, or oxalacetic acid) and a reductant (i.e. NADH or NADPH). The activity of the enzymes to produce NA from l-methionine was the highest at about pH 9. This biosynthetic activity was markedly induced by iron-deficiency stress. The synthesis of NA from S-adenosyl-l-methionine was more efficient than from l-methionine. From the results with the cell-free system reported here, we propose a revised biosynthetic pathway of MAs.

Journal Article↗

PubMed1990

[Gamma-ray spectra of 201Tl-radiopharmaceuticals with a scintillation camera--crosstalk of contaminating nuclides of 200Tl and/or 202Tl onto 201Tl-photopeaks].

In cardiac imaging with 201Tl, the collimator for low energy high resolution is generally used, and also the energy window, which is set on the spectral display of a pulse height analyzer of a scintillation camera, is chosen 70 +/- 12.5 keV. The purpose of this study is to discuss those conditions in 201Tl imaging with the scintillation camera. Two types of collimators for HR (high resolution) and ME (medium energy) were used in this experiment, and we measured the pulse height spectra of 201TlCl radiopharmaceuticals in air and in a cuboid phantom, connecting a multi-channel pulse height analyzer to the scintillation camera. As a result of measuring of the pulse height spectra, two different energies of gamma rays which are not supposed to emit from 201Tl nuclide were observed, and we also identified the presence of a small amount of 202Tl (with 439 keV) and/or 200Tl (with 368 keV) from their half-life measurements. Thus, the use of the HR-collimator with 201Tl imaging is not suitable, because the shielding effects of its septa is poor to 439 keV gamma-rays, and the scattered radiation produced by the Compton interaction contributes to the principal photopeak on the pulse height spectrum. Here, we recommend the use ME-collimator instead of the HR-one, and of the window width of 76 +/- 25 keV for increasing the count rate.

Humans↗

PubMed1989

[Comparison of SPECT images with four kinds of 99mTc collimators].

Performance of SPECT imaging systems which use a rotating gamma camera, are affected by characteristics of the detector-collimator assembly, the data acquisition method, and the filter used in image reconstruction. The purpose of this study is to examine image qualities of SPECT with different types of low energy collimators. The SPECT imaging system in this study is a rotating gamma camera ZLC-7500 (Siemens) and a data processing unit Scintipac-700 (Shimadzu). The four types of collimators compared are UHR (ultra high resolution), HR (high resolution), AP (general all purpose), and HS (high sensitivity), with 0.27, 0.66, 1.00, and 2.06 relative sensitivity, respectively. In the case of the same collimator, the spatial resolutions measured in the slice plane showed a slight difference in the FWHM values (mean values of UHR, HR, AP, and HS were 11.3 mm, 13.6 mm, 15.8 mm, and 20.4 mm, respectively.) between the center and the circumference of the field of view, in the radial direction, but a large difference in the tangential direction, with lower FWHM values (values of UHR, HR, AP, and HS were 8.4 mm, 8.7 mm, 9.3 mm, and 10.8 mm at 12 cm from the center, respectively.). In comparison of SPECT images with the four types of collimators, except for the HS collimator, image qualities of UHR, HR, and AP collimators showed only a slight difference. From the pont of view of sensitivity and spatial resolution of the collimator, it is expected that the AP collimator would be suitable for SPeCT imaging with 99mTc.

Models, Structural↗

PubMed1987