Biomedical subjects

Masatoshi Hashimoto

Publications and source records attributed to Masatoshi Hashimoto.

9 recordsLinked to original sources

PubMed2006

Examination of beam profile measurement using an imaging plate by the light exposure fading method for quality assurance of external radiation therapy.

High-resolution film dosimetry has been used for several decades to check and to measure two-dimensional dose distributions. However, in recent years, the automatic processor has been replaced by the spread of computed radiography, or has been little used hospitals. In this study, we measured the off-center ratio (OCR) of the open field, after an irradiating radiation beam was delivered to the imaging plate (IP) under conditions in which the IP was exposed to a fixed amount of light with fading, and compared these data with the OCR measured by an ionization-chamber dosimeter, which is the standard method used for measuring radiation dose. Profile measurement using IP could be achieved by performing light fading, even at a range of more than 100 MU. Further, by using a metallic filter, we succeeded in demonstrating that the profile measurement of IP in an open irradiation field could approximate the values of those obtained by an ionization chamber dosimeter. This method can serve as a simple, easy-to-use method for evaluating the QA of dose distribution in radiation therapy.

Filtration↗

PubMed2006

Abnormal collateral arterial systems in Takayasu's arteritis and Leriche's syndrome evaluated by whole body acquisition using multislice computed tomography.

Takayasu's arteritis causes various arterial changes, including wall thickening, occlusion, aneurysm, and calcification. Similarly, Leriche's syndrome causes occlusion of the abdominal aorta or iliac arteries accompanied by ischemic symptoms of the distal lower extremities. Both diseases are potentially associated with the development of unexpected collateral arteries throughout the body. We evaluated whole body arteries in subjects with Takayasu's arteritis and Leriche's syndrome using 16-slice multislice CT and concluded that it was a useful tool to detect unexpected collateral arterial systems in Takayasu's arteritis or Leriche's syndrome in a non-invasive fashion.

Aged↗

PubMed2006

[Characteristic evaluation of a real-time silicon dosimeter and measurement of entrance surface dose at radiography].

It is important to grasp how much radiation exposure has occurred through radiation diagnosis, in respect to patient explanations and radiation protection. In this examination, we used a patient skin dosimeter (PSD) that measures entrance surface dose (ESD) in real time using a fluoroscopy procedure. The PSD has the ability to display results beginning at 1 microGy. We focused our attention on the X-ray detectability of the PSD, and performed a representative evaluation with the X-ray equipment. We measured ESD under various radiographic parameters at our facility. Although the measurements were dependent on energy, we were able to measure ESD to within an accuracy of about a 5% error by putting a calibration value on energy. The PSD can measure ESD easily without requiring preparation. It is important to be aware of the exposure dose to the radiation staff, and the PSD is a very effective radiation dose-measuring tool when daily business is active.

Computer Systems↗

PubMed2006

[Elucidation of the energy absorption spectra of the (11)C beam in a plastic scintillator.].

Heavy ion therapy using the energetic (12)C beam is successfully under way at HIMAC, Japan. The method is more advantageous than traditional radiation therapy in dose concentration owing to the Bragg peak and high relative biological effectiveness. A research study using the (11)C beam for heavy ion therapy in the future has been carried out in order to develop the capability of monitoring the dose distribution. Our group has examined the total energy absorption spectrum of the (11)C beam in a plastic scintillator. We could clearly observe the total absorption peak of (11)C in the energy spectrum and, in addition, we found a broad bump structure was associated with the peak. The bump area occupies 37% of the total spectrum and it probably affects the dose calculation for an accurate treatment planning. We elucidated the mechanism that leads to the structure of the total energy absorption spectra given by (11)C and (12)C in a block of plastic scintillator. This paper describes the method in detail and gives experimental analysis results which deal with the bump structure. We could explain the bump structure using the energy spectra caused by the fragmentation reactions.

Heavy Ions↗

PubMed2005

Dependence of the response of an amperometric biosensor formed in a micro flow channel on structural and conditional parameters.

Comprehensive analysis of the behavior of an amperometric biosensor incorporated in a micro flow channel was conducted by changing the structural and conditional parameters. The device used in the characterization consisted of a thin-film three-electrode system and a silicone rubber flow channel. An enzyme, glucose oxidase, was immobilized either at the bottom of the silicone rubber flow channel or on the electrode substrate. The flow rate, concentration, position of the immobilized enzyme, and channel height were changed, and the changes in the output current and the conversion efficiency were examined. When the flow rate and/or the channel height decreased, the output current and the conversion efficiency significantly increased. The conversion efficiency also increased by decreasing the concentration. The tendency of the flow dependence was reversed when the position of the immobilized enzyme was changed from the silicone rubber side to the electrode substrate. In addition, the influence of l-ascorbic acid was reduced by placing additional working electrodes in the upper stream. l-Ascorbic acid was eliminated more effectively as the flow rate decreased and the area of the working electrode for elimination increased.

Biosensing Techniques↗

PubMed2004

[Performance evaluation of X-ray CT using visible scintillation light].

We proposed a new method of performance evaluation for X-ray CT using visible scintillation light and examined its usefulness in this study. When we scanned a plastic scintillator disk in a gantry opening of the X-ray CT, we could observe visible scintillation light. The rotation of the light-emitting area of the disk corresponded to that of the X-ray tube. We were able to record the scintillation light by digital video camera. By analyzing the area of visible scintillation light, the rotation speed of the X-ray tube, angular spread of the X-ray beam, uniformity of the incident X-rays, and change in X-ray energy were measured. No other method is available to obtain the above parameters of X-ray CT during a single CT scan. In the measurements of the uniformity of incident X-rays and change of X-ray energy, our method showed good accuracy in detecting the attenuation caused by the couch between the X-ray tube and the plastic scintillator disc. The proposed method is inexpensive and easy-to-use. We conclude that the method is a useful tool for performance evaluation as well as a maintenance tool for X-ray CT.

Evaluation Studies as Topic↗

PubMed2004

[Gonad protective effect of radiation protective apron in chest radiography].

Depending on the facility, a radiation protective apron (protector) is used to protect the gonad from radiation exposure in chest radiography. To determine the necessity of using a protector during chest radiography, we measured the effect of the protector on the gonad in this study. First, using a human body phantom, we measured the absorbed dose of the female gonad with and without the protector, using a thermoluminescence dosimeter (TLD), and confirmed its protective effect. Using the protector, the absorbed dose was reduced to 28+/-2% and 39+/-4% for field sizes of 14 x 17 inch and 14 x 14 inch, respectively. Next, we used Monte Carlo simulation and confirmed, not only the validity of the actual measurement values, but also the fact that the influence of radiation on the absorbed dose of the gonad was mostly from scattered radiation from inside the body for the 14 x 17 inch field size, and also from the X-ray tube for the 14 x 14 inch field size. Although a certain protective effect is achieved by using the protector, the radiation dose to the gonad is only a few microGy even without a protector. Thus, the risk of a genetic effect would be as small as 10(-8). Given that acceptable risk is below 10(-6), we conclude the use of a radiation protective apron is not necessary for diagnostic chest radiography.

Female↗

PubMed2004

[Shielding effect of protective seats during CT examination].

Because the exposure to radiation from CT scanning is higher than that from other X-ray diagnostic devices, it is necessary to lower this exposure. In this study, we placed a protective seat on the abdomen and dorsal side of a human body phantom. Three different kinds of CT units, with a single detector, four detectors, and 16 detectors, were used to compare the absorbed dose on the skin surface and uterus. Head and chest CT scans were taken with the standard protocol. The difference in exposure to the uterus with and without the protective shield was found to be small. Exposure to the skin surface was about 0.2 mGy without the protective seat. We found that the exposure dose to chest could be reduced as much as 50% by using the protective seat. Effective radiation differs depending on the institution, and these differences can be more than the amount that can be reduced by using the protective seat. Thus, we conclude that it is important for each institution to determine the best protocol optimization for each individual.

Female↗

PubMed2003

[Measurement of depth dose distribution using plastic scintillator].

We propose a new method to measure the depth dose distribution in matter. The method is to use organic plastic scintillator as a phantom, which has the effective atomic number close to that of human soft tissue, and to measure the position distribution of the scintillation light by a wavelength analyzer through a thread of plastic optical fiber. The purpose of this study is to examine possibility to measure the depth dose distribution with the proposed method. We carried out the following three measurements. First, we measured the effective field of view (FOV); the plastic optical fiber accepts the light from the FOV. Then, we measured the dose dependence of the amount of emission light. Finally, the light distribution in the depth direction by the present method was compared to the depth dose distribution by the ionization chamber. The results are as follows. The angular range of FOV is 7.03 degrees +/- 0.21 degrees The dose dependence shows a good linearity. In other words, the amount of emission light is proportional to the absorbed dose. Both of the light and the dose distributions are proportional each other, and they show the same attenuation in the region deeper than 15 mm. From these results, we conclude that the present method can be used for the measurement of the depth dose distribution in matter.

Fiber Optic Technology↗