The 1°C and 11C beam stop position in a homogeneous phantom was measured using the range verification system in HIMAC. This system was developed to clear uncertainty of beam range within the patient body in heavy ion radiotherapy. In this system, a target is irradiated with RI beams (11C or 10C) and the distribution of the beam end-lpoints are measured by a positron camera. To inspect the precision of the measurement, three experiments were done, simple PMMA phantom irradiation, empirical beam stop position measurements using a range shifter and boundary irradiation using PMMA and lung phantom. Results of the first two experiments were consistent. Consequently, a 0.2 mm standard deviation of statistical error measurement was possible with 250 determinations. For the third experiment, we compared the precision using 10C and 11C beams. The boundary of the PMMA and lung phantom was irradiated with both beams to maximize the positron range effect in the beam range measurement. Consequently, no significant difference was observed between the two beams in spite of the different positron range. Thus, we conclude that the 10C beam was useful for clinical application because of its good statistics owing to the short half-life.

View full abstract

The purpose of this study is to measure diagnostic x-ray spectra using a high resolution Schottky Cdte detector (TOYO MEDIC RAMTEC 413A) and to determine the best response function of Cdte detector for correcting the measured spectra with using a rise time discrimination (RTD) circuit to primary x-ray spectra. Since the measured spectra were distorted by the response of Cdte detector and did not present the true photon spectra, the correction by the stripping procedure was applied. The response function of Cdte detector has been determined by using Monte Carlo simulation method for calculating the photon interaction (K-escape, coherent scattering and Compton scattering) and incomplete charge collection by trapping of hole and use of RTD circuit. This simulation performed with various important factors (mean path length A h of hole and weight factor W, of incomplete charge collection) for finding the best response function. The photon spectra corrected with those various response functions were compared with the corrected photon spectra measured using a high purity Ge (HP-Ge) detector (PRINCETON GAMMA-TECH NIGP1013345), and the AI-attenuation curves calculated from corrected spectra and measured using the HPGe detector were compared. The best-fitted response function was determined, and the attenuation curves calculated from the spectra corrected with this response function were agreed with that measured using the HP-Ge detector within maximum error 0.03 of the attenuation rate and 5.0 % of the half value layer.

View full abstract

Single photon emission computed tomography (SPECT) is widely used for Nuclear Medicine. The low spatial resolution is mainly due to the limited collimator resolution. We have developed ordered subsets-expectation maximization (OS-EM) algorithm in. corporating three dimensional spatial resolution correction (3D-SRC; horizontal and vertical direction) for distance-dependent blurring. In this paper we evaluate the fundamental properties of OS-EM algorithm including distance-dependent resolution correction using some phantoms (cubic phantom, cardiac and brain phantoms) and 12 patients performed 99mTc-tetrofosmin myocardial SPECT. In cubic phantom, the resolution in transaxial, coronal and sagital images are significantly improved by 3D-SRC. In short axial images of cardiac phantom,3D-SRC shows more excellent images than no correction. In brain phantom, the blurring at the edge of the brain structure is improved by using OS-EM algorithm with 3DRC. In patients, the resolution in transaxial and short axial images is significant improved. These results suggest that this method improve the resolution in SPECT images and 3D-SRC is especially available in SPECT images of other axes in addition to transaxis. This method has advantage that both reconstruction and resolution correction are simultaneously performed. In the near future, we think that OS-EM algorithm incorporating attenuation, scatter and resolution correction will be used for quantitative SPECT images.

View full abstract

The telemedicine and teleconference, for example, make possible that the same qualities information can be accessed from the near facility and from the remote medical facility at 3 - 70 km away. The quality of medical care will be largely improved because high-speed network can be extended to rural areas. We set up an experimental network system to the telemedicine and teleconference using JGN (Japan Gigabit Network). The JGN is an ultra-high-speed network for the purpose of research and development. In this study, A 10 Mbps communication link of the JGN is used to transmission and reception of detailed and large medical information from remote places. Kanazawa University, NTT west kanazawa hospital, toyama city hospital and fukui red cross hospital are connected to the JGN through a router. IPsec system, which is the security protocol, is used for the security of data transmission between each facilities. In result, the date transmission rate using IPsec is 7 Mbps. The average translation rates of CT images (512x512,16bit) and MRI images (256x256,16bit) are 0.8 s/flame and 0.2 s/flame, respectively.

View full abstract

A fundamental study on quasi-parallel radiography using a polycapillary plate and a copper-target x-ray tube is described. In the experiments, the tube voltage was regulated from 12 to 22 kV, and the tube current was regulated within 3.0 mA by the filament temperature. The exposure time was controlled in order to obtain optimum x-ray intensity, and the maximum focal spot dimensions were approximately 2.0 X 1.5 mm. The thickness and the inner capillary tube diameter of the polycapillary were 1.0 mm and 25 pm, respectively. Monochromatic x-rays were produced using a 10 pm-thick nickel filter with a tube voltage of 17 kV, and these rays were formed into quasiparallel beams by the polycapillary. The radiogram was taken using a computed

View full abstract