Biomedical subjects

Yasuyuki Kawaji

Publications and source records attributed to Yasuyuki Kawaji.

4 recordsLinked to original sources

PubMed2006

[Image quality and detection performance of a direct digital radiography system].

The physical characteristics of a direct amorphous Selenium (a-Se) digital fluoroscopy and radiography system were investigated. Pre-sampled modulation transfer functions (MTF) were measured using a slit method. Noise power spectra were determined for different input exposures by fast Fourier transform of uniformly exposed samples. The MTFs of direct digital radiography systems showed significantly higher values than those of indirect digital radiography and screen-film systems. The direct digital radiography systems showed higher noise levels compared with those of indirect systems under roughly the same exposure conditions. Contrast-detail analysis was performed to compare detection by direct digital radiography systems with that of the screen-film (FUJI HG-M2/UR2) systems. The average contrast-detail curves of digital and film images were obtained from the results of observation. Image quality figures (IQF) were also calculated from the individual observer performance tests. The results indicated that digital contrast-detail curves and IQF are, on average, are equal those of the screen-film system.

Fourier Analysis↗

PubMed2005

[CR-mammography with pixel size of 50 microm and dual-sided reading system: effect of the oblique incident of the X-ray beam on imaging properties and detection].

In mammography units, the X-ray tube focal spot is located directly above the chest wall edge of the detector. Therefore, the X-ray beam is incident at a different angle along the cathode-anode axis. When the X-ray beam is incident on the imaging plate (IP) at a relatively large angle, the resolution property of a new imaging plate with dual-sided reading system would be degraded compared with the conventional imaging plate because of the parallax effect, which produces a shift in the image on two sides of the imaging plate. To evaluate the oblique incidence effect of the X-ray beam on the degradation of resolution properties and detection of simulated microcalcifications of a new CR system with a pixel size of 50 microm, its basic imaging properties and observer performance tests were compared with those of a conventional CR system. The resolution properties were evaluated by measuring modulation transfer functions (MTFs). Observer performance tests were conducted to compare the detectability of simulated microcalcifications of CR systems. Degradation of presampling MTFs for the new system is greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate. We found that the degradation of the area under the ROC curve (Az) for the new CR system was greater than that of the conventional CR system when the X-ray beam was incident at the same angle on the imaging plate.

Calcinosis↗

PubMed2002

[Canon's flat-panel detector].

We measured and evaluated digital, pre-sampling and overall imaging properties (characteristic curve, modulation transfer function (MTF), Wiener spectrum (WS), noise equivalent quanta (NEQ) ) for Cannon's flat-panel detector (FPD), Fuji computed radiography (FCR) and screen-film (S/F) systems, respectively. First, the digital and overall characteristic curves of FPD and FCR systems were more wide dynamic range than that of the S/F system. Second, the pre-sampling and overall MTF of FPD system were better than those of FCR system a little at lower spatial frequencies than 0.8 mm(-1), but the overall MTF of FPD and FCR systems were worse than that of S/F system a little at all spatial frequencies. Third, the digital and overall WS of FPD system were similar or better than those of FCR system, but the overall WS of FPD and FCR systems were worse than that of S/F system. Fourth, the pre-sampling and overall NEQ of FPD system were better than those of FCR system a little at lower spatial frequencies than 1.6 mm(-1), but the overall NEQ of FPD and FCR systems were worse than that of S/F system at all spatial frequencies. Comparison of chest phantom images showed that the FPD produced images with quality comparable to or higher than those of the FCR system. From these results, we can expect that the FPD is useful machine by using digital image processing and so on in the radiology department.

Image Processing, Computer-Assisted↗

PubMedDate not supplied

New CR system with pixel size of 50 microm for digital mammography: physical imaging properties and detection of subtle microcalcifications.

PURPOSE: To investigate the physical imaging properties and detection of simulated microcalcifications of a new computed radiography (CR) system with a pixel size of 50 microm for digital mammography. MATERIALS AND METHODS: New and conventional CR were employed in this study. The new CR system included a high-resolution imaging plate coupled with the FCR5000MA (50 microm pixel pitch) including transparent support and a dual-sided reader. The conventional CR system was coupled with the FCR9000 (100 microm pixel pitch). Modulation transfer functions (MTFs) and Wiener spectra (WS) of the new and conventional CR systems were measured. Observer performance tests were conducted to compare the effects of pixel size (50 microm vs. 100 microm) on the diagnostic accuracy of CR systems in the detection of simulated microcalcifications. RESULTS: The presampling MTF of the new CR system was higher at high frequencies than the conventional CR system. The WS of the new CR system was comparable to that of the conventional CR system at all frequencies. The area under the receiver operating characteristic (ROC) curve (Az) obtained with the new CR and the conventional CR systems were 0.84 and 0.79, respectively. Results showed that the detection of simulated clustered microcalcifications was significantly improved by use of the new CR system compared with the conventional CR system (p<0.05). CONCLUSION: The new CR mammography system improved physical imaging properties and detection of simulated microcalcifications over conventional CR mammography.

Animals↗