[Evaluation of image quality using the normalized-rank approach for primary class liquid-crystal display (LCD) monitors with different colors and resolution].

The purposes of this study were to evaluate the image quality of five types of liquid-crystal display (LCD) monitors by utilizing the normalized-rank approach and to investigate the effect of LCD monitor specifications, such as display colors, luminance, and resolution, on the evaluators' ranking. The LCD monitors used in this study were 2, 3 and 5 mega-pixel monochrome LCD monitors, and 2 and 3 mega-pixel color LCD monitors (Eizo Nanao Corporation). All LCD monitors were calibrated to the grayscale standard display function (GSDF) with different maximum luminance (recommended luminance) settings. Also, four kinds of radiographs were used for observer study based on the normalized-rank approach: three adult chest radiographs, three pediatric chest radiographs, three ankle joint radiographs, and four double-contrasted upper gastrointestinal radiographs. Ten radiological technologists participated in the observer study. Monochrome LCD monitors exhibited superior ranking with statistically significant differences (p<0.05) compared to color LCD monitors in all kinds of radiographs. The major difference between monochrome and color monitors was luminance. Therefore, it is considered that the luminance of LCD monitors affects observers' evaluations based on image quality. Moreover, in the case of radiographs that include high frequency image components, the monitor resolution also affects the evaluation. In clinical practice, it is necessary to optimize the luminance and choose appropriate LCD monitors for diagnostic images.

[Correlation between basic imaging properties and subjective evaluations of two digital radiographic X-ray systems based on direct-conversion flat panel detector].

The purpose of this study was to examine the correlation between the basic imaging properties of two digital radiographic X-ray systems with a direct conversion flat-panel detector and their image qualities, which were evaluated by the observer in hard copy and soft copy studies. The subjective image quality was evaluated and compared in terms of the low-contrast detectability and image sharpness in the two digital radiographic X-ray systems. We applied the radiographs of a contrast detail phantom to the evaluation of low-contrast detectability and analyzed the contrast detail diagrams. Finally, low-contrast detectability was evaluated by the image quality figure (IQF) calculated from the contrast detail diagrams. Also, the subjective image sharpness of human dry bones of two systems was examined and evaluated by the normalized-rank method. The results indicated that System A tended to provide superior subjective image quality compared to System B in both observer studies. We also found high correlations between IQFs and basic imaging properties, such as the noise power spectrum (NPS) and the noise equivalent quantum (NEQ). In conclusion, the low-contrast detectability of the two digital radiographic X-ray systems with a direct conversion flat-panel detector corresponded to the NPS and the NEQ in both outputs (soft copy and hard copy). On the other hand, the subjective image sharpness of human dry bones was affected by their noise properties.

[Comparison of basic imaging properties for digital radiographic systems based on a direct conversion type of flat panel detector].

The purpose of this study was to evaluate the basic imaging properties of the two latest digital radiographic X-ray systems, namely, the DynaDirect Winscope 6000 (abbr. as System A, Toshiba Medical Systems) and the Sonialvision Safire Multi (abbr. as System B, Shimadzu Corp.). These systems were based on a direct-conversion flat panel detector (FPD) of amorphous selenium. The basic imaging properties of the two systems were evaluated by measuring characteristic curves, presampled modulation transfer functions (MTFs), and noise power spectra (NPS) using DICOM images to which no resampling was performed with a matrix size of 2048x2048. In addition, noise equivalent quanta (NEQ) and detective quantum efficiency (DQE) calculated from the result of the basic imaging properties were evaluated. The characteristic curves of the two systems showed quite high linearity. The MTFs of the two systems indicated high-resolution properties, as is well known to be an advantage of the direct conversion FPD system. However, the NPS of System A showed better performance than System B under the same exposures. Therefore, the DQE of System A was higher than that of System B at all spatial frequencies.

[Effect on image data resampling in evaluation of the basic imaging properties for a digital radiographic system based on a flat panel detector].

We investigated the effect on image data resampling in an evaluation of the basic imaging properties for a digital radiographic system based on a flat panel detector (FPD). One of the latest digital radiographic systems was used in this study. This system was based on a direct-conversion FPD of amorphous selenium. The basic imaging properties of the system were evaluated by measuring characteristic curve, presampled modulation transfer function (MTF), and Wiener spectrum (WS) using DICOM image with a matrix size of 2048 x 2048. The evaluations were performed under two conditions because matrix size automatically changes according to the selection of imaging size. One of the conditions was a different matrix size between image data acquired on the FPD and the output image (DICOM image for which resampling was performed). The other condition was that these matrices be the same size (DICOM image with no resampling performed). Resampling did not affect the characteristic curves. However, MTF and the WS obtained from the resampled data were different from those of the one not resampled, which is considered to be the "inherent" basic imaging properties, and this phenomenon was remarkable, especially in terms of the MTFs. Our study indicates that the effect on resampling should not be disregarded in evaluating the basic imaging properties of digital radiographic systems. Therefore, it is mandatory to use DICOM images for which no resampling was performed in order to evaluate the inherent basic imaging properties for digital radiographic systems.

[Experimental study of pseudo-stenosis artifact on three-dimensional DSA].

Rotational three-dimensional digital subtraction angiography (3D-DSA) is very useful for interventional neuroradiology, especially in the endovascular therapy of cerebral aneurysms. However, pseudo-stenosis artifact on the vessel, which runs vertically to the rotational axis, was observed clinically. In this study, this artifact was confirmed in an experiment with 4.5-millimeter diameter vessel phantoms. The attenuation of the phantom at each degree of exposure (44 directions) was measured on the workstation (DSA pixel value). DSA pixel values were plotted from data of 10, 20, 30, 40, and 50 millimeter lengths, respectively. The saturated DSA pixel value of tangent projection on phantoms of 30 millimeters or more in length was observed. This phenomenon induces pseudo-stenosis artifact on 3D-DSA. The maximum reduction in the diameter of the phantom was 27.4% on the length of 50 millimeters. We confirmed that the two-dimensional data vertical to the rotational axis were inaccurate when a straight-coursed, long, segmented vessel was present. Under this special condition, vessels on 3D-DSA were displayed as smaller than their actual diameter.