We investigate the nonlinearity in digital X-ray images to determine the feasibility of a noise reduction process using a
mathematical model, which realizes an accurate digital X-ray imaging system. To develop this mathematical model, it is
important to confirm whether the system is linear or nonlinear. We have verified the nonlinearity of the imaging system
through an analysis of computed radiography (CR) images by using the method of surrogate, a statistical test of
nonlinearity, and the Wayland test. In the method of surrogate, we use the Fourier transform surrogate method. The
Wayland test can be used for evaluating the complexity of the orbit of a signal aggregate called the attractor
reconstructed in a high-dimensional phase space using a nonlinear statistical parameter called the translation error.
Nonlinearity is determined by statistically comparing the translation error of the original data with that of the surrogate
data. X-ray images are obtained under different conditions to investigate the effects of various tube voltages--50 and 80
kV--and dose settings--2 and 10 mAs. We extract 30 profiles from both directions, the directions vertical (V-direction)
and horizontal (H-direction) to the X-ray tube. In the H-direction, nonlinearity is found at all voltage and dose settings.
On the other hand, nonlinearity is found only at 10 mAs and 80 kV in the V-direction. Hence, it can be concluded that
nonlinearity is indicated by a decrease in the quantum mottle, and the factors of nonlinearity exhibit the comprehensive
variation produced by the digital X-ray imaging system.
KEYWORDS: LCDs, Signal detection, Medical imaging, Diagnostics, Image quality, Sensors, Mammography, Modulation transfer functions, Image compression, Health sciences
In the soft copy diagnosis, each pixel of the detector is displayed to the correspondent pixel of liquid crystal display
(LCD). But when the image is displayed at the first time, the entire image may be reduced. We examined the influence
that the difference of image reduction rate on LCD exerts on detection performance by using observer performance
experiment. Moreover, to find the best interpolation method, we investigated the several interpolation methods. We
made a simulation image which is similar to Burger phantom. This image consists of 288 signals, each of a different size
and contrast. The matrix size is the same as Phase Contrast Mammography (PCM). We gradated the simulation image by
using an MTF of a geometric blur, and the image was added to the noise image which is uniformly exposed with PCM.
Then the image was reduced by using the nearest-neighbor, the bilinear, and the bicubic methods. The reduction rates
were calculated as the ratios of the number of pixels of LCDs to those of PCM. We displayed the reduced images on
LCD and examined the detection performance. Results of physical evaluation examined before showed that sharpness
and granularity have worsened both in proportion to the reduction rate. The detection performance deteriorated as the
reduction rate becomes high. In the comparison of the interpolation methods, the detection performance of the nearestneighbor
method was worse than those of other interpolation methods. The bilinear method is the most suitable for the
reduction of the image.
The abnormal contraction of ciliary muscles due to the performance of a near visual task for several hours causes various
vision problems such as asthenopia and visual loss. However, these problems can be resolved by activating the muscles
by alternately repeating negative and positive accommodation. In this study, we have verified the effect of
accommodation training that uses the strategy of presenting a stereoscopic movie to myopic youth and measuring the
uncorrected distant visual acuity, spherical diopter (SPH), and subjective index of asthenopia obtained using a visual
analog scale (VAS). Stereoscopic movies are prepared by using the POWER 3D method (Olympus Visual
Communications Co., Ltd.), which reduces the inconsistency between the experienced and the actual senses. Thirty two
myopic students aged 20 ± 1 years (16 males and 16 females) were chosen as the subjects. One group performed the
accommodation training for 6 min, and the other group underwent a near visual task during the same period as the
control group. We concluded the following from each item of verification: (a) The accommodation training using a
stereoscopic movie had temporarily improved visual acuity. (b) This training led to a decrease in asthenopia. (c) The
training improved the near-point accommodation function.
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