Atsushi Takigawa

Trabecular Pattern Analysis Using Fractal Dimension

Feature extraction from a digitized image is advantageous for the detection of signs of disease. In this work, we attempted to evaluate bone trabecular pattern changes in osteoporosis using the fractal dimension and the root mean square (RMS) values. The relationship between the fractal dimension and the 1st moment of the power spectrum is explored, and we investigated the relationship between the results of this analysis and the bone mineral density (BMD) value which was measured using dual-energy X-ray absorptiometry (DEXA). As a result, we were able to extract useful information, using the fractal dimension and the RMS value of the radiographs (lateral view of the lumbar vertebrae), for the diagnosis of osteoporosis. Abnormal clinical cases were separated from normal cases based on the evaluation values. Negligible correlation between the BMD value and these indexes was observed.

X-ray tube voltage dependence of Wiener spectra of quantum mottle obtained by determining detective quantum efficiencies of a screen

By using the detective quantum efficiency (DQE), which rep- resents the transfer efficiencies of the signal and noise, we expressed the Wiener spectrum of the quantum mottle. Using the new equation of the quantum mottle and the equation of the structure mottle proposed in 1992, we modified our method for separating the screen mottle, and proposed a new method for obtaining the DQE. Using the new method, we experimentally obtained the tube voltage dependence of the DQE, and the density and tube voltage dependence of the Wiener spectra of the quantum mottle. To explain the tube voltage dependence of the DQEs at a spatial frequency of 0 mm 21 , we theoretically obtained the tube voltage dependence of the first and second moments of x-ray pho- ton spectra absorbed by the screen. We found that the tube voltage dependence of the DQEs was caused by the fact that the output signal from the screen varied only slightly with tube voltage, while the output noise increased. Using the tube voltage dependence of the DQEs and the number of x-ray photons incident on the screens, we explain the dependence of the Wiener spectral values of the quantum mottle.

Computer simulation on scatter-removing characteristics by grid

Monte Carlo methods have been used to evaluate the performance of x-ray grids in radiography, quantitatively. To correspond with practical arrangements in radiography, the simulations have been done in the condition of the polyenergetic cone-beam geometry and the focused grid. The scatter intensities relative to the primary intensities were calculated for various values of object thickness, field size, tube voltage, and grid ratio. The Bucky factor, contrast improvement factor, and selectivity were used for comparison of the performance of the grid. The results of the calculations are in good agreement with the limited experimental data available. This calculation result is useful for the development of optimal antiscatter grids and selection of the suitable grid in radiographic procedures.

X-ray tube voltage dependence of Rossmann's three factors in Wiener spectra of radiographic mottles of a low-speed screen/film system

We obtained the tube voltage dependence of the Wiener spectra of the radiographic mottles of the front and back emulsions made using a low-speed screen and an anticrossover film. The Wiener spectral values of the front emulsion are almost constant, while those of the back emulsion increase with the tube voltage. The spectral values of the front emulsion are greater than those of the back emulsion at most of densities. In order to investigate the reason of these phenomena, we separated the radiographic mottle into the three factors. As a result, we have found that the reason of the dependence of the radiographic mottle is that the contribution of the quantum mottle is less than that of the structure mottle. The Wiener spectral values of the structure mottle of the front screen are greater than those of the back screen for most of the tube voltages. The Wiener spectral values of the front screen decrease and those of the back screen increase with the tube voltage, and the two curves cross at high voltage. These reasons were explained from the spatial fluctuation of the thickness of the screen due to the nonuniform screen structure and the attenuation curve of the x-ray intensity. The tube voltage dependence of the quantum mottle was explained from that of the number of photons absorbed in the screen.

Trial of PACS employing magneto-optical disks

Rewritable and compact media of magneto-optical disk (MOD) was firstly employed by us to store medical images such as digital X-ray films. The purpose is to test functions of communication media or circulating media as well as of filing media. Another feature of our trial system is to involve voice recording module for diagnostic reports. Method of clinical application and development approach of our PACS with MOD is discribed in this paper. Technology assessment of our system is also briefly descussed in terms of cost-effectiveness and security problem.

Relation between radiographic mottle for double and single emulsions

The radiographic density fluctuations produced by using dual screen-film systems are designated as the radiographic mottle. The density fluctuation of the radiographic mottle for the double emulsions at a density of the double emulsions consists of those for the front and back emulsions on a radiograph. However, the relation between the Wiener spectra of the radiographic mottle for the double and single emulsions had not been studied. Hence we compared the Wiener spectra of the radiographic mottle for the double emulsions with the sum of those for the front and back emulsions on the same radiographs and with the sum of those for the emulsions at the same densities. At all densities of more than 0.62 for lower spatial frequencies (< or = 1 mm-1), the Wiener spectral values of the radiographic mottle for the double emulsions were greater than the sum of those for the front and back emulsions for both comparisons on the same radiographs and at the same densities. In order to investigate the reason of the above phenomena, we separated the Wiener spectral values of the radiographic mottle for various densities into those of the three factors, i.e., quantum mottle, structure mottle, and film granularity, and performed the same comparisons as the radiographic mottle. Also, to explain the results for the three factors, we obtained the Wiener spectral values of the spatial fluctuations of the light exposure or the fluorescence intensity and the gradients of the characteristic curves of the film for the double and single emulsions of the x-ray film. As a result of the investigation, we found that the phenomena on the radiographic mottle were caused by that (1) on the same radiographs the squares of the gradients of the characteristic curves for the double emulsions were about 5.3 times as great as those for the single emulsion at densities of more than 0.62 of the double emulsions, and (2) at the same density of more than 0.62 those were more than about 2.2 times as great as those for the single emulsion.

Blood Citric Acid Density Relationships with Steps and Lifestyle-related Disease Indices

[Purpose] This study examined factors affecting blood citric acid density in relation to lifestyle-related disease prevention. [Subjects] The subjects were 99 elderly and middle-aged women. Those receiving medication were excluded ?. [Method] We compared factors affecting life-style related diseases in two groups by quantity of blood citric acid density change. [Result] Significant differences between the groups were found in weight, BMI, degree of obesity, maximum blood pressure level, pulse pressure, RBC, Hb, Ht%, and LDL cholesterol. [Conclusion] The citric acid density results suggest that just a modest amount of exercise is effective at burning off fat.

Basic study for automatic recognition of osteoporosis using abdominal x-ray CT images

We have developed an algorithm that can be used to distinguish the central part of the vertebral body from an abdominal X-ray CT image and to automatically calculate three measures to diagnose the degree of osteoporosis in a patient. In addition, we examined whether it is possible to use these CT images as an aid in diagnosing osteoporosis. Three measures that were automatically extracted from the central part of a vertebral body in the CT images were compared with the bone mineral density (BMD) values that were obtained from the same vertebral body. We calculated the mean CT number, coefficient of variation, and the first moment of power spectrum in the recognized vertebral body. We judged whether a patient had osteoporosis using the diagnostic criteria for primary osteoporosis (Year 2000 revision, published by the Japanese Society for Bone and Mineral Research). We classified three measures for normal and abnormal groups using the principal component analysis, and the two groups were compared with the results obtained from the diagnostic criteria. As a result, it was found that the algorithm could be used to distinguish the central part of the vertebral body in the CT images and to calculate these measures automatically. When distinguishing whether a patient was osteoporotic or not with the three measures obtained from the CT images, the ratio (sensitivity) usable for diagnosing a patient as osteoporotic was 0.93 (14/15), and the ratio (specificity) usable for diagnosing a patient as normal was 0.64 (7/11). Based on these results, we believe that it is possible to utilize the measures obtained from these CT images to aid in diagnosing osteoporosis.

Reduction of patient dose on medical radiographs using scattered x rays

We propose a new method for reduction of the patient dose by using scattered X-rays in order to achieve the same density without scattered rays. The minimum perceptible thickness difference (delta) Xmin of the object was calculated using psychophysical analysis for various radiographic densities, scatter fractions and luminous exitances of the viewer. The mAs values to obtain many densities were measured using four kinds of anti-scattered X-ray grid with their scatter fractions. These measured values were applied to above calculated psychophysical results. The smallest value of (delta) Xmin for acrylate of thickness 20cm was 0.18mm, if the scattered X-rays were negligible. The value of (delta) Xmin increases with increasing scatter fraction. The perceptibility of human eye is influenced by luminous exitance of the viewer. By increasing the luminous exitance from 1500 lm(DOT)m-2 to 8000 lm(DOT)m-2, the patient dose can be reduced 33 percent in maximum under the same perceptibility of (delta) Xmin. The method of changing grid will be considered.

X-ray tube voltage dependence of three factors of radiographic mottle for single and double emulsions

We have obtained the density or x-ray tube voltage dependence of the Wiener spectra of the three factors of radiographic mottle, i.e., quantum mottle, structure mottle, and film granularity, for the double emulsions of the x-ray film. For the purpose, we proposed a method for obtaining the Wiener spectrum of each of the three factors for the double emulsions. To investigate the relation between the Wiener spectra of the quantum mottle for the double and single emulsions, we compared the Wiener spectra of the quantum mottle for the double emulsions with the sum of those for the front and back emulsions on the same radiographs. The Wiener spectral values of the quantum mottle for the double emulsions at 0 mm-1 were greater than the sums of the Wiener spectral values of the quantum mottle for the front and back emulsions at tube voltages of 50 to 100 kV. We found that this was the result which originated from the following phenomena: (1) the noise-equivalent numbers of quanta (NEQ) of the dual screens were roughly equal to the sum of the NEQ of the front and back screens; (2) the squares of the gradients for the double emulsions were more than four times on an average as great as those for the front and back emulsions.