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We analyzed the compression pressures in 2772 mammography images of 807 patients acquired by digital mammography equipment at four facilities. The analysis included the average compression pressure at all facilities, difference in compression pressure at each facility, differences between the pressures used by radiological technologists in the same facility, and difference attributed to the breast structure. We also analyzed the effects of the compression pressure on the breast thickness and mean glandular dose (MGD) at each facility. The median values of the compression pressure and breast thickness for the 2772 images at all facilities were 86.5 N and 43 mm, respectively. The compression pressures differed among the institutions. The maximum difference in the median pressures among the four facilities was 38.6 N, while the difference in the breast thickness was 6 mm. The radiological technologists working at the same facility used almost the same compression pressure. However, differences between the compression pressures used by different radiological technologists were observed. The compression pressure in a dense breast was smaller than that in a non-dense breast. The difference in the compression pressure affected the breast thickness and MGD. The results of this analysis could be utilized for an optimal imaging in future digital mammography.

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This study aims to evaluate the indices of glandular dose heterogeneity in full-field digital mammography. The distributions of GD in a breast phantom with a skin layer of 4 mm were determined using the Monte Carlo method with simulated x-ray fluence spectra. First, the GD to air kerma (GD/Kair) volume histogram was obtained from the GD distributions, which were indicated by the glandular volume (%) as a function of GD/Kair. The GD indices, namely, the maximum glandular dose (GD2%) and glandular volume percentage (%) receiving at least the mean glandular dose (MGD) (VMGD) were calculated from the GD/Kairvolume histogram. Next, the scatter plots of GD2%/MGD andVMGDwere drawn as functions of the normalised mean glandular dose (DgN). Finally, (GD2%)iand (VMGD)iwere obtained from the relationship between the GD indices and DgN for 596 clinical irradiation cases based on individual irradiation conditions. The values of GD2%/MGD were more affected by breast thickness than glandularity and tube voltage, and they decreased according to the power law of DgN for all the target/filter combinations. The values ofVMGDwere proportional to DgN and decreased with increase in the compressed breast thickness. The values of (MGD)iand (GD2%)ifor 596 clinical irradiation cases were estimated to range from 0.6-3.0 mGy to 1.1-7.0 mGy, respectively, and (VMGD)iwas in the range 32%-48%. (GD2%)iand (VMGD)iare mainly affected by breast thickness. These indices are useful for the evaluation of glandular dose heterogeneity in mammography.

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Our aim in this study was to evaluate the effect of the grid variations on the imaging performance for a computed radiographic system under identical exposure condition. Digital radiographies using a 20-cm Lucite phantom were performed without grid and with grid ratios of 5:1, 8:1, 10:1, 12:1, and 14:1. The scatter fraction, the incident dose to the image receptor, the Wiener spectrum (WS), and the noise-equivalent quanta (NEQ) were measured. Visibility of low-contrast signals was evaluated using a contrast-detail phantom. The scatter fractions decreased considerably with an increase in the grid ratio. On the other hand, the WSs were increased (the noise property deteriorated) as the grid ratio increased due to a decreased incident dose to the image receptor under the identical exposure condition. The NEQs were improved as the grid ratio increased. The high grid ratios provided higher low-contrast detectability compared to the low grid ratios. Our results indicated that the removal of scattered radiation was very effective in improvement of the NEQ in the digital system under the identical exposure condition.

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Our purpose was to evaluate the usefulness of digital magnification mammography with matched incident exposure by investigating the physical imaging properties and doing an observer performance test. A computed radiography system and a mammographic unit were used in this study. Contact and magnification radiographies of 1.2-1.8 in combination with focal spot sizes of 0.1 mm without grid and 0.3 mm with grid were performed. Physical imaging properties, namely, scatter fraction, total modulation transfer function (MTF) including the presampled MTF and the MTF of focal spot size, and Wiener spectrum (WS), were measured. Detail visibility was evaluated by use of free-response receiver operating characteristic analysis of the detectability of simulated microcalcifications. Scatter fractions decreased considerably as the magnification factor increased without grid technique. In the grid technique, scatter fractions for all magnification techniques were comparable. The total MTFs of magnification techniques with a focal spot size of 0.1 mm improved significantly compared with the conventional contact technique. However, the improvement of the total MTFs of magnification techniques with the combination of 0.3 mm focal spot size was small. The WSs degraded with an increase of the magnification factor compared with the contact technique due to the maintained exposure incident on the object. The observer performance test indicated that the 1.8 magnification technique with the 0.1 mm focal spot size provided higher detectability than did the contact technique. Digital magnification mammography under the same incident exposure conditions improved the detectability of microcalcifications.

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Our purpose in this study was to develop an automated method for segmentation of white matter (WM) and gray matter (GM) regions with multiple sclerosis (MS) lesions in magnetic resonance (MR) images. The brain parenchymal (BP) region was derived from a histogram analysis for a T1-weighted image. The WM regions were segmented by addition of MS candidate regions, which were detected by our computer-aided detection system for the MS lesions, and subtraction of a basal ganglia and thalamus template from "tentative" WM regions. The GM regions were obtained by subtraction of the WM regions from the BP region. We applied our proposed method to T1-weighted, T2-weighted, and fluid-attenuated inversion-recovery images acquired from 7 MS patients and 7 control subjects on a 3.0 T MRI system. The average similarity indices between the specific regions obtained by our method and by neuroradiologists for the BP and WM regions were 95.5 ± 1.2 and 85.2 ± 4.3%, respectively, for MS patients. Moreover, they were 95.0 ± 2.0 and 85.9 ± 3.4%, respectively, for the control subjects. The proposed method might be feasible for segmentation of WM and GM regions in MS patients.

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The goal of this study was to investigate the effect of the different luminance settings of a high-brightness color liquid-crystal display (LCD) on the detectability of a simple grayscale object with low contrast by use of receiver operating characteristic (ROC) analysis. The detectability of a high-brightness color LCD with two maximum-luminance settings (500 and 170 cd/m(2)) was compared with the detectability of a monochrome LCD (500 cd/m(2)). The two LCDs used in this study were calibrated to the grayscale standard display function. The average areas under the ROC curve (AUCs) and the standard deviations for all thirteen observers for the 500 cd/m(2) color LCD, 500 cd/m(2) monochrome LCD, and 170 cd/m(2) color LCD were 0.937 +/- 0.040, 0.924 +/- 0.056, and 0.915 +/- 0.068, respectively. There were no statistically significant differences in the average AUCs among the three LCD monitor conditions. On the other hand, the total observation time for the 170 cd/m(2) color LCD was significantly shorter than that for the 500 cd/m(2) color and monochrome LCDs (p < 0.05). Irrespective of the maximum luminance settings (500 and 170 cd/m(2)), the color LCD provided a performance comparable to the monochrome LCD for detection of a simple grayscale object with low contrast.

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PURPOSE: Brain tissue segmentation based on diffusion tensor magnetic resonance imaging (DT-MRI) data has been attempted by previous researchers. Due to inherent low spatial resolution of DT-MRI data, conventional methods suffered from partial volume averaging among the different types of tissues, which may result in inaccurate segmentation results. The purpose was to develop a new brain tissue segmentation method for DT-MRI data in which effect of the partial volume averaging is taken into account. METHODS: The method estimates the partial volume fractions of white matter (WM), gray matter (GM), and cerebrospinal fluid (CSF) within each voxel using a maximum a posteriori probability principle, based on five DT parameters (three eigenvalues, apparent diffusion coefficient, and fractional anisotropy). The authors evaluated the performance of the proposed method quantitatively by using digital phantom data. Moreover, the authors applied the method to real DT-MRI data of the human brain, and compared the results with those of a conventional segmentation method. RESULTS: In the digital phantom experiments, the root mean square error in term of partial volume fraction with the method for WM, GM, and CSF were 0.137, 0.049, and 0.085, respectively. The volume overlap measures between the segmentation results and the ground truth of the digital phantom were more than 0.9 in all three tissue types, while those between the results by the conventional method and the ground truth ranged between 0.550 and 0.854. In visual comparisons for real DT-MRI, WM/GM/CSF regions estimated by the method were more similar to the corresponding regions depicted in the structural image than those estimated by the conventional method. CONCLUSIONS: The results of the digital phantom experiment and real DT-MRI data demonstrated that the method improved accuracy in estimation and segmentation of brain tissue on DT-MRI data over the conventional method. This method may be useful in evaluating the cortical and subcortical diffusivity in neurological diseases.

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The purpose of this study was to develop a computerized method for detection of multiple sclerosis (MS) lesions in brain magnetic resonance (MR) images. We have proposed a new false positive reduction scheme, which consisted of a rule-based method, a level set method, and a support vector machine. We applied the proposed method to 49 slices selected from 6 studies of three MS cases including 168 MS lesions. As a result, the sensitivity for detection of MS lesions was 81.5% with 2.9 false positives per slice based on a leave-one-candidate-out test, and the similarity index between MS regions determined by the proposed method and neuroradiologists was 0.768 on average. These results indicate the proposed method would be useful for assisting neuroradiologists in assessing the MS in clinical practice.

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It has been reported that the severity of subcortical vascular dementia (VaD) correlated with an area ratio of white matter hyperintensity (WMH) regions to the brain parenchyma (WMH area ratio). The purpose of this study was to develop a computer-aided evaluation method of WMH regions for diagnosis of subcortical VaD based on magnetic resonance (MR) images. A brain parenchymal region was segmented based on the histogram analysis of a T1-weigthed image. The WMH regions were segmented on the subtraction image between a T1-weighted and fluid-attenuated inversion-recovery (FLAIR) images using two segmentation methods, i.e., a region-growing technique and a level-set method, which were automatically and adaptively selected on each WMH region based on its image features by using a support vector machine. We applied the proposed method to 33 slices of the three types of MR images with 245 lesions, which were acquired from 10 patients (age range: 64-90 years, mean: 78) with a diagnosis of VaD on a 1.5-T MR imaging scanner. The average similarity index between regions determined by a manual method and the proposed method was 93.5+/-2.0% for brain parenchymal regions and 78.2+/-11.0% for WMH regions. The WMH area ratio obtained by the proposed method correlated with that determined by two neuroradiologists with a correlation coefficient of 0.992. The results presented in this study suggest that the proposed method could assist neuroradiologists in the evaluation of WMH regions related to the subcortical VaD.

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Interpretations of medical images have been shifting to soft-copy readings with liquid-crystal display (LCD) monitors. The display function of the medical-grade LCD monitor for soft-copy readings is recommended to calibrate the grayscale standard display function (GSDF) in accordance with the guidelines of Japan and other countries. In this study, the luminance and display function of five models of eight general purpose LCD monitors were measured to gain an understanding of their characteristics. Moreover, the display function (gamma 2.2 or gamma 1.8) of general purpose LCD monitors was converted to GSDF through the use of a look-up table, and the detectability of a simulated lung nodule in the chest x-ray image was examined. As a result, the maximum luminance, contrast ratio, and luminance uniformity of general purpose LCD monitors, except for one model of two LCD monitors, met the management grade 1 standard in the guideline JESRA X-0093-2005. In addition, the detectability of simulated lung nodule in the mediastinal space was obviously improved by converting the display function of a general purpose LCD monitor into GSDF.

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Variation in the luminance ratio of a cathode ray tube(CRT)monitor and the ultrasonographic images at different levels of ambient light(0-150 lux)was investigated to obtain optimum ambient light in the ultrasonography suite. The maximum and minimum luminances of test patterns and ultrasonographic images were measured after three technicians independently optimized the brightness and contrast of the CRT monitor and ultrasonographic images at different levels of ambient light. Furthermore, the luminance ratio was calculated from the maximum luminance divided by the minimum luminance. When ambient light increased, it was difficult for the technicians to optimize the brightness and contrast settings of the CRT monitor to maintain a high luminance ratio at 0 lux. The luminance ratio decreased rapidly as ambient light increased up to 20 lux. However, the luminance ratio decreased gradually when ambient light was higher than 20 lux. It is necessary to take into consideration the ambient light to maintain a high luminance ratio of ultrasonographic images.

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It is known that the performance of liquid-crystal display (LCD) monitors, such as the luminance and contrast ratio, is dependent on the viewing angle. Our purpose in this study was to compare the angular performance and the effect on observer performance of different types of LCD monitors. The luminance performance and contrast ratio as a function of viewing angle (-60 degrees to 60 degrees) in each direction for two types of LCD monitors, namely, a general-purpose LCD monitor and one especially designed for medical use, were measured in this study. Furthermore, the observer performance at various viewing angles in the horizontal direction for a medical-grade LCD monitor was investigated by eight observers based on a contrast-detail diagram. The two types of LCD monitors showed notable variations in luminance and contrast ratio as a function of the viewing angle. Acceptable viewing angles in terms of the contrast ratio were much smaller in each direction than those for nominal viewing angles in the specifications provided by the manufacturers, and those for the medical-grade LCD monitor in the horizontal and vertical directions were broader than those of the general-purpose LCD monitor. There was no significant difference in observer performance between 0 degrees and 40 degrees. On the other hand, our results showed a statistically significant difference in observer performance between 0 degrees and 60 degrees.

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Our purpose in this study was to examine the potential usefulness of liquid-crystal display (LCD) monitors having the capability of rendering higher than 8 bits in display-bit depth. An LCD monitor having the capability of rendering 8, 10, and 12 bits was used. It was calibrated to the grayscale standard display function with a maximum luminance of 450 cd/m(2) and a minimum of 0.75 cd/m(2). For examining the grayscale resolution reported by ten observers, various simple test patterns having two different combinations of luminance in 8, 10, and 12 bits were randomly displayed on the LCD monitor. These patterns were placed on different uniform background luminance levels, such as 0, 50, and 100%, for maximum luminance. All observers participating in this study distinguished a smaller difference in luminance than one gray level in 8 bits irrespective of background luminance levels. As a result of the adaptation processes of the human visual system, observers distinguished a smaller difference in luminance as the luminance level of the test pattern was closer to the background. The smallest difference in luminance that observers distinguished was four gray levels in 12 bits, i.e., one gray level in 10 bits. Considering the results obtained by use of simple test patterns, medical images should ideally be displayed on LCD monitors having 10 bits or greater so that low-contrast objects with small differences in luminance can be detected and for providing a smooth gradation of grayscale.

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RATIONALE AND OBJECTIVES: An automated method for identification of patients with cerebral atrophy due to Alzheimer's disease (AD) was developed based on three-dimensional (3D) T1-weighted magnetic resonance (MR) images. MATERIALS AND METHODS: Our proposed method consisted of determination of atrophic image features and identification of AD patients. The atrophic image features included white matter and gray matter volumes, cerebrospinal fluid (CSF) volume, and cerebral cortical thickness determined based on a level set method. The cortical thickness was measured with normal vectors on a voxel-by-voxel basis, which were determined by differentiating a level set function. The CSF spaces within cerebral sulci and lateral ventricles (LVs) were extracted by wrapping the brain tightly in a propagating surface determined with a level set method. Identification of AD cases was performed using a support vector machine (SVM) classifier, which was trained by the atrophic image features of AD and non-AD cases, and then an unknown case was classified into either AD or non-AD group based on an SVM model. We applied our proposed method to MR images of the whole brains obtained from 54 cases, including 29 clinically diagnosed AD cases (age range, 52-82 years; mean age, 70 years) and 25 non-AD cases (age range, 49-78 years; mean age, 62 years). RESULTS: As a result, the area under a receiver operating characteristic (ROC) curve (Az value) obtained by our computerized method was 0.909 based on a leave-one-out test in identification of AD cases among 54 cases. CONCLUSION: This preliminary result showed that our method may be promising for detecting AD patients.

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RATIONALE AND OBJECTIVES: Conventional tractography based on the "streamline" method only partially visualizes the pyramidal tract because of fiber crossing with other white matter tracts. Recently a new tractography method based on directional diffusion function (DDF) has been proposed. This method was reported to visualize the pyramidal tract to a larger extent than conventional techniques do. To validate the DDF-based tractography method, we studied the somatotopic organization of the pyramidal tract in the posterior limb of the internal capsule (PLIC). MATERIALS AND METHODS: Pyramidal tracts in the intact hemispheres of 14 brain tumor patients were drawn using the directional diffusion function-based tractography method. Each pyramidal tract was divided into four fiber bundles according to the cephalocaudal positions of their termination in the precentral gyrus. The cephalocaudal positions in the precentral gyrus of the four fiber bundles were correlated with their positional relationships in the PLIC along the mediolateral and anteroposterior axes. RESULTS: Fiber bundles terminating more caudally in the precentral gyrus were located significantly more anteriorly in the PLIC (r = 0.59, Spearman's correlation coefficient, P < .0001). On the other hand, no significant correlation was shown between the cephalocaudal positions in the precentral gyrus of the four fiber bundles and their relative positions in the PLIC along the mediolateral axis. CONCLUSIONS: Estimated organization of the fiber bundles of the pyramidal tract in the PLIC was consistent with anatomically known somatotopic organization, which supported the validity of the DDF-based tractography method.

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Quality assurance of electronic display devices is important for maintaining reliable soft-copy image interpretations. This paper presents effects of test patterns on measurement of the luminance of liquid-crystal display (LCD) devices by use of a telescopic-type luminance meter. The luminance for different types of test patterns having different backgrounds and measurement areas was measured and compared with the results obtained with AAPM task group-18 (TG-18) LN test patterns. The luminance measured for the test patterns with a black background was lower than that measured for TG-18 LN test patterns due to the light emitted from the outside the focused area of the telescopic-type luminance meter. Also, the luminance obtained with smaller measurement areas indicated lower luminance. These tendencies were particularly obvious at low luminance. The luminance of the LCD device by use of a telescopic-type luminance meter should be measured with test patterns that have a black background and a smaller measurement area than that for the TG-18 LN test patterns.

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RATIONALE AND OBJECTIVE: Our purpose in this study is to apply an artificial neural network (ANN) for differential diagnosis of certain hepatic masses on computed tomographic (CT) images and evaluate the effect of ANN output on radiologist diagnostic performance. MATERIALS AND METHODS: We collected 120 cases of hepatic disease. We used a single three-layer feed-forward ANN with a back-propagation algorithm. The ANN is designed to differentiate four hepatic masses (hepatocellular carcinoma, intrahepatic peripheral cholangiocarcinoma, hemangioma, and metastasis) by using nine clinical parameters and 24 radiological findings in dual-phase contrast-enhanced CT images. Thus, the ANN consisted of 33 input units and four output units. Subjective ratings for the 24 radiological findings were provided independently by two attending radiologists. All clinical cases were used for training and testing of the ANN by implementation of a round-robin technique. In the observer test, CT images of all 120 cases (30 cases for each disease) were used. CT images were viewed by seven radiologists first without and then with ANN output. Radiologist performance was evaluated by using receiver operating characteristic (ROC) analysis on a continuous rating scale. RESULTS: Averaged area under the ROC curve for ANN alone was 0.961. The diagnostic performance of seven radiologists increased from 0.888 to 0.934 (P < .02) when they used ANN output. CONCLUSION: The ANN can provide useful output as a second opinion to improve radiologist diagnostic performance in the differential diagnosis of hepatic masses seen on contrast-enhanced CT.

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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.

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Diffusion tensor (DT) magnetic resonance imaging (MRI) provides the directional information of local neuronal fibers, and has been used to estimate the neuroanatomical connectivity in the cerebral white matter. Several methods for white matter tractography have been developed based on DT-MRI. However, it has been difficult to estimate the white matter tract pathways in the fiber crossing and branching region because of the ambiguity of the principal eigenvector and/or low anisotropy due to the partial volume effect. In this paper, we proposed a new method for white matter tractography, which permits fiber tract branching and passing through crossing regions. Our tractography method is based on a three-dimensional (3D) directional diffusion function (DDF), which was given by a 3D anisotropic Gaussian function defined by normalized three eigenvalues and their corresponding eigenvectors of DT. The DDF was used for generation of a 3D directional diffusion field and for determination of the connectivity between the voxels in fiber tracking. To extract the white matter tract region, DDF-based tractography (DDFT) method used the directional diffusion field instead of a threshold fractional anisotropy map, which has been used in the conventional methods, so that low anisotropy voxels in the branching and crossing regions may be included. We applied the DDFT method and two conventional tractography methods (a streamline technique and a tensorline algorithm) to DT-MRI data of five normal subjects for visualizing the pyramidal tract. Our method visualized the pathways connected to a large portion of the primary motor cortex, including foot, hand and face motor areas, passing through the crossing regions with other white matter tracts in all subjects, whereas the conventional methods showed only a small portion of the pyramidal tract. The pyramidal tract pathways estimated by our method were consistent with the neuroanatomical knowledge. In conclusion, the DDFT method may be useful in assisting neuroradiologists in estimating the white matter tracts.

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