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We constructed a mammography database of 807 Japanese women and 2,772 images obtained using five commercial full-field digital mammography (FFDM) devices at four different facilities. Five types of mammography devices fabricated by four manufacturers were used: one with a Mo target (AMULET F), one with Mo and Rh targets (Senographe DS), one with Mo and W targets (AMULET), and two with a W target (MAMMOMAT Fusion and Selenia Dimensions). The purpose of this study was to focus on the mean glandular dose (MGD) in the database and analyze the difference in the MGD of Japanese women radiographed by mammographic devices with different targets or target/filter combinations. Furthermore, we clarify the difference between the displayed and measured MGDs for the three types of mammography devices. The average compression pressure and compression breast thickness of the Japanese women in the mammography in this study were 90.9±21.7 N and 43.3±12.9 mm, respectively. The breast compression pressure slightly varied depending on the facility or FFDM device, while the compression breast thickness decreased with the increase in the compression pressure for all FFDM devices. Differences in breast compression thickness existed depending on the mammography devices. The MGDs of the two types of mammography devices using the W target were smallest (1.335±0.358, 1.218±0.464 mGy). The displayed and measured MGDs of the three types of FFDM devices had a good correlation. However, the difference between the displayed and measured MGDs of the two devices increased with the MGD.

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.

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/K air) volume histogram was obtained from the GD distributions, which were indicated by the glandular volume (%) as a function of GD/K air. The GD indices, namely, the maximum glandular dose (GD2%) and glandular volume percentage (%) receiving at least the mean glandular dose (MGD) (V MGD) were calculated from the GD/K air volume histogram. Next, the scatter plots of GD2%/MGD and V MGD were drawn as functions of the normalised mean glandular dose (DgN). Finally, (GD2%) i and (V MGD) i were 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 of V MGD were proportional to DgN and decreased with increase in the compressed breast thickness. The values of (MGD) i and (GD2%) i for 596 clinical irradiation cases were estimated to range from 0.6–3.0 mGy to 1.1–7.0 mGy, respectively, and (V MGD) i was in the range 32%−48%. (GD2%) i and (V MGD) i are mainly affected by breast thickness. These indices are useful for the evaluation of glandular dose heterogeneity in mammography.

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.

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.

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.

Purpose: Braintissue segmentation based on diffusiontensormagnetic 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 braintissue 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 maximuma 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 braintissue on DT-MRI data over the conventional method. This method may be useful in evaluating the cortical and subcortical diffusivity in neurological diseases.

The purpose of this study was to develop a computerized method for estimation of the location of a lung tumor in cine images on an electronic portal imaging device (EPID) without implanted markers during stereotactic body radiotherapy (SBRT). Each tumor region was segmented in the first EPID cine image, i.e., reference portal image, based on a multiple-gray level thresholding technique and a region growing technique, and then the image including the tumor region was cropped as a 'tumor template' image. The tumor location was determined as the position in which the tumor template image took the maximum cross-correlation value within each consecutive portal image, which was acquired in cine mode on the EPID in treatment. EPID images with 512 x 384 pixels (pixel size: 0.56 mm) were acquired at a sampling rate of 0.5 frame s(-1) by using energies of 4, 6 or 10 MV on linear accelerators. We applied our proposed method to EPID cine images (226 frames) of 12 clinical cases (ages: 51-83, mean: 72) with a non-small cell lung cancer. As a result, the average location error between tumor points obtained by our method and the manual method was 1.47 +/- 0.60 mm. This preliminary study suggests that our method based on the tumor template matching technique might be feasible for tracking the location of a lung tumor without implanted markers in SBRT.

BACKGROUND AND PURPOSE: Previous studies have suggested that use of an artificial neural network (ANN) system is beneficial for radiological diagnosis. Our purposes in this study were to construct an ANN for the differential diagnosis of intra-axial cerebral tumors on MR images and to evaluate the effect of ANN outputs on radiologists' diagnostic performance. MATERIALS AND METHODS: We collected MR images of 126 patients with intra-axial cerebral tumors (58 high-grade gliomas, 37 low-grade gliomas, 19 metastatic tumors, and 12 malignant lymphomas). We constructed a single 3-layer feed-forward ANN with a Levenberg-Marquardt algorithm. The ANN was designed to differentiate among 4 categories of tumors (high-grade gliomas, low-grade gliomas, metastases, and malignant lymphomas) with use of 2 clinical parameters and 13 radiologic findings in MR images. Subjective ratings for the 13 radiologic findings were provided independently by 2 attending radiologists. All 126 cases were used for training and testing of the ANN based on a leave-one-out-by-case method. In the observer test, MR images were viewed by 9 radiologists, first without and then with ANN outputs. Each radiologist's performance was evaluated through a receiver operating characteristic (ROC) analysis on a continuous rating scale. RESULTS: The averaged area under the ROC curve for ANN alone was 0.949. The diagnostic performance of the 9 radiologists increased from 0.899 to 0.946 (P < .001) when they used ANN outputs. CONCLUSIONS: The ANN can provide useful output as a second opinion to improve radiologists' diagnostic performance in the differential diagnosis of intra-axial cerebral tumors seen on MR imaging.

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.

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 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.

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.

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.

We investigated the clinical usefulness of a newly developed flat‑panel detector （FPD） system by com‑ paring its physical imaging properties and low‑contrast detectability with those of a current FPD system. The newly developed CsI‑based indirect FPD （Canon CXDI‑40C） and current Gd 2O2S‑based FPD （Canon CXDI‑11） systems were used. Characteristic curves resolution properties radiographic noise detective quantum efficiencies （DQEs） and low‑contrast detectability for both systems were measured. The new FPD system showed considerably lower noise levels than those of the current FPD system. DQE （0） s of the new and current FPD systems were 75％ and 35％ respectively. Observer performance tests of the contrast‑detail （C‑D） phantom indicated that the new FPD system can significantly improve low‑contrast performance over that obtainable with the current FPD system under the same conditions of exposure. The new FPD system provided approximately 50％ reduction in exposure while providing comparable detectability. The newly developed FPD system provides radiographic images with excellent inherent physical image quality and low‑contrast performance. Summary

In otorthinolaryngology, Stenvers' method is employed in radiography of the pyramid (internal acoustic meatus and semicircular canals). However, in cases of dizziness, where the prone position is difficult to achieve, we occasionally use the opposite Stenvers' method instead of the conventional one. This makes it possible to perform radiography with the patient in the supine position. Compared with the conventional Stenvers' method, the problems of this method were increases not only in the rate of magnification but also in lens dose. In this study, we evaluated these problems by employing computed tomography (CT) and a glass dosimeter with phantom as well as by clinical evaluation. The results showed no statistically significant difference between Stenvers' method and the opposite Stenvers' method in both the rate of magnification and the clinical evaluation. The increase in lens dose with the opposite Stenvers' method was not significant. We concluded that the opposite Stenvers' method was useful.

全国の乳がん検診における乳房撮影の実態を把握し, 撮影線量のガイダンスレベル設定の参考とするため, 全国104の検診施設での撮影線量を調査した。圧迫厚さ42mmの乳房に等価なファントム (RMI-156) と蛍光ガラス線量計バッジを各施設に送り, 日本放射線技術学会の乳房撮影精度管理マニュアルに記載された手順に準拠した方法による照射を依頼した。返送された蛍光ガラス線量計から入射皮膚表面の空中照射線量と実効エネルギーを求め, 平均乳腺線量を評価した。評価の精度は±8%であった。各施設の平均乳腺線量は0.5～3.7mGyの間に分布し, 平均値は1.48mGy, 標準偏差は0.52mGyであった。91施設では2mGy以下であり, これを超える施設でも, 自動露出制御機構の調整, グリッド, 増感紙フィルム系の最適化により, 容易に2mGy以下に低減できるものと期待された。標本集団に偏りがあるものの, 今回の調査結果からわが国のガイダンスレベルを設定するとすれば, 圧迫厚さ42mmの乳房に対する平均乳腺線量2mGyが適当である。

本研究では, わが国において乳癌検診にマンモグラフィを導入するにあたってのマンモグラフィの設置状況ならびに品質管理の実態, 読影可能または読影に協力できる医師数などの実態を調査し, 併せて放射線被曝リスク等について調査した。調査の結果, 1) 乳房撮影装置は全国2,380施設に備えられていた。うち104施設について乳房撮影における画質・線量の実態調査を実施した結果, 乳房撮影用増感紙一フィルム特性の感度は従来より約2倍高くなっており, 従来に比べて被曝線量の大幅な軽減が期待できることが判明した。今後は, 品質を保証するため撮影の標準化を行い, 精度管理のシステムを構築することが必要である。2) 撮影技術に関しては, 技術講習会を全国的に展開しており, その成果が現れている。技師数は充足しているが, 撮影技術, 品質管理についての教育が必要である.3) マンモグラフィ読影医師に関するアンケート調査では, 全国で2,576名の医師がマンモグラフィ読影に協力可能であり, これをマンモグラフィ検診のガイドラインに沿って, 50歳以上で隔年検診, 受診率30%とした場合, 医師1人当たりの受診者数は全国平均で920名/年 (医師2人で読影の場合は1,841名) と算出された。4) 医師の診断精度を高めるための教育システムが急務であるが, 今回実施した講習会と読影テストのROC解析の結果により, 短期間で診断精度の向上が得られ, 効果的な教育プログラムが具体化してきた。5) リスク・ベネフィット分析では, 検診により期待できる効果に比して, 被曝リスクがずっと低いことが示された。今後は検診者の多様性を考慮し, インフォームドコンセントを実施することが望ましい。以上より, マンモグラフィを導入した乳癌検診が現実的に実施可能であることが明らかとなってきた。

To determine the accuracy of transvaginal ultrasound (TVUS) and of precontrast and contrast material-enhanced magnetic resonance (MR) imaging in the differentiation of adnexal masses.Five blinded readers analyzed images of 80 masses in 72 patients. MR and TVUS images were interpreted in separate sessions. Findings were confirmed at surgery or laparoscopy.Higher diagnostic accuracy was attained with MR imaging in mature cystic teratomas and endometriomas. However, better accuracy was achieved with contrast-enhanced MR imaging and TVUS in simple cysts, cystadenomas, and malignant tumors because internal details could be visualized. Receiver operating characteristic study indicated that observer confidence was significantly higher with contrast-enhanced MR imaging than with precontrast MR imaging (P = .011) or TVUS (P = .002) in the differentiation of benign and malignant masses.Contrast-enhanced MR imaging is superior to precontrast MR and TVUS imaging in the characterization and differentiation of adnexal masses.

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.