Effects of applying high-pass filtering in pelvimetry with Martius images.

AIM: The aim of this study is to investigate whether the results of pelvimetry using original radiographic Martius images and the same images with high-pass filtering applied ("edge images") would be consistent. METHODS: A total of 30 primagravidas were included in this study. Three obstetricians independently measured the anteroposterior and transverse diameters of the pelvic inlet in the original and the edge images, recording the x- and y-coordinates of the four endpoints. A Wilcoxon signed rank sum test was performed on the coordinate data to evaluate differences between the original and edge images. RESULTS: In the analysis of all coordinate data, statistically significant differences were found in both x- and y-coordinates of the sacral promontory point (SPP). In the y-coordinate of the SPP, a statistically significant difference was found in 9 of 30 pairs of images, and in all 9 the anteroposterior diameter was shorter in the edge images compared to the original images due to the more caudal placement of the SPP. CONCLUSIONS: The coordinates of the SPP on original radiographs and their edge images were not consistent in pelvimetry using Martius images. Our results suggest that improved image contrast will allow obstetricians to better assess pelvic narrowing and cephalopelvic disproportion and even reduce radiographic dose, thereby reducing risks for pregnant women and their fetuses.

Estimation of undistorted images in brain echo-planar images with distortions using the conjugate gradient method with anatomical regularization.

PURPOSE: Although echo-planar imaging (EPI) is widely used for diffusion magnetic resonance (MR) imaging, EPI images suffer from susceptibility-induced geometric distortions. We herein propose a new estimation method for undistorted EPI images using anatomical T1 -weighted images (T1 WIs) based on the physics of MR imaging. METHODS: Our proposed method estimates the undistorted EPI image in the image domain while estimating the magnetic field inhomogeneity map using the conjugate gradient method with anatomical regularization. Our method synthesizes the distorted image to match the measured EPI image containing geometric distortions by alternately updating the undistorted EPI image and the magnetic field inhomogeneity map. We evaluated our proposed method and compared it with a nonrigid registration-based distortion correction method using simulated data and using real data. In the evaluation of the estimation of the magnetic field inhomogeneity map, we used the normalized root-mean-squared error (NRMSE) between the estimated results and the ground truth. In the evaluation of the estimation of undistorted images, we used mutual information (MI) between the undistorted EPI image and the anatomical T1 WI. RESULTS: Using the simulated data, the means and standard deviations of the NRMSE values in the nonrigid registration-based method and proposed method were 1.29 ± 0.63 and 0.64 ± 0.30, respectively. The MI values in the proposed method were larger than those in the nonrigid registration-based method in all evaluated slices. For the real data, the proposed method improved the distortion, and the MI values in the proposed method were larger than those in the nonrigid registration-based method. In the estimation of the magnetic field inhomogeneity map, the NRMSE values in our method were smaller than those in the nonrigid registration-based method. CONCLUSIONS: We demonstrated that our proposed method can estimate the regions with compressed distortions that are not well represented by the nonrigid registration-based methods. The results suggest that the proposed method could be useful in analyses combining EPI images with T1 WIs.

Comparison of intravoxel incoherent motion diffusion-weighted imaging between turbo spin-echo and echo-planar imaging of the head and neck.

OBJECTIVES: To compare image quality, apparent diffusion coefficient (ADC), and intravoxel incoherent motion (IVIM)-derived parameters between turbo spin-echo (TSE)-diffusion-weighted imaging (DWI) and echo-planar imaging (EPI)-DWI of the head and neck. METHODS: Fourteen volunteers underwent head and neck imaging using TSE-DWI and EPI-DWI. Distortion ratio (DR), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), ADC and IVIM-derived parameters were compared between the two techniques. Bland-Altman analysis was performed to analyse reproducibility between the quantitative parameters of TSE-DWI and EPI-DWI. RESULTS: DR of TSE-DWI was significantly smaller than that of EPI-DWI. SNR and CNR of TSE-DWI were significantly higher than those of EPI-DWI. ADC and IVIM-derived parameters of TSE-DWI showed higher values than those of EPI-DWI, although the difference was not significant. Bland-Altman analysis showed wide limits of agreement between the two sequences. CONCLUSION: TSE-DWI can produce better image quality than EPI-DWI, while TSE-DWI possibly exhibits different values of quantitative parameters. Therefore, TSE-DWI could be a good alternative to EPI-DWI for patients sensitive to distortion. However, it is not recommended to use both TSE-DWI and EPI-DWI on follow-up. KEY POINTS: • Head and neck DWI is especially sensitive to magnetic inhomogeneity. • The distortion of images was less with TSE-DWI than with EPI-DWI. • TSE-DWI can possibly exhibit higher ADC and IVIM-derived parameters than EPI-DWI. • Bland-Altman analysis showed unacceptable LoA in quantitative analysis between TSE-DWI and EPI-DWI. • It is not recommended to use both TSE-DWI and EPI-DWI for follow-up.

Efficacy of periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) for shoulder magnetic resonance (MR) imaging.

OBJECTIVES: To elucidate the utility of PROPELLER for motion artefact reduction on shoulder MRI and to examine the influence of streak artefacts on diagnosis of clinical images. METHODS: 15 healthy volunteers and 48 patients underwent shoulder MRI with/without PROPELLER (coronal oblique proton density-fast spin echo [PD-FSE], sagittal oblique T2-FSE). In a volunteer study, all sequences were performed in both static and exercise-loaded conditions. Two radiologists graded artefacts and delineation of various anatomical structures in the volunteer study and motion and streak artefacts in the clinical study. Mean scores were compared between sequences with/without PROPELLER. In the clinical study, mean scores of motion artefacts were compared with mean scores of streak artefacts. Wilcoxon signed-rank test was used for all comparisons. RESULTS: In both studies, PROPELLER significantly reduced motion artefacts (P<0.05). In the volunteer study, it significantly improved delineations in sagittal oblique images in the exercise-loaded condition (P<0.05). In the clinical study, streak artefacts appeared dominantly on images with PROPELLER (P<0.05), but influenced diagnosis to a lesser extent than motion artefacts. CONCLUSION: PROPELLER can reduce motion artefacts in shoulder MRI. While it does cause streak artefacts, it affects diagnosis to a lesser extent.

Efficacy of the radial acquisition regime (RADAR) for acquiring head and neck MR images.

OBJECTIVE: To investigate the efficacy of the radial acquisition regime (RADAR) for acquiring head and neck MR images. METHODS: 15 healthy volunteers underwent imaging with 4 sequences [fast spin echo T2 weighted imaging (FSE-T2WI), RADAR T2 weighted imaging (RADAR-T2WI), single-shot echo planar imaging diffusion-weighted imaging (SS-EPI-DWI) and RADAR diffusion-weighted imaging (RADAR-DWI)]. Both standard images and images during periodic mouth motion were acquired. Two radiologists scored the overall image artefacts and detectability of several anatomical structures without knowledge of sequence type. For each sequence, image distortion was quantitatively compared by the anteroposterior to right-left ratio of several anatomical structures. The mean scores of artefacts and distortion of several anatomical structures were compared using the multiple comparison test. The detectabilities were compared using the Wilcoxon signed-rank test. RESULTS: Regardless of mouth motion, RADAR-T2WI was significantly superior to FSE-T2WI in artefacts and oral-area detectability (p < 0.01), and RADAR-DWI was significantly superior to SS-EPI-DWI in terms of artefacts (p < 0.01). In terms of image distortion, RADAR-DWI was significantly superior to SS-EPI-DWI (p < 0.01). CONCLUSION: RADAR-T2WI could replace FSE-T2WI as a conventional T2WI protocol for the head and neck. For the RADAR-DWI sequence, validation studies are needed. Advances in knowledge: RADAR-T2WI was superior to FSE-T2WI with regard to artefacts and detectability, and RADAR-DWI was superior in terms of artefacts compared with SS-EPI-DWI.

Evaluation of ventricular dysfunction using semi-automatic longitudinal strain analysis of four-chamber cine MR imaging.

The aim of this study was to evaluate ventricular dysfunction using the longitudinal strain analysis in 4-chamber (4CH) cine MR imaging, and to investigate the agreement between the semi-automatic and manual measurements in the analysis. Fifty-two consecutive patients with ischemic, or non-ischemic cardiomyopathy and repaired tetralogy of Fallot who underwent cardiac MR examination incorporating cine MR imaging were retrospectively enrolled. The LV and RV longitudinal strain values were obtained by semi-automatically and manually. Receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff of the minimum longitudinal strain value for the detection of patients with cardiac dysfunction. The correlations between manual and semi-automatic measurements for LV and RV walls were analyzed by Pearson coefficient analysis. ROC analysis demonstrated the optimal cut-off of the minimum longitudinal strain values (εL_min) for diagnoses the LV and RV dysfunction at a high accuracy (LV εL_min = -7.8 %: area under the curve, 0.89; sensitivity, 83 %; specificity, 91 %, RV εL_min = -15.7 %: area under the curve, 0.82; sensitivity, 92 %; specificity, 68 %). Excellent correlations between manual and semi-automatic measurements for LV and RV free wall were observed (LV, r = 0.97, p < 0.01; RV, r = 0.79, p < 0.01). Our semi-automatic longitudinal strain analysis in 4CH cine MR imaging can evaluate LV and RV dysfunction with simply and easy measurements. The strain analysis could have extensive application in cardiac imaging for various clinical cases.

The radiological diagnosis of fenestral otosclerosis: the utility of histogram analysis using multidetector row CT.

Bone density measurements using high-resolution CT have been reported to be useful to diagnose fenestral otosclerosis. However, small region of interest (ROI) chosen by less-experienced radiologists may result in false-negative findings. Semi-automatic analysis such as CT histogram analysis may offer improved assessment. The aim of this study was to evaluate the utility of CT histogram analysis in diagnosing fenestral otosclerosis. Temporal bone CT of consecutive patients with otosclerosis and normal controls was retrospectively analyzed. The control group consisted of the normal-hearing contralateral ears of patients with otitis media, cholesteatoma, trauma, facial nerve palsy, or tinnitus. All CT images were obtained using a 64-detector-row CT scanner with 0.5-mm collimation. AROI encompassing 10 × 10 pixels was placed in the bony labyrinth located anterior to the oval window. The mean CT value, variance and entropy were compared between otosclerosis patients and normal controls using Student's t test. The number of pixels below mean minus SD in the control (%Lowcont) and total subjects (%Lowtotal) were also compared. In addition, the area under the receiver operating characteristic curves (AUC) value for the discrimination between otosclerosis patients and normal controls was calculated. 51 temporal bones of 38 patients with otosclerosis and 30 temporal bones of 30 control subjects were included. The mean CT value was significantly lower in otosclerosis cases than in normal controls (p < 0.01). In addition, variance, entropy, %Lowcont and %Lowtotal were significantly higher in otosclerosis cases than in normal controls (p < 0.01, respectively). The AUC values for the mean CT value, %Lowcont and %Lowtotal were 0.751, 0.760 and 0.765, respectively. In conclusion, our results demonstrated that histogram analysis of CT image may be of clinical value in diagnosing otosclerosis.

Evaluation of cardiac dyssynchrony with longitudinal strain analysis in 4-chamber cine MR imaging.

PURPOSE: We investigated the clinical performance of evaluation of cardiac mechanical dyssynchrony with longitudinal strain analysis using four-chamber (4CH) cine magnetic resonance imaging (MRI). MATERIALS AND METHODS: We retrospectively enrolled 73 chronic heart failure patients (41 men, 32 women; mean age, 57 years, NYHA 2, 3, and 4) who underwent a cardiac MRI in the present study. The left ventricular dyssynchrony (LVD) and interventricular dyssynchrony (IVD) indices were calculated by longitudinal strain analysis using 4 CH cine MRI. The LVD and IVD indices were compared by the Wilcoxon rank-sum test between the patients with indication for cardiac resynchronization therapy (CRT) (n = 13) and without indication for CRT (n = 60), with LGE (n = 40) and without LGE (n = 27), the CRT responders (n = 8) and non-responders (n = 6), respectively. RESULTS: LVD in the patients with indication for CRT were significantly longer than those without indication for CRT (LVD: 92 ± 65 vs. 28 ± 40 ms, P<.01). LVD and IVD were significantly longer in the patients with LGE than those without LGE (LVD: 54 ± 58 vs. 21 ± 30 ms, P<.01 and IVD: 51 ± 39 vs. 23 ± 34 ms, P<.01). LVD and IVD in the CRT responders were significantly longer than the CRT non-responders (LVD: 126 ± 55 vs. 62 ± 55 ms, P<.01 and IVD: 96 ± 39 vs. 52 ± 40 ms, P<.05). CONCLUSION: Longitudinal strain analysis with 4CH cine MRI could be useful for clinical examination in the evaluation of cardiac mechanical dyssynchrony.

Improvement of partial volume segmentation for brain tissue on diffusion tensor images using multiple-tensor estimation.

To improve evaluations of cortical and subcortical diffusivity in neurological diseases, it is necessary to improve the accuracy of brain diffusion tensor imaging (DTI) data segmentation. The conventional partial volume segmentation method fails to classify voxels with multiple white matter (WM) fiber orientations such as fiber-crossing regions. Our purpose was to improve the performance of segmentation by taking into account the partial volume effects due to both multiple tissue types and multiple WM fiber orientations. We quantitatively evaluated the overall performance of the proposed method using digital DTI phantom data. Moreover, we applied our method to human DTI data, and compared our results with those of a conventional method. In the phantom experiments, the conventional method and proposed method yielded almost the same root mean square error (RMSE) for gray matter (GM) and cerebrospinal fluid (CSF), while the RMSE in the proposed method was smaller than that in the conventional method for WM. The volume overlap measures between our segmentation results and the ground truth of the digital phantom were more than 0.8 in all three tissue types, and were greater than those in the conventional method. In visual comparisons for human data, the WM/GM/CSF regions obtained using our method were in better agreement with the corresponding regions depicted in the structural image than those obtained using the conventional method. The results of the digital phantom experiment and human data demonstrated that our method improved accuracy in the segmentation of brain tissue data on DTI compared to the conventional method.

[Analysis and visualization of diffusion tensor MRI].

In magnetic resonance imaging (MRI), the contrast mechanisms based on the water diffusion provide an understanding of the microscopic geometry of tissues and related tissue composition. To provide a general view of this rapidly developing area, the key concept in diffusion MRI and its potential applications are described. This article provides explains data acquisition of diffusion MRI, analysis, and visualization methods that are relevant to studying microstructure using diffusion tensor MRI.

Partial volume estimation and segmentation of brain tissue based on diffusion tensor MRI.

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.

Subjective similarity of patterns of diffuse interstitial lung disease on thin-section CT: an observer performance study.

RATIONALE AND OBJECTIVES: The aim of this study was to investigate the subjective similarity for pairs of images with various abnormal patterns of diffuse interstitial lung disease on thin-section computed tomography by experienced radiologists to explore a basis for selecting similar images to assist radiologists' interpretation. MATERIALS AND METHODS: Four major patterns (ground-glass opacity, nodular opacity, reticular opacity, and honeycombing) on thin-section computed tomographic images were identified by at least two of three radiologists. One radiologist manually selected 104 image pairs, in which the images in each pair had the same pattern and were similar in appearance. An additional 208 image pairs were randomly selected and evenly divided among the four patterns. These pairs were then rated for subjective similarity (on a continuous scale ranging from 0 = not similar at all to 1.0 = almost identical) by 12 radiologists. RESULTS: For radiologist-selected pairs, the mean similarity rated by the 12 radiologists was 0.72. For randomly selected pairs, the mean similarity was higher for the same pattern (0.47) than for the varying patterns (0.27) (P < .001), and among the same pattern, the mean similarity was 0.63 for ground-glass opacity, 0.58 for honeycombing, 0.45 for nodular opacity, and 0.32 for reticular opacity. The mean standard deviation for similarity ratings on all pairs given by the 12 radiologists was 0.05 (rang, 0.01-0.09). CONCLUSION: Subjective similarity ratings for pairs of abnormal images can be measured reliably and reproducibly by radiologists and will provide a basis for the selection of similar images to assist radiologists' interpretation.

Age-related microstructural changes in subcortical white matter during postadolescent periods in men revealed by diffusion-weighted MR imaging.

Continuous maturation of cerebral white matter (WM) in the postadolescent period is not fully understood. To elucidate the time course and location of possible postadolescent maturational changes in cerebral WM, we studied 60 healthy male subjects who were in their second to seventh decade using diffusion-weighted imaging. Mean diffusivity (MD) in subcortical WM was measured in 78 cortical regions in each subject's brain using an automated method. Regression analysis was used to model the age-related change in MD by either a linear or a quadratic function in each region. Age-related changes in subcortical MD were best modeled by either a linear function or a quadratic function in 27 regions including language-related regions, visual or multimodal areas in the bilateral occipital and temporal lobes, limbic areas including the bilateral parahippocampal gyri, and the bilateral postcentral and left precentral gyri. In these regions, the MD rapidly decreased until middle age and thereafter reached a plateau. Our results revealed microstructural changes in local subcortical WM and suggests a continuing maturational process in postoadolescent periods.

An investigation of radiologists' perception of lesion similarity: observations with paired breast masses on mammograms and paired lung nodules on CT images.

RATIONALE AND OBJECTIVES: We conducted an observer study to investigate whether radiologists can judge similarities in pairs of breast masses and lung nodules consistently and reproducibly. MATERIALS AND METHODS: Institutional review board approval and informed observer consent were obtained. This study was compliant with the Health Insurance Portability and Accountability Act. We used eight pairs of breast masses on mammograms and eight pairs of lung nodules on computed tomographic images, for which subjective similarity ratings ranging from 0 to 1 were determined in our previous studies. From these, four sets of image pairs were created (ie, a set of eight mass pairs, a set of eight nodule pairs, and two mixed sets of four mass and four nodule pairs). Eight radiologists, including four breast radiologists and four chest radiologists, compared all combinations of the eight pairs in each set using a two-alternative forced-choice (2AFC) method to determine the similarity ranking scores by identifying which pair was more similar than the other pair based on the overall impression for diagnosis. RESULTS: In the mass set and nodule set, the relationship between the average subjective similarity ratings and the average similarity ranking scores by 2AFC indicated very high correlations (r = 0.91 and 0.88). Moreover, in the two mixed sets, the correlations between the average subjective similarity ratings and the average similarity ranking scores were also very high (r = 0.90 and 0.98). Thus, radiologists were able to compare the similarities for pairs of lesions consistently, even in the unusual comparison of pairs of completely different types of lesions. CONCLUSION: The subjective similarity of a pair of lesions in medical images can be quantified consistently by a group of radiologists. The concept of similarity of lesions in medical images can be subjected to rigorous scientific research and investigation in the future.

Automated method for identification of patients with Alzheimer's disease based on three-dimensional MR images.

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.

MR tractography based on directional diffusion function validation in somatotopic organization of the pyramidal tract.

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.

Cortical damage in Alzheimer's disease estimation in medial and lateral aspects of the cerebrum using an improved mapping method based on diffusion-weighted magnetic resonance imaging.

RATIONALE AND OBJECTIVES: A method of estimating and mapping the cortical damage resulting from neurodegenerative diseases based on diffusion-weighted imaging was recently proposed. We improved on this method to visualize the cortical damage in Alzheimer's disease (AD) in the lateral and medial aspects of the cerebral hemispheres and to provide anatomic references. MATERIALS AND METHODS: Damage in the cerebral cortex was estimated based on diffusivity in the subcortical white matter according to a previously published method. A map of subcortical mean diffusivity (MD) was superimposed on the corresponding anatomic image so that the spatial extent of the abnormality could be anatomically localized. The right and left hemispheres were separated to evaluate the medial and lateral aspects of each hemisphere. This method was applied to 10 healthy subjects and 11 AD patients. MDs within 20 cortical regions were visually evaluated and statistically compared between AD and healthy subjects at a significance level of P < .01. RESULTS: In addition to the involvement of the lateral aspects of the bilateral parietal and temporal lobes and clear sparing of the bilateral pericentral regions that were previously reported, significant MD elevation was observed in the medial aspects of the right frontal, bilateral parietal, and right temporal lobes. The extent of MD abnormalities was easily identified by the background anatomic image. CONCLUSIONS: Results suggested that AD damage in the lateral and medial cerebral cortex can be visualized with an anatomic reference using our method.

Usefulness of artificial neural network for differential diagnosis of hepatic masses on CT images.

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.

[Image quality and detection performance of a direct digital radiography system].

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.