In computed tomography, star shape artifacts are introduced by metal objects, which are inside a patient's
body. The quality of the reconstructed image can be enhanced by applying a metal artifact reduction method. Unfortunately, a method that removes all such artifacts in order to make the images valuable for medical diagnosis remains to be found. In this study, the influence of metal segmentation is investigated. A thresholding technique, which is the state of the art in the field, is compared with a manual segmentation. Results indicate that a more accurate segmentation can lead to a preservation of important anatomical details, which are of high value for medical diagnosis.
In computed tomography (CT), the nonlinear characteristics of beam hardening are due to the polychromaticity of X-rays, which severely degrade the CT image quality and diagnostic accuracy. The correction of beam hardening has been an active area since the early years of CT, and various techniques have been developed. State of-the-art works on multi-material beam hardening correction (BHC) are mainly based on segmenting datasets into different materials, and correcting the non-linearity iteratively. Those techniques are limited in correction effectiveness due to inaccurate segmentation. Furthermore, most of them are computationally intensive. In this study, we introduce a fast BHC scheme based on frequency splitting with the fact that beam hardening artifacts mainly contain in the low frequency components and take more iterations to be corrected in comparison with high frequency components. After low-pass filtering and correcting artifacts at down-sampled projections, an artifact reduced high resolution reconstruction will be obtained by incorporating the original edge information from the high frequency components. Evaluations in terms of correction accuracy and computational efficiency are performed using simulated and real CT datasets. In comparison to the BHC algorithm without frequency splitting, the proposed accelerated algorithm yields comparable results in correcting cupping and streak artifacts with tremendously reduced computational effort. We conclude that the presented framework can achieve a significant speedup while still obtaining excellent artifact reduction. This is a significant practical advantage for clinical as well as industrial CT.
Computer-assisted diagnosis (CADx) for the interactive characterization of mammographic masses as benign or malignant has a high potential to help radiologists during the critical process of diagnostic decision making. By default, the characterization of mammographic masses is performed by extracting features from a region of interest (ROI) depicting the mass. To investigate the influence of a so-called bilateral filter based emph{flat texture} (FT) preprocessing step on the classification performance, textural as well as frequency-based features are calculated in the ROI, in the core of the mass and in the mass margin for preprocessed and unprocessed images. Furthermore. the influence of the parameterization of the bilateral filter on the classification performance is investigated. Additionally, as reference Median and Gaussian filters have been used to compute the FT image and the resulting classification performances of the feature extractors are compared to those obtained with the bilateral filters. Classification is done using a k-NN classifier. The classification performance was evaluated using the area Az under the receiver operating characteristic (ROC) curve. A publicly available mammography database was used as reference image data set. The results show that the proposed FT preprocessing step has a positive influence on the texture-based feature extractors while most of the frequency-based feature extractors perform better on the unprocessed images. For some of the features the original Az could be improved up to 10%. The comparison of the bilateral filter approach with the Median and Gaussian filter approaches showed the superiority of the bilateral filter.
Computer-assisted diagnosis (CADx) for the characterization of mammographic masses as benign or malignant has a very high potential to help radiologists during the critical process of diagnostic decision making.
By default, the characterization of mammographic masses is performed by extracting features from a region of interest (ROI) depicting the mass.
To investigate the influence of the region on the classification performance, textural, morphological, frequency- as well as moment-based features are calculated in subregions of the ROI, which has been delineated manually by an expert.
The investigated subregions are
(a) the semi-automatically segmented area which includes only the core of the mass,
(b) the outer border region of the mass, and
(c) the combination of the outer and the inner border region, referred to as mass margin.
To extract the border region and the margin of a mass an extended version of the rubber band straightening transform (RBST) was developed. Furthermore, the effectiveness of the features extracted from the RBST transformed border region and mass margin is compared to the effectiveness of the same features extracted from the untransformed regions.
After the feature extraction process a preferably optimal feature subset is selected for each feature extractor. Classification is done using a k-NN classifier.
The classification performance was evaluated using the area Az under the receiver operating characteristic curve.
A publicly available mammography database was used as data set. Results showed that the manually drawn ROI lead to superior classification performances for the morphological feature extractors and that the transformed outer border region and the mass margin are not suitable for moment-based features but yield to promising results for textural and frequency-based features.
Beyond that the mass margin, which combines the inner and the outer border region, leads to better classification performances compared to the outer border region for its own.
KEYWORDS: Computer aided diagnosis and therapy, Image segmentation, Medical imaging, Current controlled current source, Computing systems, Absorbance, Tissues, Databases
Computer aided diagnosis (CADx) systems can support the radiologist in the complex task of discriminating benign and malignant mammographic lesions. Automatic segmentation of mammographic lesions in regions of interest (ROIs) is a core module of many CADx systems. Previously, we have proposed a novel method for segmentation of mammographic masses. The approach was based on the observation that the optical density of a mass is usually high near its core and decreases towards its boundary. In the work at hand, we improve this approach by integration of a pre-processing module for the correction of inhomogeneous background tissue and by improved selection of the optimal mass contour from a list of candidates based on a cost function. We evaluate the performance of the proposed approach using ten-fold cross-validation on a database of mass lesions and ground-truth segmentations. Furthermore, we compare the improved segmentation approach with the previously proposed approach and with implementations of two state of the art approaches. The results of our study indicate that the proposed approach outperforms both the original method and the two state of the art methods.
KEYWORDS: Computer aided diagnosis and therapy, Breast cancer, Picture Archiving and Communication System, Mammography, Magnetic resonance imaging, Telecommunications, Medical imaging, Ultrasonography, Breast, Digital breast tomosynthesis
While screening mammography is accepted as the most adequate technique for the early detection of breast cancer, its low positive predictive value leads to many breast biopsies performed on benign lesions. Therefore, we have previously developed a knowledge-based system for computer-aided diagnosis (CADx) of mammographic lesions. It supports the radiologist in the discrimination of benign and malignant lesions. So far, our approach operates on the lesion level and employs the paradigm of content-based image retrieval (CBIR). Similar lesions with known diagnosis are retrieved automatically from a library of references. However, radiologists base their diagnostic decisions on additional resources, such as related mammographic projections, other modalities (e.g. ultrasound, MRI), and clinical data. Nonetheless, most CADx systems disregard the relation between the craniocaudal (CC) and mediolateral-oblique (MLO) views of conventional mammography. Therefore, we extend our approach to the full case level: (i) Multi-frame features are developed that jointly describe a lesion in different views of mammography. Taking into account the geometric relation between different images, these features can also be extracted from multi-modal data; (ii) the CADx system architecture is extended appropriately; (iii) the CADx system is integrated into the radiology information system (RIS) and the picture archiving and communication system (PACS). Here, the framework for image retrieval in medical applications (IRMA) is used to support access to the patient's health care record. Of particular interest is the application of the proposed CADx system to digital breast tomosynthesis (DBT), which has the potential to succeed digital mammography as the standard technique for breast cancer screening. The proposed system is a natural extension of CADx approaches that integrate only two modalities. However, we are still collecting a large enough database of breast lesions with images from multiple modalities to evaluate the benefits of the proposed approach on.
Computer aided diagnosis (CADx) systems have the potential to support the radiologist in the complex task of discriminating benign and malignant types of breast lesions based on their appearance in mammograms. Previously, we have proposed a knowledge-based CADx approach for mammographic mass lesions using case-based reasoning. The input of the systems reasoning process are features that are automatically extracted from regions of interest (ROIs) depicting mammographic masses. However, despite the fact that the shape of a mass as well as the characteristics of its boundary are highly discriminative attributes for its diagnosis, we have not included shape and boundary features that are based on an explicit segmentation of the mass from the background tissue in the previously proposed CADx approach. Hence, we present a novel method for the segmentation of mammographic masses in this work and describe how we have integrated this segmentation module into our existent CADx system. The approach is based on the observation that the optical density of a mass is usually high near its core and decreases towards its boundary. Because of tissue superposition and the broad variety of appearances of masses, their automatic segmentation is a difficult task. Thus, it is not surprising that even after many years of research concerning the segmentation of masses no fully automatic approach that robustly solves the problem seems to exist. For this reason, we have included optional interactive modules in the proposed segmentation approach that allow fast and easy corrective interference of the radiologist with the segmentation process.
Screening mammography is recognized as the most effective tool for early breast cancer detection. However, its
application in clinical practice shows some of its weaknesses. While clustered microcalcifications are often an
early sign of breast cancer, the discrimination of benign from malignant clusters based on their appearance in
mammograms is a very difficult task. Hence, it is not surprising that typically only 15% to 30% of breast biopsies
performed on calcifications will be positive for malignancy. As this low positive predictive value of mammography
regarding the diagnosis of calcification clusters results in many unnecessary biopsies performed on benign
calcifications, we propose a novel computer aided diagnosis (CADx) approach with the goal to improve the reliability
of microcalcification classification. As effective automatic classification of microcalcification clusters relies
on good segmentations of the individual calcification particles, many approaches to the automatic segmentation
of individual particles have been proposed in the past. Because none of the fully automatic approaches seem to
result in optimal segmentations, we propose a novel semiautomatic approach that has automatic components but
also allows some interaction of the radiologist. Based on the resulting segmentations we extract a broad range
of features that characterize the morphology and distribution of calcification particles. Using regions of interest
containing either benign or malignant clusters extracted from the digital database for screening mammography
we evaluate the performance of our approach using a support vector machine and ROC analysis. The resulting
ROC performance is very promising and we show that the performance of our semiautomatic segmentation is
significantly higher than that of a comparable fully automatic approach.
Today, mammography is recognized as the most effective technique for breast cancer screening. Unfortunately,
the low positive predictive value of breast biopsy examinations resulting from mammogram interpretation leads
to many unnecessary biopsies performed on benign lesions. In the last years, several computer assisted diagnosis
(CADx) systems have been proposed with the goal to assist the radiologist in the discrimination of benign and
malignant breast lesions and thus to reduce the high number of unnecessary biopsies. In this paper we present
a novel, knowledge-based approach to the computer aided discrimination of mammographic mass lesions that
uses computer-extracted attributes of mammographic masses and clinical data as input attributes to a case-based
reasoning system. Our approach emphasizes a transparent reasoning process which is important for the
acceptance of a CADx system in clinical practice. We evaluate the performance of the proposed system on a
large publicly available mammography database using receiver operating characteristic curve analysis. Our results
indicate that the proposed CADx system has the potential to significantly reduce the number of unnecessary
breast biopsies in clinical practice.
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