KEYWORDS: Breast, Tissues, Sensors, Data modeling, Performance modeling, Human subjects, Monte Carlo methods, Computer simulations, Imaging systems, Mathematical modeling
This study aims to characterize the effect of background tissue density and heterogeneity on the detection of irregular masses in breast tomosynthesis, while demonstrating the capability of the sophisticated tools that can be used in the design, implementation, and performance analysis of virtual clinical trials (VCTs). Twenty breast phantoms from the extended cardiac-torso (XCAT) family, generated based on dedicated breast computed tomography of human subjects, were used to extract a total of 2173 volumes of interest (VOIs) from simulated tomosynthesis images. Five different lesions, modeled after human subject tomosynthesis images, were embedded in the breasts and combined with the lesion absent condition yielded a total of 6×2173 VOIs. Effects of background tissue density and heterogeneity on the detection of the lesions were studied by implementing a composite hypothesis signal detection paradigm with location known exactly, lesion known exactly or statistically, and background known statistically. Using the area under the receiver operating characteristic curve, detection performance deteriorated as density was increased, yielding findings consistent with clinical studies. A human observer study was performed on a subset of the simulated tomosynthesis images, confirming the detection performance trends with respect to density and serving as a validation of the implemented detector. Performance of the implemented detector varied substantially across the 20 breasts. Furthermore, background tissue density and heterogeneity affected the log-likelihood ratio test statistic differently under lesion absent and lesion present conditions. Therefore, considering background tissue variability in tissue models can change the outcomes of a VCT and is hence of crucial importance. The XCAT breast phantoms have the potential to address this concern by offering realistic modeling of background tissue variability based on a wide range of human subjects, comprising various breast shapes, sizes, and densities.
KEYWORDS: Breast, Tissues, Sensors, Human subjects, 3D modeling, Data modeling, Clinical trials, Signal detection, Digital breast tomosynthesis, Composites
Virtual clinical trials (VCT) can be carefully designed to inform, orient, or potentially replace clinical trials. The focus of this study was to demonstrate the capability of the sophisticated tools that can be used in the design, implementation, and performance analysis of VCTs, through characterization of the effect of background tissue density and heterogeneity on the detection of irregular masses in digital breast tomosynthesis. Twenty breast phantoms from the extended cardiactorso (XCAT) family, generated based on dedicated breast computed tomography of human subjects, were used to extract a total of 2173 volumes of interest (VOI) from simulated tomosynthesis images. Five different lesions, modeled after human subject tomosynthesis images, were embedded in the breasts, for a total of 6×2173 VOIs with and without lesions. Effects of background tissue density and heterogeneity on the detection of the lesions were studied by implementing a doubly composite hypothesis signal detection theory paradigm with location known exactly, lesion known exactly, and background known statistically. The results indicated that the detection performance as measured by the area under the receiver operating characteristic curve (ROC) deteriorated as density was increased, yielding findings consistent with clinical studies. The detection performance varied substantially across the twenty breasts. Furthermore, the log-likelihood ratio under H0 and H1 seemed to be affected by background tissue density and heterogeneity differently. Considering background tissue variability can change the outcomes of a VCT and is hence of crucial importance. The XCAT breast phantoms can address this concern by offering realistic modeling of background tissue variability based on a wide range of human subjects.
Physical phantoms are essential for the development, optimization, and clinical evaluation of x-ray systems. These
phantoms are used for various tests such as quality assurance testing, system characterization, reconstruction evaluation,
and dosimetry. They should ideally be capable of serving as ground truth for purposes such as virtual clinical trials.
Currently, there is no anthropomorphic 3D physical phantom commercially available. We present our development of a
new suite of physical breast phantoms based on real patient data. The phantoms were generated from the NURBS-based
extended cardiac-torso (XCAT) breast phantoms, which were segmented from patient dedicated breast computed
tomography data. High-resolution multi-material 3D printing technology was used to fabricate the physical models.
Glandular tissue and skin were presented by the most radiographically dense photopolymer available to the printer,
mimicking a 75% glandular tissue. Adipose tissue was presented by the least radiographically dense photopolymer,
mimicking a 35% glandular tissue. The glandular equivalency was measured by comparing x-ray images of samples of
the photopolymers available to the printer with those of breast tissue-equivalent materials. The mammographic
projections and tomosynthesis reconstructed images of fabricated models showed great improvement over available
phantoms, presenting a more realistic breast background.
Mammography is currently the most widely accepted tool for detection and diagnosis of breast cancer. However, the
sensitivity of mammography is reduced in women with dense breast tissue due to tissue overlap, which may obscure
lesions. Digital breast tomosynthesis with contrast enhancement reduces tissue overlap and provides additional
functional information about lesions (i.e. morphology and kinetics), which in turn may improve lesion characterization.
The performance of such techniques is highly dependent on the structural composition of the breast, which varies
significantly across patients. Therefore, optimization of breast imaging systems should be done with respect to this
patient versatility. Furthermore, imaging techniques that employ contrast require the inclusion of a temporally varying
breast composition with respect to the contrast agent kinetics to enable the optimization of the system. To these ends, we
have developed a dynamic 4D anthropomorphic breast phantom, which can be used for optimizing a breast imaging
system by incorporating material characteristics. The presented dynamic phantom is based on two recently developed
anthropomorphic breast phantoms, which can be representative of a whole population through their randomized
anatomical feature generation and various compression levels. The 4D dynamic phantom is incorporated with the
kinetics of contrast agent uptake in different tissues and can realistically model benign and malignant lesions. To
demonstrate the utility of the proposed dynamic phantom, contrast-enhanced digital mammography and breast
tomosynthesis were simulated where a ray-tracing algorithm emulated the projections, a filtered back projection
algorithm was used for reconstruction, and dual-energy and temporal subtractions were performed and compared.
Data sets with relatively few observations (cases) in medical research are common, especially if the data are expensive or difficult to collect. Such small sample sizes usually do not provide enough information for computer models to learn data patterns well enough for good prediction and generalization. As a model that may be able to maintain good classification performance in the presence of limited data, we used decision fusion. In this study, we investigated the effect of sample size on the generalization ability of both linear discriminant analysis (LDA) and decision fusion. Subsets of large data sets were selected by a bootstrap sampling method, which allowed us to estimate the mean and standard deviation of the classification performance as a function of data set size. We applied the models to two breast cancer data sets and compared the models using receiver operating characteristic (ROC) analysis. For the more challenging calcification data set, decision fusion reached its maximum classification performance of AUC = 0.80±0.04 at 50 samples and pAUC = 0.34±0.05 at 100 samples. The LDA reached a lower performance and required many more cases, with a maximum of AUC = 0.68±0.04 and pAUC = 0.12±0.05 at 450 samples. For the mass data set, the two classifiers had more similar performance, with AUC = 0.92±0.02 and pAUC = 0.48±0.02 at 50 samples for decision fusion and AUC = 0.92±0.03 and pAUC = 0.55±0.04 at 500 samples for the LDA.
KEYWORDS: Sensors, General packet radio service, Data fusion, Detection and tracking algorithms, Land mines, Algorithm development, Ground penetrating radar, Metals, Signal detection, Statistical analysis
Numerous detection algorithms, using various sensor modalities, have been developed for the detection of mines in cluttered and noisy backgrounds. The performance for each detection algorithm is typically reported in terms of the Receiver Operating Characteristic (ROC), which is a plot of the probability of detection versus false alarm as a function of the threshold setting on the output decision variable of each algorithm. In this paper we present multi-sensor decision fusion algorithms that combine the local decisions of existing detection algorithms for different sensors. This offers, in certain situations, an expedient, attractive and much simpler alternative to "starting over" with the redesign of a new algorithm which fuses multiple sensors at the data level. The goal in our multi-sensor decision fusion approach is to exploit complimentary strengths of existing multi-sensor algorithms so as to achieve performance (ROC) that exceeds the performance of any sensor algorithm operating in isolation. Our approach to multi-sensor decision fusion is based on optimal signal detection theory, using the likelihood ratio. We consider the optimal fusion of local decisions for two sensors, GPR (ground penetrating radar) and MD (metal detector). A new robust algorithm for decision fusion is presented that addresses the problem that the statistics of the training data is not likely to exactly match the statistics of the test data. ROC's are presented and compared for real data.
KEYWORDS: Signal detection, Signal to noise ratio, Target detection, Interference (communication), Signal processing, Sensors, Acoustics, Data centers, Detection theory, Receivers
An optimal signal detection theory approach is presented for the determination of the presence or absence of a target observed at multiple aspects in noise, where there is uncertainty in the initial look angle at which the aspects are observed. Potential targets may be interrogated at any number of aspect angles, and receiver operating characteristics (ROCs) are presented as a function of the number of aspects observed. In order to obtain the effect on performance of the number of aspect angles and other characteristics of the signal, ROC comparisons are made for the same total signal-to-noise ratio (SNR), rather than the average SNR per aspect. Target returns from a real multiple aspect target data set, consisting of acoustic backscatter returns from several objects suspended in a tank of water, are utilized in a detection simulation. The result using the real data indicate that, for the same total signal-to-noise ratio, detection does not necessarily improve with an increasing number of look angles. Theoretical analysis shows that optimum detection for this situation occurs when the signals consisting of multiple aspects, but at different initial look angles, are highly correlated. This conclusion is supported by the real data nd shows that detection performance does not necessarily improve with the number of multiple aspect angles observed, for a given total signal- to-noise ratio, when the initial look angle is uncertain.
A hierarchical Markov random field (MRF) modeling approach is presented for the classification of textures in selected regions of interest (ROIs) of chest radiographs. The procedure integrates possible texture classes and their spatial definition with other components present in an image such as noise and background trend. Classification is performed as a maximum a-posteriori (MAP) estimation of texture class and involves an iterative Gibbs- sampling technique. Two cases are studied: classification of lung parenchyma versus bone and classification of normal lung parenchyma versus miliary tuberculosis (MTB). Accurate classification was obtained for all examined cases showing the potential of the proposed modeling approach for texture analysis of radiographic images.
Two methods for detecting dim, unresolved target tracks in infrared imagery are presented. Detecting such targets in a sequence of noisy images is very challenging from the standpoint of algorithm design as well as detection performance evaluation. Since the signal-to-noise ratio per pixel is very low (a dim target) and the target is unresolved (of spatial extent less than a pixel), one must rely on integration over target tracks which span over many image frames. In addition, since there is a large amount of uncertainty as to the pattern and location of target tracks, good algorithms must consider a large number of possibilities. The first method is based on a generalization of the Hough transform-based algorithm using the Radon transform. The second approach is an extension of a detection theory algorithm to 3-D. Both algorithms use a 3-D volume of spatial-temporal data.
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