KEYWORDS: Digital breast tomosynthesis, 3D image processing, Breast, Optical spheres, 3D acquisition, Spherical lenses, Signal detection, 3D vision, Target detection, Computed tomography
PurposeIn digital breast tomosynthesis (DBT), radiologists need to review a stack of 20 to 80 tomosynthesis images, depending upon breast size. This causes a significant increase in reading time. However, it is currently unknown whether there is a perceptual benefit to viewing a mass in the 3D tomosynthesis volume. To answer this question, this study investigated whether adjacent lesion-containing planes provide additional information that aids lesion detection for DBT-like and breast CT-like (bCT) images.MethodHuman reader detection performance was determined for low-contrast targets shown in a single tomosynthesis image at the center of the target (2D) or shown in the entire tomosynthesis image stack (3D). Using simulations, targets embedded in simulated breast backgrounds, and images were generated using a DBT-like (50 deg angular range) and a bCT-like (180 deg angular range) imaging geometry. Experiments were conducted with spherical and capsule-shaped targets. Eleven readers reviewed 1600 images in two-alternative forced-choice experiments. The area under the receiver operating characteristic curve (AUC) and reading time were computed for the 2D and 3D reading modes for the DBT and bCT imaging geometries and for both target shapes.ResultsSpherical lesion detection was higher in 2D mode than in 3D, for both DBT- and bCT-like images (DBT: AUC2D = 0.790, AUC3D = 0.735, P = 0.03; bCT: AUC2D = 0.869, AUC3D = 0.716, P < 0.05), but equivalent for capsule-shaped signals (DBT: AUC2D = 0.891, AUC3D = 0.915, P = 0.19; bCT: AUC2D = 0.854, AUC3D = 0.847, P = 0.88). Average reading time was up to 134% higher for 3D viewing (P < 0.05).ConclusionsFor the detection of low-contrast lesions, there is no inherent visual perception benefit to reviewing the entire DBT or bCT stack. The findings of this study could have implications for the development of 2D synthetic mammograms: a single synthesized 2D image designed to include all lesions present in the volume might allow readers to maintain detection performance at a significantly reduced reading time.
KEYWORDS: Signal detection, Image quality, Breast, Image processing, Image analysis, Medical imaging, Digital mammography, Digital image processing, Gold, Radiology
The channelized-Hotelling observer (CHO) was investigated as a surrogate of human observers in task-based image quality assessment. The CHO with difference-of-Gaussian (DoG) channels has shown potential for the prediction of human detection performance in digital mammography (DM) images. However, the DoG channels employ parameters that describe the shape of each channel. The selection of these parameters influences the performance of the DoG CHO and needs further investigation. The detection performance of the DoG CHO was calculated and correlated with the detection performance of three humans who evaluated DM images in 2-alternative forced-choice experiments. A set of DM images of an anthropomorphic breast phantom with and without calcification-like signals was acquired at four different dose levels. For each dose level, 200 square regions-of-interest (ROIs) with and without signal were extracted. Signal detectability was assessed on ROI basis using the CHO with various DoG channel parameters and it was compared to that of the human observers. It was found that varying these DoG parameter values affects the correlation (r2) of the CHO with human observers for the detection task investigated. In conclusion, it appears that the the optimal DoG channel sets that maximize the prediction ability of the CHO might be dependent on the type of background and signal of ROIs investigated.
KEYWORDS: Breast, 3D image processing, Signal detection, 3D modeling, Tissues, Image quality, 3D vision, 3D displays, Computer simulations, Spherical lenses
We investigate whether humans need to be shown the entire image stack (3D) or only the central slice (2D) of the lesion of breast tomosynthesis images in signal-known-exactly detection experiments. A directional small-scale breast tissue model based on random power-law noise was used. Assuming a breast tomosynthesis geometry, the tissue volumes were projected and reconstructed forming volumes-of-interest (VOI)s. Three different sizes of spheres with blurred edges were used to simulate lesions. The spheres were added on the VOIs to represent signal-present VOIs. Signal-present and signalabsent VOIs were presented during 2-alternative forced-choice experiments to 5 human observers in two modes; (i) 3D mode, in which all slices of the VOI were repeatedly displayed in ciné mode; and in (ii) 2D mode, in which only the central slice of the reconstructed VOI (where the signal-present VOIs contained the center of the spherical lesion) was displayed using 2-alternative forced-choice experiments. Percent correct (PC) of the detection performance of all observers was evaluated. No significant differences were found systematically in the PC for the 3D and 2D image viewing for this type of backgrounds. We plan to investigate these further, along with the development of a model observer that correlates well with human performance in tomosynthesis.
The channelized-Hotelling observer (CHO) was investigated on the ability to predict the human detection performance in order to assess clinical image quality objectively. CHO applied three user-selectable difference of Gaussian (DoG) channels on the images. The choice of the parameter values that comprise the DoG channel-sets of the CHO was investigated. In order to select the optimal channels, the CHO performance was compared to that of humans who scored digital mammography (DM) images in 2-alternative forced choice experiments. Square regions-of-interest (ROI)s from DM images of an anthropomorphic breast phantom with and without calcification-like signals were extracted. Images at four dose levels were acquired and the resulting signal detectability was assessed using the CHO with various DoG channel parameters. It was found that varying these parameter values affects the correlation (r2) of the CHO with human observers for the detection task investigated. It appears that the DoG channel-sets need to be adapted to the frequency content of the signals and backgrounds present in the DM images.
Mammography images undergo vendor-specific processing, which may be nonlinear, before radiologist interpretation. Therefore, to test the entire imaging chain, the effect of image processing should be included in the assessment of image quality, which is not current practice. For this purpose, model observers (MOs), in combination with anthropomorphic breast phantoms, are proposed to evaluate image quality in mammography. In this study, the nonprewhitening MO with eye filter and the channelized Hotelling observer were investigated. The goal of this study was to optimize the efficiency of the procedure to obtain the expected signal template from acquired images for the detection of a 0.25-mm diameter disk. Two approaches were followed: using acquired images with homogeneous backgrounds (approach 1) and images from an anthropomorphic breast phantom (approach 2). For quality control purposes, a straightforward procedure using a single exposure of a single disk was found adequate for both approaches. However, only approach 2 can yield templates from processed images since, due to its nonlinearity, image postprocessing cannot be evaluated using images of homogeneous phantoms. Based on the results of the current study, a phantom should be designed, which can be used for the objective assessment of image quality.
Model observers (MOs) are being investigated for image quality assessment in full-field digital mammography (FFDM). Signal templates for the non-prewhitening MO with eye filter (NPWE) were formed using acquired FFDM images. A signal template was generated from acquired images by averaging multiple exposures resulting in a low noise signal template. Noise elimination while preserving the signal was investigated and a methodology which results in a noise-free template is proposed. In order to deal with signal location uncertainty, template shifting was implemented. The procedure to generate the template was evaluated on images of an anthropomorphic breast phantom containing microcalcification-related signals. Optimal reduction of the background noise was achieved without changing the signal. Based on a validation study in simulated images, the difference (bias) in MO performance from the ground truth signal was calculated and found to be <1%. As template generation is a building stone of the entire image quality assessment framework, the proposed method to construct templates from acquired images facilitates the use of the NPWE MO in acquired images.
Standard methods to quantify image quality (IQ) may not be adequate for clinical images since they depend on uniform backgrounds and linearity. Statistical model observers are not restricted to these limitations and might be suitable for IQ evaluation of clinical images. One of these statistical model observers is the channelized Hotelling observer (CHO), where the images are filtered by a set of channels. The aim of this study was to evaluate six different channel sets, with an additional filter to simulate the human contrast sensitivity function (CSF), in their ability to predict human observer performance. For this evaluation a two alternative forced choice experiment was performed with two types of background structures (white noise (WN) and clustered lumpy background (CLB)), 5 disk-shaped objects with different diameters and 3 different signal energies. The results show that the correlation between human and model observers have a diameter dependency for some channel sets in combination with CLBs. The addition of the CSF reduces this diameter dependency and in some cases improves the correlation coefficient between human- and model observer. For the CLB the Partial Least Squares channel set shows the highest correlation with the human observer (r2=0.71) and for WN backgrounds it was the Gabor-channel set with CSF (r2=0.72). This study showed that for some channels there is a high correlation between human and model observer, which suggests that the CHO has potential as a tool for IQ analysis of digital mammography systems.
In this study it is shown that the performance of a statistical method for detection of microcalcification clusters in digital mammograms, can be improved substantially by using a second step of classification. During this second step, detected clusters are automatically classified into true positive and false positive detected clusters. For classification the k-nearest neighbor method was used in a leave-one-patient-out procedure. The sensitivity level of the method was adjusted both in the first detection step as in the second classification step. The Mahalanobis distance was used as criterion in the sequential forward selection procedure for selection of features. This primary feature selection method was combined with a classification performance criterion for the final feature selection. By applying the initial detection at various levels of sensitivity, various sets of false and true positive detected clusters were created. At each of these sets the classification ca be performed. Results show that the overall best FROC performance after secondary classification is obtained by varying sensitivity levels in both the first and second step. Furthermore, it was shown that performing a new feature selection for each different set of false and true positives is essential. A large database of 245 digitized mammograms with 341 clusters was used for evaluation of the method.
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