Papers by Ruben van Engen
Medical Physics, Nov 28, 2023
Physics in Medicine and Biology, Sep 25, 2015
Journal of medical imaging, Jun 26, 2023
In digital breast tomosynthesis (DBT), radiologists need to review a stack of 20 to 80 tomosynthe... more In 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. Method: Human 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. Results: Spherical lesion detection was higher in 2D mode than in 3D, for both DBT-and bCT-like images (DBT: AUC 2D ¼ 0.790, AUC 3D ¼ 0.735, P ¼ 0.03; bCT: AUC 2D ¼ 0.869, AUC 3D ¼ 0.716, P < 0.05), but equivalent for capsule-shaped signals (DBT: AUC 2D ¼ 0.891, AUC 3D ¼ 0.915, P ¼ 0.19; bCT: AUC 2D ¼ 0.854, AUC 3D ¼ 0.847, P ¼ 0.88). Average reading time was up to 134% higher for 3D viewing (P < 0.05). Conclusions: For 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.
Proceedings of SPIE, Mar 4, 2010
Breast tomosynthesis is an imaging modality that recently became available for breast examination... more Breast tomosynthesis is an imaging modality that recently became available for breast examination. For conventional projection mammography quality control procedures are well described. For breast tomosynthesis, on the other hand, such procedures have not yet been established. In this paper we propose a simple method and phantom for daily quality control (DQC). With DQC image quality problems arising after acceptance
Physica Medica, Dec 1, 2016
In mammography, images are processed prior to display. Current methodologies based on physical im... more In mammography, images are processed prior to display. Current methodologies based on physical image quality measurements are however not designed for the evaluation of processed images. Model observers (MO) might be suitable for this evaluation. The aim of this study was to investigate whether the non-pre-whitening (NPW) MO can be used to predict human observer performance in mammography-like images by including different aspects of the human visual system (HVS). Methods: The correlation between human and NPW MO performance has been investigated for the detection of disk shaped objects in simulated white noise (WN) and clustered lumpy backgrounds (CLB), representing quantum noise limited and mammography-like images respectively. The images were scored by the MO and five human observers in a 2-alternative forced choice experiment. Results: For WN images it was found that the log likelihood ratio (R LR 2), which expresses the goodness of fit, was highest (0.44) for the NPW MO without addition of HVS aspects. For CLB the R LR 2 improved from 0.46 to 0.65 with addition of HVS aspects. The correlation was affected by object size and background. Conclusions: This study shows that by including aspects of the HVS, the performance of the NPW MO can be improved to better predict human observer performance. This demonstrates that the NPW MO has potential for image quality assessment. However, due to the dependencies found in the correlation, the NPW MO can only be used for image quality assessment for a limited range of object sizes and background variability.
To evaluate the image quality of digital mammography systems, a contrast-detail phantom (CDMAM 3.... more To evaluate the image quality of digital mammography systems, a contrast-detail phantom (CDMAM 3.4) was developed at our institution [1]. The phantom has been designed to enable image quality assessment by a human observer, by determining threshold contrast of an imaging system as a function of object diameter. Because human assessment of phantom images is rather time consuming, and observers tend to differ in detection capabilities (making readings by a team of observers necessary), a computer program was developed for this task [2]. However, until now investigation of the correspondance of this method with human observer assessment has been limited to digitized film-screen images at one X-ray setting, assessed by a single observer. In this article, possible differences between the two methods have been evaluated for direct digital mammography, at settings leading to various image quality. Both hard- and softcopy human readings have been compared to computer detection.
European Journal of Radiology, Jun 1, 2021
To validate a candidate instrument, to be used by different professionals to assess image quality... more To validate a candidate instrument, to be used by different professionals to assess image quality in digital mammography (DM), against detection performance results. Methods: A receiver operating characteristics (ROC) study was conducted to assess the detection performance in DM images with four different image quality levels due to different quality issues. Fourteen expert breast radiologists from five countries assessed a set of 80 DM cases, containing 60 lesions (40 cancers, 20 benign findings) and 20 normal cases. A visual grading analysis (VGA) study using a previously-described candidate instrument was conducted to evaluate a subset of 25 of the images used in the ROC study. Eight radiologists that had participated in the ROC study, and seven expert breast-imaging physicists, evaluated this subset. The VGA score (VGAS) and the ROC and visual grading characteristics (VGC) areas under the curve (AUC ROC and AUC VGC) were compared. Results: No large differences in image quality among the four levels were detected by either ROC or VGA studies. However, the ranking of the four levels was consistent: level 1 (partial AUC ROC : 0.070, VGAS: 6.77) performed better than levels 2 (0.066, 6.15), 3 (0.061, 5.82), and 4 (0.062, 5.37). Similarity between radiologists' and physicists' assessments was found (average VGAS difference of 10 %). Conclusions: The results from the candidate instrument were found to correlate with those from ROC analysis, when used by either observer group. Therefore, it may be used by different professionals, such as radiologists, radiographers, and physicists, to assess clinically-relevant image quality variations in DM.
Physica Medica, 2017
In mammography, images are processed prior to display. Model observers (MO) are candidates to obj... more In mammography, images are processed prior to display. Model observers (MO) are candidates to objectively evaluate processed images if they can predict human observer performance for detail detection. The aim of this study was to investigate if the channelized Hotelling observer (CHO) can be configured to predict human observer performance in mammography like images. Methods: The performance correlation between human observers and CHO has been evaluated using different channel-sets and by including aspects of the human visual system (HVS). The correlation was investigated for the detection of disk-shaped details in simulated white noise (WN) and clustered lumpy backgrounds (CLB) images, representing respectively quantum noise limited and mammography like images. The images were scored by the MO and five human observers in 2-alternative forced choice experiments. Results: For WN images the most useful formulation of the CHO to predict human observer performance was obtained using three difference of Gaussian channels without adding HVS aspects (R LR 2 = 0.62). For CLB images the most useful formulation was the partial least square channel-set without adding HVS aspects (R LR 2 = 0.71). The correlation was affected by detail size and background. Conclusions: This study has shown that the CHO can predict human observer performance. Due to object size and background dependency it is important that the range of object sizes and allowed variability in background are specified and validated carefully before the CHO can be implemented for objective image quality assessment.
Medical Physics, 2018
PurposeTo study the feasibility of a channelized Hotelling observer (CHO) to predict human observ... more PurposeTo study the feasibility of a channelized Hotelling observer (CHO) to predict human observer performance in detecting calcification‐like signals in mammography images of an anthropomorphic breast phantom, as part of a quality control (QC) framework.MethodsA prototype anthropomorphic breast phantom with inserted gold disks of 0.25 mm diameter was imaged with two different digital mammography x‐ray systems at four different dose levels. Regions of interest (ROIs) were extracted from the acquired processed and unprocessed images, signal‐present and signal‐absent. The ROIs were evaluated by a CHO using four different formulations of the difference of Gaussian (DoG) channel sets. Three human observers scored the ROIs in a two‐alternative forced‐choice experiment. We compared the human and the CHO performance on the simple task to detect calcification‐like disks in ROIs with and without postprocessing. The proportion of correct responses of the human reader (PCH) and the CHO (PCCHO...
Medical Imaging 2006: Image Perception, Observer Performance, and Technology Assessment, 2006
As part of an EC funded project, the design for a new phantom has been proposed that consists of ... more As part of an EC funded project, the design for a new phantom has been proposed that consists of a smaller contrast-detail part than the CDMAM phantom and that contains items for other parts of an acceptance protocol for digital mammography. A first prototype of the "DIGIMAM" has been produced. Both the CDMAM phantom and the DIGIMAM phantom were then used on a series of systems and read out as a part of a multi centre study. The results with the new phantom were very similar to results obtained with the CDMAM phantom: readers scored different from each other and there was an overlap in the scores for the different systems. A system with a poor score in CDMAM had also the worst score for DIGIMAM. Reading time was significantly reduced however. There was promising agreement between automated reading of CDMAM and the scores of the DIGIMAM phantom. In order to reduce the subjectivity of the readings, computerized reading of the DIGIMAM should be developed. In a second version of the phantom, we propose to add more disks of the same size and contrast in each square to improve the statistical power of each reading.
Contrast detail analysis has been performed to compare the image quality of the Fuji FCR 5000MA C... more Contrast detail analysis has been performed to compare the image quality of the Fuji FCR 5000MA CM system to the image quality of the GE Senographe 2000D and the Kodak Min-R 2000/Min-R 2190 film/screen combination. The dose of the images was kept identical between the X-ray units. For the comparison of both digital systems 8 phantom images (CDMAM version 3.4) have been made at each exposure setting and have been read-out by a computer programme. For the comparison of the Fuji and Kodak system two CDMAM images have been made at a number of exposure settings and have been read-out by experienced readers. Results show that image quality of both digital systems is fairly comparable. For small details there is no better performance with the Fuji system, despite its smaller pixel size. The image quality of the Fuji system is slightly superior to the image quality of the Kodak system.
Medical Physics, Jun 1, 2016
PURPOSE Spatial resolution in digital breast tomosynthesis (DBT) is affected by inherent/binned d... more PURPOSE Spatial resolution in digital breast tomosynthesis (DBT) is affected by inherent/binned detector resolution, oblique entry of x-rays, and focal spot size/motion; the limited angular range further limits spatial resolution in the depth-direction. While DBT is being widely adopted clinically, imaging performance metrics and quality control protocols have not been standardized. AAPM Task Group 245 on Tomosynthesis Quality Control has been formed to address this deficiency. METHODS Methods of measuring spatial resolution are evaluated using two prototype quality control phantoms for DBT. Spatial resolution in the detector plane is measured in projection and reconstruction domains using edge-spread function (ESF), point-spread function (PSF) and modulation transfer function (MTF). Spatial resolution in the depth-direction and effective slice thickness are measured in the reconstruction domain using slice sensitivity profile (SSP) and artifact spread function (ASF). An oversampled PSF in the depth-direction is measured using a 50 µm angulated tungsten wire, from which the MTF is computed. Object-dependent PSF is derived and compared with ASF. Sensitivity of these measurements to phantom positioning, imaging conditions and reconstruction algorithms is evaluated. Results are compared from systems of varying acquisition geometry (9-25 projections over 15-60°). Dependence of measurements on feature size is investigated. RESULTS Measurements of spatial resolution using PSF and LSF are shown to depend on feature size; depth-direction spatial resolution measurements are shown to similarly depend on feature size for ASF, though deconvolution with an object function removes feature size-dependence. A slanted wire may be used to measure oversampled PSFs, from which MTFs may be computed for both in-plane and depth-direction resolution. CONCLUSION Spatial resolution measured using PSF is object-independent with sufficiently small object; MTF is object-independent. Depth-direction spatial resolution may be measured directly using MTF or indirectly using ASF or SSP as surrogate measurements. While MTF is object-independent, it is invalid for nonlinear reconstructions.
Physics in Medicine and Biology, Oct 27, 2021
Currently, quality assurance measurements in mammography are performed on unprocessed images. For... more Currently, quality assurance measurements in mammography are performed on unprocessed images. For diagnosis, however, radiologists are provided with processed images. This image processing is optimised for images of human anatomy and therefore does not always perform satisfactorily with technical phantoms. To overcome this problem, it may be possible to use anthropomorphic phantoms reflecting the anatomic structure of the human breast in place of technical phantoms when carrying out task-specific quality assessment using model observers. However, the use of model observers is hampered by the fact that a large number of images needs to be acquired. A recently published novel observer called the regression detectability index (RDI) needs significantly fewer images, but requires the background of the images to be flat. Therefore, to be able to apply the RDI to images of anthropomorphic phantoms, the anatomic background needs to be removed. For this, a procedure in which the anatomical structures are fitted by thin plate spline (TPS) interpolation has been developed. When the object to be detected is small, such as a calcification-like lesion, it is shown that the anatomic background can be removed successfully by subtracting the TPS interpolation, which makes the background-free image accessible to the RDI. We have compared the detectability obtained by the RDI with TPS background subtraction to results of the channelized Hotelling observer (CHO) and human observers. With the RDI, results for the detectability d ′ can be obtained using 75% fewer images compared to the CHO, while the same uncertainty of d ′ is achieved. Furthermore, the correlation of d ′ (RDI) with the results of human observers is at least as good as that of d ′ (CHO) with human observers.
Cancer Medicine, Mar 5, 2021
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
European Journal of Radiology, Oct 1, 2020
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Springer eBooks, 2010
An effective quality control system for digital mammography needs to evaluate the status of each ... more An effective quality control system for digital mammography needs to evaluate the status of each stage of image formation — acquisition, processing and display. Such quality control benefits greatly from the ability to make more precise and reproducible measurements than was possible with film-screen systems. On the other hand, the greater variety of system designs and general lack of experience
Proceedings of SPIE, Mar 4, 2010
As a collaborative effort between scientists affiliated with the American Association of Physicis... more As a collaborative effort between scientists affiliated with the American Association of Physicists in Medicine (AAPM) and the European reference center for breast cancer screening and diagnosis (EUREF), the Working Group on Phantoms for Breast Imaging (WGPBI) aims to develop phantoms and evaluation techniques for 2D &amp;amp;amp;amp;amp;amp; 3D breast imaging modalities. In the first phase of this collaboration, this project
Radiation Protection Dosimetry, Mar 13, 2016
Current digital mammography (DM) X-ray systems are equipped with advanced automatic exposure cont... more Current digital mammography (DM) X-ray systems are equipped with advanced automatic exposure control (AEC) systems, which determine the exposure factors depending on breast composition. In the supplement of the European guidelines for quality assurance in breast cancer screening and diagnosis, a phantom-based test is included to evaluate the AEC response to local dense areas in terms of signal-to-noise ratio (SNR). This study evaluates the proposed test in terms of SNR and dose for four DM systems. The glandular fraction represented by the local dense area was assessed by analytic calculations. It was found that the proposed test simulates adipose to fully glandular breast compositions in attenuation. The doses associated with the phantoms were found to match well with the patient dose distribution. In conclusion, after some small adaptations, the test is valuable for the assessment of the AEC performance in terms of both SNR and dose.
Journal of Medical Imaging, 2021
Purpose: To validate a previously proposed algorithm that modifies a mammogram to appear as if it... more Purpose: To validate a previously proposed algorithm that modifies a mammogram to appear as if it was acquired with different technique factors using realistic phantom-based mammograms. Approach: Two digital mammography systems (an indirect-and a direct-detector-based system) were used to acquire realistic mammographic images of five 3D-printed breast phantoms with the technique factors selected by the automatic exposure control and at various other conditions (denoted by the original images). Additional images under other simulated conditions were also acquired: higher or lower tube voltages, different anode/filter combinations, or lower tube current-time products (target images). The signal and noise in the original images were modified to simulate the target images (simulated images). The accuracy of the image modification algorithm was validated by comparing the target and simulated images using the local mean, local standard deviation (SD), local variance, and power spectra (PS) of the image signals. The absolute relative percent error between the target and simulated images for each parameter was calculated at each sub-region of interest (local parameters) and frequency (PS), and then averaged. Results: The local mean signal, local SD, local variance, and PS of the target and simulated images were very similar, with a relative percent error of 5.5%, 3.8%, 7.8%, and 4.4% (indirect system), respectively, and of 3.7%, 3.8%, 7.7%, and 7.5% (direct system), respectively. Conclusions: The algorithm is appropriate for simulating different technique factors. Therefore, it can be used in various studies, for instance to evaluate the impact of technique factors in cancer detection using clinical images.
BMC Cancer, 2020
Background In the scope of the European Commission Initiative on Breast Cancer (ECIBC) the Monito... more Background In the scope of the European Commission Initiative on Breast Cancer (ECIBC) the Monitoring and Evaluation (M&E) subgroup was tasked to identify breast cancer screening programme (BCSP) performance indicators, including their acceptable and desirable levels, which are associated with breast cancer (BC) mortality. This paper documents the methodology used for the indicator selection. Methods The indicators were identified through a multi-stage process. First, a scoping review was conducted to identify existing performance indicators. Second, building on existing frameworks for making well-informed health care choices, a specific conceptual framework was developed to guide the indicator selection. Third, two group exercises including a rating and ranking survey were conducted for indicator selection using pre-determined criteria, such as: relevance, measurability, accurateness, ethics and understandability. The selected indicators were mapped onto a BC screening pathway deve...
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Papers by Ruben van Engen