| 1. |
- Bornefalk, Hans, et al.
(författare)
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On the comparison of FROC curves in mammography CAD systems
- 2005
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 32:2, s. 412-417
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel method for assessing the performance of computer-aided detection systems on unseen cases at a given sensitivity level.
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| 2. |
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| 3. |
- Bornefalk, Hans
(författare)
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Computer-aided detection and novel mammography imaging techniques
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents techniques constructed to aid the radiologists in detecting breast cancer, the second largest cause of cancer deaths for western women. In the first part of the thesis, a computer-aided detection (CAD) system constructed for the detection of stellate lesions is presented. Different segmentation methods and an attempt to incorporate contra-lateral information are evaluated. In the second part, a new method for evaluating such CAD systems is presented based on constructing credible regions for the number of false positive marks per image at a certain desired target sensitivity. This method shows that the resulting regions are rather wide and this explains some of the difficulties encountered by other researchers when trying to compare CAD algorithms on different data sets. In this part an attempt to model the clinical use of CAD as a second look is also made and it shows that applying CAD in sequence to the radiologist in a routine manner, without duly altering the decision criterion of the radiologist, might very well result in suboptimal operating points. Finally, in the third part two dual-energy imaging methods optimized for contrast-enhanced imaging of breast tumors are presented. The first is based on applying an electronic threshold to a photon-counting digital detector to discriminate between high- and low-energy photons. This allows simultaneous acquisition of the high- and low-energy images. The second method is based on the geometry of a scanned multi-slit system and also allows single-shot contrast-enhanced dual-energy mammography by filtering the x-ray beam that reaches different detector lines differently.
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| 4. |
- Bornefalk, hans, et al.
(författare)
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Contrast-enhanced dual-energy mammography using a scanned multi-slit system : valuation of a differential beam filtering technique
- 2007
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Ingår i: Journal of Electronic Imaging (JEI). - : SPIE-Intl Soc Optical Eng. - 1017-9909 .- 1560-229X. ; 16:2, s. 023006-
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a method for single-exposure, contrast-enhanced dual-energy imaging of tumors utilizing a scanned multislit system for digital mammography. This photon-counting system employs an array of silicon strip detectors mounted in an edge-on geometry. The line detectors and pre- and post-collimator slits are carefully aligned, and the multislit setup allows differential filtering of the x-ray beam in the pre-collimator slits. A high-energy image is constructed from those lines where the filter material has been chosen to harden the x-ray beam and the low-energy image from the lines with a filter producing softer beams. Both images are obtained in the same scan, eliminating the need to change tube voltages and anode materials and minimizing the risk of motion artifacts. The method is illustrated on a purpose-built phantom, and logarithmic subtraction of the images produces images essentially free of anatomical clutter with the contrast-enhanced targets clearly visible.
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| 5. |
- Bornefalk, Hans, et al.
(författare)
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Dual-energy imaging using a digital scanned multi-slit system for mammography : evaluation of a differential beam filtering technique - art. no. 61422O
- 2006
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Ingår i: Medical Imaging 2006: Physics of Medical Imaging, Pts 1-3. - BELLINGHAM, WA : SPIE-INT SOC OPTICAL ENGINEERING. - 0819461857 ; , s. O1422-O1422
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Konferensbidrag (refereegranskat)abstract
- This paper describes a method for single exposure contrast-enhanced dual-energy imaging of tumors utilizing a scanned multi-slit system for digital mammography. This photon counting system employs an array of silicon strip detectors in an edge-on geometry. In the multi-slit setup, the line detectors and pre-collimator slits are aligned orthogonal to the scan direction. This geometry is advantageous to dual-energy imaging, since it allows differential filtering of the x-ray beam in the pre-collimator slits. A high-energy image is constructed from those lines where the filter material has been chosen to harden the x-ray beam and the low-energy image from the lines with a filter producing softer beams. Both images are obtained in the same scan, eliminating the need to change tube voltages and anode materials and minimizing the risk of motion artifacts. The method is illustrated on a purpose-built phantom and logarithmic subtraction of the images produces images essentially free of anatomical clutter with the contrast-enhanced targets clearly visible.
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| 6. |
- Bornefalk, Hans, et al.
(författare)
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Dual-energy imaging using a photon counting detector with electronic spectrum-splitting - art. no. 61421H
- 2006
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Ingår i: Medical Imaging 2006: Physics of Medical Imaging, Pts 1-3. - : SPIE. - 9780819461858 ; , s. H1421-H1421
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Konferensbidrag (refereegranskat)abstract
- This paper presents a dual-energy imaging technique optimized for contrast-enhanced mammography using a photon counting detector. Each photon pulse is processed separately in the detector and the addition of an electronic threshold near the middle of the energy range of the x-ray spectrum allows discrimination of high and low energy photons. This effectively makes the detector energy sensitive, and allows the acquisition of high- and low-energy images simultaneously. These high- and low-energy images can be combined to dual-energy images where the anatomical clutter has been suppressed. By setting the electronic threshold close to 33.2 keV (the k-edge of iodine) the system is optimized for dual-energy contrast-enhanced imaging of breast tumors. Compared to other approaches, this method not only eliminates the need for separate exposures that might lead to motion artifacts, it also eliminates the otherwise deteriorating overlap between high- and low-energy spectra. We present phantom dual-energy images acquired on a prototype system to illustrate that the technique is already operational, albeit in its infancy. We also present a theoretical estimation of the potential gain in tumor signal-difference-to-noise ratio when using this electronic spectrum-splitting method as opposed to acquiring the high- and low-energy images separately with double exposures with separate x-ray spectra. Assuming ideal energy sensitive photon counting detectors, we arrive at the conclusion that the signal-difference-to-noise ratio could be increased by 145% at constant dose. We also illustrate our results on synthetic images.
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| 7. |
- Bornefalk, Hans
(författare)
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Estimation and Comparison of CAD System Performance in Clinical Settings
- 2005
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Ingår i: Academic Radiology. - : Elsevier BV. - 1076-6332 .- 1878-4046. ; 12:6, s. 687-694
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Tidskriftsartikel (refereegranskat)abstract
- Rationale and Objectives. Computer-aided detection (CAD) systems are frequently compared using free-response receiver operating characteristic (FROC) curves. While there are ample statistical methods for comparing FROC curves, when one is interested in comparing the outcomes of 2 CAD systems applied in a typical clinical setting, there is the additional matter of correctly determining the system operating point. This article shows how the effect of the sampling error on determining the correct CAD operating point can be captured. By incorporating this uncertainty, a method is presented that allows estimation of the probability with which a particular CAD system performs better than another on unseen data in a clinical setting. Materials and Methods. The distribution of possible clinical outcomes from 2 artificial CAD systems with different FROC curves is examined. The sampling error is captured by the distribution of possible system thresholds of the classifying machine that yields a specified sensitivity. After introducing a measure of superiority, the probability of one system being superior to the other can be determined. Results. It is shown that for 2 typical mammography CAD systems, each trained on independent representative datasets of 100 cases, the FROC curves must be separated by 0.20 false positives per image in order to conclude that there is a 90% probability that one is better than the other in a clinical setting. Also, there is no apparent gain in increasing the size of the training set beyond 100 cases. Discussion. CAD systems for mammography are modeled for illustrative purposes, but the method presented is applicable to any computer-aided detection system evaluated with FROC curves. The presented method is designed to construct confidence intervals around possible clinical outcomes and to assess the importance of training set size and separation between FROC curves of systems trained on different datasets.
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| 8. |
- Bornefalk, Hans
(författare)
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Implications of unchanged detection criteria with CAD as second reader of mammograms
- 2006
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Ingår i: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 33:4, s. 922-929
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we address the use of computer-aided detection (CAD) systems as second readers in mammography. The approach is based on Bayesian decision theory and its implication for the choice of optimal operating points. The choice of a certain operating point along an ROC curve corresponds to a particular tradeoff between false positives and missed cancers. By minimizing a total risk function given this tradeoff, we determine optimal decision thresholds for the radiologist and CAD system when CAD is used as a second reader. We show that under very general circumstances, the performance of the sequential system is improved if the decision threshold of the latent human decision variable is increased compared to what it would have been in the absence of the CAD system. This means that an initial stricter decision criterion should be applied by the radiologist when CAD is used as a second reader than otherwise. First and foremost, the results in this paper should be interpreted qualitatively, but an attempt is made at quantifying the effect by tuning the model to a prospective study evaluating the use of CAD as a second reader. By making some necessary and plausible assumptions, we are able to estimate the effect of the resulting suboptimal operating point. In this study of 12 860 women, we estimate that a 15% reduction in callbacks for masses could have been achieved with only about a 1.5% relative decrease in sensitivity compared to that without using a stricter initial criterion by the radiologist. For microcalcifications the corresponding values are 7% and 0.2%. (c) 2006 American Association of Physicists in Medicine.
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| 9. |
- Bornefalk, Hans
(författare)
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Proposal and validation of a method to construct confidence intervals for clinical outcomes around FROC curves for mammography CAD systems
- 2005
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Ingår i: MEDICAL IMAGING 2005: IMAGE PROCESSING, PT 1-3. - BELLINGHAM : SPIE-INT SOC OPTICAL ENGINEERING. - 0819457213 ; , s. 675-682
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Konferensbidrag (refereegranskat)abstract
- This paper introduces a method for constructing confidence intervals for possible clinical outcomes around the FROC curve of a mammography CAD system. Given the architecture of a CAD classifying machine, there is one and only one system threshold that will yield a desired sensitivity on a certain population. The limited training sample size leads to a sampling error and an uncertainty in determining the optimal system threshold. This leads to an uncertainty in the operating point in the direction along the FROC curve which can be captured by a Bayesian approach where the distribution of possible thresholds is estimated. This uncertainty contributes to a large and spread-out confidence interval which is important to consider when one is intending to make comparisons between CAD algorithms trained on different data sets. The method is validated using a Monte Carlo method designed to capture the effect of correctly determining the system threshold.
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| 10. |
- Bornefalk, Hans, et al.
(författare)
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Single-shot dual-energy subtraction mammography with electronic spectrum splitting : Feasibility
- 2006
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Ingår i: European Journal of Radiology. - : Elsevier BV. - 0720-048X .- 1872-7727. ; 60:2, s. 275-278
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Tidskriftsartikel (refereegranskat)abstract
- We present a single-shot dual-energy subtraction mammography technique using an energy sensitive photon counting detector. An electronic threshold near the middle of the X-ray spectrum discriminates between high- and low-energy photons, and allows the simultaneous acquisition of high- and low-energy images which can be combined to suppress anatomical clutter. By setting the electronic threshold close to 33.2 keV (the k-edge of iodine) the system is optimized for dual-energy contrast-enhanced imaging of breast tumors. This method eliminates the need for separate exposures which might otherwise lead to motion artifacts. The method is illustrated in phantom images.
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