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Theoretical Detective Quantum Efficiency](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-5-320.jpg)
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Ideal Observer SNR (d')](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-6-320.jpg)
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30°, High Energy](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-10-320.jpg)
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LowEnergyMTF](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-12-320.jpg)
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21° (Measured)](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-13-320.jpg)
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Exposure Time: 164 ms](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-15-320.jpg)
![Reconstruction Filters
T. Mertelmeier, J. Orman, W. Haerer, and M.K. Dudam, in SPIE Med. Imaging (2006), p. 61420F–61420F–12.
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Spectral Apodization Filter](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-16-320.jpg)
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dSe
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dSe
= 300 µm [6.56 mR]](https://image.slidesharecdn.com/aapm2014-160222155330/85/Increasing-Amorphous-Selenium-Thickness-in-Direct-Conversion-Flat-Panel-Imagers-for-Contrast-Enhanced-Dual-Energy-Breast-Imaging-18-320.jpg)
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Similar to Increasing Amorphous Selenium Thickness in Direct Conversion Flat-Panel Imagers for Contrast-Enhanced Dual-Energy Breast Imaging
Increasing Amorphous Selenium Thickness in Direct Conversion Flat-Panel Imagers for Contrast-Enhanced Dual-Energy Breast Imaging
- 1. Digital Radiological ImagingLaboratory Increasing Amorphous Selenium Thickness in Direct Conversion Flat-Panel Imagers for Contrast-Enhanced Dual-Energy Breast Imaging David A. Scaduto, Yue-Houng Hu and Wei Zhao DEPARTMENT OF RADIOLOGY
- 2. Contrast-Enhanced Imaging Mask ImageContrast Image Subtracted Image
- 3. 0 10 2030 40 50 0.1 1 10 100 1000 10000 0.0 0.2 0.4 0.6 0.8 1.0 Adipose Tissue Fibroglandular Tissue Breast Tumor (IDC) Iodine LinearAttenuationCoefficientµ[cm -1 ] Energy [keV] W/Cu 49 kVp W/Rh 28kVp Fluence[arbitraryunits]
- 4. Current Detectors Prototype Detector 0.0 0.2 0.40.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 QuantumDetectionEfficiency a-Se thickness [mm] W/Rh 28 kVp W/Cu 49 kVp
- 5. 0 1 23 4 5 6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 DQE Spatial Frequency [cycles/mm] dSe = 200 µm dSe = 300 µm Theoretical Detective Quantum Efficiency
- 6. 0.2 0.3 0.40.5 0.6 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 0.2 0.3 0.4 0.5 0.6 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10 Normalizedd' 2 Projection Normalizedd' 2 In-Plane a-Selenium Thickness dSe [mm] Dual-Energy Subtracted Object Detectability (300 µm) FBP Reconstruction: Without Beam Obliquity FBP Reconstruction: With Beam Obliquity Projection: 0° Projection: 25° Ideal Observer SNR (d')
- 7. Effect of X-rayObliquity W. Que and J.A. Rowlands, Med. Phys. 22(4), 365–74 (1995). J.G. Mainprize, A.K. Bloomquist, M.P. Kempston, and M.J. Yaffe, Med. Phys. 33(9), 3159 (2006).
- 8. Effect of X-rayObliquity
- 9. Theoretical Blur dueto Oblique Entry 0 1 2 3 4 5 6 0.0 0.2 0.4 0.6 0.8 1.0 MTFg Spatial Frequency [cycles/mm] 10°, dSe = 200 µm 10°, dSe = 300 µm 30°, dSe = 200 µm 30°, dSe = 300 µm
- 10. Theoretical Blur dueto Oblique Entry 0 1 2 3 4 5 6 0.0 0.2 0.4 0.6 0.8 1.0 MTFg Spatial Frequency [cycles/mm] 10°, Low Energy 10°, High Energy 30°, Low Energy 30°, High Energy
- 11. Detector with ThickerConversion Layer • Prototype detector: Analogic a-Se layer increased to 300 µm • Prototype Digital Breast Tomosynthesis: Siemens Configured for dual-energy imaging • Low Energy: W/Rh • High Energy: W/Cu, W/Ti • Maximum kVp: 49 kVp Investigational Device. Limited by US Federal law to investigational use.
- 12. Presampling MTF: a-SeThickness Dependence 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 HighEnergyMTF Spatial Frequency [cycles/mm] dSe = 200 µm (Measured) dSe = 300 µm (Measured) dSe = 300 µm (Modeled) dSe = 200 µm (Measured) dSe = 300 µm (Measured) dSe = 300 µm (Modeled) LowEnergyMTF
- 13. MTF: Oblique Entry 05 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 MTF Spatial Frequency [cycles/mm] 0° (Modeled) 0° (Measured) 10° (Modeled) 10° (Measured) 21° (Modeled) 21° (Measured)
- 14. Focal Spot Motion focal spot gantry exposured v t
- 15. MTF: Focal SpotMotion 0 5 10 15 20 0.0 0.2 0.4 0.6 0.8 1.0 MTF Spatial Frequency [cycles/mm] No Focal Spot Motion Exposure Time: 77 ms Exposure Time: 128 ms Exposure Time: 164 ms
- 16. Reconstruction Filters T. Mertelmeier,J. Orman, W. Haerer, and M.K. Dudam, in SPIE Med. Imaging (2006), p. 61420F–61420F–12. 0 1 2 3 4 5 6 0.0 0.2 0.4 0.6 0.8 1.0 MTF Spatial Frequency [cycles/mm] Detector MTF (Measured) Detector MTF with FSM (Measured) Detector MTF with FSM, OE (Measured) Spectral Apodization Filter
- 17. Low Energy DQE 01 2 3 4 5 6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 DQE Spatial Frequency [cycles/mm] dSe = 200 µm [30.38 mR] dSe = 300 µm [30.38 mR]
- 18. High Energy DQE 01 2 3 4 5 6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 DQE Spatial Frequency [cycles/mm] dSe = 200 µm [6.56 mR] dSe = 300 µm [6.56 mR]
- 19. Conclusions • Increasing a-Sethickness increases QDE, DQE for high energy x-ray spectra • Effect of beam obliquity on MTF apparent in projection domain • Reconstruction filters remain dominant source of blur • Increasing a-Se thickness increases object detectability without penalty in most clinically relevant situations
- 20. Acknowledgements We gratefully acknowledge •NIH 1 R01 CA148053 • Siemens Healthcare • Analogic Canada and helpful discussion with • Dr. Olivier Tousignant, Analogic Canada
Editor's Notes
- #3 Contrast-enhanced imaging is an imaging technique wherein a radiocontrast agent is used to improve the x-ray imaging contrast of some anatomy of interest. In contrast-enhanced breast imaging, a perfusionary contrast agent is introduced into the blood to enhance the visibility of angiogenic vasculature surrounding a tumor. The technique is similar to digital subtraction angiography, wherein a mask image is acquired without the contrast agent, a contrast image is acquired, and the two are subtracted to yield an image showing only contrast enhancement.
- #4 X-ray imaging typically uses iodine as the contrast agent, due to its x-ray properties and nontoxicity. Imaging above its k-edge
- #5 Commercially available a-Se based FPI for mammography use Se layers that are 200 um. This is appropriate for conventional mammographic imaging, with a QDE nearing 100%. For HE imaging, however, the QDE is only ~55%/ Increasing to 300 um improves QDE to ~65%
- #6 Using a Cascaded Linear System Model, we can model the theoretical DQE, and we see that we’ll expect a 25% increase in the DQE(0) going from 200 to 300 um. 25% increase
- #7 By implementing the ideal observer SNR d’ into our model as the figure of merit to describe the detectability of lesions in dual-energy subtracted images, we see that increasing a-Se thickness generally improves lesion detectability for both projection images and reconstructed images from digital breast tomosynthesis. The improvement tapers off for projection images acquired at extreme gantry angles in tomosynthesis.
- #9 This is due to the effect of oblique entry of x-rays. X-rays entering at oblique angles may deposit their energy at any point between points A and B, introducing blur into our image. Simple geometry shows us that increasing the a-Se thickness will increase the potential for this blur effect. Additionally, the more penetrating x-rays in our high energy spectrum increase this effect.
- #10 These oblique entry effects are especially important in tomosynthesis with partially isocentric geometries, wherein the x-ray tube rotates around a stationary detector over some angular range.
- #11 These oblique entry effect can be modeled as described by Que and Rowlands and later Mainprize and colleagues, and as we can see, increasing Se thickness and increasing x-ray entry angle result in increased blur in our images. High energy
- #12 This is again an energy-dependent phenomenon, and we see that the effects for the high energy beam (magenta) are far more significant than for the low energy beam (cyan).
- #13 Siemens MAMMOMAT Inspiration
- #14 However, the effect of k-fluorescence on detector MTF becomes much less significant when the incident x-ray energy becomes much higher than the k-edge of selenium since k-fluorescent photons carry a smaller relative fraction of the energy of each absorbed x-ray. Thus, the relative effect of characteristic x-ray reabsorption is less in higher energy x-ray spectra. 21
- #15 These differences can be explained by considering the effect of characteristic x-ray reabsorption in the selenium layer Selenium has a k-edge of 12.7 keV, emitting characteristic x-rays K_alpha and K_betas with energies 11.2 and 12.5 respectively When an incident x-ray interacts with selenium and causes the emission of a characteristic x-ray, this secondary photon can be reabsorbed at some other point in the detector, resulting in blur and manifest as a degradation in the MTF. Obviously, both of our spectra are above the k-edge of selenium, so k-fluorescence cannot be ignored Generally, increasing incident x-ray energy increases the fraction of reabsorbed characteristic x-rays. However, as Wei showed in her 2001 paper on this phenomenon, the effect of k-fluorescence on detector MTF becomes much less significant when incident x-ray energy becomes much higher than the K-edge of Selenium since k-fluorescent photons carry a smaller relative fraction of the energy of each absorbed x-ray. Thus, the relative effect on MTF is smaller in higher energy x-ray spectra.
- #18 Low Energy 35% of 200 msec = 70 msec
- #21 DQE(0) increases from 45% to 55%, a 22% increase.