| Question 1: With regard to iterative reconstruction in CT, which of the following is true: |
| Reference: | 1) Li, K. et al, “Statistical model based iterative reconstruction in clinical CT systems. Part III. Task-based kV/mAs optimization for radiation dose reduction,” Medical Physics, Vol. 42, pp. 5209 2015.
2) Li, K. et al. “Statistical model based iterative reconstruction (MBIR) in clinical CT systems: Experimental assessment of noise performance,” Medical Physics, Vol. 41(4), pp. 041906 2014.
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| Choice A: | Noise amplitude is inversely proportional to radiation dose level. |
| Choice B: | Dose-normalized noise power spectrum remains the same across dose levels. |
| Choice C: | Contrast-to-noise ratio is still a good surrogate metric of image quality. |
| Choice D: | None of the above. |
| Question 2: To reduce image noise, which of the following strategies can be used: |
| Reference: | 1) Hsieh, J. Computed Tomography: Principles, Design, Artifacts, and Recent Advances, 3rd Edition. SPIE. (2015)
2) Willi A. Kalender, Computed Tomography: Fundamentals, System Technology, Image Quality, Applications, 3rd Edition. (2011)
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| Choice A: | Replacing extreme photon-starved measurements at a given detector pixel with a local mean value. |
| Choice B: | Performing a denoising operation on the raw counts prior to taking the log-transform. |
| Choice C: | Performing a denoising operation on the log-transformed sinogram. |
| Choice D: | Selecting a soft (smooth) reconstruction kernel. |
| Choice E: | All of the above. |
| Question 3: With regard to iterative reconstruction in CT, which of the following is not true: |
| Reference: | : C. H. McCollough et al., “Degradation of CT Low-Contrast Spatial Resolution Due to the Use of Iterative Reconstruction and Reduced Dose Levels,” Radiology 276(2), 499–506 (2015) [doi:10.1148/radiol.15142047]. |
| Choice A: | Image noise is substantially decreased. |
| Choice B: | High contrast spatial resolution is not affected. |
| Choice C: | Low contrast spatial resolution is not affected. |
| Choice D: | Contrast to noise ratio is increased. |
| Question 4: With regard to diagnostic reference levels in the United States, which of the following is not true: |
| Reference: | K. M. Kanal et al., “U.S. Diagnostic Reference Levels and Achievable Doses for 10
Adult CT Examinations,” Radiology (2017): 161911.
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| Choice A: | The DRL for the routine abdomen/pelvis exam has fallen from 25 mGy to 15 mGy CTDIvol since the last analysis of the ACR accreditation data. |
| Choice B: | The DRL for the routine head exam has not fallen since the last analysis of the ACR accreditation data. |
| Choice C: | New DRLs show that examination exposures to the U.S. adult population are generally not higher than those in other countries. |
| Choice D: | Size-specific DRLs enable facilities to more effectively optimize their CT protocols for the wide range of sizes of the patients they examine. |
| Question 5: Which of the following has had a major impact on dose reduction in CT? |
| Reference: | McCollough, Cynthia H., Michael R. Bruesewitz, and James M. Kofler Jr. "CT dose reduction and dose management tools: overview of available options." Radiographics 26.2 (2006): 503-512. |
| Choice A: | Flying focal spot technology |
| Choice B: | Automatic exposure control |
| Choice C: | Retrospective cardiac gating |
| Choice D: | Spiral CT |
| Question 6: With regard to model-based iterative reconstruction in CT, which of the following is not true: |
| Reference: | 1. Pickhardt PJ, Lubner MG, Kim DH, et al. Abdominal CT With Model-Based Iterative Reconstruction (MBIR): Initial Results of a Prospective Trial Comparing Ultralow-Dose With Standard-Dose Imaging. Am J Roentgenol 2012;199:1266-74.
2. Pooler BD, Lubner MG, Kim DH, et al. Prospective Evaluation of Reduced Dose Computed Tomography for the Detection of Low-Contrast Liver Lesions: Direct Comparison with Concurrent Standard Dose Imaging. Eur Radiol 2016 Sep 5.
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| Choice A: | Diagnostic accuracy for lesion detection is always preserved, even at very low dose levels. |
| Choice B: | Image noise can be substantially decreased over FBP. |
| Choice C: | Reconstruction times are longer compared with statistical algorithms operating in image space. |
| Choice D: | Coronal image reconstructions tend to have high subjective image quality. |
| Question 7: With regard to low-contrast lesion detection, which of the following is not true? |
| Reference: | 1. McCollough CH, Yu LF, Kofler JM, et al. Degradation of CT Low-Contrast Spatial Resolution Due to the Use of Iterative Reconstruction and Reduced Dose Levels. Radiology 2015;276:499-506.
2. Baker ME, Dong F, Primak A, et al. Contrast-to-Noise Ratio and Low-Contrast Object Resolution on Full- and Low-Dose MDCT: SAFIRE Versus Filtered Back Projection in a Low-Contrast Object Phantom and in the Liver. Am J Roentgenol 2012;199:8-18.
3. Pooler BD, Lubner MG, Kim DH, et al. Prospective Evaluation of Reduced Dose Computed Tomography for the Detection of Low-Contrast Liver Lesions: Direct Comparison with Concurrent Standard Dose Imaging. Eur Radiol 2016 Sep 5.
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| Choice A: | Low-contrast object resolution in phantoms can be impacted at 50% dose reduction. |
| Choice B: | Hypovascular liver metastases are representative of low-contrast lesions in clinical practice. |
| Choice C: | Model-based IR algorithms greatly outperform other algorithms at ultra-low dose levels. |
| Choice D: | Low-contrast lesions are more difficult to detect in clinical practice compared with high-contrast lesions. |
| Question 8: For a given protocol, which of the following is not a potential advantage of photon counting detectors over energy-integrating detectors? Photon-counting detectors: |
| Reference: | Taguchi, K., Zhang, M., Frey, E. C., Wang, X., Iwanczyk, J. S., Nygard, E., Hartsough, N. E., Tsui, B. M. W. and Barber, W. C. (2011), Modeling the performance of a photon counting x-ray detector for CT: Energy response and pulse pileup effects. Med. Phys., 38: 1089–1102. doi:10.1118/1.3539602
2. Gutjahr, Ralf; Halaweish, Ahmed F.; Yu, Zhicong; Leng, Shuai; Yu, Lifeng; Li, Zhoubo; Jorgensen, Steven M.; Ritman, Erik L.; Kappler, Steffen; McCollough, Cynthia H. (2016) Investigative Radiology, 51(7): 421-9. doi: 10.1097/RLI.0000000000000251
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| Choice A: | (Often) Have the ability to measure the energy of detected photons. |
| Choice B: | Eliminate readout noise. |
| Choice C: | Reduce photon quantum noise. |
| Choice D: | Do not weigh high-energy photons more than low-energy photons in the output signal. |
| Question 9: Bow-tie filters: |
| Reference: | Toth, T., Ge, Z. and Daly, M. P. (2007), The influence of patient centering on CT dose and image noise. Med. Phys., 34: 3093–3101. doi:10.1118/1.2748113
2. Graham, S. A., Moseley, D. J., Siewerdsen, J. H. and Jaffray, D. A. (2007), Compensators for dose and scatter management in cone-beam computed tomography. Med. Phys., 34: 2691–2703. doi:10.1118/1.2740466
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| Choice A: | Can reduce peripheral dose while maintaining image quality at the center of the patient |
| Choice B: | Can reduce scattered radiation |
| Choice C: | Performance is sensitive to the positioning of the patient |
| Choice D: | All of the above |
| Question 10: Which of the following is true for automatic tube current modulation? |
| Reference: | 1. Siva P. Raman, Pamela T. Johnson, Swati Deshmukh, Mahadevappa Mahesh, Katharine L. Grant, Elliot K. Fishman, (2013) CT Dose Reduction Applications: Available Tools on the Latest Generation of CT Scanners, J. American College of Radiology, 10(1): 37-41. doi:10.1016/j.jacr.2012.06.025
2. Kalender, W. A., Wolf, H. and Suess, C. (1999), Dose reduction in CT by anatomically adapted tube current modulation. II. Phantom measurements. Med. Phys., 26: 2248–2253. doi:10.1118/1.598738
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| Choice A: | The optimal strategy is always to flatten the signal received by the detector. |
| Choice B: | No knowledge of the shape and size of the patient is required for determining tube current modulation. |
| Choice C: | Current modulation as a function of projection angle and table position are both valuable for dose reduction. |
| Choice D: | Tube current modulation keeps the image quality the same as a fixed current acquisition for all parts of the image volume. |
