2019 AAPM Annual Meeting
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Session Title: Patient Dose Monitoring in CT with Tube Current Modulation and Multiple Series
Question 1: The width of the dose spread function at the center of the cylindrical object is caused by:
Reference:John M. Boone, Dose Spread Functions in Computed Tomography: A Monte Carlo Study, Medical Physics 36(10): 4547 (2009).
Choice A:The spread of electrons, as radiation dose, laterally
Choice B:Off focus radiation produced in the CT scanner x-ray tube
Choice C:Scattered radiation
Choice D:The penumbra of the collimators
Question 2: The dose spread function at the periphery of the phantom has a shorter range than at the center of the phantom because of:
Reference:John M. Boone, Dose Spread Functions in Computed Tomography: A Monte Carlo Study, Medical Physics 36(10): 4547 (2009).
Choice A:Solid angle effect at the periphery
Choice B:Internal reflection of x-rays at the air/phantom boundary
Choice C:Specular diffraction with small spatial irregularities at the phantom surface
Choice D:The physics of laminar flow.
Question 3: The width of the dose spread function increases with:
Reference:John M. Boone, Dose Spread Functions in Computed Tomography: A Monte Carlo Study, Medical Physics 36(10): 4547 (2009).
Choice A:Decreasing effective energy of the x-ray beam
Choice B:Reduced diameter of the phantom
Choice C:Higher tube potential
Choice D:Increasing density of the phantom
Question 4: On CT dose index, which of the following statements is true?
Reference:Robert L. Dixon. The Physics of CT Dosimetry: CTDI and Beyond. CRC Press, New York, Published April 2019, ISBN 9780367077594; Robert L. Dixon, John M. Boone. Dose equations for tube current modulation in CT scanning and the interpretation of the associa
Choice A:The correct physical description of N×T in the CTDI100 equation is a beam width
Choice B:CTDIvol depends on N×T
Choice C:Scan length L is increased by increasing pitch. Then DLP = L×CTDIvol must also increase
Choice D:If the table failed to move during the complete helical scan protocol (L=0), then DLP = 0
Choice E:None of the above is correct
Question 5: Which of the following statements is true regarding three-dimensional automatic tube current modulation technique in CT?
Reference:Mannudeep Kalra, Michael Maher, Thomas Toth et. al, Technique and applications of tube current modulation in CT, Radiology 2004; 233:649-657.
Choice A:The scanner automatically adjusts tube current in the x-y plane (image slice) to achieve constant image quality (noise)
Choice B:The tube current is automatically decreased for each sensitive organ region
Choice C:The tube current is modulated attempting to make all images have a similar noise irrespective of patient size and anatomy
Choice D:The scanner adjusts mA and kVp for different body size determined from topogram and the exam type
Question 6: Which of the following statements is NOT true regarding automatic tube current modulation in CT?
Reference:Mannudeep Kalra, Michael Maher, Thomas Toth et. al,Technique and applications of tube current modulation in CT, Radiology 2004; 233:649-657
Choice A:All vendors utilize the localizer radiograph to estimate the attenuation, size, and shape information of the patient
Choice B:Z-axis tube current modulation can be applied without the angular tube current modulation
Choice C:In SmartmA, the scanner modulates the tube current in the real-time
Choice D:Real E.C. is an angular tube current modulation technique
Question 7: Size specific dose estimator (SSDE) is able to normalize CTDIvol based on what patient size metrics?
Reference:AAPM Report No. 220: Use of Water Equivalent Diameter for Calculating Patient Size and Size-Specific Dose Estimates (SSDE) in CT, 2014
Choice A:Patient effective diameter
Choice B:Water equivalent diameter
Choice C:Patient geometric measurement in the AP or LAT direction
Choice D:All of the above
Question 8: Which of the following is not a mandatory/required data element in a CT DICOM image according to the current DICOM standard?
Reference:ftp://dicom.nema.org/MEDICAL/dicom/current/output/chtml/part03/sect_C.8.2.html
Choice A:kVp
Choice B:X-ray tube current in mA
Choice C:Data collection diameter
Choice D:Water equivalent diameter
Question 9: In a single rotation axial scan at 80 kV, 140 mAs and 16×0.625-mm beam collimation, CTDIvol is 4.66 mGy (referenced to body CT phantom). Cross-sectional average dose in the midslice (at the scan range center) of an adult (with water equivalent diameter of 30 cm) is close to:
Reference:Xinhua Li, Kai Yang, Matthew C. DeLorenzo, Bob Liu. Assessment of radiation dose from abdominal quantitative CT with short scan length. Br J Radiol 2017; 90(1074):20160931
Choice A:2 × CTDIvol
Choice B:CTDIvol
Choice C:0.5 × CTDIvol
Choice D:0.1 × CTDIvol
Choice E:0.01 × CTDIvol
Question 10: Based on the measurement of the approach to equilibrium function on the central axis of 32-cm diameter acrylic phantom, scatter to primary ratio (SPR) is close to:
Reference:Xinhua Li, Da Zhang, Bob Liu. Monte Carlo assessment of CT dose equilibration in PMMA and water cylinders with diameters from 6 to 55 cm. Med. Phys. 2013;40 (3): 031903 (10pp).
Choice A:10
Choice B:2
Choice C:1
Choice D:0.1
Choice E:0.01
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