Breast Imaging: A Core Review (44 page)

References: Hendick RE, et al. Comparison of acquisition parameters and breast dose in digital mammography and screen-film mammography in the American College of Radiology Imaging Network digital mammographic imaging screening trial.
AJR Am J Roentgenol
2010;194(2):362–369.
Michigan Department of Licensing and Regulatory Affairs. MGD results from 427 mammography machines. January 2012. Available at:
http://www.michigan.gov/images/mdch/bhs_mammo_dose_220795_7.gif

19
 
Answer C.
 When compared to routine screening, magnification views have longer exposure time. They are also associated with more motion blur, less scatter, less noise, decreased source-to-object distance and have no significant change in contrast.

References: Bushberg JY, Seibert JA, Leidholt EM, et al.
The Essential Physics of Medical Imaging
. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001:210.
Huda W.
Review of Radiographic Physics
. 3rd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2010:54–55.

20
 
Answer D.
 Breast compression obviously reduces object thickness, which reduces scatter. Lower scatter lowers image noise improving image contrast.

Reference: Barnes G.
RSNA Categorical Course in Diagnostic Radiology Physics: Technical Aspects
.
Haus A, Yaffe M, eds. Oak Brook, IL: RSNA; December 1992:59–68.

21
 
Answer C.
 This limit is specified in the NRC regulations for radioactive materials and adopted into CRCPD Suggested State Regulations, which are adopted by states with regulations over radiation machines. Is also the current standard of the National Council on Radiation Protection and Measurements (NCRP).

Reference:
Conference of Radiation Control Program Directors, Suggested State Regulations for Control of Radiation, Standards for Protection Against Radiation
, Part D; 2003.
http://www.crcpd.org/SSRCRs/dpart.pdf

22
 
Answer D.
 Since 2002, it has been shown that the thyroid dose is insignificant compared to the breast dose. Most importantly, they are neither necessary nor helpful, and their use can result in inadequate or repeat studies.

References: Kopans DB. Mammograms and thyroid cancer: the facts about breast-cancer screening. Available at:
http://www.massgeneral.org/imaging/about/newsarticle.aspx?id=2720
Whelan C, McLean D, Poulos A. Investigation of thyroid dose due to mammography.
Australas Radiol
1999;43(3):307–310.

23
 
Answer D.
 The W target with Rh filter provides the highest effective energy to maximize penetrability while minimizing the reduction in image contrast, which is critical breast imaging.

Reference: Pizzutiello R.
RSNA Categorical Course in Diagnostic Radiology Physics: From Invisible to Visible. The Science and Practice of X-ray Imaging and Radiation Dose Optimization
. Frush D, Huda Q, eds. Oak Brook, IL: RSNA; December 2006:219–234.

24
 
Answer C.
 Film is the capture, display, and storage medium. Its spatial resolution is limited by the phosphor particle size and screen characteristics, which is about 15 to 20 lp/mm. This exceeds the pixel resolution characteristics of the image recording and display of the digital imaging chain.

References: Bushberg JT.
The Essential Physics of Medical Imaging
. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2001:293–316.
Williams MB, Fajardo LL. Digital mammography: Performance considerations and current detector designs.
Acad Radiol
1996;3:429–437.

25
 
Answer C.

Reference: Ranger NT, Lo JY, Samei E. A technique optimization protocol and the potential for dose reduction in digital mammography.
Med Phys
2010;37:962–969.

26
 
Answer C.
 The question tests knowledge of units and clinical absorbed dose from current digital mammogram for an average breast. 100 millirad = 1 milligray = 1 millisievert; 300 millirads is the ACR limit for accreditation and represents a limit for an average breast that must not be exceeded. 100 millisieverts is not a measure of absorbed dose and is a huge dose in worker dose limit range. Clinical techniques for digital imaging are lower than filmscreen for the same breast thickness. While film is in the 200- to 300-millirad range, digital is in the 150- to 200-millirad or 1.5- to 2.0-milligray range.

Reference: Hendrick RE, Pisano E, Averbukh A, et al. Comparison of acquisition parameters and breast dose in digital mammography and screen-film mammography in the American College of Radiology Imaging Network Digital Mammographic Imaging Screening Trial.
AJR Am J Roentgenol
2010;194:362–369.

27
 
Answer A.
 All factors affect the acquisition side of the imaging chain. Image quality is maximizing signal-to-noise ratio (SNR) per unit of dose. Based on maximizing a figure of merit, which is the ratio of SNR to MGD, very gradually decreases with kVp. Field size and mAs are constant for a fixed breast thickness but increase MGD causing a decreased figure of merit (FOM). For the same thickness, target/filter combo strongly affected the FOM as kVp increased.

References: Ranger NT, Lo JY, Samei E. A technique optimization protocol and the potential for dose reduction in digital mammography.
Med Phys
2010;37:962–969.
Williams, et al. Optimization of exposure factors in full field digital mammography.
Med Phys
2008;35:2414–2423.

28
 
Answer B.
 Electronic magnification is a postacquisition processing technique that is analogous to enlarging an already acquired picture. It does not affect the dose employed for the image or affect the image resolution. Noise is increased with electronic magnification. Geometric magnification is the actual image magnification based on imaging technique and will affect image resolution.

Reference: Niklason L.
RSNA Categorical Course in Diagnostic Radiology Physics: From Invisible to Visible. The Science and Practice of X-ray Imaging and Radiation Dose Optimization
. Frush D, Huda Q, eds. Oak Brook, IL: RSNA; December 2006:235–241.

29
 
Answer E.
 Honeycomb-type grids (HTC) 4:1 are used in mammography. Exposure doubles even with a grid ratio of 4:1 compared to a nongrid exposure.

References: Huda W, Greene-Donnelly K.
RT X-Ray Physics Review
. Madison, WI: Medical Physics Publishing; 2011:180.
Bushong SC.
Radiologic Science for Technologists—Physics, Biology and Protection
. St. Louis, MO: Mosby; 2001:315.
Carlton RR, Adler AM.
Principles of Radiographic Imaging. An Art and a Science
. Albany, NY: Delmar; 2001:583.

30
 
Answer C.
 Mammography uses two focal spot sizes: a large and a small. For the standard CC and MLO, the large focal spot size is used, which is generally 0.3 mm.

Reference: Bushong SC.
Radiologic Science for Technologists—Physics, Biology and Protection
. St. Louis, MO: Mosby; 2001:311.

31
 
Answer E.
 The recommended SID for mammography should be from 50 to 80 cm. It is best to have a long SID and a small focal spot size for optimal sharpness and resolution.

Reference: Wentz G, Parsons WC.
Mammography for the Radiologic Technologist
. 2nd ed. New York, NY: McGraw-Hill; 1992:17.

32
 
Answer A.
 The most common focal spot size used for magnification imaging in mammography is 0.1 mm.

Reference: Valerie F, Andolina RT, Shelly LL, et al.
Mammographic Imaging: A Practical Guide
. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins; 2001:64.

33
 
Answer B.
 High-resolution monitors should be used for reading digital mammography to appreciate fine detail. A 5-megapixel monitor (2,048 × 2,560 pixel samples in the horizontal and vertical directions for portrait orientation) is recommended by the ACR.

Reference:
ACR–AAPM–SIIM Practice Guideline for Determinants of Image Quality in Digital Mammography
; 2012:6 section 4a resolution 36.
http://www.acr.org/~/media/ACR/Documents/PGTS/guidelines/Image_Quality_Digital_Mammo.pdf

34
 
Answer C.
 The x-ray field should not extend beyond the image receptor by more than 2% of the SID.

Reference: Hendrick RE, Bassett L, Botsco MA, et al.
ACR Committee on Quality Assurance in Mammography
. Reston, VA: Mammography Quality Control Manual; 1999:236.

35
 
Answer D.
 Slit camera with a 10-μm slit width.

Reference: Hendrick RE, Bassett L, Botsco MA, et al.
ACR Committee on Quality Assurance in Mammography
. Reston, VA: Mammography Quality Control Manual; 1999:321–322.

36
 
Answer D.
 Weekly imaging of the ACR phantom is done to verify whether all aspects of the imaging system are functioning properly: image quality, contrast, optical density, uniformity, and scores of the detection limits of the phantom, which are required by the ACR: four fibers, three speck groups, and three masses.

Reference: Bushong SC.
Radiologic Science for Technologists
:
Physics and Protection
. 10th ed. St. Louis, MO: Elsevier Mosby; 2013:391–393.

37
 
Answer A.
 Beryllium is a very low attenuating material that is used in the mammography tube window.

Reference: Huda W, Greene-Donnelly K.
RT X-Ray Physics Review
. Madison, WI: Medical Physics Publishing; 2011:178.

38
 
Answer B.
 Due to the anode heel effect, the cathode is placed at the chest wall.

Reference: Huda W, Greene-Donnelly K.
RT X-Ray Physics Review
. Madison, WI: Medical Physics Publishing; 2011:178.

39
 
Answer B.
 The size of the large focal spot used in mammography is 0.3 mm; 0.1 mm is incorrect. This smaller focal spot would typically be used for magnification mammography; 0.7 and 1.0 are entirely too large a focal spot for standard mammography.

Reference: Ikeda D.
Breast Imaging: The Requisites
. 2nd ed. St. Louis, MO: Elsevier Mosby; 2011:3.

40
 
Answer A.
 In mammography, the goal is to improve soft tissue contrast in order to distinguish smaller, more dense lesions (such as tiny microcalcifications) from the surrounding fibroglandular tissue. This is done by lowering the kVp (peak kilovoltage).

Reference: Ikeda D.
Breast Imaging: The Requisites
. 2nd ed. St. Louis, MO: Elsevier Mosby; 2011:2–4.

41
 
Answer D.
 Breast compression allows lower kVp values to be used, due to decrease in the thickness of the breast. Motion blur is decreased since the breast is less likely to move. There is decreased scattered radiation which leads to improved contrast. The compression allows the spread of overlying tissue, which reduces superimposition and decreases structural mottle.

Reference: Nickoloff EL.
Radiology Review: Radiological Physics
. New York, NY: Elsevier Saunders; 2005:156.

42
 
Answer D.
 This image has a poor contrast because of the exposure factors (high kvP and low mAs) for the thickness of the breast. Answer choice D is correct because of the decrease in kVp, there is increase in contrast. The radiographic contrast is also dependent on the patient as well as the image contrast. Contrast is affected by the breast thickness, density, and atomic differences of the patient, kVp, contrast material, and scatter radiation.

Answer choice A is incorrect because the MAs is a combination of the mA tube current and exposure time. Increasing the mAs increases the exposure time. Decreasing the kVp from 28 to 26 indirectly affects the exposure time in cases where phototiming is used. With a decrease in kVp, there is a compensatory increase in mAs.