Sunday Case of the Day
Physics
Authors: William Geiser, MS, DABR1
MD Anderson Cancer Center, Houston TX
History: Patient presented for screening mammogram. The radiologist noted that there “increased
motion on both CC views” limiting evaluation. MLO views were of good image quality.
30 kVp
60 mAs
100 mA
Thickness: 59
mm
17 pounds
force
32 kVp
65 mAs
100 mA
Thickness: 66
mm
24 pounds
force
Figure #: 1 CC views on
screening mammogram
27 kVp
59 mAs
100 mA
Thickness: 44
mm
11 pounds
force
28 kVp
50 mAs
100 mA
Thickness: 47
mm
10 pounds
force
Figure #: 2 MLO views on
screening mammogram
Likely cause of the
“increased motion”
is?
A. Patient Motion
B. Poor
Compression
C. Long Exposure
time
D. Poor positioning
Findings: The patient was called back for repeat CC views due to poor image quality.
1.
2.
3.
4.
Fig. 3A: RCC technical values were: 30 kVp, 60.5 mAs, 59 mm compressed breast thickness.
Fig. 3B: LCC technical factors were: 32 kVp, 65 mAs, 66 mm compressed breast thickness.
Fig. 4A RCC technical factors were: 27 kVp, 86 mAs, 40 mm compressed breast thickness.
Fig. 4B LCC technical factors were: 27 kVp, 84 mAs, 41 mm compressed breast thickness.
RCC
A
Figure #3: CC views from initial exam.
LCC
B
RCC
A
Figure #4: Repeat CC views.
LCC
B
Diagnosis:
B. Poor Compression making it hard for the radiologist to
see fine detail in the image. Required that patient be
called back for additional imaging.
Discussion:
Proper compression is important in mammography. The question is
often asked “Why do we have to compress?” We compress for a
variety of reasons.
As stated in the ACR Quality Control Manual section on Clinical Image Quality we compress for the following
reasons:
1.
Decreases breast thickness
2.
Reduces dose
3.
Reduces scatter
4.
Reduces object unsharpness
B
A
5.
Eliminates patient motion
Figure 5: Calcification showing there is
no patient motion
Even though the radiologist mentioned motion, patient motion is not the issue here, lack of compression is.
A closer review of the images did not show any patient motion artifact (see Fig. 5). Fig 5A is a calcification
seen in the RCC on the original image. Fig 5B is the same calcification on the repeated view. Neither exhibit
patient motion artifact. Answer A patient motion is incorrect.
Most mammography generators are limited to 100 mA due to the limitations of the focal spot size and anode
material (0.1 mm and Molybdenum). The system used here is a Hologic Selenia which has a 100 mA
generator. All of the exposure times are less than a second long. Answer C long exposure times is
incorrect.
The breast is positioned properly for the CC views, and if properly compressed would have spread out more
leading to better visibility of the internal structure of the breast. Answer D patient positioning is incorrect.
There are several things to note when comparing the under compressed and properly
compressed views.
•
Visibility of the internal structure of the breast is greatly improved.
•
The image appears more sharp due to the spreading of the overlapping tissues and
bringing structures closer to the detector.
•
Lower kVp in the properly compressed breast leads to improved contrast in the image.
30 kVp
60.5 mAs
100 mA
57 mm
27 kVp
85.7 mAs
100 mA
40 mm
Figure 6. Comparison of two
RCC views
References/Bibliography:
Hendrick, RE, Lawrence, B, Botsco, MA, et.al. American College of Radiology
Mammography Quality Control Manual Section on Clinical Image
Quality, 1999
Geiser WR, Haygood TM, Santiago L, Stephens T, Thames D, Whitman GJ. Challenges
in Mammography: Part 1Artifacts in Digital Mammography. AJR Am J
Roentgenol 197(12):W1023 - W1030, 12/2011