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Medical Physics 2nd Semester > Mammography (Diagnostic Radiology) > Flashcards

Flashcards in Mammography (Diagnostic Radiology) Deck (30)
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1

What is the ideal energy range of x-rays? Why?

15-20 keV

 

Offers the best balance between contrast and dose

2

Why is molybdenum target often used?

(two reasons)

Have a kEdge of ~20 keV

 

Also have an L BE of 2.5, so dropping down means 17.5 keV photons which are also in the ideal range

3

What is the purpose of applying a target filter?

To filter out the low and high energy photons

 

Remember we want it in the middle range between 15 and 20 keV

4

What two components are added together to make the effective anode angle?

 

What degree should it be greater than or equal to?

Anode angle + physical tube tilt

 

Should be atleast 22 degrees

5

True or false

0 degree anode angle tilt with a 24 physical tube tilt has a greater field coverage as 16 degree anode angle with a 6 degree tube tilt.

False, they're both above 22 degrees total. Above that angle the field coverage will be approximately the same.

6

What is the cathode side of the tube adjacent to? Why is this important? 

 

(Hint: think Heel effect)

Adjacent to patient's chest wall

 

It's the thickest part of the breast, so you want the most intensity. Cathode side is unaffected by heel effect

7

Equation for nominal focal spot size.

 

NEED TO MEMORIZE

aref = achest wall (1- tan(theta - Ø)/tan(theta))

 

achest wall = sin(theta)

theta is the the effective anode angle

phi is half of that

8

Regarding breast compression in mammo, the following effects will occur. Which contribute to contrast enhancement, which to resolution?

 

  1. Reduction of overlapping anatomy
  2. Decrease thickness - fewer scatter X-rays
  3. Decrease thickness - less geometry blur
  4. Reduces motion

  1. Contrast
  2. Contrast
  3. Resolution
  4. Resolution

9

Will breast compression cause lower or higher dose?

Lower

 

Increases contrast and resolution naturally. So you can reduce the mAs

10

Fill out the following flow logic,

 

Scatter --> Noise --> Lower contrast and SNR --> ______ ---> Higher dose

AEC

Automatic Exposure Control

11

True or false

Scatter radiation is largely independent of kV in the mammography energy range

True

12

Which of the following will lead to better detailed images? Why?

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase

  • Magnification
  • Smaller focal spot size - Less Geo blur
  • Compression - Reduces overlapping anatomy, motion blur and geometry blur

13

Which of the following will lead to better contrast images? Why?

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase

  • Magnification - Air Gap (less scatter)
  • Target/Filter changes -  Ideal Energy Range
  • Compression - Less scatter
  • Air Gap increase - Less Scatter

14

Which of the following will lead to lower dose? Why?

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase

 

  • Target/Filter changes - Idea E Range (less high and low photons)
  • Compression - AEC decreased thickness

15

Which of the following will lead to higher dose? Why?

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase

Only air gap

 

AEC will hold for longer

16

Main benefit of screen-film mammography over digital systems?

Better resolution

17

Why would you position your screen behind film?

X-ray interations are greater near the entrance surface, by having screen behind the film there's minimal light spread at the film surface

 

(better spatial resolution)

18

Fill out the following flow chart of events for Digital Mammorgraphy (CR)

 

X-ray --> _____ --> Lights ---> Trapped electrons in film ---> _______ ----> Digital signal

Screen

CR Reader

19

Main benefits of digital mammography (there's 2)

Wider dynamic range

Better contrast

20

Why does magnification mode need a smaller focal spot?

To minimize geometric blur

 

Otherwise blurred edges would be too exaggerated

21

Which of these does not lead to better resolution?

  • Smaller focal spot size
  • Larger SOD
  • Smaller OID/breast thickness
  • Higher mA/less imaging time
  • Less light spread
  • Smaller Grain/pixel size

 

None, they all do

  • Smaller focal spot size - Less geometric blur
  • Larger SOD - Less geometric blur
  • Smaller OID/breast thickness - Less geometric blur
  • Higher mA/less imaging time - Less motion blur
  • Less light spread - Less detector blur
  • Smaller Grain/pixel size - Less detector blur

22

What is the range of input signal over which a desirable contrast could be formed called?

 

What has this better range, Screen film or digital system?

Dynamic Range

 

Digital system

23

Equations for Noise, relative noise and SNR

Noise: N1/2

Relative Noise: N1/2/N  = 1/N1/2

SNR: N/N1/2 = N1/2

24

How do you account for scatter in Digital breast tomosynthesis?

You can't use an anti-scatter grid

Need to make a correction algorithm in the system

25

Formula for Mean Glandular Dose (MGD)

Dg = DgN x XESAK

 

DgN = some conversion factor you look up

XESAK = entrance skin air kerma

26

What type of breast tissue is the site of carcinogensis?

Glandular tissue

27

What is the fraction of "average breast" tissue that is glandular. What about fat?

50/50

28

Which of the following cause a higher MGD? Why?

  • Thicker Breast
  • Higher Adipose Fraction
  • Grid

  • Thicker Breast - Need more penetrating beam, higher kVp, higher deposited energy
  • Grid - Less radiation, AEC holds for longer

29

Which of the following cause a lower MGD? Why?

  • Thicker Breast
  • Higher Adipose Fraction
  • Grid

  • Higher Adipose Fraction - More x-ray attenuation in the adipose tissue, less elsewhere since thickness is same

30

Equation for detective quantum efficiency (DQE)

DQE(f) = SNR2out / SNR2in

 

Ideally, DQE = 1

 

DQE is a function of spectrum, spatial frequency and exposure