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

Mammography (Diagnostic Radiology) Flashcards

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1
Q

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

A

15-20 keV

Offers the best balance between contrast and dose

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2
Q

Why is molybdenum target often used?

(two reasons)

A

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

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3
Q

What is the purpose of applying a target filter?

A

To filter out the low and high energy photons

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

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4
Q

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

What degree should it be greater than or equal to?

A

Anode angle + physical tube tilt

Should be atleast 22 degrees

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5
Q

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.

A

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

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6
Q

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

(Hint: think Heel effect)

A

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

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7
Q

Equation for nominal focal spot size.

NEED TO MEMORIZE

A

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

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8
Q

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
A
  1. Contrast
  2. Contrast
  3. Resolution
  4. Resolution
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9
Q

Will breast compression cause lower or higher dose?

A

Lower

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

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10
Q

Fill out the following flow logic,

Scatter –> Noise –> Lower contrast and SNR –> ______ —> Higher dose

A

AEC

Automatic Exposure Control

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11
Q

True or false

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

A

True

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12
Q

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

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase
A
  • Magnification
  • Smaller focal spot size - Less Geo blur
  • Compression - Reduces overlapping anatomy, motion blur and geometry blur
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13
Q

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

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase
A
  • Magnification - Air Gap (less scatter)
  • Target/Filter changes - Ideal Energy Range
  • Compression - Less scatter
  • Air Gap increase - Less Scatter
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14
Q

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

  • Magnification
  • Smaller focal spot size
  • Target/Filter changes
  • Compression
  • Air Gap increase
A
  • Target/Filter changes - Idea E Range (less high and low photons)
  • Compression - AEC decreased thickness
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15
Q

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

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

Only air gap

AEC will hold for longer

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16
Q

Main benefit of screen-film mammography over digital systems?

A

Better resolution

17
Q

Why would you position your screen behind film?

A

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
Q

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

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

A

Screen

CR Reader

19
Q

Main benefits of digital mammography (there’s 2)

A

Wider dynamic range

Better contrast

20
Q

Why does magnification mode need a smaller focal spot?

A

To minimize geometric blur

Otherwise blurred edges would be too exaggerated

21
Q

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
A

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
Q

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?

A

Dynamic Range

Digital system

23
Q

Equations for Noise, relative noise and SNR

A

Noise: N1/2

Relative Noise: N1/2/N = 1/N1/2

SNR: N/N1/2 = N1/2

24
Q

How do you account for scatter in Digital breast tomosynthesis?

A

You can’t use an anti-scatter grid

Need to make a correction algorithm in the system

25
Q

Formula for Mean Glandular Dose (MGD)

A

Dg = DgN x XESAK

DgN = some conversion factor you look up

XESAK = entrance skin air kerma

26
Q

What type of breast tissue is the site of carcinogensis?

A

Glandular tissue

27
Q

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

A

50/50

28
Q

Which of the following cause a higher MGD? Why?

  • Thicker Breast
  • Higher Adipose Fraction
  • Grid
A
  • Thicker Breast - Need more penetrating beam, higher kVp, higher deposited energy
  • Grid - Less radiation, AEC holds for longer
29
Q

Which of the following cause a lower MGD? Why?

  • Thicker Breast
  • Higher Adipose Fraction
  • Grid
A
  • Higher Adipose Fraction - More x-ray attenuation in the adipose tissue, less elsewhere since thickness is same
30
Q

Equation for detective quantum efficiency (DQE)

A

DQE(f) = SNR2out / SNR2in

Ideally, DQE = 1

DQE is a function of spectrum, spatial frequency and exposure

Medical Physics 2nd Semester (7 decks)

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