Mammography Equipment

Question 1

Film vs Digital Mammography

Answer 1

Film
High spatial resolution (12-16 lp/mm)
Lower contrast resolution

Digital
Spatial resolution limited by pixel size (7-9 lp/mm)
High contrast resolution 
Post processing abilities
Easier to store and share

Question 2

Digital Image Acquisition

Answer 2

Detector signal is linear with radiation intensity

Most interactions are photoelectric

Question 3

Digital Mammography

Answer 3

Spatial resolution is limited by pixel size approx 7-9 lp/mm
Determined by detector element, signal spread, focal spot size
Enhanced contrast resolution
Lower dose

Question 4

generator

Answer 4

Generator – high frequency (linearity and reproducibility), constant potential. Generators are housed in tube.

Question 5

X-ray tube

Answer 5

C-arm, tube and detector are fixed
Shorter SID (60-65 cm)
Microfocal spots 0.3mm, 0.1mm
Uses anode heel effect

Question 6

X-ray tube: Cathode

Answer 6

tungsten filament, focusing cup
Cathode over the chest wall and small SID create geometric issues
The tube is off centered to compensate
Smaller effective focal spot over the chest wall
Central ray is straight at the chest wall, angled over the centre (reference axis)

Question 7

X-ray Tube: Anode

Answer 7

Anode
Effective target angle is greater 22-24°
Reference axis target angle is smaller 7.5-12°
Defines size of focal spot as measured to centre of image

Question 8

Target Material

Answer 8

Previously with film, needed characteristic radiation in 15-20 keV range
K-edge of film controlled the kV (25-27)
Targets had to be Mo or Rh

Digital technology
Tungsten
kV is 28-30

Question 9

kV and mAs

Answer 9

kV determines the contrast of the image
Optimize contrast characteristics of the target
SNR more important than contrast
Higher mAs for adequate density, but mAs is 30-40% lower with digital technology
Keep exposure times to a minimum

Question 10

Filtration

Answer 10

Beryllium window will not filter beam
Added filtration is Mo or Rh to remove low and high energy photons
More homogeneous beam
HVL – in range of 0.5 mm Al

Question 11

Indirect Detectors

Answer 11

Convert x-rays to light
Silicon diodes, CCD, phosphor flat panel
Light amplified and sent to A/D converter
Uses TFT

Question 12

Direct Detectors

Answer 12

Capture and count x-rays directly
Detect, amplify, convert to digital
Selenium flat panel
Converts x-rays to charge via electron-hole pairs
Displayed as pixels

Question 13

AEC

Answer 13

Consistent optimal image
No photocells
Measures radiation exiting breast
Must be accurate and reproducible

Question 14

Compression Device

Answer 14

Plastic composition
Minimize attenuation
Ensures breast of uniform thickness and closer to IR/detector
Delivers 25-40 lbs of force

Question 15

Grids

Answer 15

Reduce scatter, improve subject contrast
Conventional grids absorb low energy radiation
Lower grid ratio 4:1
Different interspace materials
Moving or HTC
Increased patient dose

Question 16

Benefits of digital Mammography

Answer 16

• dense breast imaging
• latitude
• lower dose

computer-aided diagnosis (AI)

storage and retrieval
remote access

Question 17

Quality

Answer 17

Calibration to check for artifacts
Detector testing
Grid artifacts
Monitor cleaning
Noise SNR and CNR