Mammography & Fluoro

Question 1

Tube Voltage???

Answer 1

25 - 35kvP

Question 2

Focal spot size (Normal vs Mag)

Answer 2

Normal 0.3mm

Mag 0.1mm

Question 3

Molybdenum

Characteristic x rays

Rhodium

Answer 3

• 17.9 and 19.5 keV

Atomic Number = 42

Molybdenum filter is 0.3mm

• 20.2 and 22.7keV

Atomic number = 45

Question 4

Exposure times??

Answer 4

Can be up to 4 seconds in dense breasts

Question 5

Compression

Answer 5

• 110 - 200N

Question 6

Magnification Mammography

Answer 6

Breast is moved 15-30 cm closer to the x-ray source, creates air gap also

Focus to film distance remains the same!!!

Magnification = FFD/FOD

(focus to film distance/focus to object distance)

GRID IS NOT USED IN MAGNIFICATION MAMMOGRAPHY

Question 7

Source to film distance??

Answer 7

65cm

Question 8

What is tube output proportional to in Mammography?

Answer 8

Proportional to kV³

Question 9

Molybdenum Filter thickness?

Answer 9

0.03mm

Question 10

Image intensifier chamber material

Answer 10

Made of:

• Glass, ceramic or aluminium

Surrounded by metal housing preventing light from reaching tube. Also shields from magnetic field

NO LEAD INSIDE TUBE

Question 11

Input Phosphor - Amount of light photons produced at input phosphor from 1 x-ray photon??

Answer 11

1 x-ray photon = 3000 light photons in BLUE part of spectrum

GREEN light produced at output

Question 12

Input window material ?

Answer 12

Aluminium or Titanium

Question 13

Which phosphor is thicker?

Answer 13

Input phosphor

Question 14

Scatter at output window - how to minimise?

Answer 14

Thick glass at output window

Question 15

Does efficieny of input screen affect gain?

Answer 15

NO

Gain is only dependent on flux gain and minification gain

Question 16

Iris

Answer 16

When brightness decreases, e.g in magnification mode - iris aperture can open to let more light in. This saves an increase in dose

In magnification - there is a change in the voltage of the intermediate electrodes

Question 17

TV Camera

Answer 17

Electron beam deposits electrons onto the surface

• each light photon from the output screen that is absorbed into the CCD gives rise to ONE electron-hole pair

Question 18

Automatic brightness control

Answer 18

DOES NOT USE 3 ionisation chambers - that is DR

• Measures brightness at the centre of the output screen and adjusts mA and kV accordingly
• Uses isowatt curves
• Curve A: increases mA and kV
• Curve B: holds kV and increases mA (higher dsoe but good for contrast studies)
• Curve C: Low dose - high kV

Question 19

Contrast study and DSA

Answer 19

mA increases when radiological thickness (not the kV as would be expected)

Question 20

Pulsed Fluoro

Answer 20

Pulse rate is between 2 and 20ms

Uses grid controlled tube

Question 21

Dose of a single exposure

Answer 21

0.1 - 5µGy

Question 22

Spatial resolution of Digital mammography vs Film?

Answer 22

Digital = 7lp/mm

Film = 15lp/mm

Question 23

Typical dose to each breast?

Answer 23

1.5 - 3mGy per breast

Question 24

What is kV of mammography unit?

Answer 24

24 - 35kV

Question 25

Focus to film distance in mammography?

Answer 25

65cm and is set

Question 26

Do grids affect spatial resolution?

Answer 26

No

Just contrast resolution