Fluoroscopy

Question 1

What is conversion factor?

Answer 1

Output luminescence/input exposure rate

• used as a measure of tube sensitivity
• measured using a luminescence meter or a calibrated dose meter
• usually in the range of 10-30µGym^-1

Question 2

What is minification gain?

Answer 2

(Diameter of OUTPUT/Diameter of INPUT)²

Question 3

What is brightness gain?

Answer 3

The product of Flux gain x Minification gain

• Flux gain: single photon at input = single electron = multiple photons at output screen
  
  • Usually 50x
• Minification gain: diameter of output/input diameter squared

Question 4

Magnification in fluoro?

Answer 4

Crossover point moved nearer to INPUT screen causes magnification

More magnification towards periphery of image (pin cushion effect)

Question 5

Input caesium iodide phosphor thickness??

Answer 5

• 0.1 - 0.4mm
• 100-400µm

BOTH ARE THE SAME

Question 6

Continuous fluoroscopy pulses?

Average dose to patient/min?

Answer 6

• Usually 25-30 pulses/sec
• 10-30mGy/min is usual dose
• Patient dose cannot excees 100mGy/min
• Dose rate to input to phosphor is 1micro Gy/sec

Question 7

Spatial resolution of Fluoro??

Answer 7

• 4-5lp/mm

Question 8

Quantum Sink

Answer 8

The point where the least amount of photons contribute to the image

• Occurs at input screen

Question 9

Tube voltage in Fluoro??

Answer 9

70-90 keV

Question 10

Bandwidth in a TV system and resolution

Answer 10

• Bandwidth determines HORIZONTAL resolution which in turn determines vertical resolution

Question 11

Plumbicon

vs

Vidacon

Answer 11

Plumbicon = low lag system and less motion blur but INCREASED NOISE

Vidacon - high lag so LESS NOISE, but blurry motion

Question 12

Contrast Testing - what is used?

Answer 12

Leeds test object

It is a low contrast disc containing circular inserts of high atomic number material producing varyng levels of contrast

Question 13

DSA

Answer 13

Mistregistration more prominent at borders between high contrast objects

Pixel shifting can only be done for entire FOV (not for specific areas in the field that have moved)

Question 14

Dual Energy

Answer 14

High kV = poor contrast

Low kV = high contrast between bone and soft tissues

Question 15

What is Fluroro DQE??

Answer 15

60% (conventional IIs are the same)

Question 16

Mammography - what is main x-ray interaction??

Answer 16

Photoelectric with L shell electrons

Mammography uses linear moving grids

Question 17

X-ray output Mammography

Answer 17

Proportional to kv³

ESD is also proportional to kv³

Question 18

Collimation in Fluoro

Answer 18

• Improves contrast
• Reduces dose
• Reduces scatter
  *

Question 19

What are Equalisation Filters?

Answer 19

• Different to collimators
• Made of lead rubber or lead acrylic sheets
• Also known as Wedge or Contour filters

They are partially radiolucent plades that privide further beam shaping in addition to collimation

Question 20

Fluoro Doses

Answer 20

Standard dose should not exceed 100mGy/min

Leakage of x-ray from the tube housing is typically 5µGy/hr at 1m distance

Scatter is about 0.1% of patient entrance dose rate at 1m

Zoom view increases patient dose

Question 21

Automatic brighness control

Answer 21

Adjusts the mA and kV to keep image brightness constant

DOES NOT adjust gain

Question 22

What is the small collimation fluoro should be capable of?

Answer 22

5 x 5 cm²