Fluoroscopy Flashcards
What is conversion factor?
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
What is minification gain?
(Diameter of OUTPUT/Diameter of INPUT)2
What is brightness gain?
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
Magnification in fluoro?
Crossover point moved nearer to INPUT screen causes magnification
More magnification towards periphery of image (pin cushion effect)
Input caesium iodide phosphor thickness??
- 0.1 - 0.4mm
- 100-400µm
BOTH ARE THE SAME
Continuous fluoroscopy pulses?
Average dose to patient/min?
- 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
Spatial resolution of Fluoro??
- 4-5lp/mm
Quantum Sink
The point where the least amount of photons contribute to the image
- Occurs at input screen
Tube voltage in Fluoro??
70-90 keV
Bandwidth in a TV system and resolution
- Bandwidth determines HORIZONTAL resolution which in turn determines vertical resolution
Plumbicon
vs
Vidacon
Plumbicon = low lag system and less motion blur but INCREASED NOISE
Vidacon - high lag so LESS NOISE, but blurry motion
Contrast Testing - what is used?
Leeds test object
It is a low contrast disc containing circular inserts of high atomic number material producing varyng levels of contrast
DSA
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)
Dual Energy
High kV = poor contrast
Low kV = high contrast between bone and soft tissues
What is Fluroro DQE??
60% (conventional IIs are the same)
Mammography - what is main x-ray interaction??
Photoelectric with L shell electrons
Mammography uses linear moving grids
X-ray output Mammography
Proportional to kv3
ESD is also proportional to kv3
Collimation in Fluoro
- Improves contrast
- Reduces dose
- Reduces scatter
*
What are Equalisation Filters?
- 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
Fluoro Doses
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
Automatic brighness control
Adjusts the mA and kV to keep image brightness constant
DOES NOT adjust gain
What is the small collimation fluoro should be capable of?
5 x 5 cm2
