Fluoroscopy (Diagnostic Radiology) Flashcards
Exposure differences between radiograph and fluroscopy
Radiograph has a larger exposure rate, but is instant.
Fluroscopy has lower exposure rate, but is held for longer. Overall two orders of magnitude larger.
Approximately how much does the image intensifier amplify the brightness by?
~10,000
Why is the input screen curved?
For accurate electron focusing
What is the function of the input phosphor in the image intensifier?
Converts x-rays into scintillation photons
Then, the scintillation photons are converted to electrons
Minification gain equation
Areainput / Areaoutput
Signal density (increases or decreases) with minification gain?
Increases
True or false
When entering magnification mode, minifaction will decrease
True
Regarding the Output phosphor what is the…
Input:
Output:
Input: Accelerated electrons
Output: Multiple photons
1 electron emits ~ 1000 light photons
What is the term called for a fall off in brightness at the periphery of an image?
Occurs from scatter form periphery contributing to center
There is no scatter outside active image to contribute to periphery
Vignetting
What is a concern of a high x-ray flux impinging on a region of the II?
Brightness saturation
Yields a maximum level of brightness and display can’t be any more bright if radiation increases. Gray scale won’t display
Nice diagram of conversion steps of image intensifier
What is a quantum sink
Result of quanta at next step being less than current step
Ex. x-rays absorbed by input screen of image intensifier
Equation for brightness gain
BG = Flux gain x minification gain
What is flux gain defined as?
light photons at output / light photons at input
A smaller area into input phosphor means that brightness gain will decrease.
Because of this, the automatic brightness control needs to compensate for the dimmer image by boosting the x-ray exposure rate (by increasing kV, mA or both).
How much does exposure rate change when cutting FOV in half?
Increases by factor of 4
When dealing with the automatic brightness control,
Increasing mA will _______ dose and ________ contrast.
increase and increase
When dealing with the automatic brightness control,
Increasing kVp will _______ dose and ________ contrast.
decrease and decrease
What is typically the limiting component of the imaging chain in terms of spatial resolution degradation?
The television display!
For thin film transistor replacing image intensifier,
Smaller detector elements sizes would ________ the spatial resolution but __________ noise. It would also _______ dose.
improve
create more
increase dose (since noise is increased, more dose is required)
What are some benefits to using flat panel detectors over image intensifiers?
All around higher QDE at all kV energies
Directly records real time image
Compact
Similar or better resolution
Can correct pixel sensitivities
Biggest con: expensive
What conversion occurs during the intermediate step of indirect detection fluroscopy?
X-ray converted to light photons
Binning detector elements will,
______ data bandwidth
_______ SNR
_______ spatial resolution
Reduce
Increase
Reduce
What is the limiting factor of the spatial resolution in a flat panel detector (FPD)?
DEL size
What is the main limiting factor of spatial resolution in image intensifier / TV system?
Video system
(can be improved with magnification, smaller FOV)
Moving anatomy closer to image receptor will ______ focal spot blur and ______ patient dose.
Decrease
Decrease
Frame averaging may produce __________ and introduce _____________
Ghost artifact
motion blur
(in whichever order)
Why is contrast resolution of fluroscopy lower compared to radiography?
Due to the lower exposure per fram (low SNR)
Benefits of pulsed fluoroscopy
Reduce motion blur
Provide better spatial resolution
Frame averagin can be used in fluoro to reduce _______
Quantum noise
Approximately what fraction of the dose is delivered in the first 3-5 cm of tissue?
1/2
Where is dose rate measured for a GI unit, and for a C-arm unit?
GI - 1 cm above table
C-arm: 15 cm from isocenter towards source
Which of the following when increased, will increase patient dose?
- kVp
- beam current
- Fluro time
- Beam filtration
- Collimation
- grid
- ABC
- Magnification
- Pulsed fluoro
- No
- Yes
- Yes
- No
- No
- Yes
- Yes or No
- Yes (total brightness gain falls, image is dimmer, ABC compensates by raising dose)
- No
What is the optimal way to position the patient to reduce dose and improve spatial resolution?
Close to image receptor, far from x-ray source
Increasing OID will have what changes to…
- Magnification
- Dose
- Scatter to image receptor
- Scatter to medical staff
- Focal spot blurring
- Magnification - increase
- Dose - increase
- Scatter to image receptor - reduce
- Scatter to medical staff - increase
- Focal spot blurring - increase
Approximately how much does scattered radiation drop for every 1 meter distance from patient?
Drops to 0.001
Ex. 3 meters away, drops to 0.0013 of original entrance
What is the approximate skin dose threshold for fluoro?
2 Gy
How does dose area product change with increased distance from source?
It doesn’t change.
DAP is the product of dose over some area. Moving away will decrease dose by inverse square law, but increase area by inverse square law.
Product remains constant
Assuming ABC maintains brightness going from FOV1 to FOV2 what is the ratio of DFOV1 to DFOV2
(FOV1/FOV2)2
