Week #12 Flashcards
What type of technology do most fluoroscopy systems use?
Television technology
What is fluoroscopy primarily used for?
Dynamic studies that require evaluation of functional anatomy
What technical factors are used for fluoroscopy?
Low mA (0.0-5mA) and high kvp
What distinguishes fluoroscopy from radiology?
Image intensifier
Several thousand times more sensitive than a standard screen film combination
A complex device that receives the image forming xray beam and converts it into visible light image
Image intensifier
What potential difference is maintained in the image intensifier?
About 25,000 V is maintained across the tube between photocathode and anode so that electrons will be accelerated to the anode
What are the 4 principal components of the image intensifier?
-vacuum enclosure
-input layer
-electronic lenses
-output layer
Converts xray signals to electrons
Input layer
Focuses the electrons
Electronic lenses
Converts the accelerated electrons into visible light
Output layer
Absorbs xray photons, converts their energy into visible light
Input layer
What is the input later made of?
Cesium iodide (csl)
Takes xray photons and converts them to light
Input phosphor
Thin metal layer that converts input phosphor light into electrons
(Called photo emission)
Photocathode
Consists of electrostatic lenses that “intensify” and focus the stream of e-
Image intensifier
Shape the electric field - focusing the electrons onto the output phosphor
Electrostatic focusing lenses
Consists of:
Anode
Output phosphor
Output window
Output layer
A thin circular aluminum plate with a hole in the middle through which electrons pass to the output phosphor
Anode
What material is the output phosphor made of?
Zinc cadmium
What is the output phosphor capable of resolving?
Approximately 4-6 lp/mm
T/F
Each photoelectron that arrives at the output phosphor produces 50-75 times as many light photons as were necessary to create it
True
The last section of the II
Part of the vacuum bottle made to be transparent to light
*this is where light photons come out
Output window
Size varies from 10-40cm
Input phosphor
Size is fairly standard at 2.5 or 5 cm
Output phosphor
What is determined by the physical size of the II?
Field of view
What might larger II’s be used for?
Gastrointestinal/genitourinary work
What might smaller II’s be used for?
(23cm)
Cardiac imaging
As magnification is increased:
A smaller area of the II is visualized
**Spatial resolution is improved
A reduction in brightness at the periphery of the image
Vignetting
The collimator adjusts to narrow the xray beam to a smaller field of view when what mode is engaged?
Magnification mode
Magnification mode results in:
Better spatial resolution
Better contrast resolution
Higher patient radiation dose
T/F
In order to minimize patient dose, the MRT should use as little magnification as possible
True
A function of the fluoroscopic unit that maintains overall appearance of the fluoroscopic image by automatically adjusting kvp, mA or both
Automatic brightness control
Decreases image noise, increases contrast resolution
Automatic brightness control
II tubes serve as the fluoroscopic image receptor
II tubes are electronically coupled to a tv monitor for remote viewing
Conventional fluoroscopy
Computer has been added, as have multiple monitors and the ability to remotely control the imaging system
Digital fluoroscopy
What are the differences between conventional vs digital fluoroscopy?
-addition of a computer
-multiple monitors
-more complex operating console
What are 2 advantages of digital fluoro?
-speed of image acquisition
-post processing to enhance image contrast
At least how many monitors are used in digital fluoro?
2
Done by regulating the cray exposure rate incident on the input phosphor of the II
Automatic brightness control
What are some methods to minimize radiation dose during fluoro?
-5 minute alarm timer
-use of pulsed/low dose mode
-use of last image hold
-minimal use of magnification feature
Enables the last live image to be shown after the operator removes their foot from the pedal/exposure switch
Last frame (image) hold
T/F
Fluoroscopic imaging sequences are not typically recorded
True
Frames from live imaging are saved as single images
What are the 2 monitors used for in digital fluoro?
-one is used to enter/edit patient data and adjust exam parameters
-the other monitor displays image acquisition and editing tools
-Thin aluminum window
-part of vacuum bottle
-curved to withstand air pressure
-vacuum is necessary to accelerate electrons across open spaces without interaction
Vacuum window
What is cesium iodide used for the input phosphor?
-long needle like crystals channel the visible light within them with minimal lateral soreading
T/F
Electrons released by the photocathode have very little kinetic energy but are accelerated by an electric field between the photocathode and anode
True
Why is the output phosphor thin?
In order to preserve high spatial resolution
The increase in energy of each electron as it is accelerated across the II
Electronic gain
What is the measurement of electronic gain?
Flux gain
The ratio of the number of light photons at the output phosphor to the number of X-rays at the input phosphor
Flux gain
The reduction in the size of the output phosphor image compared with that of the input phosphor image
Minification gain
*the reduction in image diameter leads to concentration of electrons
Ability of II to increase the illumination level of the image
Brightness gain
*most II have multiplied mode or mag mode
T/F
As the effective diameter of the input phosphor increases, the brightness gain increases
True
T/F
Brightness gain decreases with tube age and use, causing an increase in patient dose
True
Reflected light within the output window
-can reduce image contrast
Veiling glare
How is veiling glare reduced?
Increasing the thickness of the output window whereby internally reflected light eventually strikes the side of the window
Produced by increasing the voltages applied to the electrostatic focusing lenses in the II
*the electron focal spot moves farther from the output phosphor
Mag mode
T/F
When mag mode is increased, the brightness of the image is decreased
True
To maintain the same level of brightness when using mag modes, what is used?
The xray tube mA is increased by ABC
*increases patient dose
