Ch 12/15 Flashcards
Lead strips are angled to match the angle of photons in the primary beam as they diverge
Focused grid
Number of lead strips per inch or centimeter
Grid frequency
Expression of the ability of image intensifier tube to convert x ray energy into light energy and increase the brightness of image in process
Brightness gain
Primarily due to Compton interaction between x ray and photons and matter
Scatter radiation
Grid Bucky moves slightly from side to side during x ray exposure
Reciprocates
Constructed to allow a cassette to slide into place behind the grid
Grid cap
Flat panel detector fluoroscopy units operate at
50-1200 mA
Absorbs x rays and emits light
Input
Provide radiation exposure data and need to be recorded in the patient medical record
DAP/KAP and cumulative air kerma
Introduced in 1950
Image intensifier
Located inside the fluoroscopic tower
Image intensifier
Fluoroscopic image is viewed by looking at a
Television monitor
Absorption of transmitted photons by grid cause by a misalignment issue
Grid cutoff
Refers to a LARGE area of pixel being sensitive to x rays. This is important to flat panel fluoroscopy
Large fill factor
Ratio of number of light photons at the output phosphor as compared with the input phosphor
Flux gain
Absorbs light and produce electrons
Photocathode
Occurs when Sid is outside of the grid focal range
Off focus grid cutoff
Television Monitor can resolve approximately
1-2Lp/mm
When fluoroscopic image has noise or is noisy
The quantity of radiation (ma ) must be increase
because tissue has few photon being used to create the image
Base on creating GAP by increasing OID
Air gap technique
Distortion of the fluoroscopic image that appears as unequal magnification
Pinchusion appearance
Increasing collimation results in
Decreasing scatter production and high contrast
Plasma monitor contains thin layer of
Pixels and each pixel contains neon and xenon gas filled cells
MAgnification of the fluoroscopic image occurs when
Electrostatic lenses have more voltage applied creating more negative charge
Significant collimation reduces
Radiation and scatter
Reason for having the grid move slightly during exposure is to
Blur out the grid lines
Two forms of flat panel detectors may be for fluoroscopic applications
- Cesium iodide amorphous silicon indirect capture detector
- Amorphous selenium direct - capture detector
The material between grid’s lead strips must be
Radiolucent
The higher the grid ratio….
The BETTER the scatter clean up and HIGHER the contrast
Spatial resolution is not affected when using a grid
Two major factors that affects the a,out of scarred radiation
Volume of tissue irradiated and Kvp
Using magnification mode
Improves spatial resolution of fluoroscopic imaging
Electronic vacuum tube that converts the remnant beam -> light -> electrons -> light
Image intensifier
Electrostatic focusing lenses have…
Negative charge
Major problem with fluoroscopy
Images are very dim and hard to see
Has rectangular field of view and wider dynamic range
Flat panel detector
Input Is made of
cesium iodide
Refers to length of each PULSE
Pulse width
Simply a design of the unit that rapidly turns the x ray beam on and off during operation
Pulse fluoroscopy
Typical fluoroscopic system have spatial resolution capabilities in the ranges of
4-6lp/mm
Caused by using a grid with frequency similar to the cr laser scanning frequency as well as using a grid cassette in the Bucky
Moire effect
Least amount of of spatial resolution of all components of the fluoro system
Television monitor
Converting light image to an electronic image greatly improve digital imaging
CCD
Loss of brightness around the periphery of the fluoroscopic image
Vignetting
Attached directly to the input phosphor
Photocathode
Flat piece of lead with a hole in it
Aperture diaphragm
Unrestricted beam is
Round
Produces the greatest amount of scatter exiting the patient
Large field size and high kvp
When electrons are EMITTED in response to the presence of light, occurs at the PHOTOcathode
Photoemission
Range of Sid that will work with specific grids
Focal Range
Absorbs electrons and emits light
Output phosphor
Invented by Thomas Edison 1896
Commercial fluoroscope
Maintain brightness and contrast during fluoro
Automatic brightness control ABC
Located very close to the output phosphor
Anode
To produce quality fluoro images with digital decos
- Respond quickly
- Maintain large fill factor
- ASIC in place to reduce noise
Used to make adjustments in MAs when guide changes are made
Grid3 conversion factor
When grid is added or change is made to a higher ratio grid
MAs increased to compensate for reduction in radiation reaching ir
Fluoro allows imaging ion anatomy in motion
Dynamic imaging
