Ch. 25 Fluoroscopy Flashcards
What is the primary function of fluoroscope?
To provide real time dynamic viewing of anatomic structures.
Who invented the fluoroscope?
Thomas Edison in 1896
What examines moving internal structures and fluids?
fluoroscope
What are some other aspects of fluoroscopy?
cineradiography, video imaging, and digital fluoroscopy
What are the 2 main areas of angiography?
neuroradiology and vascular radiology…not fluoroscopy
What do we call the fluoroscopic procedures for angiography?
interventional radiology
Where is the image intensifier on the fluoro table?
above the patient normally, but some newer equipment has it under the table
What mA runs the fluoro tube?
less than 5 mA
Why is patient dose high if only 5 mA is being used?
b/c of longer exposure times
What is Automatic Brightness Control?
ABC is the ability of the radiologist to select an image brightness level that is maintained automatically by varying the kVp, mA or both
What are illumination levels measured in?
units of lumen per square meter or lux
Radiographs are visualized under illumination levels of…
100-1000 lux
What part of the eye is responsible for the sensation of vision?
rods and cones
Light first goes through the
cornea
light is focused onto the
retina
Between the cornea and lens is the..
iris
What does the iris do?
behaves like the diaphragm of a photographic camera by controlling the amount of light that is let into the eye
When light arrives to the retina, it is detected by the
rods and cones
What is the fovea centralis?
where the cones are concentrated at the center of the retina….No rods are at the fovea centralis
What are used for daylight vision called photopic vision.
cones
What are used for night vision called scotopic vision?
rods
What is best at perceiving small objects?
cones
What is visual acuity?
the ability to perceive small detail
What detects differences in brightness levels?
cones
What is contrast perception?
detection of differences in brightness levels
Cones perceive ____ and rods…
color; rods are color blind
What is the technique preference for fluoro?
high kVp and low mA
What is the general job of the image intensifier?
it receives the image forming x-ray beam and converts it into a visible light image of high intensity.
Like a regular x-ray tube, the image intensifier is made of…
a glass or metal envelope that gives structural support and maintains a vacuum
x-rays exit the patient and are incident on the image intensifier tube and transmitted through the glass envelope and interact with the …
input phosphor
what is the input phosphor?
cesium iodide
When an x-ray interacts with the input phosphor what happens?
the energy is converted into visible light (similar to an intensifying screen)
After the energy is converted into visible light, what happens?
it goes to the photocathode that is bonded directly to the input phosphor with a thin transparent adhesive layer
What is the photocathode made of?
a thin metal layer composed of cesium and antimony compounds
The photocathode emits …
electrons when illuminated by the input phosphor
What is photoemission?
when the electrons are emitted when illuminated by the input phosphor (similar to thermionic emission)
The number of electrons emitted by the photocathode is directly proportional to…
the intensity of light that reaches it.
What is the output phosphor?
it is on the other side of the anode and made of zinc cadmium sulfide.
What happens at the output phosphor?
it is the site where electrons interact and produce light
How do the electrons get to the output phosphor?
they have to pass through a hole in the anode
The electron path from the photcathode to the output phosphor have to be precise..why?
the pattern of electrons emitted from the large cathode end of the image intensifier tube must be reduced to the SMALL output phosphor.
What are the electrostatic focusing lenses?
devices that are responsible for controlling the pattern of electrons emitted from the large cathode end of the image intensifier tube to the small output phosphor
The electrons that arrive at the output phosphor have..
high kinetic energy and the image in a mini format
Since the electrons in the output phosphor have high kinetic energy they then create…
a high amount of light that is 50-75 times more photons than it had when it was first created
Describe flux gain
the ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor
What is minification gain?
the multiplication of light photons at the ouput phosphor compared with x-rays at the input phosphor and the minification from input phosphor to output phosphor
Brightness gain?
the ability of the image intensifier to increase the illumination level of the image measured as cd/m^2
What is veiling glare?
Internal scatter radiation int he form of x-rays, electrons and particularly light can reduce the contrast of image intensifiers
What does veiling glare reduce?
the contrast of an image intensifier tube
What does magnification mode result in?
better spatial resolution
better contrast resolution
higher patient dose
Why is spatial resolution improved in the magnification mode?
b/c only the central region of the input phosphor is used in the magnification mode
What is the set up of the output phosphor in the television monitoring system?
this portion of the image intensifier tube is coupled DIRECTLY to a television camera tube
What is most often used in television fluoroscopy?
the vidicon camera tube
What is the process of the vidicon camera tube?
it converts the light image from the output phosphor of the image intensifier into an electrical signal that is sent to the television monitor where it is reconstructed as an image on the TV screen.
What is the advantage of TV monitoring?
brightness and contrast can be controlled electronically, several observers can watch at the same time, and it allows for storage of the image in its electronic form for later playback and image manipulation.
What are 2 methods used to convert the visible image on the output phosphor of the image intensifier into an electronic signal?
thermionic TV and the solid state charge coupled device (CCD)
A vidicon serves the same function as a…
x-ray tube
What are the internal elements of the vidicon?
electron gun, electrostatic grids, and target assembly (anode)
What is the electron gun
a heater filament that supplies a constant electron current by thermionic emission
Once the electron gun does its thing, what happens?
the electrons are formed into an electron beam by the control grid, which also helps to accelerate the electrons to the anode. It is then further accelerated and focused by more electrostatic grids, goes to the anode end of the tube and interacts with the target assembly and eventually becomes an electronic signal.
There are 3 parts to the target assembly of the vidicon:
the target, signal plate, and window
Image intensifiers and TV camera tubes are manufactured so the output phosphor of the image intensifier tube is the same…
diameter as the window of the TV camera tube, usually 2.5 or 5cm
What 2 methods are used to couple the TV camera tube to the image intensifier tube?
fiberoptics and lens coupling
What is an advantage of fiberoptics method of coupling?
it is compact which makes it easy to move the image intensifier tower, it is rugged
What is a disadvantage of fiberoptics method of coupling?
it cannot accommodate the additional optics required for devices such as cine or photospot cameras.
What do you need to accept a cine or photospot camera?
lens coupling
What is modulation?
a change in a quantity or signal in response to another quantitiy or signal and is widely used in medical imaging.
In the TV monitor, the intensity of the electron beam is modulated by a..
control grid that is attached to the electron gun
video monitoring uses a rate of…
30 frames per second
What is the weakest link in image intensified fluorscopy?
the television monitor
Where is the spot film located?
between the patient and the image intensifier
The photospot camera is similar to a movie camera except that
it exposes only one frame when actiated
The entrance skin dose (ESD) for an adult averages…
30 - 50 mGy/min or 3 - 5 R/min during fluoro
Federal law and most state statutes require that under normal operation, the ESE rate shall not exceed…
100 mGy/min (10 R/min)
In IR, the fluoroscope may be equipped with a high level control which allows an ESE up to…
200 mGy/min
When are unlimited exposure rates permitted?
For recorded fluoroscopy, such as cineradiography
What type of filters are used to test automatic brightness stabilization ?
lucite, aluminum, copper, and lead filters
