Flouroscopy Flashcards
Main function of fluoroscopy is:
to provide real-time or dynamic studies of the internal organs.
Dynamic refers to:
structures or organs in motion.
How does the radiologist highlight the internal organs?
With the aid of contrast material (such as barium).
Still photos taken during fluoro are called:
“Spot” images.
Who invented fluoroscopy and when?
Thomas Edison in 1896.
How did radiologists view fluoro screens at first?
By directly exposing their eyes to the X-ray beam.
How was the original fluoro design altered to improve safety to the radiologist?
An arrangement of mirrors permitted an indirect way to view the image & the primary beam was shielded into a lead enclosure.
How did the original fluoro screen need to be viewed and what did the radiologist have to do to prepare to view the screen?
Had to be viewed in a darkened room & the radiologist would need 15 minutes of dark adaptation.
What was invented that overcame the need for the radiologist to have to adapt to the dark before viewing a fluoro screen?
Image Intensification Tubes in 1948.
Why was the invention of image intensification tubes so significant?
They raised the illumination of the fluoro screen to the level that the human eye can perceive it and where the visual acuity is the greatest.
Though the invention of image intensifiers increased safety to the radiologist and improved brightness of the image, the downside was:
loss of detail.
Where is the X-ray tube located on a fluoroscopy table and where is the image intensifier located?
The tube is under the table and the I.I. is above the patient. (Though there are some that are designed exactly opposite.)
Why are the tube and I.I. usually mounted on a c-arm?
To maintain their alignment. The c-arm permits the IR to be raised and lowered and permits scanning over the length and width of the table.
What is the carriage on the fluoroscopy machine?
The arm the supports the equipment which is suspended over the table.
What does the carriage hold within it?
It holds the I.I. tube, controls for power drive to the table, brightness control, spot image selection, tube shutters, spot imaging/cine camera and video input tube.
The carriage can be disengaged & pushed away from the table to gain access to pt, however:
an exposure cannot commence until carriage is returned to full beam intercept position.
What allows the radiologist to have their hands free to position the pt or operate the carriage?
The foot switch. Care must be taken not to unintentionally step on the switch once the fluoro unit is engaged.
What mA is the tube operated at during fluoro?
less than 5 mA (0.5 - 5.0 mA). However, the dose is still higher than conventional X-ray since the beam is on for a much longer time.
The brightness of a fluoro exam depends on:
Anatomy
kVp
mA
What type of technique is preferred for fluoro (High or low kVp and high or low mA?)?
High kVp and low mA.
What is the Automatic Brightness Control (ABC)?
A function of the fluoro unit that maintains the overall appearance of the image (its contrast and density) by automatically adjusting the kVp, mA or both.
How does the ABC work?
It either monitors the current throughout the I.I. or the output phosphor intensity and adjusts the exposure factor if the monitored value falls below preset levels.
What other names is the ABC referred to?
Automatic Dose Control (ADC) or Automatic Brightness Stabilization (ABS).
The input phosphor is made of
cesium iodide and is bonded to the curved surface of the tube itself
The image intensifier consists of five basic parts:
input phosphor photocathode electrostatic focusing lenses accelerating anode output phosphor
The cesium iodide of the input phosphor absorbs:
the remnant X-ray photon energy and emits light in response.
The photocathode is made of
cesium and antimony compounds.
When the emitted light from the input phosphor strikes the photocathode:
it emits electrons through photoemission.
The input phosphor is bonded to:
the photocathode.
The input phosphor and photocathode (or the input screen) are in a concave shape because:
to maintain the same distance between each point on the input screen and its corresponding location on the output screen.
What are the electrostatic focusing lenses and what do they do?
negatively charged plates that repel the electron stream, focusing it on the small output phosphor.
What does the accelerating anode do?
sets the electron stream in motion at a constant velocity.
Where is the accelerating anode located?
at the neck of the image intensifier near the output phosphor.
What is the potential difference between the anode and cathode of a fluoro tube?
25 kV
What is the output phosphor made of?
silver-activated zinc cadmium sulfide.
Where is the output phosphor located?
at the opposite end of the image intensifier tube, just beyond the accelerating anode.
What does the output phosphor do?
absorbs electrons and emits light in response.
How much does the image intensifier amplify the brightness of an image?
500-8000 times.
Where is the primary brightness attained?
from the acceleration and focusing of the electron beam.
Describe the tube housing.
Glass or metal envelope, which provide structural support & maintains vacuum. Encased in a lead-lined housing which absorbs the primary beam while permitting the intensified light photon image to be transmitted to the viewer.
The input phosphor contains crystals of:
cesium iodide.
Between the input screen and the output screen, something is changed about the image. What?
The image is reversed.
Input screen is which end of the image intensifier? (Anode or cathode?)
Cathode.
How is the anode charged?
Positively, therefore attracting the negative electrons.
What does the anode look like?
A circular plate with a hole in the middle to allow electrons to go through to the output screen.
Describe the output screen.
It is a fluorescent screen made of zinc cadmium sulfide. Electrons interact with the phosphor and emit light. It is very small to give high resolution.
How is light prevented from returning to the input screen from the output screen?
A filter is placed under the output phosphor.
The ratio of the number of light photons at the output phosphor to the number of light photons from the input phosphor is called:
the flux gain.
The flux gain is a measurement of:
how efficient the output screen is in converting elections to light.
The ratio of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor is:
minification gain.
Minification gain results when:
the amount of electrons that were produced at the large input screen are being compressed into the area of the small output screen.
Typical output screens have a diameter of:
1 inch.
Minification gain is simply:
an increase in brightness or intensity.
The increased illumination (or brightness gain) is due to two factors:
Flux gain and minification gain.
The ability of the image intensifier to increase the illumination level of the image is:
The brightness gain.
Brightness gain = (what two factors and how are they combined?)
minification gain x flux gain
Brightness gain of most image intensifiers is:
5,000 - 30,000
Brightness gain decreases with:
tube age and use. An increase in mA is necessary in order to compensate.
As the image intensifier tube ages, pt does increases in order to maintain brightness and when the tube can no longer be adjusted for brightness:
the I.I. must be replaced.
The illumination intensity at the output phosphor compared to the radiation intensity incident on the input phosphor is:
Conversion Factor
Conversion factor =
Output phorphor ilumination (cd/m^2) / Input exposure rate (mR/s)
Image intensifiers have conversion factors of _______ which corresponds to a brightness gain of ________
50 to 300, and 5,000 to 30,000.
Magnification is accomplished through
the use of multi field image intensifiers.
Multi-field image intensifiers are also known as
multiple field
dual field
triple field
quad field
Magnification =
input screen diameter/input screen diameter used during magnification.
How does magnification work?
By increasing the voltage on the electrostatic lenses, the electrons are focused at a point closer to the input screen. As the focal spot is changed, the image becomes larger (or smaller) at the output screen.
How does magnification produce a dimmer image?
Because the electron beam spreads further out, fewer photoelectrons end up at the output screen. mA must be increased to compensate, which results in higher pt dose.
What allows for improved image quality when using magnification?
The ABC.
Magnification mode results in:
better spatial resolution
better contrast resolution
higher patient dose.
What occurs when the intensely bright light floods the eye?
Veil glare
Veil glare causes bright light to scatter inside the eye and it reduces
contrast
When veil glare happens inside the image intensifier tube, scatter (from X-rays, electrons, etc) reduces:
contrast in the I.I. tube.
What do I.I. tubes have to reduce veiling glare?
Output phosphors.
A veiling glare signal is produced:
behind a lead disc positioned on the input phosphor.
A reduction in brightness at the periphery of an image is called
vignetting.
Any image coming from the periphery of the input phosphor is unfocused and results in:
vignetting.
Vignetting is also a result of:
poor focusing of electrons towards the periphery of the output phosphor.
The same occurrences that cause vignetting can also cause
the pincushion effect, a distortion of lines which curve inward at edges of output screen.
Good spatial resolution is associated with
a higher line pair/millimeter value.
In a 25 cm mode (referring to diameter of input phosphor), the tube can image approx __ lp/mm. In a 10 cm mode, the resolution is approx __ lp/mm.
4, 6.
Types of viewing systems to deliver the image from the output screen to the viewer:
Digital
Video
Cine
Spot Imaging.
Prior to digital viewing, the most common method of viewing fluoroscopy was:
video viewing
Video viewing was done on _______ using transmission through _______
closed circuit video, cables.
Types of camera tubes used for video viewing of fluoroscopy was:
Vidicon
Plumbicon
Charge-coupled Device (CCD)
Types of video camera tubes that were used most often:
VIdicon and Plumbicon.
The glass envelope surrounding video camera tubes did what?
Maintained a vacuum and provided mechanical support for internal elements.
How does the television monitoring system work on a fluoro machine?
Output phosphor is coupled directly to a TV camera tube (vidicon) which converts light image from output phosphor into an electrical signal that is sent to the tv monitor and reconstructed as win image on the tv screen.
Advantages to t.v. monitoring:
- Brightness and contrast can be controlled
- more than one person can observe at a time
- additional monitors can be placed in remote areas for additional viewers
- images can be stored for later playback.
Internal elements of the camera tube are:
Cathode
Electron gun
Electrostatic grids
Target assembly (anode)
The electron gun is:
a heated filament that supplies constant electron current by thermionic emission.
The control grid in the camera tube forms electrons into:
an electron beam and helps to accelerate the electrons to the anode. Also acts as a focusing cup.
Accelerator grids are:
electrostatic grids that also aid in accelerating and focusing the electron beam.
The size and position of the beam in the camera tube are controlled by:
external electromagnetic (steering coils). These are deflection coils, focusing coils, and alignment coils.
The external electromagnetic coils in the camera tube aid the electron beam to:
scan the target in a raster pattern and bring the electron beam to a point to maintain resolution.
At the same time that the electron beam scans the target in a raster pattern:
an electron beam passes through a wire mesh-like structure & interacts with the target assembly.
The target assembly consists of three layers:
The glass face plate
The signal plate
A photoconductive layer (target plate)
The glass face plate on the target assembly is located:
on the outside layer or window.
The signal plate of the target assembly is:
a thin layer of metal or graphite coated on the inside of the window. It transmits light and conducts electricity and conducts a video signal out of the tube into the external video circuit.
The photoconductive layer (target plate) on the target assembly is applied where?
to the inside of the signal plate.
What does the photoconductive layer of the target assembly do?
emits photoelectrons within hit with light.
How does the target assembly work?
Light (the image) from output phosphor of image intensifier tube strikes the window, the light is transmitted throughout the signal plate to the target. When the light hits the photoconductive layer, it becomes electrically conductive and emits photoelectrons.
Electrons are conducted from the cathode through the target and signal plate when (through the target first? Through the signal plate first? or at the same time?)?
At the same time.
The electron beam from the cathode scans the target and interacts with:
the photoconductive layer.
The interaction of the electron beam with the target and photoconductive layer causes:
the target to release the photoelectrons and the signal plate to create an electric signal which becomes the video signal leaving the camera tube.
The magnitude of the video signal leaving the camera tube is proportional to:
the intensity of light coming in from the image intensification tube.
A CCD (charge-coupled device) is:
a device that converts visible light into an electric charge. It stores charges from the light photons that are striking its photosensitive surface.
How a CCD works:
- Light strikes the CCD
- Electrons are released in proportion to the intensity of the light from the I.I. tube
- The electrons are stored in the form of a latent image.
- The stored charges are discharged as pulses creating a video signal.
Advantages of CCD:
Fast discharge time. Useful for high speed imaging. Operates at much lower voltage. Good resolution. Not as easily damaged.
The output phosphor of I.I. tube is the same diameter as:
window of television camera tube and/or the CCD.
Two methods used to attach or couple the camera to the I.I. tube are:
Fiber optics
Lens system.
Fiber optics are:
bundles of extremely small, light-conducting cables.
Advantages of fiber optics:
Compact and very durable.
Disadvantages of fiber optics:
Cannot accommodate auxiliary imaging devices (cine/spot films)
Describe lens coupling:
Much larger, more delicate, lens & mirror need to remain precisely adjusted or blurring of image will occur, necessary for cine or photospot camera.
How does a lens system work?
Len accepts light from output phosphor and converts into beam, if recording image on film, the bean is intercepted by mirror (beam-splitting mirror), part of beam transmitted to tv camera, remainder is reflected to film camera.
Video signal from tv camera is transmitted by cable to:
tv monitor where the signal is transformed into a visible image.
The TV monitor forms one end of a __________. The other end is a tv camera tube.
Closed-circuit TV system.
The components of a TV monitor are:
Television picture tube=Cathode Ray Tube (CRT)=”heart of the television monitor.”
The picture tube consists of:
Glass envelope
electron gun (cathode)
External coils (steering and focusing electron beam)
Anode (plated onto the front screen)
The monitor creates and image as the gun:
sprays a stream of electrons from the camera onto the screen phosphor.
The intensity of the electron beam in the picture tube is modulated by:
a control grid, which is attached to the electron gun.
The beam is focused by external coils.
How does the picture tube work?
Electrons interact with output phosphor, phosphor crystals emit light when struck by electrons, this light produces image on glass of screen.
When the beam is projected on the the TV screen:
it is scanned very rapidly from side to side and top to bottom. This is done in sync with the scanning beam in the vidicon (tv camera tube.).
The linear pattern produced when the beam is projected on the TV screen is:
a series of signals that represent the light intensities from the original output screen image.
The sweeping of the image on the t.v. screen starts in the upper left corner of the screen and moves across almost horizontally…this is known as:
the active sweep.
When the beam returns to the left side of the screen after the active sweep, to a point slightly below the first line, it is known as:
the horizontal retrace sweep.
How many active traces occur in a 525-line system?
262.5
The scanning beam (on a t.v. monitor) does a vertical retrace and repeats the entire sweeping pattern, however the lines are placed between the first set of lines. This is:
interlacing.
When two interlaced fields reach the bottom of the screen:
It makes one frame. The final TV image consists of many frames.
The horizontal linear pattern is known as a:
raster.
Each field on a tv monitor produced by an electron beam scans 262.5 alternate lines every _____ (time). The second field (or set of lines) are scanned the next ______(time). The entire 525-line raster pattern is scanned every ______ (time).
1/60th of a second. 1/60th of a second. 1/30th of a second.
The frame rate (on a tv monitor) is:
30 times per second (or each frame is 33 ms long).
15,750 scan lines per second.
High Def features:
More currently used More horizontal lines in each field Twice as many scan lines in either field or frame. Better detail 1050 scan lines.
Flat panel plasma display features:
- Image is made of thousands of tiny dots called pixels
- Each pixel made of three fluorescent lights (red-green-blue)
- Light contains plasma (xenon or neon gas)
- Voltage placed across gas will ionize giving off light which causes phosphors in pixels to glow.
Advatages to flat screen
light weight, easy to see, readily mounted.
Liquid crystal display features
- works in similar fashion to plasma
- pixels are filled with liquid instead of plasma
- pixels are arrayed in front of a light source or reflector
- ferroelectric liquid crystals.
Types of image recording:
Videotape recording
Static spot imaging
Videodiscs/laser discs.
Video tape recording uses:
1/2 inch VHS & high-resolution recorders.
VHS system (used in barium swallows) requires:
Hi-res cameras
recorders
tape
monitors
Static spot imaging is necessary when:
a permanent record of the fluoro exam is desired to document findings.
Cassettes are stored:
in a lead-lined compartment in the fluoro carriage.
Cassette spot:
Only certain areas of the cassette are exposed.
Automatically collimates
Can be one image or many on one cassette
RT usually loads and replaces cassettes.
Spot films cause _______ dose to pt.
higher
A photospot camera is similar to:
movie camera
A photospot camera receives its image from:
the output phosphor of the I.I. tube and therefore results in less pt exposure than cassette loaded spot film.
Video disc/laser dics/optical discs.
last almost indefinitely
records video info in laser light
Contrast is controlled by:
increasing the amplitude of the video signal.
Contrast affected by:
scattered ionizing radiation
penumbra light in input and output screens.
Light scatter within the tube itself
Resolution depends on:
line systems
What is the weakest link in the I.I. fluoro?
The t.v. monitor.
Size distortion is caused by:
the same factors that affect static radiographic magnification.
OID-OID-OID-OID-OID
Combated by bringing the I.I. as close to the pt as possible.
What is the most common solution to quantum mottle in fluoro?
increase the fluoro tube mA.
In the US, federal law requires an audible alarm after:
five minutes of fluoro.
Minimum source to skin distance for fluoro is:
15 inches for stationary fluoro
12 inches for modle fluoro
Tabletop exposure rate should not exceed:
10R/min
Lead apron and gloves must contain:
.25 mm of lead equivalent.
What is the primary source of scatter?
the patient.
Sources of radiation protection for the technologist:
Bucky slot cover
Lead rubber drape
Stand behind radiologist
Single step away front eh table decreases exposure exponentially (inverse square)
Whose responsibility is it to inform others in the room to wear a lead apron?
the radiographer’s. DO NOT INITIATE FLUORO UNTIL ALL HAVE COMPLIED.
