Physics Chapter 14 Flashcards
Know the two ways that image intensifiers improved the image process
- Brightened the image significantly (eliminated the need to dark adapt)
- Allowed for a means of immediately viewing the fluoro image (reduced radiographic dose)
Know what the conventional fluoroscopic chain consists of
x-ray tube, an image intensifier, a recording system, and viewing system
Know the 5 basic parts that make up an image intensifier
Input phosphor, photo cathode, electrostatic focusing lenses, accelerating anode, and output phosphor
Know why the input phosphor is made of cesium iodide
It absorbs remnant x-ray photon energy and emits light in response
Know the size correlation between the input and output phosphor
output phosphor is much smaller
Know how brightness gain has traditionally been found
Multiplying the flux gain by the minification gain
Know the size of the image intensifier tube
50 cm in length and 15-58 cm diameter
Know how flux gain is expressed
The ratio of the number of light photons at the output phosphor to the number of light photons emitted in the input phosphor
WHat results from the higher the conversion factor or brightness gain factor
image appears brighter because the same number of electrons is being concentrated on a smaller surface area
Know what happens as the image intensifier tube ages
The ability of the image intensifier to increase brightness deteriorates with the age of the tube
Know what happens in regards to radiation as the image intensifier tube ages
More and more radiation is necessary to produce the same level of output brightness, translating to an increased patient dose
Know how ABC commonly operates
By monitoring the current through the image intensifier or the output phosphor intensity and adjusting the exposure factor if the monitored value falls below preset levels
Know how to find the degree of magnification
Dividing the full size input diameter by the selected input diameter
Know what magnification improves
The fluoroscopist’s ability to see small structures (spatial resolution) but at the expense of increasing patient dose
Know how spatial resolution is measured
Line pairs per millimeter
Know what distortion is a result of in fluoro
Inaccurate control or focusing of the electrons released at the periphery of the photocathode and the curved shape of the photocathode
Define a pincushion appearance
The combined result is an unequal magnification (distortion) of the image
Know how a “noisy” or “grainy” image occurs
If too few x-rays exit the patient and expose the input phosphor, then not enough light is produced, which decreases the number of electrons released by the photocathode to interact with the output phosphor
Know how to fix a “noisy” image
increasing the mA
Know what the 2 devices are that convert the image from the output phosphor to an electrical image
The camera tube and charge-coupled device (CCD)
Know what the camera tube most often used is
vidicon tube
Know what the deflection coils act to accelerate
the electron beam
Know what the CCD is made from
A series of metal oxide semiconductor capacitors
Know what is sent from the capacitors
Charge is sent as an electronic signal to the tv monitor
Know what the purpose of the television monitor is
Convert the electrical signal from the camera tube to CCD back into visible light
Know what typical television monitors are called
525 line systems
Know the resolution of HIGH resolution monitors
1024 lines per frame
Know what the image intensifier is capable of resolving
Approximately 5 lp/mm whereas the monitor can display only 1-2 lp/mm
Know the 3 types of recording systems
Cassette sport film, film cameras, video recorders
Know what happens when the spot film exposure button is pressed
The cassette is moved into position between the patient and image intensifier and the machine shifts from fluoroscopic to radiographic mode and exposes the film
Know what happens in regards to radiation dose when imaging from fluoro to radiographic mode
fluoro to the radiographic mode uses a much higher radiation dose to the patient
Know what film is commonly used in the film cameras
105 mm “chip” film or 70 mm roll film
Know what the number of bits that a signal is divided into determines
the contrast resolution (number of gray shades) of the system
Know what the charge-coupled device (CCD) eliminated
Some of the problems associated with the camera tube
Know the 2 forms of flat panel detectors are used for fluoroscopic applications
- cesium iodide amorphous silicon indirect capture detector
* amorphous selenium direct capture detector
Know why the size, bulk, and weight of the fluoroscopic tower in digital fluoro is an advantage
Flat panel reduces all 3 allowing easier manipulation of tower, greater flexibility of movement and greater access to the patient during the exam
Know what the flat-panel detectors replaced
the spot0filming and other recording devices
Know why additional radiographic images are commonly not needed in digital fluoroscopy
they are capable of operating in radiographic mode
Be able to describe some of the other advantages of digital fluoro
- flat panel detectors don’t degrade with age
- more durable
- provide more information
- better contrast resolution
- higher detective quantum efficiency
- wider dynamic range
Know the advantage of digital fluoro in regards to artifacts
They do not exhibit most image artifacts such as veiling glare and peripheral distortion seen with image intensifiers
Know the advantage of digital fluoro in regards to radiation dose
50% lower radiation dose
Know why Quality Control Programs are vitally important for all ionizing radiation producing equipment
to monitor equipment performance and minimize patient dose
Know the role of the radiologist in a quality control program
supervision of the whole quality control program and process
Know the role of a radiographer in a quality control program
facilitator in the process
Know the role of the medical physicist in a quality control program
has primary responsibility for performance testing and interpretation
Know some of the responsibilities a radiographer may have in a quality control program
- Operational inspection of the equipment
- inspection of suite itself to examine the general physical condition of the room, unit, supporting electrical cables, and control booth, monitoring anywhere or deteriorating condition
- performance inspection and testing equipment
- Check following items
- bucky slot cover
- table tilt motion
- monitor brightness
- exposure switch
