Quiz 1 Flashcards
Who discovered x-rays and how?
Wilhelm Conrad Roentgen noticed a photofluorescent plate glowing while working with a Crooks tube (cathode [negative] ray tube). This mysterious energy was called an “x-ray” (x for unknown)
What was the first image of?
Roentgen’s wife’s hand
What was he first medical application of?
A boy’s wrist
Stopped; the process of reduction of x-ray beam intensity when it penetrates matter
Attenuated
Silver halide and gelatin emulsion, not used anymore because it has to be developed
Film
3 image receptor types
Film
CR
DR
Computed radiography
CR
Digital radiography
DR
Milliamp seconds
Quantity, current
mA=milliamp x seconds (time)
mAs
Killovolts peak, 30-150
Quality of the beam
Thicker body part = stronger beam
kVp
Invisible and undeveloped, radiation which varies in intensity passes to the IR and exposes it which develops this
Latent image
Latent image that is made visible
Manifest image
4 mechanical requirements for the production of x-rays
Vacuum/glass envelope
Source of electrons
Target for the electrons
High potential difference (voltage) between the electron source and the target
Pyrex to resist heat
Air is removed so gas molecules won’t interfere with x-ray production
Encases everything
Vacuum/glass envelope
Wire filament at the cathode (negative end)
Tungsten (heat resistant, M.P. of 3370 C)
Thermionic emmision
Source of electrons
Heating of filament emits electrodes; gets hot, becomes ion, radiated emission
Thermionic emission
Anode (positive end)
Tungsten
Produce x-rays
Target for the electrons
High voltage transformer increases incoming voltage
High potential difference (voltage) between the electron source and the target
Wave with a repeating pattern
Sine wave
Distance between crest and valley
Aplitude
Distance between crest to crest or valley to valley
Average of diagnostic x-ray = 0.1 nm
Less than 1 is directly ionizing
Wavelength
Can remove an electron from orbit
Directly ionizing
Number of times per second a crest passes a given point
Frequency (v)
X-rays are emitted from a point and spread out in all directions equally
Divergent
If the distance from an x-ray source is doubled, the intensity of radiation is reduced four times; conversely if the distance from the x-ray is halved, the intensity of radiation is increased four times
The intensity of radiation is inversely proportional to the square of the distance
Inverse square law
Beam comes out straight into middle of field
Central axis
A cross section of the beam used for imaging
Radiation field
A photon in the center of the radiation field and perpendicular to the long axis
Central ray
When the primary bean interacts with matter, some of the energy is absorbed
Emitted in random directions
Not useful in imaging
Hazard to patients and radiographers
Scatter radiation
When x-rays leave the tungsten filament (cathode) side, it hits the target (anode) on the focal point
After hitting the focal point the x-rays diverge out into space in the shape of a cone
Anode rotates and increases surface area so focus spot isn’t one little point, all energy made into heat so heat isn’t on one point
Primary beam
Radiation source
Includes the cathode and anode
Contains two filaments situated in a focusing cup
X-ray tube
Negative
Tungsten (high melting point)
Directs electrons
Cathode
2 filaments contained in the x-ray tube
Small
Large
Finer detail but lower exposure (extremities), directed to smaller focal point
Small filament
Less detail but larger exposure (abdomen), directed to larger focal point
Large filament
Directs electrons to the focal spot on the target, hold small and large filament
Focusing cup
Disc-shaped and rotates to give more surface area for heat dissipation
Anode
Tube is located in a protective housing
Incorporates shielding for non-useful radiation
Protects and insulates the tube
Provides a base for attachments for manual manipulation
Collimator
Tube housing
Boxlike device mounted beneath the radiation port
Allows variation of radiation light field size
Coincides with a light field which indicates the size of the radiation port (light field that coincides with radiation field)
Controls on the front allow for adjustment for x and y dimensions
Control size and shape of beam
Piece of metal
Better quality image by changing size
Collimator
Tube is mounted to a ceiling or vertical support Movement directions (x and y axis)
Tube support
5 tube support motions
Longitudinal Transverse Vertical Rotation Roll (tilt, angle)
Long axis of table
Longitudinal
Across the table
Transverse
Further or closer to patient and IR
Vertical
Tube can be turned, anode goes from patient’s head to their left
Rotation
Tube can be angled towards the head, feet or wall bucky
Roll (tilt, angle)
The support assembly will set into a specific location that’s standard for imaging (72cm for chest or 40cm for abdomen)
Detents in ceiling where tube will lock in, standard set up for various x-rays
Detenting
Functions as support and movement
Radiographic table
3 types of radiographic tables
Vertical
Floating
Tilt
Can move x and y (wherever you want)
Floating table
Can rotate to bring the foot of the table to the ground for fluoroscopy
Tilt table
Located beneath the table
Moving grid with a tray that holds the IR
Can be moved along the length of the table to match up with the x-ray table
Buckey
Located between the table and IR, blocks x-rays that move north and south
Made of thin lead strips
Must be carefully aligned with the beam; divergent with path of beam, larger at IR than towards the front
Often moves during exposure to blur the image of the lead strips
Grid
Increases voltage
Tube housing gets power from this, which provides the high voltage necessary for x-ray production
Housed in a large cabinet in the x-ray room
New technology allows for these to be located in the control console
Transformer
Produces dynamic/moving images
Patient drinks barium to show less dense tissue
Fluoroscopy
Radiographs taken during fluoroscopy
Spot films
Reduces the radiation required to produce an image
Tower over the fluoroscopic screen
Contains a photomultiplier tube
Image intensifiers
Brightens and enhances the image
Enhanced image is digitized
Often have a timer to remind staff to keep exposure times reduced (5 minutes)
Photomultiplier
4 main factors of radiographic exposure
Time (T)
Milliamperage (mA)- current, quantity (number of rays)
Kilovoltage (kVp)- quality, strength
Source-Image Distance (SID)
How long the exposure will continue
Electronic timers give a wide range of settings
Combined with milliamperage (mA), it’ll determine the quantity of radiation
Assuming the current (milliamperage) remains constant, a longer exposure will make a darker radiograph
Patient dose is directly proportional to exposure time
Can range from 0.001 seconds to several seconds
Automatic exposure controls
Exposure time
Function to terminate the exposure when desired quantity of radiation is given
Automatic exposure controls (AECs)
Measure of current flow rate, determines the number of electrons (quantity) available to produce x-rays
Also determines how much time is needed to reach a desirable mAs
A high setting will mean less time is needed to reach a desired radiographic density, less time during exposure means less image blurring patient motion (can be involuntary motion such as respiration or heartbeat or voluntary motion)
Increments for settings are usually whole numbers divisible by 50 or 100 (50, 100, 200, 400, 400 or 500)
When it’s multiplied by the exposure time (s), the product is mAs, which is the amount of radiation in the exposure
Changing this may often vary which filament is used
Generally 150 or less uses the small filament and small focal point
If 200 or more, uses the larger filament and larger focal point
More means more heat accumulation in the anode
Milliamperage (mA)
Voltage potential across the x-ray tube
1 = 1000 volts
Voltage determines the speed of electrons, which determines the amount of kinetic energy and therefore the amount of x-rays produced
Increased gives more energy and shorter wavelengths
A more penetrating beam gives a larger exposure to the IR (a larger percentage of the x-rays penetrate the patient)
Increase in this increases the image darkness
Beam quality
Key factor for varying image contrast
Settings range between 40-150 with increments of 1-2
Low settings are used for smaller parts, high settings are used for thicker body parts
Kilovoltage
Degree of difference between dark and light areas
Difference in orbital density between adjacent structures
Primarily controlled by kVp; can also depend on patient, film and IR characteristics and amount of scatter
Increase kVp = decrease this
Contrast
Distance between the tube and the IR
Source to Image Distance (SID)
SID
A primary factor because it determines the amount of radiation intensity that reaches the IR
Remember the inverse square law
As the intensity of radiation that reaches the IR is varied a change in mAs must be made to give an equivalent exposure
Distance
Hold the film and serve as a tight, rigid structure to protect the film and hold the intensifying screen
Most contain two intensifying screens, one in front and one behind the film
Casettes
Coated with phosphors that emit light when exposed to x-rays
Function to reduce the exposure required to produce an image (this lowers patient dose and spare the tube from additional workload)
Crystal type, size and thickness determine the amount of exposure required
Intensifying screens
Manufactured to correspond to the light emitted by intensifying screens
Has emulsion coating on both sides to respond to light from intensifying screens –> this decreases required by half
Both sides of the emulsion are identical so there’s no specific orientation for placement
FIlms
Must be correctly stored to prevent fog; must be clean, cool and dry
Film boxes on edge and use older films first then the newer ones
Only touch corners of film when handling and avoid bending
Analog (hard films) can be scanned to digital systems with a film digitizer
Film processing
4 steps in conventional film development
Remove film from cassette in darkroom
Feed the film into the automatic processor
Put a new film in the cassette while in darkroom
Processor will beep when the film is done and it’s safe to turn on the lights
Most facilities have left film
Benefits: save space, less time, no processing chemicals, producing digital electronic image
Filmless radiology
2 basic types of filmless radiology
Computed radiography (CR) Digital radiography (DR)
IR is an imaging plate with photostimuable phosphors encased in a special cassette
Once exposed the cassette is inserted in a special processor that uses a laser to convert the latent image to a visible one that’s captured by a photomultiplier tube that emits an electronic signal that’s then digitized and stored in a computer
Computed radiography (CR)
Uses special radiographic tables and upright cabinets that contain radiation receptors that transmit a digital signal to a computer, no cassette or processing involved
Disadvantages: technical limitations, cost
Digital radiography (DR)
Both CR and DR can automatically adjust the visual quality of the image so it’s hard to determine if there’s over or under exposure
To compensate for this digital processing systems have a number called the exposure index (EI) numbers, s or something else depending on manufacturer specification
IR systems
Computer hardware and software used to manage digital images in healthcare
Provide archive for storage of images from all digital images in healthcare
Connect images to patient database information
Facilitate printing and transfer of images
Display images and information at workstations
Picture archiving and communication system (PACS)
More exposure received = darker image
Image visibility depends on overall blackness and difference between back and white area
Image-optical density
Primarily controlled by mAs
Film radiography: more mAs = darker image
Filmless radiography: radiographic density is controlled by the computer
Image quantity
The overall blackness of an image, aka radiographic density
Best: dark and light enough to see anatomic detail
Optical density (OD)
The sharpness of the image
Image detail
6 factors of detail
Distance between x-ray source and IR (SID); increase SID = increase detail
Distance between the object and IR (OID), increase OID = decrease detail
Size of screen crystals and thickness of phosphor layer
Size of pixels in digital systems
Focal spot size, smaller focal point = increase detail
Patient motion
Variation in size or shape of the image compared to the object it represents
Distortion
