Name the 4 things needed to produce x-rays and what makes each item.
1. Vacuum-The xray tube
2. Source of Electrons-Fillaments within the Cathode
3. Method to accelerate the electrons-kVp
4. Method to stop the electrons-the target(ANODE)
What is primary radiation?
The x-ray beam before it interacts with the patient.
What is Attenuation?
Weakening of the beam as it interacts with matter (absorbed radiation is part of attenuation, it has been completely attenuated)
What is Scatter Radiation?
When x-ray photons interact with matter and change direction (some attenuation occurs as well). This type of radiation is not useful.
What is Remnant Radiation?
Radiation that exits the patient and creates the image on the image receptor.
What does Radiolucent mean?
Radiation photons easily penetrate this type of material.
Ex: Objects NOT visible on an x-ray.
What does Radiopaque mean?
Radiation photons are attenuated in this type of material.
Ex: Visible objects on an x-ray.
What is Density?
The amount of blackening on the film which is a result of the amount of x-ray exposure it receives.
What is Contrast?
The difference in adjacent densities on a film.
High Contrast
fewer shades of gray with big differences between these shades; created using low kVp
Low Contrast
many shades of gray with slight differences between these shades; created using high kVp
What is Recorded Detail?
The sharpness of an image; demonstrates distinct borders
Distortion
misrepresentation of the size or shape of an object
What is Umbra?
An accurate shadow which has distinct borders
What is Penumbra?
An inaccurate shadow which lacks distinct/clear borders
What is a Latent image?
Captured image which cannot be visualized
What is an Indirect capture system?
X-ray photons strike a scintillator that reacts by producing visible light that hits the amorphous silicon which conducts electrons into the detector. The TFT array sends the electrical charge to an intensifying screen.
What is a Cassette-Based System?
Looks similar to a conventional cassette, but uses PSP which captures and stores the image. The PSP works with a conventional x-ray room and is made very similarly to an intensifying screen.
What is a Film Screen (analog) System?
Uses a combination of film that is sensitive to a specific color of light and a polyester screen coated with crystals that luminesces this specific color of light. This image must go through a developing process consisting of developing, fixing, washing, and drying.
What is a Direct Capture System?
X-ray photons are absorbed by a scintillator and converted into an electrical signal (electrons) which is stored in the TFT which is made up of pixels.
What is a Cassette-less System?
Uses a detector that is permanently enclosed in a rigid protective housing. This detector may be direct or indirect capture.
What Factors affect image density? (Controlling factor first)
mAs
Patient Factors
kVp
Distance
Beam Modification
Grids
Image Receptors
What is the formula for mAs?
mA * Time =mAs
What determines the penetrating ability of an x-ray photon?
kVp
The higher the kVp, the greater its energy and penetrating ability.
What are the 2 important distances we have discussed so far?
SID and OID
What is SID?
Source to image receptor distance- the distance from the x-ray tube to the image receptor
What is OID?
Object to image receptor distance- the distance from the object (body part) to the image receptor
What happens to the intensity of the beam as SID increases?
Intensity decreases
What are 3 methods of radiation protection?
Time
Distance
Shielding
What is the Inverse Square Law?
Increasing the distance from the source of the x-ray beam greatly reduces the quantity of radiation
What is the formula for the Inverse Square Law?
New intensity = Old distance^2Old intensity New distance^2
What is the difference between the inverse square law and the exposure/density maintenance formula?
The inverse square law explains what happens to beam intensity when a distance is changed. The density maintenance formula tells us how to adjust our mAs in order to maintain the original density when distance has been changed.
What is the exposure/density maintenance formula?
Original mAs = Original Distance^2New mAs New Distance^2
What are the 2 methods we use to modify the primary beam?
Filtration
Beam limitation
How does collimating (filtration and beam limitation) affect the density/exposure on the IR (assume no other changes have been made)?
Increasing filtration decreases the density/exposure on the IR
Limiting/decreasing the field size decreases the density/exposure on the IR
What is a grid and how is it used?
And how does a grid affect density/exposure?
A grid is a device with lead stips placed between the patient and the IR which "catches" scatter radiation before it reaches the IR. It decreases radiographic density/exposure.
Explain what happens to 1) radiographic density/exposure 2) patient exposure 3) recorded detail when film/screen speed increases?
1) If no other changes have been made, a faster speed will increase radiographic density/exposure.
2) As film-screen speed increases, patient exposure decreases.
3) As film-screen speed increases, recorded detail decreases.
What is Window leveling?
Allows the technologist to control the image brightness
What is exposure latitude?
Range of exposure that will make a diagnostic image
What is exposure index?
Numeric representation of how much exposure reached the IR
What is window width?
Allows the technologist to control the image brightness
What is automatic rescaling?
The first step in image processing where the brightness of the image is adjusted (to allow for consistent brightness across images)
List the factors that affect radiographic contrast, listing the primary factor first
kVp
Patient factors
Contrast media
mAs (only affects contrast when the IR is grossly over or under exposed)
Beam modification
IR
Grids
List the most common causes of motion
Voluntary patient motion
Involuntary patient motion
Equipment motion
How can motion be eliminated?
Good communication
True/False: When there is no OID (the part is against the IR), there is no magnification.
False
What causes shape distortion?
Misalignment of the tube/beam, part or the IR
How should the beam, part and IR be aligned?
The beam should be perpendicular to the part and the IR. The IR and part should be parallel to each other.
True/False: The image intensifier and flouro tube move independently of one another.
False
What is the purpose of the collimator?
It has shutters that move to adjust/limit the field size of radiation.
What part of the x-ray tube/bucky determines the amount of mAson the control panel>
AEC- Automatic exposure control
What is a bucky?
A device that holds the IR and uses a grid.
What are the "set points" for a tube called?
Detents
What is it called when we take a still image on the flouro machine?
A spot film
When using a digital portable x-ray machine, what is the name of the cord that links the detector to the computer?
Tether
Measures the amount of exposure in the air
Roentgen
Measures how much radiation has been absorbed (in any medium).
Rad
This measurement lets us express biologic response of exposure to individuals based on the specific type of radiation received.
REM
Measures the rate of decay or activity.
Curie (or Bacquerel)
True/False: Monitoring devices protect the wearer
False
What is the annual dose for an occupational worker?
5 rem/year
What is the cumulative dose for an occupational worker?
