Week 1 Flashcards
What is radiography dependent on?
Radiography
depends on
density
differences
Name the technical parameters
- Positioning of patient and tube = FFD (focus to film distance), tube angle
- Exposure (kVp and mAs)
- Collimation
- Centring
How does the kilovoltage peak work?
It accelerates the electrons from cathode to anode, so it determines the strength of the power
How does the kVp change when we increase?
The beam power increases, meaning the penetration & scattering increases, and lowers the image contrast
How does Milliampere-Seconds (mAs) relate?
Measure the number of x-rays taken.
Why is ‘s’ important in mAs?
s is a measure of the electrons production
duration in the tube; meaning ‘s’ prescribes
how long mA will las
Why is ‘mA’ important?
More mA will lead to more photons reaching the
detector
When we increase mA,
↑ ↑ image density
↑ number of photons
↑ number of interactions
↑ patient absorbed dose
Why does the tissue appear whiter?
The denser the tissue, the more x-rays are absorbed - the ‘Whiter” (more ‘Radiopaque’)
Radioluscent
Radiolucent refers to materials that allow the passage of X-rays through them, resulting in a dark or black image on a radiograph.
- Have lower density and absorb less radiation
Why is radiographic contrast important?
High contrast (low kVp)= abrupt density differences. Subtle details
can be missed or not imaged.
Low contrast (high kVp)= more scatter will exit the patient and add
unwanted density or fog
Why is ALARA Principle important
guides and ensures that we minimise the radiation levels
How can ALARA be achieved
Time = ↓ time spent near radiation source
* Distance = ↑ distance from radiation source
* Shielding = lead gown on the radiographer
How is the patient protected
- Minimal number of projections
- Appropriate exposure parameters
- Accurate collimation
- Immobilisation to reduce possible
movement - Pregnancy check
- Gonad shielding- sometimes
CR stands for
Computed radiography
DR stands for
Digital radiography
Explain how analog xrays work
film is placed in casette & under the patient; an exposure is made when x-ray is taken; film is developed
Explain how CR works
casette with imaging plate is used. Plate is exposed to radiation, plate stores info in matrix, plate goes into scanner and digital image produced
Explain how DR works
Detector is used for exposure, detector is used for radiation, image instantly available on monitor
We need to ensure
Each projection (radiograph produced) needs to be
evaluated alone and as a part of the protocol (all
projections) to determine its value to the
examination (Critiquing)
What is kVp?
kVp controls acceleration of electrons from
Cathode to Anode
* It determines the power and strength of
the penetration through a body part
* It determines the quality of the x-ray beam
How will the x-ray look in denser materials
The denser the tissue, the more x-rays are absorbed. And the ‘Whiter” or ‘Radiopaque’ the area will be
