Lecture 2: Accessory Equipment Flashcards
What is a collimator?
Restricts the x-ray beam to a confined area; helps focus the x-rays
What type of collimators are there?
Diaphragm; Cylinder; Light Beam Collimator (most common)
What’s the purpose of the collimator?
- Improve image quality.
2. Radiation safety: Limit area of exposure (limits scatter radiation too)
What effect does excess scatter have on an image?
reduces image contrast; degrades the image
What purpose does a Grid serve?
prevents scatter radiation from hitting the image receptor and improves image contrast; reduces scatter radiation
What is a Grid?
Lead strips situated parallel to Xray beam
When should you use a grid?
> 10 cm thick
How should the grid be aligned relative to the x-ray beam?
Perpendicular to the beam, at the appropriate distance
What is the Grid Ratio?
Height (h) of the lead strips relative to the diameter (D) of the opening –> h/D = Grid Ratio
The higher the ratio, the BETTER it is at removing scatter radiation.
How does using a Grid influence darkness of an image?
Grid reduces darkness, must increase mAs to compensate for that.
Increases exposure time too.
What are the needed increase in mAs?
5: 1 2x mAs
8: 1 3x mAs – best for private practice
12: 1 4x mAs
What is intensifying screen for? Where is it?
Absorbs X - radiation and converts to LIGHT radiation
Inside the cassette - white sheet inside
How much direct radiation is in a film exposure
only about 1% (rest is light radiation)
What in the screens does the absorption and conversion to light radiation?
Phosphor Crystals
What is the effect as Phosphor Crystals get thicker or larger?
Lose RESOLUTION but gain efficiency
