Scatter Radiation 1 Flashcards
Scatter Radiation
is any radiation that has been changed from its original path.
• It occurs as a result of x-rays interacting with atoms of matter
Greatest source of scatter radiation is the patient
Primary X-rays or useful beam
The x-rays between the source and the patient
Secondary or remnant X-rays
The x-rays between the patient and the image receptor
Secondary x-rays are made up of both primary and scattered x- rays
Scatter Effect
The more scatter, the more noise or fog in the image, losing quality in the image.
What does scatter radiation do to an image?
Scattered radiation reduces image quality and causes a loss of radiographic contrast due to a graying or clouding of the image, commonly called fog (film/screen) or noise (digital).
The amount of scatter radiation that is created is affected by what 4 factors?
- Area of radiation field
2.kVp - Part thickness
- Tissue density
Area of radiation field
The greater the area of field, the greater the amount of scattered radiation that is produced (and vice versa).
KVp
As kVp is increased, the production of scattered radiation increases, and a higher percentage of these x-rays will reach the image receptor.
Part thickness
The thicker the part, the more scattered radiation will be produced because more matter is present to interact with x-rays.
Tissue density
The greater the tissue density, the greater the amount of scattered radiation because more atoms are in the path of the x-ray beam.
A comparison of two regions of the body with different tissue densities in terms of radiation exiting the part:
- Chest – 50% scattered radiation; 50% primary
- Abdomen – 90% scattered radiation; 10% primary
Grid
Invented in 1913 by Dr. Gustave Bucky in Chicago.
• This device should be used anytime: • part thickness exceeds 10 cm
• and/or above 70 kVp.
• This is the most common device to prevent scatter radiation from reaching the image receptor.
What types of materials are grids made out of?
- Radiolucent
- Radiopaque
Radiopaque strips
0.05 mm wide
Radiolucent strips
0.33 mm wide
The principle behind the grid is
Primary x-rays can pass through the radiolucent interspace material while scattered x-rays are absorbed in the radiopaque strips.
What are the main types of grids?
- Linear
- Crosshatch or cellular
- Multi-hole
- Virtual
Linear
consists of one set of lead strips that run in a straight line in one direction.
These are most often installed in table Bucky’s.
What are the 2 basic types of linear grids?
- Parallel
- Focused
Parallel linear grid
When viewed from the side, the lead strips run parallel to each other.
• Used for small size image receptors, long SID, or mobile radiography
Focused linear grids
Lead strips are focused toward a convergence point, a process known as canting.
• This is found in most exposure rooms and used for routine SID’s and any image receptor size.
Where are focus grids found?
In table bucky’s because the tube can be locked over the center of the grid and image receptor.
Criss-cross, cross hatch,or cellular grids
Most efficient grid for removing scattered radiation because there are two sets of lead strips mounted at 45 or 90 degrees to each other.
Disadvantages of cross hatch grids
no angling of the x-ray beam, higher patient dose, and centering is critical.
What are the 2 types of cross hatch grids?
- Orthogonal
- Rhombic
Orthogonal cross hatch grid
Lead strips are mounted at 90 degree angles to each other.
Rhombic cross hatch grid
Lead strips are mounted at 45 degree angles to each other.
Multi hole grids
This type of grid was developed to be used with early CR systems to prevent Moire’ artifacts.
What are moire or zebra patterned artifacts?
when the grid lines and the CR scan lines are similar in number and run in the same direction.
Virtual grid
Not a physical grid like the previous types
• It is a software program that reduces gray shades created by scatter in DR images.
• This system can reduce patient dose up to 50%
Lead content
the amount of lead used in the construction of a grid and measured in units of grams/cm2.
Grid focusing distance
Formally called grid radius
This is the proper SID that a focused grid will operate due to the alignment of the lead strips with the x-ray beam.
Grid cutoff
absorption of primary or useful radiation by the grid, resulting in an underexposed radiograph.
Stationary Grid
the grid does not move during the exposure. Results in grid lines in the resulting image.
Grid Lines
shadows of lead strips appearing on the radiograph.
Moving Grid
– invented in 1920 by Dr. Hollis Potter.
• It is designed to eliminate grid lines by moving the grid during the exposure, and can be found in three basic types:
1. Single -stroke
2. Recipromatic
3.Reciprocating
A moving grid requires a 15% increase in mAs over a stationary grid.
Single stroke
Spring activated and found only in older equipment
Reciprocating
Grid is moved by a solenoid
Recipromatic
Uses an electric motor to move the grid
Potter Bucky diaphragm
Formal name for the assembly that contains the grid, the device that moves the grid, and the metal tray that holds the image receptor and mounted below the tabletop of a radiographic unit.
Known as Bucky for short
Grid latitude
Margin of error for centering the primary beam to the grid
