43 terms


Scattered radiation affects The radiographic image by causing?
1. Fog
2. Reduced Contrast
3. Reduced recorded detail
Which of the following factors will affect the quantity of scattered radiation fog on a radiograph?
1. kVp
2. Field Size
The most effective method of reducing scattered radiation fog on a radiograph is to?
Use a grid or Bucky
The effectiveness of a grid is determined by the grid ratio which is?
The relationship between the height of the lead strips And the width of the spaces between them.
As compared with an 8:1 radio grid a 12:1 ratio
grid will?
Clean up scattered radiation more effectively.
On a radiograph, the appearance of decreased density on the side of the image is most likely caused by?
Grid Cutoff caused Off Level:
tube angled against grid lines
Grid angled (not + to the beam)
Grid Cut off caused by Off Center:
CR not properly centered to grid (most common in mobile)
A moving grid may be part of a radiographic table or upright unit and is called a?
Bucky Grid
The frequency of a stationary grid affects the?
Visibility of grid lines
As a general rule, a grid or Bucky should be used when the part thickness is greater than?
10 to 12 cm.
What three things can cause Grid cut off ?
1. Lateral angulation
2. Sid out o the focal range. 3. Position of the x-ray beam off center to one side of the grid.
What 2 things can reduce scatter radiation?
1. Using an air gap
2. Using a smaller field size
In the diagnostic range of kVp settings (50 to 100 kVp), the majority of scattered radiation will be from which interaction with Matter?
Compton effect
Total absorption of an x-ray photon by the atom of the body part is termed?
The photoelectric effect.
T or F Higher kVp results in more scattered radiation fog.
T or F The effectiveness of a grid is determined by the grid ratio.
T or F High frequency or stationary grids move during the exposure.
False Moving grids are Called a Bucky, High Frequency grids that Don't move are called Stationary grids.
T or F A grid with strips that are parallel to each other is called a crosshatch grid.
False A crosshatch grid is composite of two grids with the Lead strips at right angles to each other Also called a crossed grid
T or F an air gap with increased OID increase the intensity of scattered radiation at the image receptor (IR)
False Increasing the OID will decrease the intensity of scatter radiation at the film.
T or F A grid ratio of 12:1 would be used for mobile radiography.
False For general purpose and chest radiography
T or F The number of lead strips per inch is called grid frequency.
T or F ^ tissue thickness = ^ interactions = ^ scatter = ^ fog
(^ = increase)
T or F The patient is the principal source of scattered radiation in radiography
T or F A grid is placed between the patient and the IR
T or F Compton scatter travels in a forward direction only
False Compton travels in all directions
Coherent scatter travels forward
T or F Scatter radiation fog reduces the visibility of detail
What two factors that will affect the volume of tissue irradiated?
1. Part thickness
2. Field size
When the kVp is increased, will quantity of secondary radiation fog be increased or decreased? Why?
The quantity of fog is increased because the scatter produced with Higher kVp has greater energy.
What is the typical radiographic appearance of grid cutoff caused by using an SID that is outside the grid's focal range?
It will show normal radiographic density in the center and decreased density with lengthwise streaks and apparent grid lines on both sides
For what radiographic examination is an air gap commonly used instead of a grid?
The lateral projection of the cervical spine.
How might the image of a vertebra on a spot film differ from the image of the same vertebra as a part of a 35 x 43 cm radiograph of the spine?
Spot film shows increased image quality because of the reduction of scattered radiation fog. Recorded detail will also be improved because of the decrease in distortion that results when the area of clinical interest is centered to the central ray.
How would you determine when to use a grid?
By using the technique chart, because this chart will indicate grid use when the average adult part size is sufficient to require a grid. When in doubt measure the part and use a grid if 10 to 12 cm or greater
What are the Grid Applications for 5:1 and 6:1, 8:1, 12:1, and 16:1?
5:1 & 6:1 Grid cassettes, mobile radiography.
8:1 General purpose
12:1 General purpose, chest radiography
16:1 High kilovoltage radiography only (special procedures and Vascular)
What does a Moving grid do?
Is called a Bucky, and the moving grid during the exposure blurs the image of the grid lines so that the grid image is not visible on the film.
What does a stationary gird do?
They don't move during the exposure, should have many very fine lines (high frequency) to avoid objectionable grid lines on images, Commonly used today in upright cassette holders.
(cutoff doesn't result when the x-ray tube is off center lengthwise or angled along the length of the lead strips)
Grid cutoff occurs when the x-ray tube is centered to one side of the grid rather than to the focal center line. Cutoff also occurs when the x-ray tube is angled toward one side of the gird, rather than perpendicular to its center. The same effect is encountered if the grid is tipped side to side in relation to the primary beam.
What is a Parallel grid?
The radius of a parallel gird is infinity. A grid with strips that are parallel to each other rather than focused. Parallel grids can be used for radiography at very long SID's because the useful portion of the x-ray beam is nearly perpendicular to the grid when the distance is great. They are available only in lower ratios. Parallel grids are also used in fluoroscopic spot film devices
What is a crosshatch grid
Also called a crossed grid
A composite of two grids with the lead strips at right angles to each other. A crosshatch grid is desirable because it has an effective ratio that is greater than the ratios of the two grids.
What is an air gap?
This is another method of reducing fog. Is an air space between the patient and the film, in other words a large object image receptor distance (OID).
Grid cutoff, is Undesirable attenuation of the primary x-ray beam by the grid cause by misalignment between grid and x-ray beam causes?
1. Lateral decentering,
2. Source image receptor distance outside focal range,
3. Lateral angulation or grid off level,
4. Grid reversed.
Methods of scatter radiation fog control.
1. Use grid device - grid place between patient and film to absorb scatter
2. Use air gap - increased object-image receptor distance decreases scatter intensity at film
3. Minimize field size - decreases volume of scattering tissue
4. Decrease kilovoltage - decreases energy of scatter and increases researchers contrast
Grid cut off on one side is most likely due to :
Off center
Off level
Grid cut off on both sides is most likely due to :
Off focus
Upside down grid
Which grid cutoff is more extreme:
Off focus or Upside down grid
Upside down