CONTROL OF SCATTER RAD Flashcards
What percentage of x-rays incident on the patient reach the image receptor?
Approximately 1%.
What does compression of anatomy improve in radiography?
It improves spatial resolution, contrast resolution, and lowers patient dose.
Why is compression particularly important in mammography?
It helps to achieve better image quality and lower patient dose.
Name two types of x-rays responsible for optical density and contrast on a radiograph.
- X-rays that pass through the patient without interacting
- scattered x-rays within the patient.
X-rays that exit from the patient.
Remnant xrays
X-rays that exit and interact with the image receptor.
image-forming xrays
Name one effect of proper collimation.
Less scatter radiation, reduced patient dose, and improved contrast resolution.
List three factors that increase scatter radiation.
kVp, field size, and patient thickness.
What is the effect of increased kVp on scatter radiation?
Increase scatter radiation, reduce image contrast.
What happens to patient dose when kVp is decreased?
Patient dose increases due to the need for higher mAs.
How does increased field size affect scatter radiation?
It increases scatter radiation.
What is used to reduce scatter radiation in thick body parts?
compression paddle
The visible difference between light and dark areas on an image.
image contrast
The ability to image and distinguish soft tissues.
contrast resolution
What effect does scatter radiation have on image contrast?
It reduces contrast, making the image appear dull or gray.
Name two devices used to reduce scatter radiation.
Beam restrictors, grids.
What is the primary purpose of collimation in radiography?
To reduce patient dose and improve contrast resolution.
What are the three types of beam restrictors?
Aperture diaphragm, cones or cylinders, and variable-aperture collimators.
What is the simplest beam-restricting device?
Aperture diaphragm.
Name one application of the aperture diaphragm.
Trauma and dental radiography
What is the primary advantage of using cones and cylinders?
They reduce scattered radiation and improve image contrast.
What is the most commonly used beam restrictor?
Variable-aperture collimator.
X-rays produced in the anode but not at the focal spot.
off-focus radiation
Collimators that automatically adjust the radiation field to the size of the image receptor.
positive-beam limiting (PBL) devices
What is the total filtration equivalent required in radiography?
2.5 mm Al.
A device used to reduce scatter radiation in the remnant x-ray beam.
grid
What is the principal function of a grid?
To improve image contrast.
Where is a grid placed in relation to the patient and image receptor?
Between the patient and the image receptor.
What material are grid strips typically made of?
Radiopaque material, usually lead.
What are the three important dimensions of a grid?
Grid strip thickness (T), interspace width (D), and grid height (h).
Who demonstrated the technique for reducing scatter radiation that reaches the image receptor?
Gustav Bucky in 1913.
What is the formula for grid surface x-ray absorption?
Width of grid strip / (width of grid strip + width of interspace) x 100.
The height of the grid divided by the interspace width (h/D).
grid ratio
What is an advantage of a high-ratio grid?
It is more effective in cleaning up scatter radiation.
What is a disadvantage of a high-ratio grid?
It increases patient dose.
What grid ratios are commonly used in general radiography?
8:1 to 10:1.
What grid ratios are used in mammography?
4:1 to 5:1.
The number of grid strips per centimeter.
grid frequency
It reduces the visibility of grid lines on the radiograph.
high-frequency grid
What range is typical for grid frequency?
25-45 lines per centimeter.
What is the formula for calculating grid frequency?
10,000 μm/cm ÷ (T + D) μm/line pair.
What is the purpose of interspace material in a grid?
To maintain precise separation between the lead strips.
What are two common interspace materials in grids?
Aluminum and plastic fiber.
Name one advantage of using aluminum as interspace material.
It does not absorb moisture (nonhygroscopic).
What is a disadvantage of using aluminum in grids?
It increases primary beam absorption, raising patient dose.
What material is preferred for interspaces to minimize patient dose?
Plastic fiber.
What characteristics are essential in grid strips?
They should be thin and have high absorption properties.
What is the contrast improvement factor (k) in grid performance?
The ratio of radiographic contrast with a grid to that without a grid.
What is the typical value of k for most grids?
Between 1.5 and 2.5.
The ratio of incident to transmitted radiation through a grid.
Bucky factor in radiography
What is a high Bucky factor indicative of?
Higher patient dose due to the grid’s increased scatter removal efficiency.
How does increasing kVp affect the Bucky factor?
It increases the Bucky factor, requiring higher exposure.
The simplest grid type, with parallel grid strips.
parallel grid
The undesirable absorption of primary x-rays by the grid.
grid cutoff
What causes grid cutoff in a parallel grid?
Occurs at short SID and large area IR.
A grid made by sandwiching two parallel grids together at right angles.
crossed grid
Name one advantage of a crossed grid.
It cleans up scatter radiation more effectively than a single parallel grid.
What is a major disadvantage of a crossed grid?
It is susceptible to grid cutoff.
A grid with strips parallel to the path of primary x-rays to minimize cutoff.
focused grid
What is an off-level grid error?
When the central ray is not perpendicular to the grid, causing grid cutoff.
What is an off-center grid error?
When the grid is shifted laterally, leading to partial grid cutoff.
What is an off-focus grid error?
Occurs when the SID does not match the grid’s focal distance, causing edge cutoff.
What is the effect of an upside-down grid?
Severe or complete grid cutoff at the edges of the image.
A method where the image receptor is placed 10-15 cm away from the patient to reduce scatter.
air-gap technique.
What is an advantage of the air-gap technique?
It reduces scatter radiation and enhances image contrast.
What is a disadvantage of the air-gap technique?
It causes image magnification and focal spot blur.
What is the mAs increase factor for a 5:1 grid?
2x
What is the kVp increase for a 5:1 grid?
+8-10 kVp.
What is the mAs increase factor for an 8:1 grid?
4x
What is the kVp increase for an 8:1 grid?
+13-15 kVp.
What is the mAs increase factor for a 12:1 grid?
5x
What is the kVp increase for a 12:1 grid?
+20-25 kVp.
What is the mAs increase factor for a 16:1 grid?
6x
What is the kVp increase for a 16:1 grid?
+30-40 kVp.
What is the main purpose of collimation in radiographic imaging?
To limit the x-ray beam to the area of interest.
What happens if the x-ray beam size exceeds the IR?
Patient dose and scatter radiation increase.
Why is a moving grid used?
To reduce visible grid lines on the radiograph.
What are the two types of moving grids?
Reciprocating and oscillating grids.
Who invented the moving grid?
Hollis Potter in 1920.
A motor-driven grid that moves back and forth during exposure.
reciprocating grid
A grid that oscillates in a circular fashion around the grid frame.
oscillating grid
How does a moving grid affect patient dose?
It increases patient dose by about 15%.
What is the preferred grid ratio for kVp below 90?
up to 8:1
What grid ratio is recommended for kVp above 90?
Greater than 8:1.
The x-ray that travels along the center of the useful beam.
central ray
A type of off-center grid error due to improper alignment of the grid and x-ray tube.
lateral decentering
What is the typical kVp range for chest radiography using the air-gap technique?
180-300 cm SID.
How does grid ratio affect radiographic technique?
Higher grid ratios require higher technique and increase patient dose.
What does SID stand for?
Source-to-image distance.
What is the purpose of grid lines?
They reduce scattered radiation in specific directions but can appear as lines on the radiograph.
What grid ratio generally requires no additional technique increase?
No grid ratio or 1x increase.
What material in grids improves durability but increases primary absorption?
Aluminum interspace material.
What is the effect of grid cutoff on image quality?
It reduces optical density and can cause underexposure.
How does patient dose compare with a moving vs. stationary grid?
A moving grid increases patient dose.
What is an advantage of focused grids over parallel grids?
Focused grids reduce grid cutoff.
What is the purpose of a grid in mammography?
To enhance contrast while using low-ratio grids like 4:1 to 5:1.
What technique can serve as an alternative to grid use?
Air-gap technique.
How does compression improve radiographic imaging?
It reduces thickness, which lowers scatter and improves resolution.
What is a disadvantage of crossed grids?
prone to grid cutoff and increase patient dose.
What is required for the proper function of a focused grid?
Correct alignment with the x-ray tube focal distance and position.
