Beam Restriction Flashcards
What factors influence the amount of Compton scatter?
- Beam restriction (collimation)
- Thickness & density of the part
- kVp
How does increasing kVp affect Compton scatter?
Increasing kVp increases the amount of scatter relative to the photoelectric effect
What is the purpose of using grids in radiography?
To absorb scatter radiation produced within the patient
What is the impact of using grids on image quality and patient dose?
Using grids improves image contrast at the expense of patient dose
What must be done to compensate for the use of a grid?
Technique must be increased to compensate for the use of a grid because grids remove part of the primary beam
Fill in the blank:
More available _______ leads to increased scatter.
[electrons]
What is one method to reduce patient dose and scatter radiation?
Restricting the beam or collimating
How does collimation affect patient dose?
It decreases the amount of radiation that interacts with the patient and reduces the patient dose
Proper collimation is essential for optimal radiation safety.
What is the effect of properly collimating the beam?
It reduces the amount of scatter produced
This is achieved by limiting the interaction of photons with matter.
True or False: Collimation increases the amount of scatter radiation.
False
Proper collimation actually reduces scatter radiation.
Fill in the blank: Collimation _______ the amount of matter that the photons can interact with.
Reduces
What is the maximum allowable collimation limit on all four sides for tabletop exams?
1 inch beyond the anatomy of interest
What is the starting point for collimation size?
The size of the image receptor
This helps to ensure that the entire area of interest is adequately covered.
What are the 4 major benefits of proper collimation?
- Reducing scatter radiation
- Reducing unnecessary exposure by the primary beam
- Increasing contrast
- Reducing patient dose
True or False: Beam restriction (collimation) does not impact patient dose.
False
What is the effect of atomic number on scattering according to Bushong?
Atomic number has no effect on the likelihood of scattering.
True or False: Atomic number directly affects scatter.
False.
Atomic number does not directly affect scatter, although it influences the amount of scatter due to density.
What device is primarily used to restrict the primary beam field size in radiography?
Collimator.
The collimator is the most commonly employed beam restrictor in radiography.
What accessory do most collimators now include?
Positive beam limitation (PBL) device
The PBL device automatically adjusts the beam to match the size of the image receptor.
True or False: The field size should never be greater than the image receptor size.
True
This guideline is essential to prevent unnecessary exposure and ensure optimal image quality.
What are the typical standard sizes for image receptors mentioned?
14x17 or 17x17
These sizes are commonly used in radiographic imaging.
How many sets of shutters do collimators typically have?
2 sets (sometimes 3)
The additional set may be used for specific applications or enhanced functionality.
What is the purpose of entrance shutters in a collimator?
To help remove off-focus radiation
Off-focus radiation can degrade image quality by adding unwanted exposure.
Fill in the blank: Field size should never be greater than the _______.
[image receptor size]
Adhering to this guideline is crucial for effective radiographic practice.
The second set of collimator shutters are controlled by the ______________?
technologist
What does the light field in x-ray imaging use to project the area of the x-ray beam?
Light reflected off a mirror
Why is proper adjustment of the mirror necessary in x-ray imaging?
To accurately display the location of the exposure field
What is the accuracy requirement for light field/x-ray beam coincidence testing?
Within +/- 2% of the SID
What test is used to check the light field/x-ray beam coincidence?
Penny test (at 40” SID)
What is the diameter of the penny used in the penny test?
.80”
What percentage of 40” does the penny’s diameter (.80”) represent?
2%
According to the penny test, where must the light x-ray field not fall?
Outside of the penny
What is the effect of using a collimator on the x-ray beam?
It results in some filtration of the x-ray beam due to the primary beam passing through the mirror in the collimator.
This filtration is approximately 1 mm Al/Eq.
What do some collimator units project in relation to the photo timer sensors?
They project the location of photo timer sensors in the light field.
This feature aids in ensuring accurate exposure settings.
What aids in centering the beam with the image receptor in a collimator?
An alignment light.
This helps radiologic technologists to accurately position the x-ray beam.
What is the definition of Penumbra in imaging?
Penumbra is a geometric unsharpness around the periphery of the image, also known as edge unsharpness.
It occurs due to the spread of x-ray photons being created in all areas of the focal spot.
What causes Penumbra in x-ray imaging?
X-ray photons are created in all areas of the focal spot rather than at just a single point.
This results in x-rays originating from slightly different spots on the anode taking slightly different angles to hit the same point on the detector.
True or False: Penumbra is beneficial for image clarity.
False
Penumbra introduces unsharpness, which can reduce the clarity of the image.
Fill in the blank: Penumbra is also known as _______.
edge unsharpness
What effect does the angle of x-ray photons have on Penumbra?
The angle of x-ray photons affects the sharpness of the image periphery.
Different angles from slightly different spots on the anode contribute to the geometric unsharpness.
What is the primary function of shutters in imaging?
To reduce penumbra along the periphery of the beam due to their greater distance from the focal spot
Penumbra refers to the partial shadow or gradation of light around the edges of a beam.
What do the angles of the primary phato from the tube gumbra do?
Intersect with the structures of interest at varying angles when creating the image
This technique enhances the detail and accuracy of the imaging process.
What are aperture diaphragms and cones/cylinders used for?
To restrict the beam
These devices were historically used but are not common in modern practice.
Fill in the blank: The devices historically used to restrict the beam include _______ and cones/cylinders.
[aperture diaphragms]
What is the significance of the focal spot in imaging?
It is the point from which the beam originates and affects the quality of the image produced
The focal spot size can significantly influence image sharpness and resolution.
What is an aperture diaphragm?
A flat sheet of metal, usually lead, with an opening cut in the center attached to the x-ray tube head.
It is the simplest of all beam-restricting devices.
How is the field size calculated using an aperture diaphragm?
By using the aperture dimensions and the SID (Source to Image Distance) and SDD (Source to Detector Distance).
The text humorously notes that the calculation won’t be demonstrated.
What types of machines typically use aperture diaphragms?
Dedicated chest or head units, trauma units, and dental equipment.
These machines are designed in fixed applications with a fixed image receptor and fixed SID.
True or False: Aperture diaphragms are used in mobile imaging applications.
False
They are designed for fixed applications.
Fill in the blank: The aperture diaphragm is attached to the _______.
[x-ray tube head]
What materials are commonly used for the aperture diaphragm?
Lead
Lead is used due to its radiation shielding properties.
What is the primary function of an aperture diaphragm?
To restrict the x-ray beam size.
This helps improve image quality and reduce patient exposure.
What is the significance of fixed SID in relation to aperture diaphragms?
It allows for consistent imaging results.
Fixed SID means that the distance from the x-ray source to the image receptor remains constant.
What is an Aperture Diaphragm?
A device that allows the field to cover an area just smaller than the image receptor
It is used in radiography to limit the area exposed to radiation.
What are the disadvantages of using an Aperture Diaphragm?
Greater amount of penumbra and off-focus radiation due to the proximity to the tube port
This can affect image quality by creating blurred edges.
How can the effectiveness of an Aperture Diaphragm be enhanced?
By supplementing it with cones and cylinders
These additional devices help to further restrict the radiation field.
What is the primary difference between a cone and a cylinder?
A cone has a flared extension, while a cylinder does not flare.
What shape do both cones and cylinders have at their base?
Circular aperture.
Fill in the blank: A cone has an upper diameter that is _______ than the bottom flared end.
smaller
What are cones and cylinders described as in their function?
Essentially circular aperture diaphragms.
True or False: A cylinder has a smaller upper diameter compared to its base diameter.
False
What is the primary benefit of using cones and cylinders in imaging?
Greater detail visibility
Cones and cylinders reduce scatter, making images appear sharper.
List some applications of cones and cylinders in imaging.
- Head work - sinuses or skulls
- Spine work - spot films
- Cross-table hip
- Dental
These applications utilize the advantages of cones and cylinders for improved image clarity.
True or False: Cones and cylinders are used to increase scatter in imaging.
False
Cones and cylinders are designed to reduce scatter, enhancing image quality.
Fill in the blank: Cones and cylinders are primarily used for greater _______ in small areas.
detail visibility
This refers to the ability to see finer details in the image.
What is the primary benefit of using cylinders in radiology?
Reduces the amount of irradiated material and therefore patient dose
Cylinders also reduce scatter and increase contrast.
What is the ideal function of beam restrictors?
Decrease field size to anatomy of interest
This reduces unnecessary tissue exposure and scatter.
What are the effects of using beam restrictors on contrast?
Contrast increases and visibility of detail increases
The scale of contrast shortens.
Name two types of ancillary devices used in radiology.
Lead blockers and lead masks
These devices are tailored for specific uses during procedures.
Fill in the blank: Ancillary devices are generally designed with a ______ in mind.
special need
True or False: Beam restrictors can increase unnecessary tissue exposure.
False
Beam restrictors are designed to decrease unnecessary tissue exposure.
What is the purpose of lead masks in radiology?
To restrict the beam to a specific shape for a particular examination
This helps in focusing the radiation on the area of interest.
What is a lead blocker?
A device placed on the radiographic table during lower spine radiography to absorb scatter from soft tissue.
Lead blockers help improve image quality by reducing scatter radiation.
How does a lead blocker function during radiography?
It helps to absorb the scatter produced in the soft tissue of the patient’s back.
This is particularly important in the lateral position of lower spine imaging.
What is a lead mask?
A device cut to correspond to the desired field size and secured to the end of the collimator.
Lead masks are used to improve image quality by reducing scatter.
What shape were lead masks sometimes cut into for cerebral angiography?
Keyhole shape.
This shape was specifically designed to enhance image quality by minimizing scatter.
Fill in the blank: A lead mask is usually cut to correspond to the _______.
[field size desired]
True or False: Lead masks can improve image quality by reducing scatter.
True
This is a key function of lead masks in radiographic procedures.
