Radiation Principles in Imaging Techniques

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Questions and Answers

What is the recommended change in mAs when reducing field size from 14” x 17” to 8” x 10”?

Increase mAs by 10%

Decrease mAs by 20%

Keep mAs the same

Increase mAs by 40% (correct)

Which type of body part would result in more scatter radiation during imaging?

A lumbar spine (correct)

A child’s leg

A thin arm

A cervical spine

What happens to scatter radiation as tissue thickness increases?

It decreases exponentially

It becomes negligible

It remains constant

It increases relative intensity (correct)

How can image quality be improved in the case of obese patients?

By taking the film with compression Signup and view all the answers

Which of the following is NOT a type of beam restricting device?

Incinerator Signup and view all the answers

What is the purpose of matching the light field and x-ray beam?

To avoid collimator cut-off Signup and view all the answers

What feature do many newer collimators provide to assist in centering the beam?

A bright slit of light Signup and view all the answers

What function do the motorized shutters serve in units manufactured between 1974 and 1994?

To provide automatic collimation Signup and view all the answers

What device is used to match the beam to the film size at fixed SID’s?

A scale on the collimator Signup and view all the answers

How is the image size automatically collated to the film size?

Through a sensor in the Bucky and a motor Signup and view all the answers

What is the primary effect of proper collimation on patient dosage?

It reduces the amount of ionizing radiation. Signup and view all the answers

Which of the following is a benefit of reducing scatter radiation through collimation?

It improves imaging quality by enhancing contrast. Signup and view all the answers

What is the most common beam restricting device used in diagnostic radiography?

Light Localizing Variable Aperture Collimator Signup and view all the answers

How does proper collimation affect the volume of irradiated tissue?

It decreases the volume of irradiated tissue. Signup and view all the answers

What role does the light localizing variable aperture collimator play in radiographic procedures?

It restricts the x-ray beam to improve precision. Signup and view all the answers

What is the most common device for beam restriction in diagnostic radiography?

Collimator Signup and view all the answers

What are rays that do not originate precisely from the focal spot called?

Off-focus radiation Signup and view all the answers

Which component controls off-focus radiation in a collimator?

First stage shutters Signup and view all the answers

What is used to restrict the x-ray beam beyond the initial collimation?

Adjustable second stage shutters Signup and view all the answers

How is light localization achieved in a collimator system?

Through a small projector lamp and mirror Signup and view all the answers

What is the purpose of a positive-beam limiting (PBL) device?

To limit the x-ray beam to the size of the film Signup and view all the answers

What happens if the beam is not centered to the film?

Collimator cut-off will occur on the top or bottom of the image Signup and view all the answers

What condition leads to side-to-side collimator cut-off?

When the film is not pushed into the Bucky Signup and view all the answers

According to collimation rules, how should the collimation be set?

Slightly less than film size or to the area of clinical interest Signup and view all the answers

What requirement is imposed by the FDA regarding the PBL device?

It must automatically adjust to different film sizes Signup and view all the answers

Study Notes

Patient or Part Thickness

Scatter radiation increases when imaging thicker body parts compared to thinner body parts.
A lumbar spine film will have more scatter than a cervical spine film because of the greater thickness.

Tissue Thickness

As tissue thickness increases, more x-rays undergo multiple scattering events.
Scatter radiation intensity increases with increasing tissue thickness.

Patient thickness

Patient thickness is generally uncontrollable, but imaging methods can be adjusted to improve image quality.
Using compression during imaging reduces tissue thickness in obese patients.

Types of Beam Restricting Devices

Diaphragms, Cones, and Collimators are all beam restricting devices.

Aperture

Apertures are the simplest form of collimation.
Proper collimation reduces patient dose by minimizing irradiated tissue volume.
It also minimizes scatter radiation, which improves image contrast.

Light Localizing Collimator

The light-localizing variable aperture collimator is the most common beam restricting device in diagnostic radiography.

Collimator

X-rays are not always emitted precisely from the focal spot.
These off-focus rays contribute to image blur.
First stage shutters control off-focus radiation.
Second stage shutter pairs are adjustable to restrict the beam’s size.
A projector lamp and mirror are used to project the collimator settings onto the patient for precise localization.
The light field and x-ray beam should match to avoid collimator cut-off.
A scale on the collimator is used to match the film size for specific Source-to-Image Distances (SIDs).
Modern collimators use a bright slit of light to center the beam and film.
Units manufactured between 1974 and 1994 used motorized shutters to automatically collimate images to the film size.
This was known as a Positive Beam Limiting (PBL) device, which is now required by the FDA.

Collimator Cut-Off

If the beam is not centered to the film, collimator cut-off will occur at the top or bottom of the image.
If the tube is not centered to the Bucky or if the film is not pushed into the Bucky, side to side collimator cut-off will occur.

Collimation Rules

Collimation should be slightly less than film size or to the area of clinical interest, whichever is smaller.

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Description

This quiz focuses on the principles of radiation exposure and scatter radiation related to patient thickness and imaging methods. It covers beam restricting devices and the importance of collimation in improving image quality and safety. Test your knowledge on how these factors play a role in radiographic procedures.