RAD 125 Exam 4

What is mAs directly proportional to?

The quantity of radiation reaching the patient and the amount of remnant radiation reaching the image receptor (IR).

How is mAs related to exposure time when maintaining exposure to the image receptor?

mAs and exposure time are inversely related. If exposure time increases, mA can decrease to maintain the same mAs, and vice versa.

What is wide dynamic range?

Digital image receptors can detect a wider range of radiation intensities exiting the patient, making them less dependent on mAs than film-based imaging systems.

How is image brightness adjusted in digital imaging?

Image brightness can be adjusted during computer processing to compensate for low- and high-exposure errors.

What does kVp affect?

The amount and penetrating ability of the x-ray beam, as well as the amount of radiation exposure to the image receptor.

How does kVp affect a digital image?

Its effect is similar to the effect of mAs because both influence the amount of radiation reaching the image receptor.

What happens when too much radiation reaches the IR because of excessive kVp?

The computer may adjust the brightness to an appropriate level, but the patient receives excessive radiation exposure.

What happens when too little radiation reaches the IR because of insufficient kVp?

increased quantum noise decreases image quality

Why is kVp not typically manipulated just to change IR exposure?

Because kVp also affects radiographic contrast.

What is the 15% rule?

Changing kVp by 15% has approximately the same effect on IR exposure as doubling the mAs or reducing the mAs by 50%.

When kVp is increased by 15%, what mAs adjustment maintains the same IR exposure?

Reduce the mAs by half.

When kVp is decreased by 15%, what mAs adjustment maintains the same IR exposure?

Double the mAs.

How does higher kVp affect radiographic contrast?

Higher kVp decreases radiographic contrast.

How does lower kVp affect radiographic contrast?

Lower kVp increases radiographic contrast.

How does increasing kVp affect x-ray absorption and transmission?

Higher kVp increases beam penetration and the number of x-rays transmitted through the patient.

What factors determine the desired level of radiographic contrast?

• Type and composition of the anatomic tissue.

• Structures that must be visualized.

• The diagnostician's preference.

How does focal spot size affect the image?

affects image sharpness.

Which focal spot size should be used for every exposure according to the slide?

The smallest focal spot size available.

How does SID affect radiation intensity reaching the patient?

SID and radiation intensity are inversely related. As SID increases, radiation intensity decreases.

What must be changed when SID changes to maintain IR exposure?

mAs must be adjusted.

How does SID affect the image?

image distortion and spatial resolution.

What factors does OID affect?

• Radiation intensity reaching the image receptor.

• Amount of scatter radiation reaching the image receptor.

• Magnification.

• Spatial resolution.

How does limiting scatter with a grid affect radiographic image quality?

It improves radiographic image quality and increases contrast

What is the grid conversion factor for no grid?

1

What is the grid conversion factor for 5:1?

2

What is the grid conversion factor for 6:1?

3

What is the grid conversion factor for 8:1?

4

What is the grid conversion factor for 12:1?

5

What is the grid conversion factor for 16:1?

6

How does changing the x-ray field size affect tissue irradiation?

Any change in field size changes the amount of tissue irradiated.

What happens when a larger x-ray field is used?

• More tissue is irradiated.

• More scatter radiation is produced.

• More radiation reaches the image receptor.

• Radiographic contrast decreases.

What happens when a smaller x-ray field is used?

• Less tissue is irradiated.

• Less scatter radiation is produced.

• Less scatter reaches the image receptor.

• Radiographic contrast increases.

What determines exposure techniques and radiation output?

The type of generator being used.

How do generators with more efficient output affect exposure technique settings?

They require lower exposure technique settings to produce an image.

Why must x-ray generators be calibrated periodically?

To ensure they produce consistent radiation output.

What minimum aluminum filtration is required for x-ray tubes operated above 70 kVp ?

2.5 mm

What happens when tube filtration increases?

The percentage of higher-penetrating x-rays to lower-penetrating x-rays increases, which increases scatter.

When can a compensating filter be used?

When imaging an anatomic area that varies greatly in tissue thickness.

Where is a compensating filter placed?

In the primary beam.

What is the purpose of a compensating filter?

To produce a more uniform exposure to the image receptor across areas of different tissue thickness.

What technique adjustment is needed when using compensating filters?

An increase in mAs is required to maintain overall IR exposure.

How does part thickness affect beam attenuation?

A thick part absorbs more radiation, while a thin part transmits more radiation.

What must be changed when part thickness increases or decreases to maintain IR exposure?

mAs must be adjusted.

What affects contrast?

The anatomic structures being imaged.

How does changing kVp affect subject contrast?

alters absorption and transmission within anatomic tissues

Increasing mAs

• Increases primary beam quantity reaching the patient

• Increases exiting beam quantity reaching the IR

Decreasing mAs

• Decreases primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR

Increasing kVp

• Increases primary beam quantity & quality reaching the patient

• Increases exiting beam quantity reaching the IR

Decreasing kVp

• Decreases primary beam quantity & quality reaching the patient

• Decreases exiting beam quantity & quality reaching the IR

Smaller & Larger focal spot size

• No effect on primary beam reaching the patient

• No effect on exiting beam reaching the IR

Increasing SID

• Decreases primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR

Decreasing SID

• Increases primary beam quantity reaching the patient

• Increases exiting beam quantity reaching the IR

Increasing OID

• No effect on primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR & Scatter

Decreasing OID

• No effect on primary beam quantity reaching the patient

• Increases exiting beam quantity reaching the IR & scatter

CR angle increasing

• Decreases primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR

Increasing grid ratio

• No effect on primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR & scatter

Decreasing grid ratio

• No effect on primary beam quantity reaching the patient

• Increases exiting beam quantity reaching the IR & Scatter

Increasing Collimation

• Decreases primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR & Scatter

Decreasing Collimation

• Increases primary beam quantity reaching the patient

• Increases exiting beam quantity reaching the IR & Scatter

Single-phase generator

• Decreases primary beam quantity & quality reaching the patient

• Decreases exiting beam quantity & quality reaching the IR

High frequency generator

• Increases primary beam quantity & quality reaching the patient

• Increases exiting beam quantity & quality reaching the IR

Adding a compensating filter

• Decreases primary beam quantity reaching the patient

• Decreases exiting beam quantity reaching the IR

What is the primary source of scatter radiation?

Compton interactions.

What are the two major factors affecting the amount of scatter radiation produced and exiting the patient?

• Volume of tissue irradiated.

• Kilovoltage peak (kVp).

What determines the volume of tissue irradiated?

• Part thickness.

• X-ray beam field size.

How does higher kVp affect scatter radiation exiting the patient?

Higher kVp increases the energy of scatter radiation exiting the patient.

Why must scatter radiation be controlled?

Scatter radiation is detrimental to radiographic image quality because it adds unwanted exposure, or fog, to the image without adding patient information.

How does scatter radiation affect radiographic contrast?

decreases radiographic contrast.

How does increased scatter radiation affect radiation exposure?

Scatter produced within the patient or higher-energy scatter exiting the patient affects exposure to the patient and anyone within close proximity.

How do beam-restricting devices reduce scatter radiation?

They decrease the x-ray beam field size and the amount of tissue irradiated, reducing the amount of scatter radiation produced.

What is the purpose of radiographic grids?

They improve radiographic image quality by absorbing scatter radiation exiting the patient, reducing the amount of scatter reaching the image receptor.

What are the purposes of beam restriction?

• Limits patient exposure.

• Reduces scatter radiation produced within the patient.

• Improves radiographic contrast by reducing scatter.

What does a beam-restricting device do to the primary beam?

It changes the shape and size of the primary beam.

What happens when collimation is increased?

Field size decreases.

What happens when collimation is decreased?

Field size increases.

What are the effects of beam restriction?

• Patient dose decreases.

• Scatter produced within the patient decreases.

• Scatter exposure to the image receptor decreases.

• Radiographic contrast increases.

What is an aperture diaphragm?

A flat piece of lead with a hole, called an aperture, displaced directly below the x-ray tube window.

Why can an aperture diaphragm cause unsharpness around the radiographic image?

Because the aperture is close to the radiation source, or focal spot, a large area of unsharpness surrounds the image.

What is a cone or cylinder?

An aperture diaphragm with an extended flange attached to it.

What feature may a cone or cylinder have to increase its length?

Its flange can telescope, increasing its total length.

Where are cones and cylinders attached?

They slide onto the tube directly below the window.

What are the advantages and limitations of cones and cylinders?

• They limit unsharpness surrounding the image.

• They come in limited sizes.

• They may not be interchangeable among tube housings.

• Cylinders are more useful than cones.

What shape of projected field do cones and cylinders almost always produce?

A circular projected field.

Where is the collimator located?

Immediately below the tube window.

How many sets of lead shutters does a collimator have?

Two or three sets of lead shutters that limit the x-ray beam.

What equipment is included in a collimator?

• A white-light source and mirror to project a light field onto the patient.

• An x-ray field measurement guide in case of light failure.

• A plastic template with crosshairs.

What is another name for an automatic collimator?

A positive beam-limiting (PBL) device.

What does an automatic collimator do?

It automatically adjusts the size and shape of the primary beam to the size and shape of the image receptor.

What is a radiographic grid made of?

Very thin lead strips or lines with radiolucent interspaces between them, designed to absorb scatter radiation emitted from the patient

What materials make up a grid?

• Thin lead strips or lines.

• Radiolucent interspace material separating the lead lines.

• An aluminum front and back panel covering the lead lines and interspace material.

What is a linear grid?

A grid in which the lead lines run in only one direction.

What is a cross-hatched grid?

A grid in which the lead lines run at right angles to one another.

What is a nonfocused grid?

A grid whose lead lines run parallel to one another.

What is a focused grid?

A grid whose lead lines are angled to match the angle of divergence of the primary x-ray beam.

What is the advantage of focused grids?

They allow more transmitted photons to reach the image receptor.

What is the convergent point or convergent line used to determine?

The focal distance of a focused grid.

What is focal distance, also called grid radius?

The distance between the grid and the convergent line or point.

What is focal range?

The recommended range of source-to-image receptor distances (SIDs) that can be used with a focused grid.

What is a stationary grid?

A grid that does not move during the exposure.

What is a wafer (slip-on) grid?

A grid that matches the size of the cassette and is placed on top of the image receptor.