Unit 1 Test Physics

An examination requires 80 mAs at 180cm SID. If the distance is changed to 90cm SID what should be the new mAs setting?

20 mAs

A grid is made with interspace material that is 600um thick. The height of the grid is 6000um. What is the grid ratio?

10:1

Which of the following grid errors would result from an improperly positioned grid?
Off-center grid
Upside down grid
Off level grid
Off focus grid

Off level grid

Scatter increases with which of the following? Choose all that apply.
Large field size
Low kvp
Large patients
High kvp

Large field size, large patients, high kvp

True or false. Scatter increases contrast on an image

False

The ability of a system to distinguish between similar tissues is called:

Contrast resolution

And underexposed radiograph would have _______ optical density.

Low

Match the description with the correct beam restriction device: Field size is determined by the distal end of the structure

Cones and cylinders

Match the description with the correct beam restriction device: Has a fixed lead opening and consistent SID

Aperture diaphragm

Match the description with the correct beam restriction device: Has the most efficient beam restriction

Collimator

True or false. The fixed KVP/variable mAs technique chart will provide more adequate penetration of the part then the variable KVP/fixed mAs.

True

Does collimation increase or decrease patient dose?

Decrease

Does collimation increase or decrease contrast?

Increase

Does collimation increase or decrease density?

Decrease

When filtration is added will scatter increase or decrease

Increase

When filtration is added does the quality of the beam increase or decrease

Increase

When filtration is added does image contrast increase or decrease

Decrease

True or false: the heart and thoracic spine of a chest x-ray would have a higher optical density than the lung fields.

False

The density control settings (+2, -2, +1), adjust what with each number?

The exposure time

Collimators help control radiation produced at a location other than the focal spot. This is called:

Off-focus radiation

What technique chart would typically produce an image with a shorter scale of contrast?

Variable kvp/ fixed mAs

Exposure technique charts are based on what?

The thickness of the anatomic part

Which grid has the ability to clean up the most scatter and has the highest patient dose?

Crossed grid

The number grid strips per centimeter is known as:

Grid frequency

The pivot point about which the x-ray tube and IR move in tomography is called the:

Fulcrum

What controls the number of x-rays produced

mA

Which of the following conditions would require a decrease in technique?
Pleural effusion
Pneumonia
Bowel obstruction
Ascites

Bowel obstruction

Which of the following types of x-rays contribute to forming the image? Choose all that apply
1.X-rays that interact with the patient and are absorbed
2.X-rays that arrive at the IR and are transmitted without interacting
3.X-rays that are scattered in th

2 and 3

An increase in mAs would result in an increase or decrease in optical density?

Increase

An increase in SID would result in an increase or decrease in optical density?

Decrease

An increase in collimation would result in an increase or decrease in optical density?

Decrease

How does KVP affect the contrast of an image? An increase in KVP causes a ___________ in contrast.

Decrease

Which of the following factors must increase when using the airgap technique? Check all that apply.
1. OID
2.kVp
3. SID
4. mAs

1, 3 and 4

Which of the following is not a prime exposure factor?
kVp
OID
Exposure time
SID

OID

You x-ray a patient and the anatomical part requires 120 KVP. Which grid ratio would be appropriate?

16:1

Mobile imaging uses _______ ratio grids.

Lower

__:__ is satisfactory for <90 kVp

8 to 1

__:__ is recommended for exams >100kVp

16 to 1

General fixed equipment uses __:__ or __:__

10 to 1 or 12 to 1

Grid strips made out of ___________ material.

Radiopaque

Interspace material made out of _____________ material.

Radiolucent

True or false: aluminum absorbs more primary x-rays

True

True or false: plastic fiber interspace material has a lower patient dose

True

True or false: aluminum material requires a higher mAs

True

True or false: grid interspace material is radiopaque

False

During magnification radiography, the OID increases while the ________ remains constant.

SID

You are attempting to x-ray a patient who cannot hold still and needs to use a short exposure time. Which factor needs to be increased as a result of this shorter exposure time?

mA

True or false: during tomography, a larger angle creates a thicker slice of anatomy.

False

Located in front of the IR so that radiation interacts with the detector before interacting with the IR

Ionization Chamber

An exit type of device that measures radiation after it passes through the IR

Phototimers

The sharpness or detail of an image is measured by:

Spatial resolution

True or false: mAs is the main factor that controls optical density

True

An image with a lot of shades of gray would be:

Low contrast

When a grid is used does contrast increase or decrease?

Increase

Which factor is increased when using a grid to maintain adequate density?

mAs

Situation: artifact produced by an improperly positioned radiographic tube.
NOT by an improperly positioned grid.
Results in.... grid cutoff across entire image, underexposed image (low OD), light image

Off-level

A tilted IR under a patient will result in a Off-_______ grid.

Level

Situation:
Grid positioned correctly.
Central ray is not centered to grid.
Problem with focused grids.
Center of focused grid must be positioned directly under x-ray tube target.
Results in....
Grid cut off across entire image.
Underexposed image (low OD)

Off center

Situation:
Problem with focused grids.
Radiographs taken at SIDs unspecified for that grid.
The farther the grid is from the specified focal distance, the more severe the grid cutoff. Positioning at proper SID more important with high ratio grids (less ex

Off-focus

Most common : grid is both off _________ and off _________.

Center focus

What grids are the most common in diagnostic radiography?

Focused grids

Higher ratio grids result in higher or lower patient dose?

Higher

mAs is increased ___% for every cm of air gap.

10

Air gap = Equivalent to using an __:__ grid.

8 to 1

air gap technique is not affective with ____ kVp

High

Airgap technique is only useful at ____ kVp and below because most scatter radiation is side scatter.

90

What controls contrast?

kVp

Key factor that controls OD

mAs

Longer SID = _________ spatial resolution

Increased

added filtration = _________ scatter and __________ image contrast.

Increased decreased

An increase in KVP will result in a _________ in contrast

Decrease

An increase in grid ratio will result in a __________ in contrast.

Increase

An increase in beam restriction will result in an ___________ in contrast.

Increase

An increase in milliampere seconds will result in an ____________ in contrast.

Decrease

Magnification radiography increases patient radiation dose by about ___x normal dose because grids are not used.

3