Physics and Digital radiography

Question 1

The shorter the wavelength the (more or less)? The energy

Answer 1

Less

Question 2

All the following are properties of X-rays except..

No mass
Negative charge
Travel in a straight line
Penetrate all matter to some degree

Answer 2

Negative charge is false

X-rays have no charge

Question 3

What is the dose limit for occupational exposed personnel to X-rays?

Answer 3

50 mSv/yr

General public limit is 1 mSv/yr

Question 4

How can radiation dose me reduced?

Answer 4

Time
-rotate personnel/fewer repeats

Distance
-inverse square law

Shielding

Question 5

What is the inverse square law?

Answer 5

Intensity of radiation decreases with he square of the distance from the source

Eg. Double the distance -> 1/4th intensity

Question 6

If the distance between you and the x-ray source decreases from 40” to 30”, by how much does the radiation intensity change?

Answer 6

(40^2) / (30^2)

Question 7

T/F: electrons travel from cathode to anode to generate an x-ray

Answer 7

True

Question 8

The number of X-rays produced is proportional to what properties at the cathode?

Answer 8

Amount of filament current (mA) and time that current is on (s)

Question 9

T/F: doubling mAs, doubles the number of X-rays produced

Answer 9

True

Question 10

________ between anode and cathode makes the anode attract electrons.

Answer 10

Voltage (quantified as kVp, kilovolt peak)

Question 11

What effect will increasing the kVp have on an X-ray?

Answer 11

Greater voltage difference -> electrons travel faster -> higher energy

Question 12

What is a “high-frequency” X-ray?

Answer 12

Normally a current from the anode alternates positive to negative–> only positive half of the time

High-frequency means the anode is made positive all the time, producing higher yield X-rays

Question 13

When the electrons interact at the anode, they are converted into heat. How does the target not melt?

Answer 13

Made of tungsten (high melting point - 6191F)

Target spins to dissipate heat

Question 14

T/F: Exposure =blackness

Answer 14

TRUE

Question 15

An _______ radiograph is too light

Answer 15

Underexposed

Question 16

Is you have an image that is cloudy white, how could you improve it?

Answer 16

It is underexposed

1. Increase mAs -> more X-rays produced
2. Increased kVp-> higher energy and more penetration

Question 17

If you radiograph image is too dark, how can you improve it?

Answer 17

It is overexposed

1. Decrease mAs -> fewer X-rays produced
2. Decrease kVp-> lower energy, less through patient

Question 18

T/F: to increase exposure of a X-ray, kVp can be doubled

Answer 18

False

• mAs are usually doubled
• kVps are usually only changed by 16-20%, which is equivalent to doubling the mAs

Question 19

A high contrast image has ____kVp and _____mAs

Answer 19

Low; high

Question 20

A low contrast image has ______kVp and _______mAs

Answer 20

High; low

Question 21

Is a high or low contrast image used for the thorax

Answer 21

Low

Air in lungs already acts as contrast medium

Question 22

In a radiograph of a thorax using 5mAs and 100kVp, the image is very cloudy, the you want to correct the image, how should you do so?

A. 2.5mAs, 100kVp
B. 5mAs, 84kvp
C. 10mAs, 100kVp
D. 5mAs, 120kVp

Answer 22

D.

Question 23

When using a grid to reduce scatter, you need to change the mAs by _________ due to absorption of primary ray beam by lead

Answer 23

2-3x

Question 24

What is the purpose of an intensifying screen?

Answer 24

Convert X-ray photons to light photons -> expose X-ray film

Question 25

T/F: intensifying screens reduce movement artifacts, reduce patient exposure, and increase tube life

Answer 25

True

Question 26

All of these except.. would cause a radiograph to be too dark

KVp or mAs too high 
X-ray tube to close to film 
Technique set for grid, but grid not used 
Underdeveloped 
Light leak in darkroom

Answer 26

Underdeveloped

Question 27

Which of the following would cause a radiograph to be too light

KVp or mAs too high 
X-ray tube to close to film 
Technique set for grid, but grid not used 
Underdeveloped 
Light leak in darkroom

Answer 27

Underdevelopment

Question 28

The colour in a digital photograph is dependent on??

Answer 28

Wavelength of light striking a pixel

Question 29

T/F: More pixels mean better detail

Answer 29

True

This means pixels must be small enough to obtain good resolution

Question 30

What is in a DICOM file?

Answer 30

Image

Header (practice, patient, and device info)

Question 31

What type of digital radiography has an image plate in cassette-like housing?

Answer 31

Computed radiography (CR)

-cassettes must be processed in a plate reader

Question 32

What type of digital radiography has a flat panel detector?

Answer 32

Direct digital radiography (DR)

Question 33

How do DR and film differ?

Answer 33

It appears that detail is better with digital, however the inherent detail of film is better.

It is the contrast of DR that is better

Question 34

What are the advantages of digital radiography?

Answer 34

Professional image
No darkroom, film, envelope
Post processing
Teleradiology

Exposure latitude
Contrast optimization

Question 35

What is exposure latitude?

Answer 35

Extent to which a film/ image plate/ flat panel can be over or underexposed and still achieve an acceptable result

Question 36

T/F: digital imaging has exposure latitude meaning that the exposure factors are not important

Answer 36

False

Underexposure -> grainy images

Question 37

Sigificant overexposure on a digital X-ray can result in ??

Answer 37

Image dropout

Question 38

What is contrast optimization ?

Answer 38

Smoothing of the gray scale

-light areas are made darker and dark areas are made lighter

Question 39

T/F: exposure factors are lower in digital than with film-screen systems

Answer 39

False

Exposure factors are about the same