Factors Affecting Image Quality

Question 1

What is image quality?

Answer 1

The optimal features of an image that allow us to effectively interpret an image

Question 2

Why does the image need to be representative of the patient’s actual anatomy?

Answer 2

So that we can reduce any factors that could distort the image

Question 3

What does the inverse-square law say?

Answer 3

The further we are from the source of radiation, the less radiation we ‘re exposed to

Question 4

What happens to the density as the distance increases?

Answer 4

The density decreases

Question 5

What happens to the dose when the distance increases?

Answer 5

The dose decreases

Question 6

What is the SID?

Answer 6

The source to image distance (from x-ray tube to detector)

Question 7

What is the OID?

Answer 7

The object to image distance (from patient to detector)

Question 8

What is the SOD?

Answer 8

Source object distance (from x-ray tube to patient)

Question 9

What is the SID also known as?

Answer 9

FRD

Question 10

What is the OID also known as?

Answer 10

ORD

Question 11

What is the SOD also known as?

Answer 11

FOD

Question 12

What does FRD mean?

Answer 12

Focus to receptor distance (from x-ray tube to receptor)

Question 13

What does ORD mean?

Answer 13

Object to receptor distance (from patient to receptor)

Question 14

What does FOD mean?

Answer 14

Focus object distance

Question 15

What continues to happen when the OID is increased?

Answer 15

The x-rays continue to go in another direction as they pass through the object

Question 16

Will objects further or closer to the image receptor be magnified more?

Answer 16

Objects further away

Question 17

Should the body part being imaged be close or far from the image receptor?

Answer 17

As close to the image receptor as possible

Question 18

Why do we have to label if an image of the chest was taken AP instead of PA?

Answer 18

Because in AP, the heart will be magnified more than PA, so the radiologist knows that the increased size isn’t du to abnormalities- it’s due to positioning.

Question 19

When do we use AP for a chest x-ray?

Answer 19

If the patient can’t stand up against the wall bucky

Question 20

What is the purpose of getting the patient’s chest against the wall Bucky?

Answer 20

So we can get the heart as close to the imaging detector as possible

Question 21

What do we do to reduce the magnification?

Answer 21

Increase the SID

Question 22

What will happen to the intensity of the x-ray beam if the SID increases?

Answer 22

The intensity decreases

Question 23

If we change the SID, what factor do we have to change?

Answer 23

mAs

Question 24

What happens to the intensity in the x-ray beam if we increase the distance from the source?

Answer 24

The intensity decreases

Question 25

If you double the distance from the focus, the x-ray beam will be …. of its original intensity

Answer 25

1/4

Question 26

How can we get the same beam intensity at double the distance?

Answer 26

Increase the mAs

Question 27

In what direction should the object and image receptor be together?

Answer 27

Parallel

Question 28

In what direction should the central ray and the receptor be together?

Answer 28

Perpendicular

Question 29

What would happen if the object and receptor aren’t parallel, and if the central ray isn’t perpendicular to the receptor?

Answer 29

The image may be distorted

Question 30

Why might image distortion be done on purpose?

Answer 30

To display anatomy in a certain way, e.g. an oblique hand

Question 31

What are the consequences of the object not being parallel to the image receptor? (3)

Answer 31

The image will be distorted Different aspects of the image will be magnified The object may be elongated or foreshortened, so fractures or pathologies could be missed

Question 32

What is the consequence of the central ray isn’t perpendicular to the image receptor?

Answer 32

The image will be distorted

Question 33

What factors can contribute to unsharpness in an image? (2)

Answer 33

Patient movement Focal spot size

Question 34

Does this chest x-ray have movement unsharpness or no movement unsharpness?

Answer 34

No movement unsharpness

Question 35

Does this chest x-ray have movement unsharpness or no movement unsharpness?

Answer 35

Movement unsharpness

Question 36

Is the focal point pre-set or do we have to set it up?

Answer 36

It should be pre-set

Question 37

What is the focus?

Answer 37

The area that’s bombarded by the x-rays

Question 38

What can the focus be altered to be? (2)

Answer 38

Broad focal spot Fine focal spot

Question 39

How many anodes does the cathode have?

Answer 39

2 anodes

Question 40

When imaging a larger body part, do we use a broader or finer focal spot?

Answer 40

Broader focal spot

Question 41

When imaging a smaller body part, do we use a broader or finer focal spot?

Answer 41

Finer focal spot

Question 42

What is the issue with using a larger focal spot size?

Answer 42

The larger the focal spot size, the larger the area of penumbra (unsharpness)

Question 43

What are the issues with using a finer focal spot size? (2)

Answer 43

Finer focal spots are a more concentrated area, so more heat is produced, which could damage the anode The image is also more susceptible to motion unsharpness