IN4: Introduction to imaging

Question 1

What is the principle of X-ray?

Answer 1

1) High voltage release an e- from a cathode into a vacuum.
2) High velocity e- collides with anode.
3) 1% of resulting energy is emitted as X-ray & 99% of it is heat.

Question 2

What happens to X-rays that are not absorbed?

Answer 2

They hit the detector plate & are converted to electrical signals that are processed & digitally displayed.

Question 3

If the image is white, what is its radiodensity?

Answer 3

It’s radiopaque.

Question 4

What is the absorption of X-ray when the image is white?

Answer 4

High

Question 5

If the image is white, how many X-rays hit the plate?

Answer 5

Few X-rays

Question 6

If the image is black, what is its radiodensity?

Answer 6

It’s radiolucent.

Question 7

What is the absorption of X-ray when the image is black?

Answer 7

Low

Question 8

If the image is black, how many X-rays hit the plate?

Answer 8

a lot

Question 9

Classify tissues/substances from most to least radiodense.

Answer 9

Metal > Bone > Soft tissue/fluid > Fat > Gas/air

Question 10

Do X-rays give a 2D or 3D image?

Answer 10

2D

Question 11

What does CT stand for?

Answer 11

Computed tomography

Question 12

Does CT give a 2D or 3D image?

Answer 12

3D

Question 13

How does CT work?

Answer 13

It takes many X-rays of a section (like slicing that section).

Question 14

What does MRI stand for?

Answer 14

Magnetic Resonance Image

Question 15

What does MRI use to work?

Answer 15

Magnetic fields and radio waves

Question 16

What does MRI map?

Answer 16

The water content of the body.

Question 17

What does black mean in an MRI?

Answer 17

Low water

Question 18

What principle does ultrasound use?

Answer 18

The reflection of sound waves on tissues & the piezoelectric effect (conversion of mechanical energy to electrical energy).

Question 19

What does an hyperechoic image look like and what does it mean?

Answer 19

It looks white & means that a lot of sound waves are reflected.

Question 20

What does an hypoechoic image look like and what does it mean?

Answer 20

The image is grey & not many sound waves are reflected.

Question 21

What does an anechoic image look like and what does it mean?

Answer 21

It looks black & no sound waves are reflected.

Question 22

What are the advantages of X-ray?

Answer 22

• Mobile, cheap, quick & easy to use.

Question 23

What are the advantages of CT?

Answer 23

• High contrast resolution allows small lesions to be seen.
• No superimposition
• 3D image
• Can see different angles.

Question 24

What are the advantages of MRI?

Answer 24

• No harmful radiation
• Gives detail fo soft tissue structures
• Can help to determine chronicity of disease

Question 25

What are the advantages of ultrasound?

Answer 25

- "Live" image - Mobile - No harmful radiation - Cheap

Question 26

What are the disadvantages of X-rays?

Answer 26

- harmful radiation - Only 2D image - Superimposition means you might miss things

Question 27

What are the disadvantages of CT?

Answer 27

- Equipment is expensive - Harmful radiation - limited for large animals - not mobile

Question 28

What are the disadvantages of MRI?

Answer 28

- Expensive - not mobile - Limited for large animals - difficult to interpret

Question 29

What are the disadvantages of ultrasound?

Answer 29

- Can't scan through gas or bone - limited depth of view - only 2D - Affected by skill of operator