Imaging of head and neck

Question 1

How do CT scans work?

Answer 1

X-ray source
X-rays pass through tissues
detector on opposite side

detector picks up varying amounts of X-rays depending on density of tissue structures

Question 2

How does the density of tissues affect X-rays passing through them?

Answer 2

Denser tissue
more X-rays absorbed, fewer X-rays pass through to detector

Less dense tissue
fewer X-rays absorbed, more X-rays pass through to the detector

Question 3

How does the amount of X-rays passing through the tissue affect the CT image?

Answer 3

Fewer X-rays absorbed, more X-rays passed through to detector, darker on image

More X-rays absorbed, fewer X-rays passed through to detector, lighter on image

Question 4

What is the order of the following tissues from most dense to least dense

• fluid
• bone
• fat
• soft tissue and blood

Answer 4

Bone

Soft tissue and blood

Fluid

Fat

Question 5

What is the advantage of CT over plain X-rays?

Answer 5

Can better differentiate between subtle differences in density of different tissues

Question 6

What are the advantages of plain radiography?

Answer 6

Cheap

Readily available

Low radiation

Visualising bony structures