64 - CT Scan Imaging of the Thorax

Question 1

Mechanism behind computer tomography

Answer 1

Similar to X-ray (fire X-rays from a cathode-ray tube through patient), but tube and receiver rotate around patient. Detect x-rays with a scintillation crystal or gas ionisation.

Question 2

Units used in CT scanning to measure x-ray attenuation

Answer 2

Hounsfield units.

Question 3

Range of Hounsfield units between which most biological tissues lie

Answer 3

-100 to 100 Hounsfield units

Question 4

What can CT scans better differentiate than x-ray?

Answer 4

Soft tissues (EG: can see chambers of the heart, lung fissures)

Question 5

How is a CT scan taken?

Answer 5

With patient lying flat. Feet-up

Question 6

How is a CT-scan normally read?

Answer 6

From feet-up

Question 7

Answer 7

CT SCAN

Question 8

Reconstruction orientations of CT scans 1) 2) 3)

Answer 8

1) Axial - from the feet up 2) Coronal - from the front 3) Sagittal - from the left

Question 9

Divisions of thorax in a CT scan

Answer 9

Do not need to divide mediastinum, lungs into zones like you do in a CXR, as the resolution is high enough to distinguish these things

Question 10

How can mediastinum and lungs be differentiated in a CT scan?

Answer 10

Changing the contrast

Question 11

Answer 11

Cavitating lung mass

Question 12

Answer 12

Oesophageal cancer. Oesophageal wall is extremely thickened

Question 13

CT chest scan vs CXR

Answer 13

1) CT scan has good spatial resolution, and much better contrast discrimination 2) CT machine is very expensive, exposes patient to high doses of radiation