27 Medical Cat

Question 1

What does CAT stand for and why do we opt for it over x ray s

Answer 1

Computerised axial tomography
- computerised as computer processes signals to produce image
- axial because it’s in a plane
- tomography, tomkrhalju kwans slice

It allows us to get a 2D cross sectional slice of a patient, make a 3d image, and also differentiate between similar attenuation coefficients
- now since we can for soft tissue with contrast medium calm, but I’d you don’t want that, or want to differniate between OVERLAPPING BONES! Then a CAT scan will be needed, as x ray can’t do over,align bones

Question 2

CAT scan components

Answer 2

Horixntsl examination tray that can move in and out
Of a GANTRY, ring

• this houses an x ray tube l and oppsite to it x ray detectors
• the x ray tube rotates with the x ray detectors around the patient

2) there can be cat scanners with stationary x ray detectors all around the ring, and x ray tube moving , but wayyy more expensive

Question 3

Explain how CAT a scan works?

Answer 3

1) patient lies on the horizontal tray and is lowered into the ring at CONSTANT SPEED
2) In the ring is x ray tubes and OPPSITE to it a strip of x ray detectors, which rotate around the patient.
3) the x ray tube emits a THIN FAN SHAPED BEAM of x rays at the patient , and the x ray detectors send the resulting signals to a computer . Differnt tissues will attenuate the x rays differently based on their attenuation coeffeicjt, and the resulting x rays intensities are recorded by the x ray detectors, which send these signals to the computer to process an image
4) after one full rotation, the computer can then produce a 2D cross sectional slice of the patient .
5) after kne full rotation thr tray moves a bit, hence throughout the whole scan the x ray tube will have spiralled around the patient
6) the computer can then process all the 2 d slices to make a 3d image of the patient

Question 4

Why do patients have ti be extremely still during the cat scan

Answer 4

If they move, it will produce a blurry image as it won’t be possible to tell where the x rays came from

This could pose a problem for children etc, who wouldn’t want to be strapped and might be scarred

Question 5

Advantages of cat , disavantage if x ray

Answer 5

Can image similar attenuation coeffeint media , without need of contrast medium

Can produce a 3 d MODEL of the patient which can identify better

Question 6

Disadvantages of cat scan , advantages of x ray

Answer 6

1) specialist cat scanner is needed and is expensive
2) patient must be still, and this could be hard for children, long duration tok
3) the dosage of x ray is much more, PROLONGED beam of s ray which is much higher dose than a single beam

Question 7

Why mus the beam be thin fan shaped.

Answer 7

Allows for reduced superimposition if tissues which is the problem with x ray

The thinner the beam the thinner the slice, more accurate

Question 8

Would we use contrast medium in a cat scan?

Why would we

Answer 8

We don’t need, but if REALLY want to define then yh calm! For esa,ple blood flow

This also means we can CREATE A 3D IMAGE so it’s calm

Question 9

General advantage for scans

Answer 9

Is non invasive technique used ti idnedity anything if concern or the patient so goof