Chapter 27.3 Cat Flashcards
What does cat stand for and what does it mean
Computerised axial Tomography
Tomography is to do with any SLICES of images
Computerised is when it uses a computer to produced the image
Axial is images taken in the axial plane
What are the main componetnd in a cat scanner?
- An X RAY TUBE
- a rotating detector opposite (can be whole but more expensive)
- a tube to house the patient with a horizontal tray that SLIDES THE PATIENT IN AT CONSATNT SPEED
Computer to process and produce image
Explain how a CAT scanner works?
1) patient is put on tray and moved in to scanner at constant speed
2) x ray tube produces a THIN FAN SHAPED BEAM OF X RAYS that is few mm thick
- This is attenuated differently due to different tissues
- and all the DIFFERENT intensities are collected by the rotating detector , SENDS TO COMPUTER
- the x ray tube rotates around the patient
- in ONE full rotation, one 2d cross sectional slice can be made
3) by the time one rotation is made the tray has moved it in a bit more. A new scan is made and a new 2d cross section is created
4) after whole scan of body done, the computer can COLLATE all the 2d slices to make a 3d image of the body WHICH can be zoomed in on or rotated
How is a 3d image made?
After one complete revolution produceinf one 2d cross section of the body, the horinxtal tray is moved a bit more closer
- as a result in the next revolution, a NEW slice is made
All these slices can be computerised into ONE 3D model!
Again all steps and KEY WORDS 6 marker
How does a Cat scan work?
Cat tube consists of a rotating x ray tube with a rotating detector band oppsite to it, a horinxtal tray that moves the patient in at constant speed, and also a tube
- patient pushed in at CONSTSNT speed
- the x ray tube produces a THIN FAN OF X RAYS (key) that are attenuated differently due to different tissues having different coeffeicmt in the body.
- these different intensities are detected by the detector and send to a computer to process
- after one full rotation a 2d slice cross section can be produced and seen
However by the time one rotation happens they move along the tray so a new can happen
Once whole body scanned all the 2d slices can be collated to produce a 3d image which can be rotated and zoomed
Why do patients have to be extremely still during cat scan
Because then it will produce a blurry image csn’t tell where x rays came from
Advantages of cat scan (disadvantage of x ray: (2) IMPORTANT
+ can be used to produce 3d models of the patient which can help identify problems better
+ can easily distinguish between soft tissues of SIMILUAR attenuation coefficients (whereas x ray you need a contrast medium which is effort)
Disadvantages of CAT SCAN (advantages of x ray) (3)
- cat scans use a prolonged beam of x ray, which is a much higher dose than a single beam for a normal x ray scan. So radiation dose much higher
- required patients to be extremely still. For children and other patients this could be VERY HARD
- much more expensive and longer than a normal x ray !
Why must a thin beam of x ray must be used in cat scan
The thin the beam is the thinner the cross sectional slice is
If the beam wasn’t thin there would be superimposition of tissues which is the problem we have with x rays, this isolated thin parts of tissue That we can get right easily and then collated them
Can contrast mediums be used in cat scans too even tho they mich easily differntiate between soft tissue ? And why?
Yes we can use it if we REALLY WANT TO ISOLATE SOMETHING LIKE BLOOD FLOW! And also create a 3 d image too
General advantage of x ray / cat scanner?
Can see abnormalities in patient without having to do anything invasive which means just cutting up body so lit not have to toucb
