89. Computed Tomographyrename
yaboiemil's version from 2016-02-04 14:50
Section1. An image in computed tomography is NOT a shadow of an X-ray on film.
2. It is the computer reconstruction of a transversal cross-section of a patients
body, using the attenuation of the x-ray to calculate the density of the tissue
and therefore discover what the internal cross section looks like.
3. There have been many generations of CT scans:
|First Generation||1 thin ray. 1 detector. Moves slowly across to produce 1 cross section.|
|Second generation||1 fanned out ray. 1 longer detector. Moves slowly across to produce 1 cross section.|
|Third generation||1 fanned out ray. 1 arched longer detector. Entire system rotates around patient to produce 1 cross section.|
|Fourth Generation||1 fanned out ray. Detectors completely surround patient. Only x-ray tube rotates around. Shorter exposure.|
|Spiral CT Scanner||Patient moved 5mm longitudinally each cross section. Combined to produce 3D image.|
4. The 3D image is produce when the patient is moved longitudinally 5mm, after every cross section is completed. This can
be assembled together to give a 3D image.
5. Hounsfield units are the units used to assess how attenuating a medium is for x-rays.
|Mu T||Attenuation coefficient of the medium|
|Mu W||Attenuation coefficient of water|
|k||constant numerical value of 1000|
Common values for mediums you should know:
|White Brain matter||30|
Clinical importance of CT scans:6. Provide good resolution of soft tissues
7. Good for planning surgery of tumors
8. Resolution can be improved by contrast agents
9. DISADVANTAGES: High dose (10mSv)
Common doses of Radiation:
|CT Scan||10 mSv|