6. Computed Tomography - Principles, Indications, Contraindications

Question 1

Principles:

Answer 1

Uses xrays to produce cross-sectional images (slices) of body

Different tissues = different xray attenuation (absorption+scattering) = contrast in imaging

Less dense tissue = hypoattenuation = hypodense (lungs) = dark

Denser tissue = hyperattenuation = hyperdense (bone) = bright

EMITTER of xrays rotate around the patient
DETECTOR on opposite site absorbs penetrated xrays

Question 2

Image processing:

Answer 2

Radiation changed into electrical signal and transmitted to computer system —> calculates/analyzes data from each detector in each level —> reconstructs multiple 2D cross-sectional images

Some modern CT scanners reproduce 2D computer images into 3D images

Common: scans before/after IV contrast —> enhanced tumor lesion

Question 3

Hounsfield units:

Question 4

Windowing:

Question 5

Indications:

Question 6

Contraindications:

Question 7

Types:

Answer 7

Single-slice
Multi-slice

Conventional
Helical/spiral

Dual-source

Electron-beam: cardiac imaging

CT VRT: 3D

Question 8

Advantages/disadvantages: