Computed tomography

What is the function of computed tomography?

Produces cross-sectional images through anatomy

What are the advantages of using computed tomography?

Images acquired in slices

Visualises soft tissue and blood vessels

Large areas can be imaged quicker

What are the three components of a CT machine?

Gantry

Injector pump

X-ray table

What are the two components of the gantry?

X-ray tube

Detectors

What are the principles of CT scanning?

Continually rotating tube where the patient moves through

What are the functions of the detector?

Measures the amount of attenuation

Array of detectors in an arc divide the body into linear strips

Each detector is equidistant to the focal spot

Where is data stored?

Matrix or data set

Each single square is a pixel

What is the volume of tissue?

Voxel, corresponded to by each pixel

What are the units used for attenuation?

Hounsfield units

How is the image digitised?

Numbers are assigned to each detector based on the amount of attenuation

Each pixel has a numerical value based on algae attenuation

Calculations indicate the opacities of each voxel

What is slip ring technology?

Allows patient to move continually through the gantry while the x-ray tube rotates

What is spiral or helical CT?

Constant x-ray production while patient moves through gantry

What are the advantages of spiral or helical CT?

Reduces acquisition time

Continuous coverage of anatomy

Live tracking of injected contrast agents

What is dual source CT?

Uses two x-ray tubes with different kV values and two detectors

Often used for cardiac imaging

Fast temporal resolution