CT scanners - basics of operation
12 Nov 2013
The principle of CT imaging relies on measuring the transmission of kilovoltage x-rays through various angles around a patient. The reconstructed images provide ‘attenuation maps’ displaying the various linear attenuation coefficients of the anatomical structures in the body. The attenuation coefficients are converted to CT numbers (in Hounsfield units) and displayed on the monitor as varying shades of grey.
Early CT scanners acquired data at a rate of one slice per rotation with typical slice widths of 5 – 10 mm. Modern multi-slice scanners can acquire up to 320 simultaneous 0.5 mm slices resulting in faster acquisition times and improved spatial resolution with consistent image quality for reconstructions performed in any plane.
Three scanning modes are available on CT scanners: axial, helical and cine. The most commonly used is the helical mode where the couch moves at a given speed through the gantry as the attenuation data is acquired. This allows faster volume coverage and the acquisition of a volume of data from which slices can be reconstructed at arbitrary positions along the scan axis.
Until recently, the reconstruction method used in CT scanning was filtered back projection with a number of specific reconstruction kernels (from smooth to sharp) available on the scanners for different imaging tasks. In the last few years the increasing speed of computers has allowed the implementation of iterative reconstruction methods in CT with potential for dose and artefact reduction.
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Early CT scanners acquired data at a rate of one slice per rotation with typical slice widths of 5 – 10 mm. Modern multi-slice scanners can acquire up to 320 simultaneous 0.5 mm slices resulting in faster acquisition times and improved spatial resolution with consistent image quality for reconstructions performed in any plane.
Three scanning modes are available on CT scanners: axial, helical and cine. The most commonly used is the helical mode where the couch moves at a given speed through the gantry as the attenuation data is acquired. This allows faster volume coverage and the acquisition of a volume of data from which slices can be reconstructed at arbitrary positions along the scan axis.
Until recently, the reconstruction method used in CT scanning was filtered back projection with a number of specific reconstruction kernels (from smooth to sharp) available on the scanners for different imaging tasks. In the last few years the increasing speed of computers has allowed the implementation of iterative reconstruction methods in CT with potential for dose and artefact reduction.
0.5 CPD credit
Watch the video and complete the online self-reflection form. Go to my "My events to download your CPD certificates.
You must login to watch the videos to get your CPD.