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CancerQuest > Introduction to Patient Information > Introduction to Cancer Detection and Diagnosis > Computed Tomography (CT) > CT Scan: Imaging Results

CT Scan: Imaging Results

CT vs Conventional X-ray

Conventional x-ray lacks the ability to provide detailed information about internal structures. A major limitation of conventional x-rays is that the output is a 2 dimensional image of 3 dimensional structures. Additionally, many different body tissues have similar abilities to absorb x-rays. X-ray images are not able to detect difference between these tissues. X-ray is not an exact science and a large portion of the x-rays emitted are scattered (bounced away) from the patient, producing a less than complete image. CT resolves these problems; it can provide a 3 dimensional image of an internal structure, it can detect differences in tissue density, and the x-rays can be focused directly on specific areas, producing a clear image.⁽¹⁾

Image courtesy of the NCI

Advances in CT

Spiral/Helical Computed Tomography (SCT)

A newer version of CT, Spiral CT, is capable of producing images more rapidly than conventional CT. The patient lies on a table that moves through a large opening in the machine. The x-ray source and detectors spin around the patient. In most CT scanners the source/detector unit rotates around the patient in less than 1 second, topping out at 330ms. Each rotation of the unit produces anywhere from 16 to 64 slices depending on the machine. These slices are compiled by a computer and combined to create a high resolution 3 dimensional image. Because each rotation can produce 64 slices and takes less than 1 second, the total time needed for a complete CT scan is generally less than 1 minute.⁽²⁾

References for this page:

1. RA Robb. X-ray computed tomography: from basic principles to applications. Annual Review of Biophysics and Bioengineering. 1982;11:177-201. [PUBMED]
2. WA Kalednder. X-ray computed tomography. Physics in Medicine and Biology. 2006; 51: R29-R43. [PUBMED]