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CT or CAT Scan

  • Saturday, 16 May 2009 02:43
  • Last Updated Friday, 25 November 2011 01:26
CT ScannerCT imaging combines specialist x-ray equipment and computer software to produce multiple images of the brain. Because a CT scan uses an ultra-thin, low dose X-ray beam, radiation exposure is minimized but is still present. Unlike standard X-rays which take a two dimensional picture of the whole area of the body being examined, CT has the ability to image that same area of the body one cross-section or "slice" at a time. These cross-sectional images reveal more details than normal x-rays and are often used when a Brain Tumour is suspected but not yet confirmed. However MRI gives even more detailed information about brain tumours (see below) and is therefore more commonly used for follow-up after diagnosis.
Before the CT scan begins, the patient is given an injection of a special dye (contrast) material, usually into a vein in the arm. This dye helps make any abnormal tissue more obvious on the scan pictures, as the contrast material tends to concentrate in the tumour. The CT scanner is a large, box like machine with a short tunnel in the centre of it. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you will be the x-ray tube emitting x-ray beams, and a set of electronic x-ray detectors. These are located opposite each other in a ring, called a gantry. Together they measure the amount of radiation being absorbed throughout your head. At the same time as the gantry is spinning around you, the examination table is moving through the scanner, so that the x-ray beam follows a spiral path; hence this technique is called helical or spiral CT.CT Scanner

The computer workstation that processes the imaging information is located in a separate room, where the technologist operates the scanner and monitors your examination. A special computer program processes this large volume of data to create two-dimensional crosssectional images of your brain. A CT scan of the head is usually completed within 10 minutes.

3D CT SCANS

Developments in scanning technology meant that the next generation of CT scanners have greater computer speeds and multiple detectors, enabling them to obtain multiple slices with continuous table movement and a single rotation, covering the body in a matter of seconds. These scanners, called "multislice CT" or "multidetector CT" allow thinner slices to be obtained in a shorter period of time, resulting in more detailed images which can be amalgamated to give a 3D image of the brain and brain tumour.

Interpretation of Scans

A Neuroradiologist interprets the computer images produced by CT, MRI and PET scans. The pictures help establish a tentative diagnosis of tumour type and grade, indicate changes in your tumour through comparison with previous scans, or give more detailed information if a more accurate form of scanning is undertaken than on previous occasions. However, only examination of an actual sample of tumour tissue gained through a biopsy or surgical resection can provide an exact diagnosis of tumour type and grade.

Sources:

ABTA’s Primer for Brain Tumours downloaded 17.5.09 from http://neurosurgery.mgh.harvard.edu/abta/primer.htm

Colorado Springs Imaging, downloaded 18.5.09 from http://www.coloradospringsimaging.com/index.php

PatientInfo UK, downloaded 18.5.09 from http://www.patient.co.uk/showdoc/27000361/

Radiology Consultants of North Dallas, downloaded 18.5.09 from http://www.rcnd.com/AboutUs.html

Radiology Info, downloaded 17.5.09 from http://www.radiologyinfo.org/en/info.cfm?PG=headct

Image Source: 1. Wikimedia Commons, 2. Stock.xchng

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