Computerized Tomography in Relation to the Diagnosis of Gliomas

Abstract

Computerized axial transverse tomography (CT) is rapidly becoming an important and reliable tool for the radiographic detection of gliomas as well as other intracranial masses. The concept was developed by Mr. G. N. HOUNSFIELD (3) and has provided radiologists with a virtually non-invasive method of producing a scan of the variations in x-ray absorption in multiple sections of the brain. The system described by HOUNSFIELD consists of an x-ray tube with a collimated beam mounted on a frame directly opposite two collimated sodium iodide crystal detectors. The patient’s head is placed in a rubber cap surrounded by water which lies between the x-ray tube and the detector crystals. The x-ray beam and the detectors scan the patient’s head in a linear fashion taking 160 readings of x-ray transmission through the head. After each scan, the frame containing the x-ray tube and detector is rotated 1° and the process is then repeated. After the frame has rotated 180 and taken 160 readings for each degree of rotation, there will be a total of 28,800 readings of x-ray transmission. These readings are then processed by a mini-computer and a picture is displayed on a cathode ray tube in the form of an 80 × 80 matrix in which each point has a numerical value indicating the coefficient of absorption for a volume of material in the slice measuring 3mm × 3mm × 13mm. The absorption coefficients may be printed out on a line printer or viewed on a cathode ray tube. By varying the window width and window level on the cathode ray tube, it is possible to make accurate measurements of the coefficient of absorption of any point in the matrix.