MUST FOR EVERY PHYSICIAN• CT HEAD is an extremely useful diagnostic tool used routinely in the care of A&E patients.• The treating physician needs to be able to accurately interpret and act upon certain CT findings without specialist (e.g., radiologist) assistance, because many disease processes are time dependent and require immediate action.• It has been shown that even a brief educational intervention can significantly improve the physician’s ability to interpret cranial CT scans.
SCHEME OF THE LECTURE• BASIC PRINCIPLES OF CT SCAN• NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS• ILLUSTRATIONS
HISTORY• Sir Godfrey hounsfield-1972• Nobel prize in 1979• Original scanners took approximately 6 minutes to perform a rotation (one slice) and 20 minutes to reconstruct. Despite many technological advances since then, the principles remain the same.
PARTS1) Gantry- which houses X ray apparatus2) X ray tube-akin to that in a X ray machine.3) Detectors4) Patient couch5) Viewing console
PRINCIPLE• Uses X rays applied in sequence of slices across the organ• Images reconstructed from X ray absorption data• X ray beam moves around the patient in a circular path
PRINCIPLE…..• CT scan provides a 3D display of the intracranial anatomy built up from a vertical series of transverse axial tomograms.• Each tomogram represents a horizontal slice through the patient’s head.
TECHNIQUE…..Slice thickness mayvary, but in general, it isbetween 5 and 10 mmfor a routine Head CT
BASICS….• X-RAYS ARE ABSORBED TO DIFFERENT DEGREES BY DIFFERENT TISSUES• Always describe CT findings as densities- isodense/hypodense/hyperdense.• Higher the density = whiter is the appearance• Lower the density = darker the appearance• Brain is the reference density• Anything of the density as brain= isodense• Higher density than brain= hyperdense ( skull is the best example)• Anything darker (lower density) than brain= hypodense( CSF and air are classical examples)
HOUNSFIELD UNITS• Related to composition & nature of tissue• Represent the density of tissue• Also called as CT NUMBER
air --- 1000fat ---70Pure water 0Csf +8White matter +30Gray matter +45blood +70Bone/calcification +1000
AXIAL SECTIONS OF CT HEADPOSTERIOR FOSSA CUTS-ABOVE THE FORAMEN MAGNUM LEVEL-LEVEL OF THE FOURTH VENTRICLE-ABOVE THE FOURTH VENTRICULAR LEVEL-TENTORIALSUPRATENTORIAL CUTS-THIRD VENTRICULAR LEVEL-LATERAL VENTRICULAR LEVEL-ABOVE THE VENTRICULAR LEVEL