2. 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.
3. SCHEME OF THE LECTURE
• BASIC PRINCIPLES OF CT SCAN
• NORMAL NEUROANATOMY AS SEEN ON HEAD
CT SCANS
• ILLUSTRATIONS
5. 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.
6. PARTS
1) Gantry- which houses X ray apparatus
2) X ray tube-akin to that in a X ray machine.
3) Detectors
4) Patient couch
5) Viewing console
7.
8. 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
10. 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.
13. 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)
14. HOUNSFIELD UNITS
• Related to composition & nature of tissue
• Represent the density of tissue
• Also called as CT NUMBER
15. air --- 1000
fat ---70
Pure water 0
Csf +8
White matter +30
Gray matter +45
blood +70
Bone/calcification +1000
18. AXIAL SECTIONS OF CT HEAD
POSTERIOR FOSSA CUTS
-ABOVE THE FORAMEN MAGNUM LEVEL
-LEVEL OF THE FOURTH VENTRICLE
-ABOVE THE FOURTH VENTRICULAR LEVEL
-TENTORIAL
SUPRATENTORIAL CUTS
-THIRD VENTRICULAR LEVEL
-LATERAL VENTRICULAR LEVEL
-ABOVE THE VENTRICULAR LEVEL