4. 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.
5. 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
6. X-RAY TUBE
1.X-ray tube & collimator
2.Detector assembly
3.Tube controller
4.High freq. generator
5.Onboard computer
6.Stationary computer
INTERNAL STRUCTURE
OF GANTRY
1)xray tube-akin to that
in a x ray machine.
2)detectors
3)gantry- which houses
xray apparatus
4)patient couch
5)viewing console
7. PRINCIPLE
1. Internal structure of an object can be
reconstructed from multiple projections of the
object.
2. Uses X rays applied in sequence of slices
across the organ
3. Images reconstructed from X ray
absorption data
4. X ray beam moves around the patient in a
circular path
5. CT scan provides a 3D display of the
intracranial anatomy built up from a vertical
series of transverse axial tomograms.
6. Each tomogram represents a horizontal
slice through the patient’s head.
Beam of light projected in two direction's,
detecting two different shadows
11. 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)
12. HOUNSFIELD UNITS
•
Hounsfield Unit (HU)- mean attenuation of x-rays by
different tissues.
•
Related to composition & nature of tissue
•
Represent the density of tissue
•
Also called as CT NUMBER
13. DESCRIPTION OF TISSUE APPROX. HU DENSITY
Air --- 1000 HYPODENSE
Fat ---70 HYPODENSE
Pure water 0 ISODENSE
CSF +8 ISODENSE
White matter +30 HYPERDENSE
Gray matter +45 HYPERDENSE
Blood +70 HYPERDENSE
Bone/calcification +1000 HYPERDENSE
22. 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
67. Bacterial meningitis
Indicatations for ct Head
before lumbar puncture-
to look for obstructive hydrocephalus-to prevent herniation
to conform meningeal involvement—by meningeal
enhancement
68. Meningitis complications suggested by seizures, altered
sensorium, focal deficits
Encephalitis- cerebral edema is seen
others
cerebral abscess
epidural/sub dural empyema
arteritis leading to infarct
hydrocephalus
seen well effaced
Gyri and sulci
Normal parenchyma
cerebral edema
74. •
Non contrast ct normal or may show
complications
•
On contrast basal enhancing exudates,meningeal
anhancement, tubeculomas with ring
enhancement,ependimitis
Basal exudate enhancement
Tuberculomas with perilesional edema
Coalising tuberculomas
76. •
Stages
vesicular stage- live stage
only hypo dense lesion with out perilesional edema/ring
enhancement
colloidal stage- perilesional edema with ring enhancement
granular stage- scolex gets calcified resulting in central hyper density
nodular stage- entire lesion gets calcified nodular stage-
vesicular stage- colloidal stage- granular stage- nodular stage-
77. •
Tuberculous granuloma neurocysticercosis
>20 mm size <20mm
large perilesional edema usually small area
irregular margine regular margin
Coalising lesions noncoalising
These findings are not pathognomic,above signs can be seen viceversa
neurocysticercosis
TUBERCULOMAs
central dot sign
Stary sky
78. 78
CT scan of the brain showing
early signs of a left middle
cerebral artery ischaemic CVE.
In this picture only loss of
definition of the gyri are seen
clearly (look at cortical surface
under red arrow and compare to
other side)
Acute Infarct
79. 79
MCA infarction: on CT an area
of hypoattenuation appearing
within six hours is highly specific
for irreversible ischemic brain
damage
Acute Infarct