Normal CT BRAIN
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Transcript of Normal CT BRAIN
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RADIOLOGICAL ANATOMY OF NORMAL CT BRAIN
DR. PIYUSH OJHADM RESIDENT
DEPARTMENT OF NEUROLOGYGOVT MEDICAL COLLEGE, KOTA
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LOBES OF BRAIN
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MEDIAL SURFACE OF THE BRAIN
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CT History
SIR GODFREY N. HOUNSFIELD
• 1979 Nobel Laureate in Medicine
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COMPUTED TOMOGRAPHY (CT)
• Also known as Computer Assisted Tomography (CAT)
• The term Tomography refers to a process for generating 2D image slices of an examined organ of three dimensions (3D).
• Based on differential absorption of X- ray by various tissues.
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Structure of CT scan collimator
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TECHNIQUE
• Patient is placed on the CT table in a supine position and the tube rotates around the patient in the gantry.
• To prevent unnecessary irradiation of the orbits, Head CTs are performed at an angle parallel to the base of the skull.
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• Slice thickness may vary, but in general, it is between 5 and 10 mm for a routine Head CT.
• Intravenous contrast is not routinely used, but may be useful for evaluation of tumors, cerebral infections.
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• The degree of x-ray absorption by various tissues is expressed and displayed as shades of gray in the CT image.
• Darker shades correspond to lesser attenuation.
• The shades of gray correspond to a number on an arbitrary linear scale, expressed as Hounsefield Units(HU). (-1000 to +3000)
• WINDOWING- changing the settings to preferentially display tissues of interest in image. Eg. Bone window in cases of craniofacial trauma.
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Pure water has an HU value of ‘0’.
DESCRIPTION Approx. HU DENSITY
Calcium > 1000 Hyperdense
Acute blood 60-80 Hyperdense
Grey matter 38 (32-42) Hyperdense(light grey)
White matter 30 (22-32) Hyperdense(dark grey)
CSF 0-10 ISODENSE
Fat -50 to - 80 Hypodense
Air - 1000 Hypodense
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Low density High density
CSF Bone
Fluid (Edema) Calcification
Air Blood
Fat Contrast
Metallic Foreign Bodies
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CT ARTIFACTS
Artifacts are distortions or errors in the image that are unrelated to the object scanned .
Most common artifacts in CT are
• Motion artifacts
• Streak artifacts
• Beam hardening artifacts
• Partial volume averaging artifacts
• Ring artifacts
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MOTION ARTIFACT
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STREAK ARTIFACTSCause: Presence and movements of objects of very high density(contrast media, metallic implants,surgicalclips)
Appearance: Streaks
REMEDY:-
•Remove the offending object if possible.
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RING ARTIFACT DUE TO DEFECT IN DETECTOR SYSTEM OF THE MACHINE
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CT Scan
• Advantages –– Easy availabilty– Fast– Better for bone and acute blood,lesions of skull
base and calvarium– Calcification– Less limited by patient factors
• Disadvantages-– high radiation– poor visualisation of posterior fossa lesions
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Normal CT
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Systemic Approach to Head CT & MRI
Interpretation
• Symmetry – Compare left and right side of the cranium
• Midline – Look for midline shift
• Cross-sectional anatomy – Review anatomical landmark for each section.
– Brain tissue : gray matter, white matter , intracerebrallesions
– CSF space : ventricle (dilated or not)
– Skull and soft tissue : scalp swelling, fractures, sinuses, orbit
• Subdural windows : Look for blood collection adjacent to the skull
• Bone windows : Skull, orbit and sinuses, intracranial air
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Normal CT of Brain
• Ventricles are normal sized,
the grey versus white
distinction is clear.
• Midline is straight.
• Sulci are symmetrical on
bothsides.
• Skull is intact with no
scalp edema.
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1 day 1 year 2 years
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AXIAL SECTIONS OF CT HEAD
POSTERIOR FOSSA CUTS• Above the Foramen Magnum Level• level of the Fourth Ventricle• Above the Fourth Ventricular Level• Tentorial Cuts
Supratentorial Sections :• third ventricular level• lateral ventricular level• above the level of Lateral Ventricle
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A
B
CD
E
F
G
ABOVE THE LEVEL OF FORAMEN MAGNUM
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A
B
CD
E
F
G
AT THE LEVEL OF FOURTH VENTRICLE
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A
B
C
D
E
F
ABOVE THE LEVEL OF FOURTH VENTRICLE
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A
BC
D
E
F
G
H
I
AT THE THIRD VENTRICULAR LEVEL
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AB
C
D
E
F
G
AT THE LATERAL VENTRICULAR LEVEL
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B
A
C
D
E
F
G
ABOVE THE VENTRICULAR LEVEL
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A
B
C
D
ABOVE THE VENTRICULAR LEVEL
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Physiologic Calcification