CT Basics

CT BRAIN - BASICS

Frankfurt plane plane

HOUNSFIELD UNITS •

Numeric information in each pixel of ct image

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Related to composition & nature of tissue

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epresent t e ens ty o t ssue Also called as CT NUMBER

air fat Pure water

--- 1000 ---70 0

White matter

+30

Gray matter

+45

blood

+70

Bone/cacification

+1000

CT /MRI •

I.

CT PICTURE WHITE MATTER IS DARKER THAN GREY MATTER SINCE LIPID CONTAINING MATERIAL IS RADIOLUCENT 

•

MR PICTURE GREY

T1WI

T2WI

MATTER

DARK

BRIGHT

WHITE

BRIGHT

DARK

CSF

GREY

WHITE

TO

I.

CSF IS BLACK

DARK

Step wise approach 1. Ventricles/ cisterns 2. Cortex 3. Deep gray matter 4. Focal lesions 5. Bone 6. Extracranial soft tissue 7. Para nasal sinuses

LV FRONTAL HORN

3V

OCCIPITAL HORN

FORAMEN OF MONRO

4V

TEMBORAL HORN

AQUEDUCT OF SYLVIUS

COMMON SECTIONS AXIAL SECTIONS

CORONAL SECTIONS

SAGITTAL SECTIONS

POSTERIOR FOSSA

-FRONTAL HORN LEVEL

-MID SAGITTAL LEVEL

CUTS -ABOVE THE MAGNUM

FORAMEN

LEVEL

-LEVEL OF THE

-THIRD VENTRICULAR LEVEL

FOURTH

-PARASAGITTAL LEVEL THROUGH THE LATERAL

VENTRICLE -

-MID VENTRICULAR

VENTRICULAR LEVEL

LEVEL

VENTRICULAR BODY

- TENTORIAL

SUPRATENTORIAL CUTS -THIRD VENTRICULAR LEVEL -LOW VENTRICULAR LEVEL -ABOVE THE VENTRICULAR LEVEL

-OCCIPITAL HORN LEVEL

-LATERAL ORBITAL LEVEL

ABOVE THE LEVEL OF FORAMEN MAGNUM

VA MEDULLA TONSIL INT OCC PROT

4V CM

LEVEL OF FOURTH VENTRICLE

Optic nerve CPCISTERN TEM HORN

PONS MCP

4V

LEVEL ABOVE FOURTH VENTRICLE

OLF SULCUS SYLV FISSURE

SUPRA SELLAR CISTERN 

AMB CIST

MB

4V  vermis

THIRD VENTRICULAR LEVEL

LOW VENTRICULAR

Above ventricle level

Cerebral Arterial Territory • MCA-most of lateral hemisphere, Basal

ganglia, insula, • ACA-Inferomedial basal ganglia,ventromedial

, hemispheres, 1 cm supero medial brain convexity • PCA-Thalami, midbrain, posterior 1/3of 

medial hemisphere, occipital lobe, postero medial temporal lobe

• Anterior Choroidal artery 

branch of ICA supply part of the hippocampus, the posterior limb of the internal capsule • Medial lenticulostriate arteries Branches of the A1-segment of the anterior cerebral  artery. They supply the anterior inferior parts of the basal nuclei and the anterior limb of the internal capsule . • Lateral lenticulostriate arteries Branches of the horizontal M1-segment of the middle cerebral artery . They supply the superior part of the head and the body of the caudate nucleus , lentiform nucleus and the posterior limb of the internal capsule

ACA MCA

PCA

• AICA- inferolateral

part of pons, middle cerebellar peduncle, floccular region, anterior petrosal surface of cerebellar hemisphere • PICA-posteroinferior surface of cerebellar , , • Superior cerebellar artery -superior aspect of 

cerebellar hemisphere (tentorial surface), ipsilateral superior vermis, largest part of deep white matter including dentate nucleus, pons

Water shed infarct

Cerebral ischemia •

Significantly diminished blood supply to all parts(global ischemia) or selected areas(regional or focal ischemia) of the ra n

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Focal ischemia- cerebral infarction

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Global ischemia-hypoxic ischemic encephalopathy(HIE),hypotensive cerebral infarction

Goal of imaging •

Exclude hemorrhage

•

Identify the presence of an underlying structural lesion such as tumour , vascular malformation ,subdual hematoma that can mimic stroke

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Identify stenosis or occlusion of major extra- and intracranial arteries

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Differentiate between irreversibly affected brain tissue and reversibly impaired tissue (dead tissue versus tissue at risk)

•

Infarct vs pneumbra •

In the central core of the infarct, the severity of hypoperfusion results in irreversible of  cellular damage . , in which either:  –

The critical flow threshold for cell death has not reached  – Or the duration of ischemia has been insufficient to cause irreversible damage.

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Hyper acute infarct(2 weeks)

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Old infarct(>2 months)

CT-Hyperacute infarct •

Hyperdense MCA sign-acute intraluminal thrombus

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Attenuation of lentiform nulei

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Dot sign-occluded MCA branch in sylvian fissure

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Insular ribbon sign  –grey white interface loss along the lateral insula

Dense mca sign

‘ loss of insular ribbon’

M C A DOT SIGN

ATTENUATION OF LENTICULAR NUCLEUS

CT- Acute infarct •

Low density basal ganglia

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Sulcal effacement

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Wedge shaphed parenchymal hypo density area t at nvo ves ot grey an w te matter

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Increasing mass effect

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Hemorrhagic transformation may occur -15 to 45% ( basal ganglia and cortex common site) in 24 to 48 hours

CT – sub acute infarct •

PLAIN CT

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Wedge-shaped area of decreased attenuation involving gray/white matter in typical vascular distribution

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Mass effect initially increases, then begins to diminish by 7-10 days

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H’gic transformation occurs in 15-20% of MCA occlusions, usually by 48-72 hrs

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CECT

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Enhancement patterns typically patchy

•

May appear as early as 2-3 days , persisting up to 8-10 weeks

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"2-2-2" rule = enhancement begins at 2 days, peaks at 2 weeks, disappears by 2 months

CT-chronic infarct •

Plain ct

•

Focal, well-delineated low-attenuation areas in affected vascular distribution

•

sulci become prominent; ipsilateral ventricle enlarges

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Dystrophic Ca++ may occur in infarcted brain but is very rare

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CECT: No enhancement

INFARCT / TUMOUR •

CLINICAL HISTROY

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DISTRIBUTION

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SHAPES

•

GRAY / WHITE INVOLVEMENT

•

ADVANCED IMAGING

VENOUS INFARCT •

HISTROY

•

BEYOND VASCULAR DISTRIBUTION

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HAEMORRHAGIC INFARCT

•

THORMBUS IN VENOUS SINUSES

•

SYMMETRICAL LOW ATTENUATION IN DEEP GRAY MATTER - DEEP CEREBRAL VEIN THORMBUS

EDEMA/ INFARCT •

INFARCT TYPICAL VASCULAR DISTRIBUTION GRAY MATTER INVOLVEMENT

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NOT CONFINED TO VASCULAR DISTRIBUTION MOSTLY INVOLVES WHITE MATTER

PCA INFARCT

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ACA INFARCT

WATERSHED INFARCT

Old infarct