Download - Ct brain basics and anatomy
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CT BRAIN-BASICS AND ANATOMY
M3 BRAINSTORMING23/11/09
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HISTORY Sir Godfrey hounsfield-1972 Nobel prize in 1979 with cormack six generation of scanners Latest 128 multidetector ct
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PRINCIPLE Internal structure of an object can
be reconstructed from multiple projections of the object.
Uses x rays applied in sequence of slices across the organ
Images reconstructed from xray absortion data
Xray beam moves around the patient in a circular path
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PARTS
1)xray tube-akin to that in a x ray machine.
2)detectors 3)gantry- which houses xray
apparatus4)patient couch5)viewing console
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HOW A CT SCAN IS DONE
A motorized table moves the patient through the CT imaging system
a source of x-rays rotates within the circular opening, and a set of x-ray detectors rotates in synchrony on the far side of the patient.
In axial CT, which is commonly used for head scans, the table is stationary
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In helical CT, which is commonly used for body scans, the table moves continuously as the x-ray source and detectors rotate, producing a spiral or helical scan
Data processed by computer to form image
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TYPES
Spiral ct- uses principle of volumetric acquisiton. no respiratory misregistration
EBCT-coronary calcium measurement HRCT CT cisternography and myelography
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INDICATIONS
Acute changes in mental status Focal neurologic findings Trauma Suspected SAH Initial evaluation of conductive
hearing loss
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CT 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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CT DENSITY MEASUREMENT Hounsfield units Water-0HU Air- -1000 HU Calcification- +1000HU Fat-100HU CSF-3HU Grey matter-38HU White matter-30HU Fresh blood-70-80HU
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CECT
To detect abnormal disrution caused by tumor,abscess ,infarct etc
Uses ionic or non ionic contrast(6 fold reduction in allergic reactioin 0.04%)
In normal CNS vessels,pituitary choroid and dura enhance
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Indications for non ionic contrast Prior adverse reaction BA Allergy or atopy hx <2yr RF(Cr>2) Cardiac DM Severe debilitation
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Recommedations in renal failure
CREATININE RECOMMENDATION
<1.5 Ionic/non ionic 2ml/kg upto 150ml total
1.5-2 Non ionic. If DM 1ml/kg/hr x10hr hydration
2-2.5 Non ionic, C/I for diabetics
>3 Non ionic ,only to patient receiving dialysis in 24hr
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INTERPRETATION OF CT BRAIN 1-GENERAL INFORMATION 2-EXTRACRANIAL TISSUE 3-CRANIAL BONE 4-BLOOD 5-CSF FLOW A-VENTRICULAR SYSTEM B-CISTERNS 6-BRAIN TISSUE A-MASS LESIONS B-SULCI & GYRI C-GRY & WHITE DIFFERENTIATION
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Low density High density
Csf Bone
Fluid Calcification
Air Blood
Fat Contrast
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I-EXTRACRANIAL TISSUE
II-CRANIAL BONES
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III-BLOOD
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III-VENTRICULAR SYSTEM
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LV
V3
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IV-BRAIN TISSUE
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V3
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Physiologic calcifications
Chorid plexus-rare before 10yrs Basal ganglia-rare before 40ys Pineal gland-common after 30 yr
rare before 10yr Falx Dentate nuclei
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