CT BRAIN-BASICS AND ANATOMY

M3 BRAINSTORMING23/11/09

HISTORY Sir Godfrey hounsfield-1972 Nobel prize in 1979 with cormack six generation of scanners Latest 128 multidetector ct

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

PARTS

1)xray tube-akin to that in a x ray machine.

2)detectors 3)gantry- which houses xray

apparatus4)patient couch5)viewing console

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 

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

TYPES

Spiral ct- uses principle of volumetric acquisiton. no respiratory misregistration

EBCT-coronary calcium measurement HRCT CT cisternography and myelography

INDICATIONS

Acute changes in mental status Focal neurologic findings Trauma Suspected SAH Initial evaluation of conductive

hearing loss

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

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

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

Indications for non ionic contrast Prior adverse reaction BA Allergy or atopy hx <2yr RF(Cr>2) Cardiac DM Severe debilitation

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

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

Low density High density

Csf Bone

Fluid Calcification

Air Blood

Fat Contrast

I-EXTRACRANIAL TISSUE

II-CRANIAL BONES

III-BLOOD

III-VENTRICULAR SYSTEM

LV

V3

IV-BRAIN TISSUE

V3

Physiologic calcifications

Chorid plexus-rare before 10yrs Basal ganglia-rare before 40ys Pineal gland-common after 30 yr

rare before 10yr Falx Dentate nuclei