INTRODUCTION TO CRANIAL CT

Hospital Eva Peron

DR.LAPAL MA, DORIAN

INTRODUCTION

CT is the most useful neuroimaging study in emergency medicine it readily detects acute blood collections and intracranial lesions causing mass effect.

MRI is superior for imaging parenchymalabnormalities and has replaced CT in most nonemergency neurodiagnosis

GUIDELINES: (NICE)

• The national institute for health and clinical excellence (NICE) is a special health authority of the english nationa health service (NHS), serving, both English NHS and the Welsh NHS. It was set up as the National Institute for Clinical Excellence in 1999

The Lancet, Volume 357, Issue 9266, Pages 1391 -1396, 5 May 2001

BASIC PRINCIPALES OF CT

ATTENUATION COEFFICIENT

The ability to block x rays as they pasoothrough a substance (attenuation).For a given body tissue, the amount of attenuation is relatively constant an is known as that tissue’s attenuation coefficient.

Sir Jeffery Hounsfield: mapping of attenuation coefficient

THE CT HOUNSFIELD SCALE

WINDOWING

• It allows the CT scan reader to focus on certain tissues within a set parameters. Most CT imaging includes windows that are optimized for brain, blood and bone.

• BRAIN : W 155 L 40

• STROKE : W 30 L 30

• SUBDURAL: W 150 L 5

• BONE: W 3000 L 570

WWINDOWING

BRAIN (W 155 L 40) STROKE (W 30 L 30)

WINDOWING

BONE (W3000 L 570) SUBDURAL (W150 L 5)

HEAD CT ARTIFACTS

Effects tha can potentially inhibit the ability to accuerately interpret the images

Motion

Metal artifacts

Beam Hardening: when small amount of hypodensebrain tissue is immediately adjacent to dense bone

Partial volume: arises when the imaged area contains different types of tissue. Ej: brain and bone, an intermediate density will be represented that may have the appearace of blood

HEAD CT ARTIFACTS

HEAD CT ARTIFACTS

HEAD CT ARTIFACTS

•Oriented obliquely.•Reduces the number of slices that are degrade by artifacts.•CT: the frontal lobes are anterior, but posteriorly, the cerebelum is seen, rather than the occipital lobes

HOW TO READ A HEAD CT

HOW TO READ A HEAD CT

MNEMONIC: BLOOD CAN BE VERY BAD

• Blood: Acute (white), subacute (gray), chronic (black)

• Cisternas

• Brain:

– symmetry

– Gray-white differentiation

– Shift

– Hyper/hypodensity

MNEMONIC: BLOOD CAN BE VERY BAD (cont.)

• Ventricles:

– Dilatation

– Compression/shift

• Bone

– Fracture (asymmetry)

– Symmetry (suture)

– Air in mastoid cell