CT Brain Basics and approach

1. A Systematic Approach to CT Brain
P.R.Sai Prashanth
First Year DM PG
Department of Neurology

2. TECHNIQUE
• Patient is placed on theCT
table in asupine position
and the tube rotates
around the patient in the
gantry.
• Toprevent unnecessary
irradiation of the orbits,
HeadCTsare performed
at an angle parallel tothe
baseof the skull.

3. • Thedegree of x-ray absorption by various tissues is
expressed and displayed asshadesof gray in the CT
image.
• Darker shadescorrespond to lesserattenuation.
• Theshadesof gray correspond to anumber on an
arbitrary linear scale, expressed asHounsefield Units
(HU).
• WINDOWING-changing the settings to preferentially
display tissues of interest in image. Eg.Bone window
in casesof craniofacialtrauma.

4. Types of Windowing

5. PurewaterhasanHUvalueof ‘0’.
DESCRIPTION Approx. HU DENSITY
Calcium >1000 Hyperdense
Acute blood 60-80 Hyperdense
Greymatter 38 (32-42) Hyperdens
e (light
grey)
White matter 30 (22-32) Hyperdens
e (dark
grey)
CSF 0-10 ISODENSE
Fat -50 to -80 Hypodense
Air - 1000 Hypodense

6. Low density High density
CSF Bone
Fluid (Edema) Calcification
Air Blood
Fat Contrast
Metallic Foreign
Bodies

8. CTARTEFACTS
Artifacts are distortions or errors in the image
that are unrelated to the object scanned.
Most common artifacts in CTare
• Motion artifacts
• Streak artifacts
• Beamhardening artifacts
• Partial volume averagingartifacts
• Ringartifacts

9. MOTIONARTIFACT

10. STREAKARTIFACTS
Cause:Presenceand
movements of objects ofvery
high density(contrast media,
metallic implants,surgical clips)
Appearance: Streaks
REMEDY:-
•Removethe offending object if
possible.

12. • The high energy photons are less affected by
tissues

13. RINGARTIFACTDUETODEFECTIN DETECTOR
SYSTEMOFTHEMACHINE

14. CTScan
• Advantages –
– Easyavailabilty
– Fast
– Better for bone and acute blood,lesions ofskull
baseand calvarium
– Calcification
– Lesslimited by patient factors
• Disadvantages-
– high radiation
– poor visualisation of posterior fossalesions

16. Image Aquisition
• The desired image plane parallel to the orbito
meatal line is selected on the sagittal localizer
image.
• Posterior fossa in 2-3mm cuts to minimize
beaming artefacts and supratentorial in 5mm
cuts.

27. • *-Volume effects of orbit and petrous bone
• 93-Pericallosal artery
• 145-Optic chiasm
• 147-Pitutary stalk

30. • Star shaped supra sellar cistern
• MCA cistern
• Perimesencephalic cistern

33. • Quadrigemial cistern and ambient cistern
• 130-falx
• 123-Hyper dense choroid through monro
• 133-Lat.Ventricle
• 134-3rd Ventricle

35. • External capsule
• Claustrum
• Extreme capsule
• 148-Pineal gland calcification
• 123-Choroid plexus
• 131-Upper parts of tentorium
• 105-Vermis
• 112-Occipital lobe

43. • Bracket sign of pars marginalis is the superior
most extent of cingulate sulcus

54. • 85a-ICA
• 79a-Pterygopalatine Fossa

56. • 152-Medial end of NL duct
• 163-Clinoid process
• 147-Pit stalk
• 85a-carotid siphon

59. • 150-Lens
• *-ophthalmic artery
• 151-lacrymal gland

61. • 47A-Sup.Rectus
• 46-LPS

62. Normal Variants
• Physiological decrease in cortex volume is
called Frontally emphasized brain involution
• Physiological hyperosteosis- Steward Morel
syndrome

64. • Incomplete fusion of septum pellucidum
called Cavum of septum pellucidum

66. THANK YOU