1. CT BASICS AND CT BRAIN

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

3. 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

4. PARTS 1)xray tube-akin to that in a x ray machine. 2)detectors
3)gantry- which houses xray apparatus
4)patient couch
5)viewing console

5. CT scan machine

6. 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 

7. 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

8. TYPES Spiral ct- EBCT-coronary calcium measurement HRCT
uses principle of volumetric acquisiton.
no respiratory misregistration
EBCT-coronary calcium measurement
HRCT
CT cisternography and myelography

9. INDICATIONS Acute changes in mental status Focal neurologic findings
Trauma
Suspected SAH
Initial evaluation of conductive hearing loss

10. CT Advantages – Disadvantages- 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

11. CT DENSITY MEASUREMENT
Hounsfield units
Water-0HU
Air HU
Calcification HU
Fat-100HU
CSF-3HU
Grey matter-38HU
White matter-30HU
Fresh blood-70-80HU

12. 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

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

14. 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

22. 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

23. Low density
High density
Csf
Bone
Fluid
Calcification
Air
Blood
Fat
Contrast

24. I-EXTRACRANIAL TISSUE
II-CRANIAL BONES

25. III-BLOOD

26. III-VENTRICULAR SYSTEM

27. LV V3

28. IV-BRAIN TISSUE

29. V3

30. Physiologic calcifications
Chorid plexus-rare before 10yrs
Basal ganglia-rare before 40ys
Pineal gland-common after 30 yr rare before 10yr
Falx
Dentate nuclei

31. Choroid Plexus and Pineal Gland Calcifications

32. Calcification of Falx Cerebri

33. Thank You!