Computed Tomography (CT) uses X-rays and mathematical analysis to produce cross-sectional images of the body. Sir Godfrey Hounsefield developed the first CT scanner in 1972. CT has gone through several generations of technological advancement, using evolving X-ray sources, detector arrays, and motion systems to improve image quality and acquisition speed. CT images provide information about tissue density measured in Hounsfield units. CT is used for diagnostic imaging and has applications like CT angiography and perfusion imaging with contrast agents.

1. Computed Tomography
-Dr Prathmesh Mishra
Sr1 Neurosurgery

2. HISTORY & INTRODUCTION
• First CT scan was developed by Sir Godfrey
Hounsefield in 1972, hayes, UK.
• Mathematical principles of CT was developed by
Radon, 1917
• Works on principle of X-rays
• Measures the density of tissues being studied

3. • Transmitted radiation is measured by detectors located
in the Gantry.
• It is a movable frame that contains the x-ray tube
including collimators and filters, detectors, Data
Acquisition System (DAS), rotational components
including slip ring systems and all associated
electronics such as gantry angulation motors.
• Lasers or high intensity lights within or mounted on the
gantry which serves as an anatomical positioning guide

4. • View the CT scan as though you were looking up at it
from the patient’s feet.
• The density at a given point on an image represents
the
x-ray attenuation properties
within the patient along a line
between the x-ray focal spot
and the point on the
detector corresponding to
the point on the image.

5. GENERATIONS OF CT
First generation CT scans
• Finely collimated x-ray beam (pencil beam) was used in
first-generation CT images.
• Single radiation detector.
• Translate-rotate motion.
• Head CT only;
not used for other parts.

6. Second Generation
• Linear array of about
30 detectors, single x-ray tube,
rotate/translate motion,
• narrow angle (10 ° ) fan beam

7. 3rd Generation
• A fan beam X-ray source is used several hundred
radiation detector
The curvilinear detector array provides constant distance
between source and each detector resulting in good
image
reconstruction.
360 degree rotate-rotate mention.

8. 4TH generations
• Fourth generation was developed principally to
suppress ring artifacts. Several thousand individual
detectors.
• The mechanical motion is rotation of the x-ray source
around a fixed detector array (rotate stationary).
• As the fan beam passes across each detector, and
image projection is acquired.
• Imaging time is 1 s or less.

9. 5th Generation
• A novel CT scanner has been developed
specifically for cardiac tomographic imaging.
• This “cine-CT” scanner does not use a
conventional x-ray tube.
• Cine-CT systems, also called electron beam
scanners, are marketed primarily to
cardiologists.

10. 6th Generation
• In the early 1990s, the design of third- and fourth-
generation scanners evolved to incorporate slip ring
technology.
• A slip ring is a circular contact with sliding brushes that
allows the gantry to rotate continually, untethered by
wires.
• The use of slip-ring technology eliminated the inertial
limitations at the end of each slice acquisition, and the
rotating gantry was free to rotate continuously

11. 7th Generation
• Multiple detector array computed tomographic (MDCT)
scanners use several, closely spaced, complete
detector arrays. With no table translation (nonhelical
acquisition), each detector array acquires a separate
axial CT image.
• Single detector – less spatial resolution
• MDCT – slice thickness depend on detector size

12. TYPES OF CT
Sequential CT :
• Single slice with single rotation of tube
• Time consuming & suboptimal resolution
Helical / Spiral CT
• Speed
• Reconstruction

13. POST-IMAGE PROCESSING
• Multiplanar reformating :
For patients who cannot be positioned properly
• 3D CT :
For spatial information / surface characteristics
facial # / anomalies
• CT Angiography :
for vascular injuries
100-120 ml contrast required

14. CT NUMBER / HOUNSEFIELD
UNIT

15. CT TERMINOLOGIES

18. • Gray matter - 35-40 HU
• White matter - 30-35HU
• Flowing blood - 40HU
• Ac Hematoma - 70-90HU ( depend on Hb)
• Calcification - >80HU
• Fat - -100HU
• CSF - 0-10HU
• Bone - +800- 1000HU

19. CONTRAST MEDIA IN CT
• Ionic contrast :
sodium / methylglucamine - hyperosmolar contrast
contrast reactions
not to be given intrathecal
• Non-Ionic contrast : nearly iso-osmolar
few contrast reactions

20. CT PERFUSION
• Iodinated contrast
• Select area of interest
• Scan repeated at interval after contrast
• Diamox challenge test with 1gm ACZ after contrast scans
• Repeated scans till 10mins
• Values calculated : CBV Cerebral Blood Volume
CBF Cerebral Blood FLow
MTT Mean Transit Time
TTP Time To Peak

21. • Ischemic Stroke : increased MTT & decreased CBF
• Stenosis : Decreased CBV CBF Increased MTT &
TTP
• Steal : Stenosis pattern after ACZ challenge
• PWI has more artifact than CTP