CAT scan

1. CAT Scan/CT Scan
Computed Axial Tomography
Computed Tomography
Ravi

2. Basic principles
• Mathematical principles of CT were first
developed in 1917 by Radon
• Proved that an image of an unknown object
could be produced if one had an infinite
number of projections through the object

3. X-Rays
• photons produced by an electron beam
• similar to visible light, but higher energy!

4. X-Rays - Physics
• Associated with inner shell electrons
• As the electrons decelerate in the target through
interaction, they emit electromagnetic radiation
in the form of x-rays.
• patient between an x-ray source and a film ->
radiograph
 cheap and relatively easy to use
 potentially damaging to biological tissue

5. Basic principles
• Plain film imaging reduces the 3D patient
anatomy to a 2D projection image
• 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

6. Basic principles (cont.)
• With a conventional radiograph, information with
respect to the dimension parallel to the x-ray
beam is lost
• Limitation can be overcome, to some degree, by
acquiring two images at an angle of 90 degrees to
one another
• For objects that can be identified in both
images, the two films provide location
information

7. CT - basics
• CT's primary benefit is the ability to separate
anatomical structures at different depths within the
body.
• A form of tomography can be performed by moving
the X-ray source and detector during an exposure.
• Anatomy at the target level remains sharp, while
structures at different levels are blurred.
• By varying the extent and path of motion, a variety of
effects can be obtained, with variable depth of
fieldand different degrees of blurring of 'out of plane'
structures.

8. CT Basics

10. CT & CAT
•CAT stands for Computerized Axial Tomography
which was later changer to just CT or rather
Computerized Tomography.
•The scanners originally only did axial images
(referring to the plane of the image) but later
became able to do other planes such as coronal
or saggital imaging and can now do anything with
the block of information it collects.

11. Computed Axial Tomography
• Godfrey Newbold
Hounsfield introduced
the system to the public
in 1972
• Nobel Prize in 1979
• It looks like a donut
– Made up of a series of X-
ray sources and sensors
– Tomogram

12. Process and Procedure
• X-ray + Axial view +
Computer Imaging = CAT
Scan
• X-ray + (digital) Computer
Imaging = CT scan
• Provides cross-sectional
views and images of body
organs and structures
• Pixel, Radiodensity, Voxel,
Windowing
• Contrast Material

13. Computed Axial Tomography
• Also called CAT scanning or “CT”
• Image formed using a rotating thin beam(s) of
ionizing radiation
• Image “slices” reconstructed by computation
• The image formed is related to the subjects
density
• Image display on computer or multiple films
• New technology is multislice helical scanner

14. CT - principle
• Because contemporary CT scanners offer
isotropic, or near isotropic, resolution, display of
images does not need to be restricted to the
conventional axial images.
• Instead, it is possible for a software program to
build a volume by 'stacking' the individual slices
one on top of the other. The program may then
display the volume in an alternative manner.

15. Tomographic images
• The tomographic image is a picture of a slab of the
patient’s anatomy
• The 2D CT image corresponds to a 3D section of the
patient
• CT slice thickness is very thin (1 to 10 mm) and is
approximately uniform
• The 2D array of pixels in the CT image corresponds to an
equal number of 3D voxels (volume elements) in the
patient
• Each pixel on the CT image displays the average x-ray
attenuation properties of the tissue in the corrsponding
voxel

17. Tomographic acquisition
• Single transmission measurement through the
patient made by a single detector at a given
moment in time is called a ray
• A series of rays that pass through the patient at
the same orientation is called a projection or view
• Two projection geometries have been used in CT
imaging:
– Parallel beam geometry with all rays in a projection
parallel to one another
– Fan beam geometry, in which the rays at a given
projection angle diverge

24. diagnostic Uses
• The Head
– Hemorrhaging, cerebrovascular accidents, trauma
• The Abdomen, Pelvis, and Chest
– Cancers, pneumonia, infection
– Barium Sulfate
• The Spine and Bones
– Vertebrae, disc, spinal cord definition, and bone
density
– Indicator of Osteoporosis
• Cardiac CT angiography.

25. CT - diagnostic use
Cranial
• diagnosis of cerebrovascular
accidents and intracranial
hemorrhage
• CT generally does not exclude
infarct in the acute stage of a
stroke. For detection of
tumors, CT scanning with IV
contrast is occasionally used
but is less sensitive than
magnetic resonance imaging
(MRI).

26. CT - diagnostic use
Chest
•CT is excellent for detecting both acute and chronic
changes in the lung parenchyma.
•For evaluation of chronic interstitial processes
(emphysema, fibrosis, and so forth), thin sections with high
spatial frequency reconstructions are used - often scans are
performed both in inspiration and expiration. This special
technique is called High resolution CT (HRCT).
•For detection of airspace disease (such as
pneumonia) or cancer, relatively thick
sections and general Purpose image
reconstruction techniques may be adequate.

27. CT - diagnostic use
Abdominal and pelvic
• CT is a sensitive method for diagnosis of abdominal diseases. It
is used frequently to determine stage of cancer and to follow
progress. It is also a useful test to investigate acute abdominal
pain.
• Renal/urinary
stones, appendicitis, pancreatitis, diverticulitis, and bowel
obstruction are conditions that are readily diagnosed and
assessed with CT.
• CT is also the first line for detecting solid organ injury after
trauma.

28. CT – step by step

29. CT – step by step

30. CT – step by step

31. CT – step by step

32. Benefits:
• Painless procedure…other than needing great
deal of patience
• Alternative to catheters and other guide
camera options
• A good option for those weary of enclosed
spaces
• Usually preferred over MRI, and costs less!!!
• Improved technology has lead to Spiral and
Helical Scans…faster processes

33. Spiral and Helical Scanners
• Spiral
• Circular Path
• Constant gantry rotation and readings
• Less exposure to radiation
• Faster scan = better accuracy when patient
must hold their breath

34. Potential Risks
• Exposure to Radiation
– Reduced with Spiral Scan
• Reaction to contrast material
– Diabetics
– Isovue
• Pregnant and nursing women should not be
exposed

35. Investigating Emotionality and
Psychopathology
• Dementia
• Anorexia Nervosa
• Neurological Abnormalities
• Schizophrenia

36. THANKS

37. CT - diagnostic use
Cardiac
• With the advent of subsecond rotation combined with multi-
slice CT (up to 64-slice), high resolution and high speed can be
obtained at the same time, allowing excellent imaging of the
coronary arteries (cardiac CT angiography).
• Images with an even higher temporal resolution can be
formed using retrospective ECG gating. In this technique, each
portion of the heart is imaged more than once while an ECG
trace is recorded. The ECG is then used to correlate the CT
data with their corresponding phases of cardiac contraction.
Once this correlation is complete, all data that were recorded
while the heart was in motion (systole) can be ignored and
images can be made from the remaining data that happened
to be acquired while the heart was at rest (diastole). In this
way, individual frames in a cardiac CT investigation have a
better temporal resolution than the shortest tube rotation
time.