Computerized tomography (CT) scans provide cross-sectional images of the body by using X-rays, while magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce detailed images of organs and tissue. CT scans depict bone structures more clearly than MRI, while MRI provides better soft tissue contrast and detection of certain abnormalities without radiation exposure. Positron emission tomography (PET) scans use radioactive tracers to detect metabolic activity throughout the body at a cellular level, offering highly sensitive functional imaging but with a higher cost and less spatial resolution than CT or MRI.

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4. •Computer-assisted
tomography (CAT
or CT) provides
virtual cuts through
the body based on
the signals created
by an X-ray source
that moves around
the body in the
plane.

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10. Tissue Appearance
BONE WHITE
CALCIFIED TISSUE WHITE
CLOTTED BLOOD WHITE
GRAY MATTER LIGHT GREY
WHITE MATTER MEDIUM GREY
CSF NEARLY BLACK
WATER NEARLY BLACK
AIR BLACK
The only component of brain better seen on CT scan is calcification, which
may be invisible on MRI.

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14. Nuclei of all atoms are thought to spin about an axis randomly oriented in space.
Place in magnetic field, axis of all odd-numbered nuclei(mainly hydrogen) align with
the magnetic field.
When exposed to a pulse of radiofrequency waves- axis of nucleus deviates away
from the magnetic field.
When the pulse terminates, the axis of the spinning nucleus realigns itself with the
magnetic field.
During this realignment, it emits its own radiofrequency signal.
MRI scanners collect the emissions of individual realigning nuclei and use computer
analysis to generate a series of 2-D images that represent the brain.

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APPEARENCE
BONE WHITE
WHITE MATTER LIGHT GREY
GREY MATTER MEDIUM GREY
WATER/CSF/AIR BLACK

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APPERENCE
GRAY MATTER MEDIUM GREY
WHITE MATTER DARK GREY
CSF/WATER WHITE

22. MRI Scan CT Scan
Detailed pictures in soft tissues Less detailed compared to MRI scans
Bony structures are less detailed as
compared to CT
Bony structures are more clear and
detailed
No known side effects on radiation
and very few side effects on MRI
contrast scans
Little side effects. Frequent radiations
and CT scans might rarely cause
cancer
Due to the structure and sound,
Claustrophobia patients may need to
take anaesthesia
Procedure is very simple and does
require anaesthesia
Higher cost They are less expensive than MRI
Duration of MRI scan is much longer CT scan procedure is quicker
Pts. with metal or certain medical
implants are not able to undergo
MRI’s due to the magnetic field pulses
Can be performed with no risk to
medical implants or metal

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32. •It is based on
the detection of
the products of
radioactive
decay from
radioactively
labelled tracers

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41. Injected with radio labelled
material
Gamma rays emitted
detected by scanner
Translated into 2D image
These images added
together to get a 3D image

42. SPECT PET
SINGLE PHOTON POSITRON
99MTC OR I123 11C OR 18F
SHORT HALF LIFE LONGER HALF LIFE
LESS SENSITIVE HIGHLY SENSITIVE(100 TIMES MORE
THAN SPECT)
LOW SPATIAL RESOLUTION SUPERIOR SPATIAL RESOLUTION
CHEAPER AND EASILY AVAILABLE COSTLY, NOT EASILY AVAILABLE
•SPECT is used in the early diagnosis of alzheimer’s
disease

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