IMAGING TECHNIQUES OF BRAIN

1. NEUROIMAGING
- ASHISH BUDHWAR

2. NEUROIMAGING
 It is the process of imaging the brains structure to
assess brain functions and diagnosis.
 The study of brain is incomplete without imaging the
structure of the brain, imaging of the brain is
necessary not only for research but also for
diagnosing diseases like tumors and lesions.
 Since conventional X-rays are useless in
neuroimaging as the brain consists of more or less
similar tissues performing different functions. So
better techniques are used in brain imaging.

3. TECHNIQUES USED IN BRAIN IMAGING
 Following methods are useful in brain imaging.
1. CONTRAST X-RAY
2. COMPUTED TOMOGRAPHY
3. POSITRON EMISSION TOMOGRAPHY
4. M.R.I
5. fM.R.I

4. CONTRAST X-RAY
 It involves injecting a substance that absorbs x-rays
more or less than the surrounding brain tissues. The
injected substance then highlights the contrast
between the compartment and the surrounding
tissue during x-ray photography. Making the injected
area appear different from the surrounding tissue.
 A good example of contrast x-ray technique is the
cerebral angiography.

5. CEREBRAL ANGIOGRAPHY
 This technique involves injecting a radio-opaque dye
into a cerebral artery to visualize the cerebral
circulatory system during x-ray photography.
Cerebral angiograms are most useful to study the
brain circulation and localizing vascular damage.
Also, the displacement of blood vessels from their
normal position also can indicate the location of a
tumor.

6. CEREBRAL ANGIOGRAPHY

7. COMPUTED TOMOGRAPHY
 It is revolutionary process founded in 1970s. It combines
multiple x-rays to create a combined image of the brain.
 The machine consists of a cylindrical x-ray tube that
projects an x-ray beam through the head on an x-ray
detector mounted on the other side. The projector and
the detector automatically rotate around the head of the
patient at one level of the brain and collect several x-rays
which are combined by a computer to generate a CT
SCAN. This process is repeated for 5-7 different levels of
the patient’s brain to obtain 3-D representations of the
brain.

8. CT SCAN

9. POSITRON EMISSION TOMOGRAPHY
 It was the first brain imaging technique to provide
images of brain activity rather than brain structure.
These functional brain images are very much helpful
in the study of the brain structure and its functions.
 In a commonly used method of P.E.T, radioactive
Fluorodeoxyglucose (FDG) is injected into the
patient’s carotid artery (artery of the neck that feeds
the ipsilateral cerebral hemisphere).

10. POSITRON EMISSION TOMOGRAPHY
 Because of the similarity of FDG to GLUCOSE, the
primary source of energy to the brain, FDG is rapidly
taken up by active cells. But unlike Glucose, FDG
cannot be metabolized, so it accumulates in active
neurons or in associated astrocytes until it is
gradually broken down.
 The scan therefore images the levels of
radioactivity(indicated by color coding) in various
parts of the brain.

11. POSITRON IMAGING TOMOGRAPHY
 Therefore, if a PET scan is taken of a patient
engaging in some activity, such as reading, after FDG
is administered, the PET scan will indicate the areas
of the brain that were most active during the activity.
 PET scan are not the images of the brain, it is merely
a colored map of the amount of radioactivity present
in the particular area.
 PET scan is useful in identifying the distribution of
the neurotransmitters, receptors and transporters in
the brain.

12. PET SCAN

13. MAGNETIC RESONANCE IMAGING
 An MRI is a structural brain imaging procedure in
which high resolution images are constructed from
the measurement of radio frequency waves that
hydrogen atoms emit as they align with a powerful
magnetic field.
 An MRI provide better brain structure images than
CT. Despite this, the MRI is capable of producing
images in 3 dimensions.

14. MAGNETIC RESONANCE IMAGING

15. FUNCTIONAL MRI
 Functional MRI is the use of MRI technology to
produce functional images of the brain. fMRI has
become the most influential tool of cognitive
neuroscience and is widely used for medical
diagnosis.
 Functional MRI produces images representing the
increase in oxygen flow in the blood to active areas of
the brain. This is possible because of the two
attributes of blood in brain which are;

16. FUNCTIONAL MRI
 First, the active areas of the brain take up more
oxygenated blood than they need for their energy
requirements and thus oxygenated blood
accumulates in active areas of the brain.
 Second, oxygenated blood has magnetic properties
that influence the radio-frequency waves emitted by
hydrogen atoms in an MRI.
 The signal recorded by the fMRI is called the BOLD
signal which is Blood Oxygen Level Dependent
signal.

17. fMRI

18. ADVANTAGES OF fMRI
 fMRI has 4 advantages over PET;
1. Nothing is injected in the volunteer/patient
2. It provides both structural and functional images of
the brain.
3. It’s spatial resolution is better than PET and CT.
4. It is capable of producing 3-D images of activity
over the entire brain.

19. DISADVANTAGES OF fMRI
 The images provides by fMRI are only the images of
the BOLD signal which is very complex when related
to neural activity.
 Also the fMRI has poor temporal resolution. It takes
2-3 seconds to measure the BOLD signal and many
neural responses such as action potentials, occurs in
the millisecond range.