In the area of neuroscience research the brain
tomography (mental imagery) is most popular technique, and has been helpful for
the study of interior picturing of the body. In yore time,
to find the images of brain peoples have to suffer with various effort, but now
the new solution to find the images inside the brain is ‘Optical Brain imaging’
.The ability to obtaining the pictures of brain is possible because of
observing the intensity changes in back scattered light, called intrinsic
optical signals (IOS) that corresponds to fluctuations in blood oxygenation and
volume associated with neural activity.
The field of biomedical imaging of the brain has experienced rapid
growth now-a-days. These developments have been fuelled by the advances in
electronics and improved computation which revolutionized the practice of
diagnostic radiology, resulting in substantial improvement in clinical
application. So we can say that by the help of other engineering branches like
electronics and computer science, this luminous and enormous field of medical
has been fruitful.
Actually, the brain is the most important part of the body which is
responsible for all of the activities. Hence the examination and diagnosis of
brain is very important and to see the functioning of the brain the pictures of
the images are required. There are so
many ways by which one can find the images of the brain. But some of them are
costly, huge and the most important is picture quality that is not clear. The
EEG (electro encephalography) and MEG (magneto
encephalography) approaches have problems in estimating the spatial
position of the activation. Size, cost and the difficulties involved in
measuring in the bore of a magnet limit the use of MRI to specific research
applications in functional studies. The solution of these problems is ‘Optical
Brain Imaging”.
The Optical Brain Imaging (NIRS-Near Infrared) technique has proved to
be extremely successful in monitoring the physiological variability in the
analytical responses, with a reasonable spatial resolution. The method relies
on measuring the oxygen-dependant changes in the absorption spectrum of
haemoglobin to measure cerebral haemo dynamics and oxygenation changes. The
relatively low absorption of near infrared light (650-950 nm) in biological
tissue allows the non-ionizing light to penetrate through the skin and skull
and hence to sample the brain tissue under, enabling in vivo monitoring of
brain tissue. The Hitachi OT system uses a relatively simple continuous-wave
NIRS approach which allows one to measure the changes in oxy-haemoglobin
(∆HbO2) and deoxy-haemoglobin (∆HHb) concentrations.
Role of
optical fiber:-
Further
distinction is often made in the case of fiber sensors as to whether measured
act externally or internally to the fiber. Where the transducers are external
to the fiber and the fiber merely registers and transmits the sensed quantity,
the sensors are termed extrinsic sensors. Where the sensors are
embedded in or are part of the fiber and
for this type there is often some modification to the fiber itself the sensors
are termed internal or intrinsic sensors. Examples
of extrinsic sensors are moving gratings to sense strain, fiber-to-fiber
couplers to sense displacement, and absorption cells to sense chemistry
effects. Examples of intrinsic sensors are those that use micro bending losses in the fiber to sense strain, modified fiber
claddings to make spectroscopic measurements, and counter-propagating beams
within a fiber coil to measure rotation.
OIS Tomography, is
‘intrinsic’ cause it doesn’t use any other extrinsic marker like fluorescent
dyes. This technique helps light to trace CBF(cerebrum blood flow), a popular
for brain activity. Increased activity in a particular area of the brain causes
demand for resources such as ‘oxygen ‘and ‘glucose’, which triggers an increase
in blood flow to the active area. The increased metabolism and brain tissue,
which can be detected as changes in the reflectivity of incident light. Near-infrared (NIR) imaging techniques are a versatile and
increasingly popular means of studying blood flow and oxygenation in human
tissue. They exploit the significant differences in the absorption spectra of
the oxygenated and deoxygenated forms of haemoglobin at near-infrared
wavelengths. By measuring the changes in the intensity of diffusely transmitted
near-infrared light across a region of tissue. It is Possible to gain
well-localized information about blood oxygenation and hemodynamic. Optical
configuration is the application of NIR techniques to produce spatially
resolved, Two-dimensional images of changes in both oxy haemoglobin (HbO2) and
de-oxy haemoglobin (HbR).
Optical configuration is
most commonly used to observe the hemodynamic response of surface areas of the
brain to a chosen stimulus. OC has been used extensively to study the
functional activation of the motor and visual cortices as well as being used in
the studies of language processing and development.
Optical Absorption of Haemoglobin:
The change observation lies in differences between the absorption
spectra of oxy haemoglobin (HbO2) and de-oxy haemoglobin (HbR) .changes in
scattering properties are due to increased blood volume, which brings
additional fluid, cells and other blood components into the active area. Obtaining the pictures of brain is possible
because of observing the intensity changes in back –scattered light, called
intrinsic optical signals (OIS),that corresponds to fluctuations in blood
oxygenation and volume associated with neural activity. While
much information can be derived from imaging at a single wavelength, the use of
spectroscopy adds a powerful dimension: the ability to monitor metabolism
.Because the absorption spectra of HbR and HbO2 intersect at several points, it
is possible to derive the level of oxygenation in the blood, which is an
indicator of metabolic activity. Indeed, it has been shown that the time course
of IOS signals varies with wavelength, depending on whether HbR or HbO2 is the
dominant blood chromaphore. The use of three wavelengths, one where HbR is
dominant, one where HbO2 is dominant, and one at the isosbestic point where the
two spectra intersect is sufficient to determine the ratio of Hb to HbO2, and
account for changes in reflectivity due to blood volume.
By the help of some mathematical and analytical approaches we can enhanced the optical brain imaging. For the better image optimization, we can use the image processing tools and the whole system is combined in one consign with minimum hardware requirement. The optical brain imaging is one of the latest areas of research. The electronics and biomedical engineering are benefited by these fields which can solve the problems of many diseases in which the diagnosis is required like stoke, brain hammers, clotting in brain, etc.
Anoop Tiwari
Asst.Professor
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