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said one, suddenly proud of her injury.
“Yes. These are just some examples of ‘medical imaging’. With the help of these tools, a doctor can diagnose diseases and treat patients. The signals used to form images are called electromagnetic waves, which consist of electric and magnetic fields oscillating at right angles to each other. The electromagnetic waves, radio waves, infrared radiation, visible rays, ultraviolet rays, X-rays and visible rays are all segments of the electromagnetic spectrum, distributed according to their frequency and wavelength. Of these, the visible light is what helps us see and observe the world. When light is used in medical imaging, it is called optical imaging. This is what helps the doctor see things non-invasively, without actually cutting into the human body. Frequency and wavelength are important characteristics of light that our eyes can perceive. There is another special property called polarization
that helps you to see things beyond what you see!” Madhu explained.
“Huh?” they sat with their brows furrowed.
“As I said before, light
is also an electromagnetic
wave. When the electric field
component of the light travels in
a particular direction, it is said
to be polarized. If it oscillates
in the horizontal direction, the
light is said to be horizontally
polarized. The light could
also be polarized vertically or
circularly. These are called the
states of polarization. Sunlight
is a source of unpolarized
light since the vibrations are in
random directions. Polarizers
are materials used to direct
the electric field vector of light
to travel in a particular direction, decided by
Ms. Mahima Sharma BS || 163
its axis. This is what polarized sunglasses are also made of.
“This property of polarization is also very useful in medical diagnosis, where by just looking at the tissue could give out information about what is happening within the body. Take cancer for instance, as the normal cells become cancerous, it undergoes cellular changes such as an increase in number, size and content. When light is illuminated on these biological tissues, it undergoes several changes after it interacts with the tissue. The light could bounce back after striking the tissue, which is called reflection. Or the light could pass through the tissue, which is called transmission. The light could also get absorbed by the tissue or scatter in different directions. The light exiting the tissue can give information about the structure and function of the tissue based on the optical changes that occur within. You do know what tissue in
biology is, don’t you?” Madhu elaborated.
“Yes. A tissue is a group of cells. But what does polarization have to do with this?” was the prompt reply followed by a question.
“This is what we are studying in our laboratory. When you know and fix the polarization state of the light at the input, and observe the polarization state at the output, you can study how much of the polarization would have changed because of the property of the object. This gives an idea about what is inside the object,”
“Just like X-ray vision?” came a smart reply.
“Yes, you have an enhanced vision to observe something that
The electromagnetic waves, radio waves, infrared radiation, visible rays, ultraviolet rays, X-rays and visible rays are all segments of the electromagnetic spectrum, distributed according to their frequency and wavelength. Of these, the visible light is what helps us see and observe the world. When light is used in medical imaging, it is called optical imaging. This is what helps the doctor see things non-invasively, without actually cutting into the human body.