Antennas in Medical Applications

Antennas are Everywhere

You might me aware of the term “Antennas” in general whether or not you understand the exact working of antenna. Where ever there is Wireless Communication, there is involvement of antenna. The shape and size of antenna might be different according to the purpose of it.

Consider the most used device of user life: A mobile phone and a television, both of these devices use wireless technology as their medium for data exchange.

So, what is the use of Antenna in a network?

There are many reasons for it, but the most important one is that they provide a simple way to transfer signal (or data) where other methods are impossible.

An interesting and very purposeful use of antenna is in medical science. A few such application is Wireless capsule endoscopy (WCE) system to capture the images of the human digestive tract and also Microwave Imaging (MWI) used in breast cancer screening and head hemorrhage detection.

Wireless capsule endoscopy (WCE):

It is generally used to record images of the digestive tract for medical applications. The main purpose for this method is to examine the area of small intestine which are not very well explored by the traditional types of endoscopy, like colonoscopy and esophagogastroduodenoscopy. These traditional techniques are painful and quite time consuming, while WCE is non-invasive and painless. Here a small capsule is need to be swallowed by the patient consisting a tiny camera onto the capsule. This camera moves along the intestinal tract and takes images, which are then transmitted to the receiver unit out of the patient’s body.

The Antenna used in capsule transmitter and on-body receiver are important components in WCE. Embedded antennas are put in the capsule cavity. While the other components are placed in the interior cavity of the capsule. The range of frequency between 400 to 600 MHz do the minimum harm to human tissue, while serving our purpose of endoscopy. For the capsule antenna to be insensitive to the human tissue magnetic antennas are preferred over electric antennas.

Antenna is looped patterned on 100 micro meter thick flexible substrate, which allows bending and wrapping around the capsule. Copper of 19micro meter thickness is used as a conductor material on substrate. The antenna does not have a ground plane in order to avoid strong mirror current, which reduces antenna efficiency.

It is quite impossible to control the orientation of the capsule during endoscopy, so the orientation is taken to be random. The result that the capsule orientation does not have a significant impact on antenna’s transmission.

Microwave Imaging (MWI):

Next medical application of antennas is in MWI whish stands for Microwave imaging which is a screening technique for detecting breast cancer and also brain hemorrhage. It uses the concept of monostatic or multi static radar-type measurements Medical Microwave Imaging (MMWI) typically comprise two stages. The first stage aims at eliminating the strong back reflection from the skin that masks the response from the embedded tumors. This is called the

skin artifact removal. The second stage aims at reconstructing the reflectivity of the inner tissues.

Antennas play an important role and strongly influence both stages of the imaging process, especially because they need to operate in close proximity of the body for link budget reasons. In fact, the faint scattered signals from tumors are additionally attenuated by the body penetration loss, while SAR considerations limit the maximum incident power. The extreme proximity of the antenna to the body requires that some otherwise overlooked antenna characteristics be properly accounted in the imaging signal post-processing.

To highlight the relevance of the near-field antenna characterization for MMWI, it makes sense to define a MMWI scenario as an example. We consider a breast cancer-screening scenario, where patient is laying in prone position, on the examination bed. It takes monostatic single antenna setup that scans around the breast. The image generated by the antenna is constructed from the antenna’s reflection coefficients measured at these antenna positions versus frequency, using a Vector Network Analyzer (VNA)

For Head and Brain Strokes this technique is used for of detection of any blood clots in the brain with the help of antennas. Ten identical slot bowtie antennas are placed wall of antenna array holder. The advantage of this antenna element design is suppressed radiation outside the imaging area, symmetry of radiated field, mechanical stiffness, and easy, and repeatable production. The front side of the realized antenna and the modules of measured reflection coefficients of all 10 antenna elements laid on the surface of a liquid head phantom.

Blog Created by:

Mugdha Dhopade

Chandsab Bangi

Sagar Shedge

Sara Chabuskwar

Sakshi Nagare