Doctor using blood pressure meter

Sensors used in medicine now

Medicine is the science concerned with the study, prevention, diagnosis and management of disease. As the popular saying goes: ‘what can be measured can be managed’. We’re expanding that saying to ‘What can be measured can be studied, prevented, diagnosed and managed’, and all the measurements in medicine are obtained from medical sensors.

These include everything from a simple thermometer used for measuring body temperature to the sophisticated Magnetic Resonance Imaging scanner used for generating images of the internal organs of the body. Based on the level of body invasion, the sensors can broadly be categorised into:

  1. Contact sensors - operate by being in contact with the skin of the patient to sense temperature, heart rate or blood oxygen content. Examples are the sensors most commonly found in homes such as a thermometer, blood pressure monitor, pulse oximeter, to name a few. Many of these are passive sensors because of their ability to operate without requiring an external power supply, making them extremely portable. They do not need direct access to the internal state of the body, making them extremely safe to use. The most upcoming trend in contact sensors includes wearable sensors (such as the FitBit and Apple Watch) that remain in contact with the skin and safely monitor body activity.

  2. Non-contact sensors - can sense certain attributes of the body from a distance and do not need invasive access to the internal state of the body. These sensors are a product of recent technological developments, such as body motion tracking using 3D cameras for analysis of biomechanics, and estimation of heart rate from face flush rate. However, this category could also include sensors that may not invade the body through an incision on the skin, but through the clever use of magnetic fields and electromagnetic waves. X-Rays scanners are used to study the bone structure of the body by passing radiation through the body. CAT (Computational Axial Tomography) scanners (which look like a giant cylinder with a hole in the middle that the patient goes into head first) use a similar technique to study cross-sections of the brain. Excessive exposure to radiation however is harmful to the body. Magnetic Resonance Imaging (MRI) is a technique that uses strong magnetic fields and radio waves to generate images of the internal organs of the body. The MRI scanner looks similar to the CAT scanner, but is extremely safe to use. Another extremely safe imaging technology is the Ultrasound scanner, popularly depicted in the media as the hand-held scanner used for visualising the baby inside a pregnant mother’s womb. Similarly fMRI (functional MRI) scanners are used for observing brain activity through blood glucose concentration levels in the brain.

  3. Invasive sensors - While contact sensors are used for everyday monitoring, non-contact sensors are used for routine monitoring, invasive sensors are generally used either for a targeted diagnosis or during a surgical procedure to monitor the intervention. These sensors require specialized training to operate and are usually used in a professional clinical setting. Sensors include optical fibre based sensors such as the Endoscopic sensors, which tend to have a slender and tubular structure. These are inserted into the body through a surface incision and help visualize the trajectory of a surgical instrument inside the body, giving the surgeon the choice of minimising surface incisions to visually observe the procedure. A surgical procedure called Arthroscopy uses this technique to operate on a body through a minimally invasive keyhole incision, greatly reducing the risk of damage to surface tissues during surgery. This is also referred to as keyhole surgery. Similar optic sensors are also used for measuring bile concentration in the stomach and for measuring the oxygen content of the blood accurately in real time. However, extreme care is required during operation of these sensors as the risks of accidents of using such sensors include internal blood clot formation, constriction of blood flow around the sensor, induced spasms in the veins and interference with other natural bodily functions.

Advances in science and technology have made such sensors possible, and medical science is currently being advanced through their use. The rate of success of disease study, diagnosis and management has improved greatly because of this and is still rapidly increasing. Today we are witnessing the perfect marriage of science, technology and medicine to create the medical sensors of the future through better sensor materials, better machine intelligence and better understand of our underlying biology.

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