BIOMEDICAL INSTRUMENTATION: AN OVERVIEW

Solomon C. Nwaneri, PhD, Department of Biomedical Engineering, University of Lagos, Nigeria. E-mail: snwaneri@unilag.edu.ng

Biomedical instrumentation involves the use of measuring systems  to solve problems in humans and animals.  Humans and animals do get ill or sustain injury and need diagnosis and treatment. With the help of medical instrumentation systems, the presence of some physical quantity could be determined helping physicians to make better diagnostic decisions and judgement. In a world plagued by multifarious diseases, the benefits of biomedical instrumentation systems cannot be over-emphasized. Hence, it is imperative to have a good knowledge of how a measuring system works, as this knowledge is needed in the design and development of medical devices and equipment. 

There are primarily five major components of medical instruments. They are:

1. Measurand  

2. Sensor

3. Transducer

4. Signal conditioner

5. Display System

THE MEASURAND 

The measurand simply refers to the physical quantity that the instrument is designed to measure. For example the measurand that a thermometer is designed to measure is temperature. The measurand that a Sphygmomanometer is designed to measure is blood pressure. Generally, the body of humans and animals are the source of the measurand. 

SENSOR

The sensor is the part of the instrument that detects the biological signal. In a thermometer for instance, the sensor is what detects the temperature from the body. Sensors constitute an essential part of medical devices as without them the device will not be able to pick the measurand from the object being measured. Many biomedical sensors are generally inexpensive and readily available.  Sensors could be implantable or non-implantable. Biomedical sensors should be biocompatible and safe for use. 

TRANSDUCER

The transducer is the part of the instrument that converts one form of energy to another. The form of energy the sensor detects cannot be processed without conversion to electrical energy. A transducer consists of the sensing element and the transduction element. The major types of transducers include piezoelectric, chemical, photovoltaic, electrical, mechanical, pressure transducers etc.


SIGNAL CONDITIONING

Generally, biological signals are often very weak and contain a lot of noise. These signals need to be amplified and the noise has to be removed for the signals to be accurately processed. This is the purpose of signal conditioning. 

MICROPROCESSORS/MICROCONTROLLERS

After signal conditioning, the signals are processed by microprocessor/microcontrollers which interpret the information presented to it and sends it to the output unit. Common microprocessors/microcontrollers include PIC-18 Q40 microcontrollers, RX family, Atmel AVR etc.

DISPLAY

The results of the processed signal are usually displayed in various forms. The results can be displayed through:

  • Visual displays using LCD screens for example blood pressure monitors..
  • Audio form - Alarms
  • Printed form - ECG results are usually printed on a tracing paper.


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