BASIC MEDICAL

INSTRUMENTATION SYSTEM
Presented by,
Abhyarthana Bisoyi
Assistant Professor
School of Electronic Sciences
Odisha University of Technology and Research (OUTR)
INTRODUCTION
 The primary purpose of medical instrumentation is to measure or determine the
presence of some physical quantity that may, in some way, assist the medical
personnel to make better diagnosis and treatment.
 The majority of the instruments are electrical or electronic systems, although
mechanical systems such as ventilators or spirometers are also employed.
 Certain characteristic features, which are common to most instrumentation
systems, are also applicable to medical instrumentation systems.
 Any medical instrument would comprise of the following four basic functional
components:
1. Measurand
2. Transducer/Sensor
3. Signal Conditioner
4. Display System
5. Alarm System
6. Data Storage
7. Data Transmission
GENERAL BLOCK DIAGRAM OF A MEDICAL
INSTRUMENTATION SYSTEM
MEASURAND
 The physical quantity or condition that the instrumentation system measures
is called the measurand.
 The source for the measurand is the human body which generates a variety
of signals.
 The measurand may be on the surface of the body (electrocardiogram
potential) or it may be blood pressure in the chambers of the heart.
TRANSDUCER/SENSOR
 Transducer:
 A transducer is a device that converts one form of energy to another.
 Because of the familiar advantages of electric and electronic methods of
measurement, it is the usual practice to convert into electrical quantities all non-
electrical phenomena associated with the measurand with the help of a transducer.
 For example, a piezo-electric crystal converts mechanical vibrations into an
electrical signal and therefore, is a transducer.
 The primary function of the transducer is to provide a usable output in response to
the measurand which may be a specific physical quantity, property or condition.
 In practice, two or more transducers may be used simultaneously to make
measurements of a number of physiological parameters.
 Sensor:
 Another term ‘sensor’ is also used in medical instrumentation systems.
 Basically, a sensor converts a physical measurand to an electrical signal.
 The sensor should be minimally invasive and interface with the living system with
minimum extraction of energy.
SIGNAL CONDITIONER
 It converts the output of the transducer into an electrical quantity suitable
for operation of the display or recording system.
 Signal conditioners may vary in complexity from a simple resistance
network or impedance matching device to multi-stage amplifiers and other
complex electronic circuitry.
 Signal conditioning usually includes functions such as amplification,
filtering (analog or digital) analog-to-digital and digital-to-analog
conversion or signal transmission circuitry.
 They help in increasing the sensitivity of instruments by amplification of the
original signal or its transduced form.
DISPLAY SYSTEM
 It provides a visible representation of the quantity as a displacement on a
scale, or on the chart of a recorder, or on the screen of a cathode ray tube or
in numerical form.
 Although, most of the displays are in the visual form, other forms of displays
such as audible signals from alarm or foetal Doppler ultrasonic signals are
also used.
 In addition of the above, the processed signal after signal conditioning may
be passed on to:
1. Alarm System
2. Data Storage
3. Data Transmission
ALARM SYSTEM
 The upper and lower adjustable thresholds indicates when the measurand
goes beyond preset limits.
DATA STORAGE
 Maintains the data for future reference.
 It may be a hard copy on a paper or on magnetic or semiconductor
memories.
DATA TRANSMISSION
 Using standard interface connections so that information obtained may be
carried to other parts of an integrated system or to transmit it from one
location to another.
 In most of the medical instrumentation systems, some form of calibration is
necessary at regular intervals during their operation.
 The calibration signal is usually applied to the sensor input or as early in the
signal conditioning chain as possible.
STIMULUS
 In many measurements in the medical field, some form of stimulus or
energy is given to the patient and the effect it has on the patient is
measured.
 The stimulus may be visual in the form of flash of light or audio tone or
direct electrical stimulation of some part of the nervous system.
 A typical example is that of recording of the evoked response with EEG
machine when visual/ audible stimulus is given to the subject under test.
CONTROL SYSTEM
 In some situations, it is required to have automatic control of the transducer,
stimulus or signal conditioning part of the system.
 This is achieved by using a feedback loop in which part of the output from
the signal conditioning or display device is fed back to the input stage.
 Control and feedback may be automatic or manual.
 Almost all measuring and recording equipment are now controlled by
microprocessors as this makes it possible to design equipment that requires
minimal user intervention, calibration and setup procedure.
 IN VIVO AND IN VITRO
 Measurements in the medical field can be classified into two types:
1. in vivo
2. in vitro

 In vivo measurement is made on or within the living organism itself, such