biomedical instrumentation paper presentation ppt

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INSTRUMENTATION & CONTROL ENGG. DEPTT.

GOVERNMENT POLYTECHNIC, GANDHINAGAR

BIOMEDICAL INSTRUMENTATION

1. Bio-electric Amplifiers

1.1 Bioelectricity.

1.2 Bioelectric amplifiers and their properties.

1.1 Bioelectricity

Ref. Book Name : Handbook of Biomedical Instrumentation ,Khandpur)

• Muscles and nerves are the two internal source which generate� electric signal in human body.

• Bioelectric potentials are generated at cellular level and source of� these potential is ionic in nature.

• A cell consist of ionic conductor separated from outer part by semi� permeable membrane , through which some ions can pass.

• Sodium (Na+), potassium(K+) and chloride (Cl-) are main ions involved� in process of producing cell potentials.

• Cell membrane allows entry of K+ and Cl- but Na+ is not allowed and is� surrounds across the membrane.

• This results in concentration of sodium ion more on outside the cell.

• A cell has negative charge along the inner surface of its membrane and� positive charge along the outer portion.

• The unequal charge distribution is result of electrochemical reactions and� process occurring within living cell and potential measured is called� resting potential.

• The cell in such condition is said to be polarized. A decrease in resting� membrane potential difference is called depolarization.

• The distribution of positively charged ions on outer surface and negatively� charged ions inside cell membrane results in difference of potential across� it and cell acts as biological battery.

• The internal resting potential within a cell is -90mv approx with reference� to outside of cell.

• When cell is excited or stimulated the outer side of cell membrane� becomes negative with respect to interior. This process is called� depolarization and cell potential changes to +20mv approx.

• Reploarization takes

place in short time when�cell regains its normal

state in which inside of

membrane is again

negative with respect to�outside.

• Repolarization is

necessary in order to re-�establish the resting�potential.

http://t3.gstatic.com/images?q=tbn:ANd9GcQg5HEip6v7ZnXzH7FlloIi9SOzJkNPoh0KsEqkAY986uSv-68n

• The excitation wave in muscle� causes its contraction.

• Every contraction of muscle results� in production if an electric voltage.

• These voltages are called action� potentials because they are� generated by action of muscles.

• After complete contraction,

repolarization takes place resulting

in relaxation of muscle and its�returning to original state.

http://books.google.co.in/books?id=C-

rbT_c69oUC&pg=PR3&dq=handbook+of+biomedical+instrumentation+by+r+s+khandpur&hl=en&sa=X&ei=fGIAT6f-�BJGIrAfH6_HfDw&ved=0CDQQ6AEwAA#v=onepage&q&f=false

1.2 Bioelectric Amplifiers and its properties

• The bioelectric signals are in millivolt which are required to be amplified.

• The following are the amplifiers used for it.

 Differential amplifier

 Instrumentation amplifier�  Carrier amplifier

 Chopper amplifier�  Isolation amplifier

1.2.1 Differential Amplifier

• These type have three input terminals out of which one is arranged at� reference potential and other two are live terminals.

• the two transistors with their respective collector resisters( R1 and R2)� form a bridge circuit.

• If the two resistors and characteristic of two transistors are identical, the� bridge is balanced and potential difference- across the output terminal is� zero.

http:// faculty.ksu.edu.sa/tuleimat/Documents/Part%202%20Amplifiers%20%20Applications.ppt

• If we apply signal at terminals 1 and 2 which are equal in

amplitude but opposite in phase with reference to the ground.�This signal is known as differential mode signal.

• Because of this signal if the collector current of t1 increases, the� collector current of t2 decreases by the same amount and vice-

• This results in difference voltage between the two output� terminals that is proportional to the gain of transistors.

• But if the signal applied to each input terminal is equal in

amplitude and is in same phase called common-mode input�signal.

• The change in current flow through both transistors will be same,� the bridge will remain balanced and voltage between output� terminals will remain zero.

• Thus, the circuit provides high gain for differential mode signal� and no output for common mode signals.

1.2.2 Instrumentation Amplifier

• Instrumentation amplifier is a precision differential voltage gain device.

• It consist of 3 op-amps and 7 resistors.

• The amplifier A1 and A2 works as a buffer amplifier. And A3 will act as� differential amplifer.

• Basically, connecting a buffered amplifier to basic differential amplifier� makes an instrumentation amplifier.

http:// www.ece.msstate.edu/courses/design/2007/autopilot/SD2_final_document.pdf

• A3 op-amp and its four equal R form a differential amplifier with gain� of 1.

• The variable resistor Rvar is varied to balance out any common -� mode voltage.

• V1 is applied to positive input terminal and V2 to negative input� terminal.

• The output of both the op-amps is amplified and fed to A3.

• V0 is proportional to difference between the two input voltages.

1.2.3 Carrier Amplifier

• A carrier type of amplifier is used to obtain zero frequency� response of dc amplifier and stability of capacitance coupled

• It consist of oscillator and capacitance amplifier.

• The oscillator is used to energize transducer with an alternating� carrier voltage.

• Therefore output of transducer will be amplitude (AM) signal.

Strain gauge� transducer

Carrier oscillator

amplifier rectifier

Phase sensitive

Direct writing

• The modulated AC signal is then fed to multi- stage capacitance� coupled amplifier.

• The first stage produces amplification of AM signal.

• The second stage only respond to signal frequency of carrier.

• After amplification, signal is demodulated in phase- sensitive� demodulated circuit.

• This helps to extract amplified signal voltage after filter circuit.

• The voltage produced by demodulator is given to recorder .

1.2.4 Chopper Amplifier

• This type of amplifier make use of chopping device, which

converts slowly varying direct current to an alternating form with

amplitude proportional to input direct current and with phase

dependent on polarity of original signal.

• The alternating voltage is then amplified by ac amplifier whose� output is rectified back to get an amplifier direct current.

• This is done to reduce drift problem using for narrow bandwidth.

Low pass filter�R 2 R2

2 nd stage amplifier

Ac amplifier

demodulator

• The amplifier gets low dc offset voltage and bias current by chopping� low frequency components if input signal then amplifying this� chopped signal in ac amplifier A1.

• Output of ac amplifier is then demodulated.

• The low frequency components are derived form input signal by� passing it through low-pass filter.

• The filter output is then amplified in second stage amplifier A2.

• The output is the differential amplification of high frequency and low� frequency signals.

1.2.5 Isolation Amplifier

• Isolation amplifier are used for providing protection against� leakage currents.

• They break the ohmic continuity of electric signals between input� and output of amplifier.

• Three methods are used in it

1. Transformer isolation

2. Optical isolation

3. Capacitive isolation

1.2.5.1 Transformer isolation

• It uses either frequency-modulated or pulse-width modulated� carrier signal with 30kHz as carrier signal.

• It consist of internal dc to dc converter having 20KHz oscillator,� transformer, rectifier and filter to supply isolated power.

http:// farm1.static.flickr.com/119/311074942_ee65522dfb.jpg

1.2.5.2 Optically isolated amplifier

• Here isolation is achieved by optically.

• A separate battery operated circuit supplies power to the patient

circuit and signal of interest is converted into light by bight source LED.

• The light falls on phototransistor on output side, which converts light� signal into electrical signal.

1.2.5.3 Capactively coupled isolated amplifier

• It uses digital encoding of input voltage and frequency modulation to� send the signal across differential capactive barrier.

• Separate power supply is needed on both sides of barrier.

2.0 Medical Electrodes and transducers:

• 2.1 ECG, EEG, EMG medical electrodes.

• 2.2 Working Principle of following Biomedical Transducers:

− 2.2.1 Body Temperature transducers.

− 2.2.2 Blood Pressure Transducer� − 2.2.3 Blood Flow Transducer� − 2.2.4 Pulse Transducers� − 2.2.5 Respiration Transducer

2.1 Electrodes for ECG

1. Limb electrodes:

• They are rectangular or circular� surface electrodes.

• They are applied to the surface of� the body with electrode jelly.

• They offer 2 to 5K Ω.

• The electrodes are held in� position by elastic strap.

• They are called limb electrodes as� they are best suitable for

application in four limbs of body.

http://een.iust.ac.ir/profs/Behnam/MedEngPrinc/Electrodes_Ch%�205.ppt

2. Floating electrodes

• The interface can be stabilized by use of floating electrodes in

which metal electrode does not make direct contact with the skin.

• The principle of this electrode is to eliminated movement artifact� by avoiding any direct contact of the metal with skin.

• The only conductive path between metal and skin is electrolyte� paste or jelly which forms an electrolyte brigde.

Commonly Used Biopotential Electrodes

Double-sided

Adhesive-tape

(a)� Snap coated with Ag-AgCl External snap

Electrolyte gel�in recess

(b) Reusable

Gel-coated sponge

Plastic cup

Plastic disk

Tack Dead cellular material�Capillary loopsGerminating layer

Floating Electrodes

http://een.iust.ac.ir/profs/Behnam/MedEngPrinc/Electrodes_Ch%205.ppt

3. Pre gelled disposable�electrode

• The main design feature of these� electrodes which helps in

reducing the possibility of�artifacts, drift and baseline�wandering is the provision of�high- absorbency buffer layer�with isotonic electrolyte.

• This layer absorbs the effect of� movement of electrode in

relationship to the skin and�create polarization similar to�half-potential.

• It consist if large disk of plastic foam material with silver plated disk on� one side attached to silver-plated snap.

• A lead wire with snap is then snapped on to the electrode and used to� connect the assemble to monitoring system.

• The silver plated disk serves as electrode and may be coated with Agcl� layer.

• A layer of electrolyte gel covers the disk.

• The electrode side of foam is covered with an adhesive material that is� compatible with skin.

4. Air jet ECG electrodes

• Air jet electrodes are Ag-Agcl electrodes encased within a medical� silicon cup bounded by skin - engaging rim.

• The contact area is a layer of synthetic sintered carbon by titanium� screw.

• Ambient air is drawn to small compressor and passed to electrodes at� constant of 3.8 psi.

• As the air passes through venturi air jets the electrodes [produce� constant vaccum of 2psi at contact.

• The constant vacuum allows� electrodes to remain attached� to body.

• The system uses a compressor� to pump ambient air into

distribution box.

• From the distribution box, ten� pvc wires carry air and

stainless lead wires to the air�jet electrodes.

2.1 Electrodes for EEG

• Chloride silver disc mainly used for EEG.

• Contact with scalp is made via electrolytic paste through washer.

• A pad electrode which is made from silver rod belled out at the� end and padded with sponge material.

• It is screwed into an insulated mount and held in place on head� with rubber cap.

• Another type EEG electrodes consist of multiple fine chloride silver� wires fixed in rigid plastic cup.

• The plastic cup is fixed to the� scalp with an adhesive.

• It is filled with jelly through a� hole in top.

• In this electrode , contact with� tissue is made via electrolyte� bridge so that jelly in contact

with electrode metal is not

distributed by scalp movement.

2.1 Electrodes for EMG

• Needle electrodes for EMG

consist of fine insulated�wires placed so that their�tips are in contact with�nerve , muscle or other�tissue.

• The remaining part of wire� is covered with some form� of insulation to prevent� shorting.

• The wires are either surgically implanted by means of hypodermic� needle, leaving the wire electrode in place.

• With this type of electrode the metal electrolyte interface takes� place between uninsulated tip of wire and the electrolytes of� body.

• The hypodermic needle is sometimes part of electrode.

• The wires forming the electrodes are carried inside the needle

which creates the hole necessary for insertion protects the wires�and act as grounded shield.

• A single wire inside the needles serves as unipolar electrode� which measures potentials at point of contact with respect to� some indifferent reference.

2.2.1 Body temperature transducers

The following transducers can be used to measure body

temperature:

Thermocouples

Electrical resistance thermometer

Thermistors

Radiation thermometry

2.2.1.1 Thermocouples

• When two wires of different materials� are joined together at either end ,

forming two junctions which are

maintained at different temperatures,�thermo- emf is generated causing a

current flow around the circuit. this

arrangement is called thermocouple.

• The junction at higher temperature is� termed as hot or measuring junction

and other is lower temperature called�cold or reference junction.

http://images.brighthub.com/61/D/61D7EA338D54D6291D91FDBDBEBB99E74BA0F5E1_large.jpg

• The thermal emf and current produced is proportional to the� temperature difference existing between the junctions.

• Therefore, we get temperature measurement by inserting one

junction in or on the surface at medium whose temperature is to be�measured and keeping other at lower and constant temperature.

• Measurable emf is produced proportional to temperature difference� between the two junctions.

• The reference junction is held at 0 c inside a vacuum flask containing� melting ice.

2.2.1.2 Electrical resistance thermometer

• The temperature dependence of

resistance of certain metals makes

it convenient to construct

temperature transducer.

• Platinum or nickel are used for� measurement of skin, rectal and

oesophageal temperature.

• The measurement of resistance is� carried out by using Wheatstone

http://sengerandu.files.wordpress.com/2011/06/image005.gif

• The variable resistance made from constantan which has a very� low temperature coefficient of resistance.

• The measuring coil and its connecting leads are place in one� arm of bridge circuit with dummy pair of leads connected in� opposite arm.

• In this way, changes in resistance of coil leads with ambient� temperature are cancelled out by corresponding changes in

compensating leads.

2.2.1.3 Thermistors

• Thermistors are oxides of metals like manganese, cobalt and� nickel which have large negative temperature coefficient of� resistance that is as resistance decreases temperature will� increases.

• Operational amplifier circuit may be used to measure the� current in thermistor as function of temperature.

• They are available as wafers required for applying to skin surface� , rods which can be used for rectal , oral or similar insertions and

tiny beads so small that they can be mounted at tip of

hypodermic needle for insertion into tissues.

http://cache.daylife.com/imageserve/0emacdgePAbQe/280x516.jpg

2.2.1.4 Radiation thermometry

• Any material placed above absolute zero temperature emits� electromagnetic radiation from its surface.

• The cooler the object the lower the frequency of emitted� electromagnetic waves and less power emitted.

• The detector used for measuring the emitted infrared radiations� are thermopiles, pyroelectric sensors, photoconductive cells.

• A pyroelectric sensor is used to measure tympanic membrane� temperature measurement.

• A pyro electric sensor develops an electric charge that is funciton of� its temperature gradient.

• Temperature variation from infrared light striking the crystal

changes the crystalline orientation, resulting in development of an

electric charge.

2.2.2 Blood pressure transducer

• The basic principle behind all the pressure transducer is that the

pressure to be measured is applied to flexible diaphragm which gets�deformed by the action of pressure exerted on it.

• This motion of diaphragm is then measured in terms of an electrical� signal

• The diaphragm is a thin flat plate of circular shape, attached firmly by� its edge to wall of containing vessel.

• The most commonly used pressure transducers which make use� of diaphragm are of following types:

 Capacitance manometer: in which diaphragm forms one plate of� capacitor.

 Differential transformer: where diaphragm is attached to core of� differential transformer

 Strain gauge: where the strain gauge bridge is attached to� diaphragm.

2.2.2 .1Capacitance manometer

• In capacitance manometer a change in distance between the plates� of capacitor changes its capacitance.

• One of the plate is metal membrane separated from fixed plate by� air.

• Changes in pressure that change the distance between the plates� thereby change the capacitance.

• If this element is contained in high frequency resonant circuit the� changes in capacitance vary the frequency of resonant circuit to� produce a form of frequency modulation.

• With suitable circuitry , blood pressure information can be obtained� and recorded .

http://www.omega.com/literature/transactions/volume3/images/highfig06.gif

2.2.2 .2 Differential transformer

• In this device two secondary coils are wound oppositely and� connected in series.

• If the spring - loaded core is symmetrically positioned the

induced voltage across one secondary coil opposes the voltage�of other.

• Movement of core changes this symmetry and the result is a� signal developed across the combined secondary coil.

http://accessscience.com/loadBinary.aspx?aID=9311&filename=704500FG0010.gif

2.2.2.3 Strain gauge

• The principle of strain gauge is that� if a very fine wire is stretched its

resistance increases.

• If voltage is applied to the

resistance the resulting current

changes with resistance variation

according to ohm’s law.

• Thus forces responsible for the

strain can be reduced as function of�current.

http://sub.allaboutcircuits.com/images/00432.png

• Four strain gauges are mounted on diaphragm or membrane and� these resistance are connected to form a bridge circuit.

• Initially all resistances are equal when no pressure or strain is� applied.

• The gauges are attached to the pressure diaphragm in such a a

way that as the pressure increases two of them stretch while other�two contract.

• When pressure changes unbalance the bridge a voltage appears� between output terminals proportional to the pressure.

2.2.3 Body flow transducer

Ref. Book Name : Medical Instrumentation , John webster

1. Magnetic blood flow meter:

Magnetic blood flow meter are based on the principle if magnetic

• A permanent magnet or electromagnet placed around the blood

vessel generate a magnetic field perpendicular to direction of

blood flow.

• The voltage induced in moving blood column is measured with

stationary electrodes located on opposite sides of blood vessel and

perpendicular to the direction of magnetic field.

http://clinical.medicalengineer.co.uk/diagrams/elecflow.jpg

• In block diagram of blood flow meter , the oscillator is used a� control signal to gate as well as to drive magnet.

• Signals obtained from probes are passed to preamplifier and then� to gate.

• The gated detector makes the polarity of output signal reverse� when flow direction reverse.

• The flow pulses are obtained at output of gate detector which can� be filtered to obtain average flow.

2. Ultrasonic blood flow meter:

In ultrasonic blood flow meter, a beam of ultrasonic energy is

used to measure velocity of flowing blood.

This can be done by two methods:

Transit -time method

Doppler method

 In transit time, a pulsed beam is directed through a blood vessel at� small angle and its transmit time is then measured.

 A short pulse is transmitted alternately in the upstream and� downstream directions.

 The difference between upstream and downstream transit time is� proportional to velocity of flowing blood.

 In Doppler type : oscillator operating at frequency of MHz� excites a piezoelectric transducer.

• This transducer is attached to the wall of blood vessel and

sends ultrasonic beam with frequency into the flowing blood.

• A small part of transmitted energy is scattered back and is� received by second transducer arranged opposite side.

• Because scattering occurs mainly as result of moving blood cells� the reflected signal has different frequency due to doppler� effect.

• The doppler frequency is proportional to velocity of flowing� blood.

http://clinical.medicalengineer.co.uk/diagrams/ultrasound.jpg

2.2.4 Pulse transducer

The pulse transducer measures the volume of blood.

The method used for detection of pulse changes due to blood flow

Electrical impedance changes

Strain gauge

Optical change

• In impedance method , volume� changes in segment of limb are� reflected as impedance changes.

• These impedance changes are due� to changes in conductivity of� current path with each pulsation of� blood.

• Electrodes contact the skin through� suitable electrolyte jelly or paste to� form an electrode interface and to� remove the effect of skin

resistance.

http://www.usra.ca/files/images/generation.jpg

• In strain gauge method , volume change is measured as

change in diameter at certain cross section of finger , toe or�other segment of body.

• Change in diameter is sensed through use of mercury strain� gauge in which it consist of segment of small diameter elastic

tubing wrap around the limb.

• With each pulsation of blood that increases the diameter of� the limb the strain gauge expands thus increasing its� resistance.

• In optical method , the device operates on principle that

volume changes in limb, result in changes in the optical density�through and beneath the skin.

• A light source in an opaque chamber illuminates small area of� fingertip or other region to which transducer is kept.

• Light scattered and transmitted through the capillaries of region� is picked by photocell.

• As capillaries fill with blood the blood density increases thereby� reducing amount of light reaching the photocell.

• The result causes resistance changes in photocell that can be� measured on Wheatstone bridge.

2.2.5 Respiratory transducer

The following are used to measure the respiratory

Displacement method

Thermistor method

Impedance pneumograph

2.2.5.1 Displacement method

• The respiratory rate can be determined by changes in the� thoracic volume.

• These changes can be sensed by means of displacement

transducer like strain gauge or variable resistance element.

• The transducer is held by elastic band, around the chest.

www.vhlab.umn.edu/~bmen3701/Documents/Biopac8.pdf

• The respiratory movement result in resistance changes of

strain gauges element connected as one arm of Wheatstone�bridge circuit.

• Bridge output varies with chest expansion and yields signals� corresponding to respiratory rate.

• Changes in the chest circumference can be detected by rubber� tube filled with mercury.

• With the expansion of chest during inhale, the rubber tube� increases in length and thus resistance of mercury from one� end of this tube to other changes.

2.2.5.2 Thermistor method

• Since air is warmed during its passage through lungs and the� respiratory tract, there is temperature difference between� inspired and expired air.

• This temperature difference can be sensed by using thermistors� placed in front of nostrils by means of suitable holding device.

• In case the difference in temperature of outside air and that of

expired air is small the thermistors can be initially heated to some�temperature and variation of its resistance with respect to�respiration rate can be detected.

• Exhalation causes cooling effect to thermistor temperature vary.

http://www.vhlab.umn.edu/~bmen3701/Documents/Biopac8.pdf

2.2.5.3 Impedance pneumograph

• This is indirect method which gives relation between respiration� rate and thoracic impedance change.

• This method consist of high frequency current oscillator , which� is passed to electrodes placed on surface of body and detecting� the modulated signal.

• The output from the oscillator is applied to two outer� electrodes.

• The frequency modulated signal is then amplified and given to� demodulator circuit.

http://www.zuniv.net/physiology/book/images/13-2.jpg

2.2.5.4 Co2 method

• The measurement is based on absorption property if infrared� rays by gases like co2.

• When the infrared rays are passed through the expired air� containing co2, some of rays are absorbed by it.

• There is proportion heat loss with rays the detector changes� heat loss effect into electrical signal.

http://www.capnography.com/images/Physics/IR.gif

• The detector has two identical portions separated by thin flexible� metal diaphragm.

• Because of absorption of co2 in analysis cell beam falling on test� side of detector is weaker than reference side.

• The gas in reference side is more heated than test side.

• As a result diaphragm is pushed slightly to analysis side of� detector.

• The infrared beams are chopped at 25Hz and alternating signal� which appears across detector is amplified and recorded.

3.0 Electrocardiograph:

3.1 The ECG waveform.

3.2 The standard lead system.

3.3 Block Diagram and working principle of ECG

3.4 ECG preamplifiers

3.5 ECG machine faults and troubleshooting.

3.6 Cardiac stimulation and life support equipment-

• Defibrillators, Defibrillator circuits, Cardio-version

• Pacemaker, pacemaker classification

3.1 The ECG waveform

• Each action potential in the heart originates near the top of right� atrium at a point a called Sino atria (SA)node.

• The pacemaker is group of specified cells that generate action� potentials at regular rate.

• To initiate the heart beat the action potentials generated by SA� node propagate in all directions along the surface of both atria.

• The wave front of activation travels parallel to surface of atria� toward junction of atria and ventricles.

http://www.sads.org.uk/heart.jpg

• The wave terminates at point near center of heart called� atriventricular(AV) node.

• t this point some special fibers act as” delay line” to provide� proper timing between action of atria and ventricles.

• After delay line, the excitation spread to all parts of both� ventricles by bundle of His.

• The fibers in this bundle called purkinje fibers, which divide

into two branches to initiate action potentials in two ventricles.

3 distinct waves are

produced during

cardiac cycle

• P wave caused by

atrial depolarization

• QRS complex caused� by ventricular

depolarization

• T wave results from� ventricular

repolarizat

http://www.cerritos.edu/charbut/AP201/ECG.ppt

• The P wave represents� depolarization of atrial� muscles.

• The QRS complex is combined� repolarization of atria and� depolarization of ventricles� which occur simultaneously.

• The T wave is the wave of� ventricular repolarization,

where as U wave is after�potentials in muscle of

ventricles.

http://server.oersted.dtu.dk/31610/images/ECGintervals3.gif

3.2 The standard lead system

• Two electrodes placed over different areas of heart and connected� to galvanometer will pick up the electrical currents resulting from� potentials difference between them.

• The resulting tracing of voltage difference at any two sites due to� electrical activity of heart is called “LE D”.

• The lead system is classified as:

a) Bipolar leads

b) Unipolar leads

Standard leads

Bipolar leads

Bipolar leads and Unipolar leads

http://t2.gstatic.com/images?q=tbn:ANd9GcTFAX5c5ZyiJ4PTKEftgt9-ZmvfDruIntGD7rIRw8d_CJA6AsepgDWnPollPg

3.3 Block diagram and working principle of ECG�machine

• The potentials picked up by patient electrodes taken to lead selector� switch.

• By means of capacitive coupling , the signal is connected to differential� amplifier.

• The amplified output is given to power amplifier which is push pull� differential type.

• The base of one input is driven by signal of preamplifier.

• The base of other transistor is driven by feedback signal resulting from� pen position and connected via frequency selective network.

• The output of power

amplifier is fed to pen

motor, which deflects the�writing arm on paper.

• Frequency selective

feedback network is R-C�network , which provides�necessary damping of

• The auxiliary circuit

provide 1mv calibration�signal and automatic

blocking of amplifier

during a change in

position of lead switch.

http://1.bp.blogspot.com/_jQ-v-

9IkLys/TUAuP3zvEiI/AAAAAAAAAVM/0BwEohCtfNk/s1600/mice�r.bmp.jpg

3.4 ECG Pre amplifier

http://openeeg.sourceforge.net/doc/modeeg/images/amp_block_�diagram.gif

• Different signals obtained from RA, LA and RL is given to low-pass� filter.

• After filtration, high voltage and over voltage protection circuit is� used so that amplifier can withstand large voltages during� defibrillation.

• The lead selector switch is used to drive required lead configuration� and give it to dc amplifier.

• A a dc level of 1mv is given to amplifier by pushbutton for calibration� of amplifier.

• Isolation of patient circuit is obtained using low capacitance

transformer whose primary winding is driven from 100 KHz oscillator.

• The transformer secondary is used to obtain isolated power supply of� 6v for operating the devices.

http://www.ti.com/graphics/blockdiagram/blockdiagram_images/6�163.gif

3.5 ECG machine faults and Troubleshooting

1) Interference from power line:

This interference is due to:

• Stray effect of alternating current on patient.

• Because of alternating current fields due to loops in patient cable.

• Loose contacts on patient as well as dirty electrodes.

• Machine or patient is not properly grounded

• Disconnected electrode.

2) Shifting of baseline:

• A wandering baseline is due to movement of patient or electrodes.

• It is also due to slow establishment of electrochemical equilibrium at� electrode skin interface.

3.6 Defibrillator circuit

• The rapid spread of action potential over the surface of atria causes� these two chambers of heart to contract together and pump blood� through AV valves into ventricles.

• After some time delay, ventricular muscles synchronously activated� to pump blood.

• A condition in which this necessary synchronization is lost is know as� fibrillation .

• Electric shock to the heart can be used to reestablish normal cardiac� rhythm.

• Electric machines that produce energy to carry out this function are� know as defibrillator .

Defibrillator circuit

http://coep.vlab.co.in/userfiles/5/image/l2_3.png

• In this circuit , a half wave rectifier driven by step up transformer is used� to charge the capacitor.

• The voltage to which capacitor is charged is determined by variable auto� transformer in primary circuit.

• The capacitor is to discharge when electrodes are placed on body by� changing the switch position.

• The capacitor discharged through electrodes, delivering the energy.

• Inductor is used to shape the wave in order to eliminate a sharp,� undesirable current spike.

Cardio version Pacemaker

• The rhythm beating of heart is due to triggering pulses that originate� in area of right atrium called SA node.

• In abnormal condition, this natural pacemaker unable to function or� triggering pulse does not reach the heart muscle because of blocking� by damaged tissue, the synchronization gets disturbed.

• By giving external electrical stimulation impulses to heart muscle, it is� possible to regulate the heart rate.

• These impulses are given by electronic instrument called “ Pacemaker ”

Classification of Pacemaker

Fixed rate Pacemaker

• The pulse generator are fixed� rate of asynchronous device

that produce pulses at fixed

rate and independent of any

natural cardiac activity.

• The power supply is necessary� to supply energy to the

pacemaker circuit.

• The oscillator establishes the� pulse rate for pacemaker, which

is given to pulse output circuit�that provides stimulating pulse�to the heart.

• This pulse is conducted along

Power supply

lead wires to cardiac electrodes.

On demand Pacemaker

• The demand pacemaker are� synchronous type pulse

• After each stimulus, the� timing circuit resets itself and

wait for interval to provide�next stimulus.

• If during the intervals a� natural beat occurs in the

ventricle, the feedback circuit

detects QRS of ECG signal

from electrodes and amplifies�it.

• The signal is used to reset the� timing circuit.

Output circuit Electrodes

Timing circuit

Reset circuit

4.0 Electroencephalograph

4.1 Electro-encephalography.

4.2 EEG electrodes and the10-20 electrode placement system

4.3 EEG amplitude and frequency bands.

4.4 Block Diagram and working principle of EEG Machine.

4.1 Electroencephalography

• The bioelectric potentials generated by neuronal activity of brain is� called electroencephalography.

• The interior of neuron is at potential of -70mv relative to exterior.

• When a neuron is exposed to stimulus above threshold, a nerve

impulse seen as change in membrane potential is generated which�spreads in the cell resulting in depolarization of cell.

• The EEG signal can be picked up with electrodes either from scalp or� directly from cerebral cortex which is normally 100uv.

4.2 EEG Electrodes and 10 -20 electrode�placement system

Nasion : point between the forehead and the skull

bump at the back of the skull

F rontal, T emporal, P arietal, O ccipital, C entral

z for the central line

Even numbers ( 2 , 4 , 6 ) right hemisphere, odd ( 1 , 3 , 5 ) left

www-lehre.inf.uos.de/~fscharno/ EEG . ppt

The International 10/20

(Ref: Handbook of Biomedical Instrumentation ,Khandpur)

• Electrodes are identified according to their position of head.�  Fp: frontal polar

 F: frontal

 C: central�  P: parietal�  T: temporal�  O: occipital

 Z: midline elctrodes

• Odd numbers refer to electrodes on left side of head and even� numbers represent on right side.

• The pattern of electrodes on the head and the channels they are� connected is called montage.

4.3 EEG amplitude and frequency bands

• The basic EEG range is classified into following four bands for� EEG analysis.

1) Delta : 0.5 - 4Hz. They occur in deep sleep and in serious organic� brain disease.

2) Theta : 4 - 8Hz. They are found in children and also occur during� emotional stress in adults.

3) Alpha : 8 - 13Hz. It is principle component of EEG and is an� indicator of state of alertness of brain.

4) Beta : 13 - 22Hz. They occur during intense mental activity.

EEG in the States of Vigilance

Frequency Ranges

4.4 Block diagram and working principle of EEG�machine

• Montage: A pattern of electrodes on the head and the channels they� are connected to is called Montage.

• Electrode montage selector: it a large panel containing switch that� allow user to select which electrode pair will have signals subtracted

from each other.

• Preamplifier: every channel has individual , multistage, ac coupled,� very sensitive amplifier with differential input and adjustable gain.

• Sensitivity control: the overall sensitivity of EEG machine is gain of� amplifier multiplied by sensitivity of writer.

• Filters: EEG contain muscle artifacts due to contraction of scalp and� neck muscles which are removed using low pass filter.

• Notch filter: tuned at 50 Hz so as to eliminate mains frequency� interference.

• High pass filter: the upper cut off frequency is controlled by it.

• Writing part: the pen motors used in EEG machine have frequency� response of 90Hz.

• Paper drive: this is provided by synchronous motor.

5.0 Medical Ultrasonic equipments

5.1 Physics of Ultrasound

5.2 Ultrasonic foetal monitors,

5.3 Echoencephalography.

5.4 Echocardiography.

5.5. Working Principle and Diagram of color Doppler ultrasound

5.1 Physics of ultrasound

• Ultrasonic waves are sound waves have frequency range� above 20KHz.

• Transmission of ultrasonic wave motion can be :�  Longitudinal

 Transverse�  Shear

• The longitudinal waves are used because it can be� propagated in all types of media.

http://www.ndt-

ed.org/EducationResources/CommunityCollege/Ultrasonics/Calib�rationMeth/Graphics/prop.gif

1) Characteristic Impedance:

It is defined as product of density of medium with velocity�of sound in same medium.

it determines the degree of reflection and refraction at�interface between two media.

2) Wavelength and frequency:

ultrasonic waves pass only through a medium and�transmitted as mechanical vibrations.

for medical applications, 1 to 15 MHz are used.

3) Velocity of propagation:

the velocity of propagation of wave is determined by

density of medium , it is traveling through and stiffness of�medium.

ed.org/EducationResources/CommunityCollege/Ultrasonics/Grap

http://www.antonine-

hics/Sound_Beam.jpg

education.co.uk/physics_a2/options/Module_6/Topic_5/US_

4) Absorption of ultrasonic energy:

in soft tissues, absorption coefficient depends on frequency and�therefore, for given amount of energy loss, lower frequency�ultrasonic signal would travel more than higher frequency signal.

5) Resolution : it is defined as the ability of system to differentiate� between closely relation structure.

6) Generation and detection of ultrasound:

to generate and detect ultrasonic waves piezoelectric effect is

materials with high mechanical Q factor are suitable as

Transmitter where as those with low mechanical Q and high�sensitivity as receivers.

5.2 Ultrasonic foetal monitor

• The Foetal heart rate is detected by ultrasonic using Doppler shift� principle.

• The Doppler shift based ultrasound foetal blood flow detector contain� two piezo electric crystal.

• The transmitting crystal emits ultrasound and back-scattered� ultrasound is detected by receiving crystal.

• The back scattered ultrasound frequency would be unchanged if the� reflecting object is stationary.

• If the reflecting object is moving, it would be foetal heart blood

vessel, then back scattered frequency is higher as blood is

approaching the probe and lower if it is moving away from the probe.

http://cache.freescale.com/files/graphic/block_diagram/3680_BD03_FHRM_TN.jpg

• Signal processing for FHR determination can be based either on� detecting the foetal heart valve motion or an detecting the heart� wall motion.

• The oscillator produces 2MHz frequency which is applied to� transmitter crystal transducer.

• The reflected beam is received by receiver crystal transducer and fed� to amplifier and demodulator circuit.

• The output of demodulator consist of Doppler frequency which is� then amplified and rectified.

• The rectified output is again filtered and given to one shot� multivibrator to obtain FHR which is then displayed.

5.3 Echoencephalography

• Echoencephalography is example of A-scan display ultrasonic� imagining.

• This type of scan offers one dimension information.

• Imaging system consist of pulsed ultrasound piezoelectric crystal� is used to transmit the signals and echoes are received through

• The echo signals are applied to Y deflecting plates of CRT so that� they are displayed as vertical blips as the beam is swept across� the CRT.

http://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/OCT�_B-Scan_Setup.GIF/375px-OCT_B-Scan_Setup.GIF

5.4 Echocardiography

• This is Doppler technique in blood flow measurement.

• Pulsed Doppler ultrasound can be used to measure the velocity� gradient across blood vessel as well as velocity of heart wall or� specific valves in the heart.

• Echocardiogram use M scan technique of ultrasound imagining.

• If one of echo sources is a moving structure then the echo dots� of light from that structure will also move back and front.

• If the dots are made to move with electronic sweep, from

bottom to the top of the screen at pre-scaled rate of speed, the�moving dots will trace out the motion pattern of moving�structure. This display is known as M mode display.

• The amount of vertical displacement is proportional to the

strength of echo and distance along the horizontal trace

represents the time of sound travel in tissue, thereby permitting�accurate measurement of tissue depth between any two echo�sources.

5.5 Working principle and Block diagram of color

Doppler ultrasound machine

• Color Doppler ultrasound machine is based on measurement of local� flow velocity in real time and display the surrounding structures in� color coded form together with section scan of vessel walls.

• The color can be red or blue indicates the direction of blood flow.

• The intensity of color indicates velocity of flow.

• The probe is mechanically coupled to the position resolver which� gives electrical output proportional to the movements of probe.

• The position of spot on the CRT screen corresponds to that of� sampling volume.

• When sampling volume is within blood vessel, the spot is intensified� and stored when Doppler signals are received.

• A vessel is imaged by moving the probe over the skin surface and by� adjusting the probe/sampling volume distance until the sampling

volume has been swept through the section of vessel.

• The Doppler frequency shift is measure of size and direction of flow� velocity.

• The incident ultrasound is scattered by the blood cells and scattered� wave is received by second transducer.

• The frequency shift due to moving scatters is proportional to the� velocity.

6.0 Therapeutic instruments:

6.1 Working Principle & Block Diagram of electro-surgery machine

6.2 Working Principle & Block Diagram of Hemo-dialysis machine.

6.3 Principle of Electromyography, Muscle Stimulators.

6.1 Working Principle & Block Diagram of�electro-surgery machine

• High frequency currents are used for cutting and coagulation.

• For this surgical machine depends on the heating effect of� electric current.

• When high frequency current flows through the sharp edge of� wire loop or the point of needle into the tissue, there is high� concentration of current at this point.

• The tissue is heated and get torn by boiling of cell fluid.

http://t0.gstatic.com/images?q=tbn:ANd9GcS1XIZJO_rvkG51F-�F3M77IVEMF-dZ9PrpOyNvMo7NpDAMCu5Q7O93FJHbGzA

• To produce high frequency power, power supply is applied to RF� oscillator.

• The high frequency signal produced by RF oscillator is modulated� according to particular action required.

• A function generator produces the modulation waveform according� to mode selected by operator.

• The RF power output is turned on or off by means of control circuit� connected to hand or foot switch operated by surgeon.

• The modulated signal is then amplified by power amplifier.

• The output circuit couples the power generated to electrodes to

6.2 Principle of Hemo-dialysis Machine

• Dialyzer is the artificial kidney which replace the function of� natural kidney , by removing waste products from blood.

• An artificial kidney is a dialyzing unit which operates outside� the patient’s body.

• It receives blood from artery via plastic tubing.

• The dialysate is electrolyte solution and dialysis takes place� across membrane and then return of dialyzed blood to vein.

http://www.baxter.com/images/patients_and_caregivers/therapies�/renal/acute_kidney_treatment/crrt_diffusion.jpg

• The dialyzing membrane has holes through which waste

produces from the blood are able to pass into the dialysate fluid�from where they are washed away.

• The dialysate fluid is free of waste product molecules and� therefore they tend to distribute throughout the blood and� dialysate.

• This movement of waste product molecules from blood to� dialysate results in cleaning of blood.

6.2 Working Principle & Block Diagram of Hemo-� dialysis machine .

• The haem-diaylsis machine performs five function:

 Mixes the dialysate.

 Monitor the dialysate.

 Pumps the blood and controls amount of anti- coagulants.

 Monitors blood for presence of air and drip chamber pressure.

 Monitor ultra-filtration rate.

http://www.gml-dialyza.cz/Obrazky/hemodialysis.JPG

• There are basic units of machine: Exchanger and Dialysate delivery� system.

• The Exchanger chamber consist of dialysate and patient’s blood� separated by semi - permeable membrane.

• The waste product from blood are diffuse to dialysate, then� thrown away.

• The Dialysate is made up of water with various solutes.

• It is pumped to dialysis chamber where it removes metabolic� waste products and then discarded.

6.3 Principle of Electromyography, Muscle

Stimulators.

• When an action potential occurs simultaneously in all muscle fibers� in one motor unit, the resulting external electrical effect is small,� spike-like potential which can be detected with electrodes placed� on the surface of the muscle.

• A surface electrical recording of the spiking activity derived� from one or more motor units is called an electromyogram, or� EMG.

• During repeated firing of a motor unit, the amplitude and

waveform of a motor unit spike tend to be constant. Spikes

from different motor units may be distinguished from one another�based on differences in amplitude and waveform.

http://www.ableweb.org/volumes/vol-21/12-drewes.pdf

7.0 Medical Laboratory Instrumentation and�Monitoring

• 7.1 Working Principle , Block Diagram and Applications of Blood

Cell Counter, Blood pH Analyzer and Autoanalyser.

• 7.2 Monitoring instruments - Alarms, Respiration rate

monitor, Heart beat monitor, Temperature monitor.

7.1 Working principle of Blood counter

• Blood is poor conductor of electricity and certain diluents are good� conductors.

• For a cell count, therefore blood is diluted and suspension is done� through a small orifice.

• By means of constant current source, a direct current is maintained� between two electrodes located on both side of orifice.

• As blood cell is carried through the orifice it displaces some of the� conductive fluid and increases the electrical resistance between the

electrodes.

• A voltage pulse of magnitude proportional to cell volume is� produced.

©J.Paul Robinson, Purdue University BMS 631 - LECTURE1.PPT

7.2 Blood pH analyzer

• The levels of oxygen and carbon dioxide which can be� carried by haemoglobin are affected by the acidity [pH] of

• If a glass membrane separates two solutions of different

hydrogen ion concentration a potential difference develops

that is proportional to the hydrogen ion gradient between the

• A potentiometric electrode is designed to measure the� potential between the sample and a buffer solution .

http://www.frca.co.uk/article.aspx?articleid=100389

http://www.frca.co.uk/images/cap2.jpg

• A measuring silver/silver chloride electrode is encased in a bulb of� special pH-sensitive glass and contains a buffer solution that� maintains a constant pH.

• This glass electrode is placed in the blood sample and a potential

difference is generated across the glass, which is proportional to the�difference in hydrogen ion concentration.

• The potential is measured between a reference electrode (in

contact with the blood via a semi-permeable membrane) and the�measuring electrode.

• Both electrodes must be kept at 37°C, clean and calibrated with� buffer solutions of known pH.

7.2 Autoanalyzer

• The autoanalyzer is sequentially measures blood chemistry and� displays this on a blood chemistry and displays this on a graphic

readout graphic readout

This is accomplished by This is accomplished by

 Mixing Mixing

 Reagent reagent�  Reaction Reaction

 Colorimetric measurement in continuous stream

faculty.ksu.edu.sa/Alhamwi/.../MLI-C12- autoanalyzer .pdf

• The sampler feeds the samples into the analyzer in time sequence.

• A proportioning pump is used to meter the sample and reagent.

• Mixing is achieved by injecting air bubbles.

• The mixture is incubated while flowing through heated coils.

• The air bubbles are removed and solution flows through chamber of� colorimeter.

• An electronic ratio recorder the output of reference and sample� photocells.

7.2 Monitoring instruments

• The main objective of patient monitoring are:

 Organizing and displaying information.

 Displaying multiple parameters.

 Processing the data to set alarms on abnormal conditions.

 Providing information based on automated data .

http://i.cmpnet.com/planetanalog/2010/08/C0614-Figure1.gif

8.0 Radiological Equipments.

8.1 Block diagram and operation of an X-Ray machine.

8.2 Types and uses of X-Ray machines.

8.3 Introduction to Tomography and Computerised Axial Tomography

(CAT) technique.

8.1 Block diagram and operation of an X-Ray

http://www.daenotes.com/electronics/industrial-electronics/x-rays#axzz1iD6PDxvJ

• High voltage source and high voltage transformer

• High voltage source is responsible for providing high voltage to� the H.V transformer for a decided time. The H.V transformer� produces 20 KV to 200 KV at the O/P.

• High voltage rectifier

• This rectifier rectifies the high voltage produced by the H.V.T and� supplies them to the anode of the X-ray tube.

• Thermal overload detector

• If the heat is exceed from a specified value, and then the thermal� over load detector is used to turn off system .

• Rotor control

• Most of the X-ray tube anodes are rotated by an induction motor, in� order to limit beam power at any spot and helps to cool the anode.

• Pulse duration timer

• The duration of the time must be very small so that the patient does� not receive the excessive dose.

• Aluminum Filter

• The X-ray beam used in the medical field which contains a broad band� of frequencies. To eliminate these effects Aluminum filter is used.

• Collimator

• An external collimator placed between patient and filter to pass rays� only on region of interest on body.

• Diaphragm

• X-rays inside the patient create x-ray scattering, which tends to

burned the image to absorb the scattered x-rays and eliminate the�burning of an image a lead grid is used which is called diaphragm.

• Film and lead shield

• The x-rays passed from the desired region of the patient body are

made to strike on the film where they produce an image of the body

soft and hard parts. A lead shield is use to collect the x-rays after�striking on film.

 Types of X-ray machine:

CT Scanner : It takes two dimensional pictures of the individual and� produces digital radiographs.

Bone X-ray Machine: The x-ray tube is attached to a flexible arm that can� be moved depending on what part of the body needs to be x-rayed.

Linear Accelerator: The shoot intense beams of radiation to tumors to kill� the cancer without affecting the rest of the body.

Backscatter X-ray: Backscatter x-ray machines are used for airport security� and baggage checks.

http://www.daenotes.com/electronics/industrial-electronics/x-�rays#axzz1iD6PDxvJ

 Uses of X-ray Machine:

• Detection of the fraction in bones.

• Infection of lungs, kidneys and other injury.

• Presence of Tumour.

• X-rays are used for treatment for Tumour.

8.3 Introduction to Tomography and

Computerised Axial Tomography (CAT) technique

http://www.profstelmark.com/1199_CT/7%20Physical%20principles%20of%20CT.ppt

• Computed Tomography is based on the x-ray principle; as x-rays pass� through the body they are absorbed or weakened at differing levels.

• Inside the CT machine is a semi-circular detector that measures the x-� rays strength.

• This detector and the x-ray tube are mounted on a rotating frame that� spins around the body of the patient taking roughly 1000 snapshots

from different angles; every 360 degree rotation, a 'slice' is scanned.

• Images can be reconstructed

9.0 Miscellaneous

9.1 Theory of Macroshock and Microshock, Physiological

effects of Electricity on the human body.

• 9.2 Line Isolation Systems.

9.1 Theory of Macroshock and Microshock,

Physiological effects of Electricity on the human

• Macro shock: occurs when the

human body becomes a conductor

of electric current passing by

means other than directly through�the heart. This effect can readly

occur with the use of medical

electrical equipment as the natural�resistance of the skin to current�flow is often reduced or bypassed�by electrodes and electorde paste�or by invasion into mucous

http://www.medtek.ki.se/medicaldevices/album/Ch%203%20�Electricity%20safety/slides/F%203-1%20%20Macroshock.jpg

• Micro shock:

• Certain medical electrical

procedures involve the

introduction of an electrical

conductor in direct contact with a�ventricular heart muscle.

• Micro shock may not be obvious� as no outward and physically� visible stimurus or contraction

http://www.medtek.ki.se/medicaldevices/album/Ch%203%20Electricity%20safety/slides/F%2�03-3%20Microshock.jpg

9.2 Line Isolation Systems.

•A line isolation monitor

is used with such system�that continuously

monitors for the first�ground fault, during

which case it simply

informs the operators to�fix the problem. The�single ground fault does�NOT constitute a hazard!

http://users.rowan.edu/~polikar/CLASSES/ECE404/Lecture20.ppt

• Normally, when there is a ground-fault from hot wire to ground, a large� current is drawn causing a potential hazard, as the device will stop� functioning when the circuit breakers open.

• This can be prevented by using the isolated system, which separates� ground from neutral, making neutral and hot electrically identical. A� single ground-fault will not cause large currents, as long as both hot

conductors are initially isolated from ground!

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Biomedical Instrumentation

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A study of the electrical bio-impedance of tumors, Morimoto (1993) Measurement System: Three-electrode method, frequency range 0-200kHz, a thin coaxial.

BIOPOTENTIAL AMPLIFIERS

Chapter 1. Basic Concepts of Medical Instrumentation Walter H. Olson

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Chapter 5-Webster Biopotential Electrodes

BIOMEDICAL INSTRUMENTATION

1 IV. Electrodes In order to measure biopotentials, we must convert the ionic activity of the excitable cells of interest to electrical signals. In order.

Biopotential electrodes A complex interface Basics of Instrumentation, Measurement and Analysis 2011, 2012.

Chapter 5. Biopotential Electrodes Michael R. Neuman

Biopotential electrodes A complex interface Summer School Timisoara 2002R. Hinz.

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EMG ELECTRODES. Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed.

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Copyright © 2014 John Wiley & Sons, Inc. All rights reserved.

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Biomedical Instrumentation Amplifiers - PowerPoint PPT Presentation

Biomedical Instrumentation Amplifiers

Presented by-md. bashir uddin roll: 1215502 dept. of bme kuet, khulna-9203 – powerpoint ppt presentation.

• Medical devices or instruments which are used to facilitate patient care, as well as biomedical research are known as medical instrument.
• Devices such as pacemakers, ultrasound machines, EKGs and blood pressure devices are just a few of the devices that are used in the biomedical field.
• A branch of biomedical engineering that deals with the knowledge of medical instruments and their application to the medical field is known as medical instrumentation.
• Generally medical instruments can be grouped in two broad heads
• a) Diagnostic
• b) Therapeutic
• These are further subdivided into two or more sub groups
• Basic and Sophisticated,
• (ii) Mechanical, Electro-Mechanical Electronic
• Measuring Instrument - Blood Pressure Instrument
• Recording Instrument ECG Machine
• Monitoring Instrument Heart Rate Monitoring
• Imaging Instrument MRI Machine
• Therapeutic Instrument ICU Ventilator Instrument
• ECG Machine
• It has capacity to monitor multi parameters of a patient
• Examples NIBP, IBP, Heart Rate,
• Body Temperature.
• ECG Tracing
• Normal and abnormal condition of patient
• Alarm facilities for monitoring parameters
• Alarm ensured physician and nurse attention
• An ICU Ventilator instrument Is used for those patients who are unable to take breath normally
• An instrumentation (or instrumentational) amplifier is a type of differential amplifier that has been outfitted with input buffers,
• Which eliminate the need for input impedance matching
• Thus make the amplifier particularly suitable for use in measurement and test equipment.
• Amplifier used in medical field is called medical instrumentation amplifier.
• A type of differential amplifier
• No need of impedance matching
• Outfitted with input buffers
• Very low DC offset
• Very high open-loop gain
• Very high common-mode rejection ratio
• Very high input impedances.
• A preamplifier (preamp) is an electronic amplifier that prepares a small electrical signal for further amplification or processing.
• A preamplifier is often placed close to the sensor to reduce the effects of noise and interference.
• It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio (SNR).
• The noise performance of a preamplifier is critical.
• Wide range of input sensitivities
• Covered virtually all signal sources
• Calibrated zero suppression to expanded desired portion of an input
• Rejects noise or unwanted signal components by using low pass filtering
• Capacity neutralization
• Current injection
• Low leakage current
• Low dc drift suitable for intracellular measurements through high resistance fluid-filled electrodes
• Differential amplifiers
• Ac coupled amplifiers
• Carrier amplifiers
• DC amplifiers
• Chopper input dc amplifiers
• Chopper stabilized dc amplifiers
• DC bridge amplifiers
• Isolation Amplifiers
• Particularly suitable for use in measurement and test equipment.
• Instrumentation amplifiers are used where great accuracy and stability of the circuit both short- and long-term are required.

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bioMEDical Instrumentation system

Jul 26, 2014

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bioMEDical Instrumentation system. By: Engr. Hinesh Kumar. Outline. Generalized Medical Instrumentation Systems Components of Medical Instrumentation Systems PC Based Medical Instruments Systems Operational Modes Medical Measurement Constraints Classifications of Biomedical Instruments

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bioMEDical Instrumentation system By: Engr. Hinesh Kumar

Outline • Generalized Medical Instrumentation Systems • Components of Medical Instrumentation Systems • PC Based Medical Instruments Systems • Operational Modes • Medical Measurement Constraints • Classifications of Biomedical Instruments • Measurements Input Source • Characteristics of Instrument Performance • System Static & Dynamic Characteristics • General Design Criteria & Process of Medical Instruments • Commercial Medical Instrumentation Development Process

Basic Instrumentation System

Generalized Medical Instrumentation System * Elements and connections shown by dashed lines are optional for some applications.

Generalized Medical Instrumentation System

Components of Medical Instrumentation System • Measurand • Sensor / Transducer • Signal Conditioning • Output Display • Auxiliary Components

Measurand • The physical quantity, property, or condition that the system measures is called measurand. • The accessibility of the measurand is important because it may be: • Internal (Blood Pressure) • On the Body Surface (Electrocardiogram) • Emanate from the body (Infrared Radiation) • Derived from Tissue Sample (such as Blood or a Biopsy)

Cont… • Most medically important measurands can be grouped in the following groups: • Biopotential, • Pressure, • Flow, • Dimensions (Imaging), • Displacement (Velocity, Acceleration, And Force), • Impedance, • Temperature, And • Chemical Concentrations • The measurand may be localized to a specific organ or anatomical structure.

Sensor • The transducer is defined as a device that converts one form of energy to another. • A sensor converts a physical measurand to an electric output. • The sensor should respond only to the form of energy present in the measurand, to the exclusion of all others. • The sensor should non invasive and minimally invasive.

Signal Conditioning • Simple signal conditioners may only amplify and filter the signal or merely match the impedance of the sensor to the display. • Often sensor outputs are converted to digital form and then processed by specialized digital circuits or a microcomputer. • For example, signal filtering may reduce undesirable sensor signals. • It may also average repetitive signals to reduce noise, or it may convert information from the time domain to the frequency domain.

Output Display • The results of the measurement process must be displayed in a form that the human operator can perceive. • The best form for the display may be: • Numerical • Graphical, • Discrete or Continuous, • Permanent or Temporary • Visual / Hearing

Auxiliary Components • A calibration signal with the properties of the measurand should be applied to the sensor input or as early in the signal-processing chain as possible. • Many forms of control and feedback may be required to elicit the measurand, to adjust the sensor and signal conditioner, and to direct the flow of output for display, storage or transmission. • The control and feedback may be automatic or manual.

Cont… • Data may be storedbrieflyto meet requirements of signal conditioning or to enable operator to examine the data that precede alarm conditions. Or data may be storedbeforesignal conditioning, so that different processing schemes can be utilized. • Conventionalprinciples of communication can often be used to transmit data to remote displays at nurses’ stations, medical centers, or medical data-processing facilities.

PC Based Medical Instruments • Personal computer are popular in medical field and also software is largely commercially available and the users can purchase and use it. • Computer are widely accepted in the medical field for data collection, manipulation, processing and a complete workstations for a variety of applications. • A personal computer becomes a workstation with the simple installation of one or more “instruments-on-a-board” in its accessory slots.

PC Based Medical Instruments Typical configuration of PC based Medical Instruments

Cont… • Fig illustrates the typical configuration of a PC based workstation. System is highly flexible and can accommodate a variety of inputs, which can be connected to PC for analysis, graphics and control. • Basic elements in the system include sensors or transducers that convert physical phenomena into a measurable signal, a data acquisition system, an acquisition/analysis software package or programme and computing platform. • The systems works totally under the control of software.

Cont… • PC medical instruments are gaining in popularity for several reasons including price, programmability and performance specifications. • Software development, rather than hardware development, increasingly dominates new product design cycles. • This includes operating systems, devices drivers, libraries, languages and debugging tools.

Categories of Measurement • There are three general categories of measurement • Direct Measurement • Indirect Measurement • Null Measurement

Direct Measurement • Direct measurement are made by holding the measurand up to some calibrated standard and comparing two. • Example: Meter stick ruler used to cut a piece of coaxial cable to the correct length. • You know that the cable must be cut to a length of 24 cm, so hold a meter stick (the standard or reference) up to the piece of the cable. Measuring cable with a meter stick

Indirect Measurement • Indirect measurement are made by measuring something other than the actual measurand. • Indirect methods are often used when direct measurements are either difficult or dangerous. • Example: on might measure the temperature of a point on the wall of a furnace that is melting metal.

Indirect Measurement of blood pressure Measuring point on a furnace

Null Measurement • Null measurement are made by comparing a calibrated source to an unknown measurand and then adjusting either one or the other until difference between them is zero. • Example: An electrical potentiometer is such an instrument; it is an adjustable calibrated source and a comparison meter (galvanometer). The reference voltage from the potentiometer is applied to one side of the zero center galvanometer, and the unknown is applied to the other side of galvanometer. • The output of the potentiometer is adjusted until the meter reads zero difference.

Example of Null Measurement

Instruments Operational Modes • Direct / Indirect Mode • Sampling and Continuous Modes • Generating and Modulating Modes • Analog and Digital Modes • Real time and Delayed Time Modes

Direct / Indirect Modes • Direct Mode • Desired measurand can be interfaced directly to a sensor because the measurand is readily accessible • If the sensor is invasive, direct contact with the measurand is possible but expensive, risky and least acceptable. • Temperature • Heartbeat • Indirect Mode • Desired measurand can not be interfaced directly and not accessible • Morphology of internal organ: X-ray shadows • Volume of blood pumped per minute by the heart: respiration and blood gas concentration • Pulmonary volumes: variation in thoracic impedance plethysmography

Sampling Mode and Continuous Mode • Sampling Mode • Sampling can change so slowly that they may be sampled infrequently. • Body Temperature • Ion Concentration • Continuous Mode • Frequent or constant monitoring of measurand • Electrocardiogram • Respiratory Gas Flow

Generating and Modulating Modes • Generating Mode • Generating sensors produce their signal output from energy taken directly from the measurand. • Also known as self-powered modes. • Example: Photovoltaic cell is a generating sensor because it provides an output voltage related to its irradiation, without any additional external energy source. • Modulating Mode • Modulating sensors use the measurand to alter the flow of energy from an external source in a way that affects the output of the sensor. • Example: Photoconductive cellis a modulating sensor; to measure its change in resistance with irradiation, we must apply external energy to the sensor.

Analog and Digital Modes • Analog Modes • Analogue or Continuous signal is able to take any value within a dynamic range. • Most currently available sensors operate in the analog mode. • Digital Modes • Digital or Discrete signal is able to take on only a finite number of values. • The advantages of the digital mode of operation include greater accuracy, repeatability, reliability, and immunity to noise.

Real Time and Delayed Time mode • Real Time Mode • Sensor acquire the signal in real-time mode • The result are displayed immediately • Delayed Time Mode • Display results are delayed due to image processing such as averaging and transformations.

General Constraint In Design of Medical Instrumentations Systems • Medical equipment are primarily used for making measurements of physiological parameters of the human body and also in some cases as stimulus or some kind of energy is applied to the human body for diagnosis and treatment. • Some of important factors, which determine the design of a medical measuring instrument, are: • Measurement Range: Generally the ranges are quite low compared with non-medical parameters. Most signals are in microvolt range. • Frequency Range: Most of the biomedical signals are in the audio frequency range or below and many signal contain dc and very low frequency components

Cont…. • The signal to be measured imposes constraints on how it should be acquired and processed. • Many measurand in living systems are inaccessible. • Placement of sensor(s) in/on the body plays a key role in medical instrumentation design. • Magnitude and frequency range of medical measurand are very low. • Interference and cross-talk artifacts. • Proper sensor interface with measurand cannot be obtained. • Medical variables are seldom deterministic (varying with time).

Cont…. • Many medical measurements vary widely among normal patients, even when conditions are similar. • Safety of patient and medical personnel also must be considered. • Safe levels of stimulation or applied energy are difficult to establish, • External energy must be minimized to avoid any damage. • Equipment must be reliable, easy to operate, and durable. • Government regulations.

Common Medical Measurands

Classifications Of Medical Instruments • Medical Instruments can be classified in the four categories • Quantity that Sensed • Principle of Transduction • Organ System • Clinical Medicine Specialties

Classifications • Quantity That Sensed Advantage of this classifications is that it makes different methods for measuring any quantity easy to compare. • Pressure • Flow • Temperature • Principle of Transduction • Resistive • Inductive • Capacitive • Ultrasonic (Sound waves) • Electrochemical (pH probe, Hydrogen Sensor)

Cont… • Organ System Isolates all important measurements for specialists who need to know only about a specific area • Cardiovascular Systems • Pulmonary System • Nervous System • Endocrine System

Cont…. • Clinical Medicine Specialties This approach is valuable for medical personnel who are interested in specialized instruments. • Pediatrics • Obstetrics • Cardiology • Radiology.

Measurement Input Sources • Desired Inputs: Measurands that the instrument is designed to isolate. • Interfering Inputs: Quantities that accidentally affect the instrument as a consequence of the principles used to acquire and process the desired inputs. • Modifying Inputs: Quantities that cause a change in the input –output relations of the instrument.

Example: ECG Signal Measurement • Desired Input: ECG voltage (Vecg) • Interfering Input: 60/50 Hz noise voltage, displacement currents • Modifying Input: – orientation of the patient cables when the plane of the cable is perpendicular to the magnetic field the magnetic interference is maximal Figure: Simplified electrocardiographic recording system Two possible interfering inputs are stray magnetic fields and capacitive coupled noise. Orientation of patient cables and changes in electrode–skin impedance are two possible modifying inputs. Z1 and Z2 represent the electrode–skin interface impedances.

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