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An Overview . . .

X-ray machine

Radio graphic and fluoroscopic techniques

Computer tomography

MRI

Ultrasonography

Endoscopy

Thermography

Different types of biotelemetry systems and patient monitoring

Electrical safety.

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X Ray Machine

An X ray image is created with high density, high contrast and

high sharpness on film

Density or Darkness is proportional to the amount of X rays that

penetrate the film

Contrast is a measure of the darkness of the desired image

compared to its surroundings

Sharpness or Clarity is influenced by the distortions in the X ray

beam

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High - VoltageSourceControl

PulseDuration

Timer

FilamentCurrentControl

Rotor Control

ThermalOverloadDetection

High VoltageTransformer

High VoltageRectifier

X-Ray

Tube

Collimator

Patient

IntensifyingScreen

Film

LeadShield

BuckyDiaphragm

Block Diagram of an X Ray Machine

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Power Supply Arrangement

Aluminium Filters Collimator

Bucky Diaphragm

Lead ShieldAll these components are used to

Improve the quality of the image

Increase the contrast

Improve resolution

Minimize the dose of X rays used on the patient

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TubeFilament

Transformer

mAControl

kVControl

Contactor

Timer

HighVoltage

Tansformer

HighVoltageRectifier

X RayTube

High VoltageTransformer

220 V


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The mains voltage is stepped up by a high voltage transformer

The kV control gives the necessary input to the X ray tube to

produce the required wavelength of X rays

A contactor linked with a timer is used to deliver the X ray output inthe required time interval

Then it is given to a high voltage transformer followed by a high

voltage rectifier

The output is applied across the anode and cathode of the X ray tube

A circuit with mA control and tube filament transformer is present in

order to provide the necessary current for the filament of the cathode

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Aluminium Filters

Emitted X rays contain a broad range of frequencies

X rays at unwanted frequencies only increase the patient dose and

decrease the image contrast

Aluminium filters absorb lower X ray frequencies and hence the

intensity of low frequency X rays incident on the patient is

reduced

Thus the negative effects produced by the low frequency X raysare greatly reduced

Simply, the aluminium filters confine the X rays to the region of

interest

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X Ray Tube Anode

ExternalShutter

LightReflector

Lamp

InternalShutter

X Ray Beam

Collimator

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Collimator

Placed between the patient and aluminium filter

It is an aperture diaphragm which restricts the beam falling on the

patient

Does the necessary shaping of the X ray beam Consists of a shutter with a rectangular or circular hole of suitable

size or four adjustable lead strips which can be moved relative to

each other

A lamp and reflective pattern on the patient

This is used to locate where the X rays will strike and position the

beam accordingly

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ScatteredRadiation

PrimaryRadiation

Patient

BuckyDiaphragm

X RayFilm

LeadVanes

Bucky Grid

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Bucky Grid

To reduce scattered radiation, which may produce poor sharpnessin the image, the region of the patient being examined must be

compressed

The bucky grid is introduced in between the patient and the film

cassette to improve the sharpness of the image

Consists of thin lead vanes separated by spacers of a low

attenuation material

The lead vanes are usually angled so that the primary radiation

which carries the information can pass between them while the

sacttered radiation from the object strikes the lead vanes and is

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Radiography and Fluoroscopy

S. No. Radiography Fluoroscopy

1 X ray image is developed

by photosensitive film

X ray image is developed by

photoelectric effect and

fluorescence principle

2 High geometric resolutioncan be obtained

Fair resolution can be obtained

3 Wide range of contrast can

be obtained

Contrast can be increased by

introducing electronic image

intensifier

4 Patient is not exposed to X

rays during examination of

the X ray image

Patient is exposed to X rays

during examination of the X ray

imagewww.eeecube.com

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5 Patient dose is low Patient dose is high

6 Permanent record is

available

Permanent record can be made

by inserting video tape recorder

7 Image can be obtained after

developing the film and the

examination cannot be made

before developing the film

Immediately image can be seen

and examination can be finished

within a short time

8 Movement of organs cannot

be observed

Movement of organs can be

observed (Real time experiment)

9 Efficiency is more Efficiency is lesser in direct

fluoroscopy, can be increased

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Computer Tomography

Also called Computerized Axial Tomography or Computer Transmission

Tomography

Principle

Measurements are taken from the transmitted X rays through the body and

contain information on all the constituents of the body in the path of the X ray

beam

Using multi directional scanning of the object, multiple data are collected

Mathematical Basis

If the total attenuation long rows and columns of a matrix is measured, theattenuation of the matrix elements at the intersection of the rows and columns

can be computed

The number of mathematical operations necessary to yield clinically applicable

and accurate images is so large that a computer is essential to do themwww.eeecube.com

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Back Projection Reconstruction

2 0

1 3

Suppose the actual attenuation values, normalised to zero, are

represented by 2*2 matrix,

Step 1

Each number in the matrix represents the attenuation of the spacewhere it is located

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Step 2 (First Estimate)

The first estimate is obtained adding the elements along the

rows and replacing them with the sum

2 2

4 4

Step 3 (Second Estimate)

Add the elements along the columns and replace them with

the sum

3 3

3 3

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Step 4 (Third Estimate)

Add the elements along the north east diagonal and replace

them with the sum

2 1

1 3

The second estimate is obtained adding the above matrix to

the first estimate

2 2

4 4

3 3

3 3

5 5

7 7+ =

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The third estimate is obtained adding the above matrix to the

second estimate

5 5

7 7

2 1

1 3

7 6

8 10+ =

Step 5 (Fourth Estimate)

Add the elements along the north west diagonal and replace

them with the sum

5 0

1 5

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The fourth estimate is obtained adding the above matrix to

the third estimate

7 6

8 10

5 0

1 5

12 6

9 15+ =

Step 6 (Final Image)

Normalize the fourth estimate to zero by subtracting 6 from

each element

6 0

3 9

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Then divide this by 3 to yield final image

2 0

1 3

The final matrix is the same as the first one

The numbers in the matrix correspond to the attenuations of locationson a tissue slice having the same spatial relationship as the matrix

numbers

It is seen that the final image has the same attenuation as the actual

transverse slice but the values are obtained from external measurements

of attenuation using CT

The computer does similar calculation in large scale and

finds the matrix valueswww.eeecube.com

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Camera

Output UnitAnd Storage

Patient

DedicatedMicroprocessor

CRT

TimingkV + mAControl

TubePositionControl

High VoltageSupply

X RayTube

Detectors

Detector Scanner

DataBus

ControlBus

Block Diagram for a Computer Tomography Scanner

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The timing, anode voltage (kV) and beam current (mA) are controlled by a computer

through a control bus

The high voltage d.c. power supply drives an X ray tube that can be mechanically

rotated along the circumference of a gantry

The patient is lying in a tube through the centre of the gantry

The X rays pass through the patient and are partially absorbed

The remaining X ray photons impinge upon several of as many as 1000 radiation

detectors fixed around the circumference of the gantry

The detector response is directly related to the number of photons impinging on it

and in turn to tissue density

When the photons strike the detector they are converted to scintillations

The computer senses the position of the X ray tube and samples the output of the

detector along a diameter line opposite to the X ray tube

The output unit then produces a visual image of a transverse plane cross section of

the patient on the cathode ray tube

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Sources of errors and scan artifacts

Noise

Motion artifacts

Artifacts due to high differential absorption in adjacent tissues

Technical errors and computer artifacts

Applications of Computer Tomography Central Nervous System

Orthopedics and Bone Tumours

Thorax

Abdomen and Pelvis

Neck

Radiography Planningwww.eeecube.com

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Magnetic Resonance Imaging

Makes use of RF region of the electromagnetic spectra to provide an

image

A patient is placed in placed in an external magnetic field which

causes the magnetization of protons of hydrogen atoms in the body Due to magnetization, these protons align about the external

magnetic field

Now a radio frequency pulse at resonance frequency is transmitted

into the patient under controlled and prescribed condition

The individual proton responds by emitting a frequency signal

called nuclear magnetic resonance signal

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These signals, during their return from high energy states to ground

state, are picked up by the RF coils and produce an image

Advantages

Superior contrast resolution

Direct multi - planar imaging, slices in the sagittal, coronal an

oblique directions can be obtained directly

Absence of harmful radiations like x rays, Y rays, positrons

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Magnetic Resonance Phenomenon

Our body consists of millions of atoms

Nearly 80% are hydrogen atoms

Each hydrogen atom has one proton in the nucleus It is spinning and hence a nuclear magnetic moment is associated

with it

The value of the moment depends on the mass, charge and the rate

of spin of the nucleus

Normally the spinning of the nuclei is random and the associated

magnetic moment can be pointed in any direction

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In the presence of a large external magnetic field, its axis rotation

will precess about the magnetic field

At equilibrium the lower state has more nuclei than the higher state

Using radio frequency radiation with an energy exactly equal to the

energy difference between two nuclear energy states, one can

achieve population inversion by raising the nuclei from lowerenergy state to higher energy state

The excited nuclear spins will slowly return to its equilibrium

emitting a radio frequency signal called Nuclear Magnetic

Resonance (NMR)

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MRI instrumentation

A magnet is present which provides a strong, uniform, steady magnet field

Superconducting magnets are used, they are cooled to liquid helium

temperature and can produce very high magnetic fields

The signal to noise ratio of the received signals and image quality are better

than the conventional magnets

Different gradient coil systems produce a time varying, controlled spatial

non magnetic fields indifferent directions

The patient is kept in this gradient field space

Transmitter and receiving R.F. coils are present surrounding the site on

which the image is to be constructed

There is a superposition of a linear magnetic field gradient onto the uniform

magnetic field applied to the patient

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CoilCoilCoil

Magnet

Patient

TransmitterCoil

ReceiverCoil

R.F. PowerAmplifier and

Transmitter

R.F. Generator X GradientPower

Y GradientPower

Z GradientPower

SignalAverage

Receiver

Pre - amplifier

Interface

Computer Display

Image Storage

Signal Processing Unit

Block Diagram of a

MRI System

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When the superposition takes place, the resonance frequencies of the precessing

nuclei will depend on the positions along the direction of the magnetic field

gradient This produces a one dimensional projection of the structure of the three

dimensional object

By taking a series of these projections at different gradient orientations using X,

Y and Z gradient coils a two or three dimensional image can be obtained

The gradient magnetic field can be controlled by computer and that field can be

positioned in three time invariant planes (X, Y and Z)

The transmitter provides the R.F. signal pulses

The received nuclear magnetic resonance signal is picked up by the receiver coil

By two dimensional Fourier Transformation the image is constructed by the

computer and is displayed on the television screen

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Ultrasonography

Technique by which ultrasonic energy is used to detect the state of the

internal body organs

Bursts of ultrasonic energy are transmitted from a piezoelectric or

magnetostrictive transducer through the skin and into the internal anatomy

When this energy strikes an interface between two tissues of differentacoustical impedance, reflections (echoes) are returned to the transducer

The transducer converts these reflections to an electric signal

This electric signal is amplified and displayed on an oscilloscope at a distance

proportional to the depth of the interface

Ultrasonic diagnosis differs from radiological (X ray) diagnosis in that no

shadow images are obtained

The cross sectional or linear images are obtained through parts of the body

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Ultrasonic imaging is safe

Uses mechanical energy at a level which is not harmful

Hence it is called a non invasive technique

Potential applications

Neurology to find brain tumor

Ophthalmology to find any foreign objects in eye

Cardiology to determine the cross section of the heart and the

heart rate

Gynecology to monitor the fetus growth and to indicate the

presence of twins

To identify breast cancers

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Front PanelControls

ComputerTransducer

PositionData

Transducer ReceiverSignal

Processing

ImageStorage

Display

Block Diagram of a Computer Controlled Ultrasonic Image Forming System

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Ultrasonic Imaging Instrumentation

The transducer position data are fed to the computer

The computer sends this information to signal processing unit

It also receives the signals from the receiver and controls the

receiver sensitivity

Proper depth gain compensation is calculated by the computer and

given to the signal processing unit

The ultrasonic velocity is calculated and given to display unit Using the image storage unit, the patient information is displayed

Digital real time scanners are used for displaying ultrasound images

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.

.

A/D

TV Synchronous Signal

Generator

ReceiverCircuit/

DGC Circuit

Memory

Control

D/A

ColourCoder

MixingCirciut

T.V.Monitor

. .

Probe

Patient

Digital Real Time Ultrasonic Scanner

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The echoes from the patient body surface are collected by the

receiver circuit

Proper depth gain compensation is given by DCG circuit

The received signals are converted into digital signals and are

stored in the memory

Meanwhile, the scan converter control receives signals of transducer

position and TV synchronous pulses and generates X and Y address

information which is fed to the digital memory

The stored digital image signals are processed and colour coded andare given to digital to analog converter

Then they are fed into video section of the television monitor

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Endoscopes

Tubular instrument used to inspect or view the body cavities which are notvisible to the naked eye normally

In each endoscope there are two fiber bundles

One is used to illuminate the inner structure object

The other is used to collect the reflected light from that area

From this we can view the inner structure of the object

There are two types flexible and rigid

Sometimes it is equipped with small forceps for taking sample of tissue biopsy specimens for microscopic studies

In the endoscope, at the object end there is an assembly of objective lens

and prism and at the viewing end, there is an eye lens

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SynchronousFilter Shutter

Endoscope

Firing Controland

Timing Unit

EncapsulatedQuartz Fibreguide

Micropositioner

Lens System

Power Meter andHeat Sink

Power Supply

High PowerArgon Laser

Partial BeamSplitter

Endoscopic Laser Coagulator

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It uses argon ion laser as high energy optical source and endoscope as the

delivery unit

Argon ion lasers are very useful in the coagulation of blood vessels since itsgreen light is highly absorbed by the red blood vessels and hemoglobin

It is also advantageous to use argon ion lasers for photocoagulation of

retina because of its smaller beam diameter and its ability do coagulation

without affecting the surrounding healthy tissue

To control gastric hemorrhage photocoagulation is adopted

With the help of endoscope, the output from the argon ion laser is delivered

to the required spot to arrest the gastric bleeding

Laser beam can be moved in any direction using the flexible endoscope

Using an endoscope the beam can be delivered to the required site as well

as viewed for proper alignment

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Thermography

Process of recording true thermal images of the surfaces of objects

under study

The thermal images are maps of temperature

Contain both qualitative and quantitative information

Types

Infrared Thermography

Liquid Crystal Thermography

Microwave Thermography

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Infrared Thermography

Operation

A chopper is inserted in front of a infrared radiation detector

Infrared radiation from body and from black body for calibration

enter the detector

The detected output by detector is amplified and led to phase

sensitive detector

The detected signal by phase sensitive detector is amplified and

given to analog meter or digital meter and the absolute temperature

of an object is calibrated and displayed

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Body Surface

Chopper Detector Preamplifier Demodulator CRT

ReflectingScanning

Mirror

Synchronization Pulses to CRT

Simplified Block Diagram of a Thermographic Equipment

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Every thermographic equipment is provided with a special camera that

scans the object

A display unit is provided for displaying the thermal picture on the screen

The camera contains an optical system in the form of an oscillating flat

plane mirror

This mirror scans the field of view at a very high speed horizontally and

vertically

It also focuses the collected infrared radiation onto the chopper

The chopper disc interrupts the infrared beam so that a.c. signals are

produced which are amplified and demodulated further

The demodulated signals are given to the Cathode Ray Tube in

synchronization with scanning mechanism

The signals are displayed on the screen by intensity modulation

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Liquid Crystal Thermography

Liquid crystals are a class of compounds which exhibit colour

temperature sensitivity

In this method, the temperature plate consists of a blackened thin

film support into which encapsulated liquid crystals cemented to a

pseudo solid powder have been incorporated

Thermal contact between the skin surface and plate produces colour

change in the encapsulated liquid crystals

Red for relatively low to violet for high temperatures

In infrared thermograms it is vice versa

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A good Thermographic equipment should have

Short frame time (less than 4 seconds)

High resolution (more than 100, 000 picture elements)

A small size and light weight optical head

A wide spectrum band detector near the wavelength of 10 microns

Interfaces for image processing

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Medical Applications of Thermography

Healthy Cases

Tumors

Inflammation

Diseases of Peripheral Vessels

Burns and Perniones

Skin Grafts and Organ Transplantation

Collagen diseases

Orthopedic Diseases Brain and Nervous Diseases

Hormone Diseases

Examination of Placenta Attachment

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Bio - Telemetry

Electrical technique for conveying biological information from a

living organism and its environment to a location where this

information can be observed or recorded

Used for

Monitoring patients in hospital from a remote location

Monitoring astronauts in space

Monitoring patients who are on the job or at home

Monitoring the athletes who are running a race

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Essential Components of a Bio Telemetry System

Transducer converts the biological variable into electrical signal

Signal Conditioner amplifies and modifies this signal for effective

transmission

Transmission link - connects the signal input to the readout device

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BiologicalSignal Transducer Conditioner

TransmissionLink

Read out Device

ECGEEGEMG

Electrodes

Temperature ThermistorBlood Pressure Strain GaugeStomach pH Glass Electrode

Amplifier &Filter

RadioFrequency F.M.

Transmitter

Video RecorderTape Recorder

C.R.OX.Y Recorder

Block Diagram of a Bio Telemetry System

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Design of a Bio Telemetry Systems

Telemetering system should be selected to transmit the bio electric

signals with maximum fidelity and simplicity

There should not be any constraint for living system

The size and weight of the telemetry system should be small

Should have more stability and reliability

Power consumption should be very small

In the case of wire transmission, the cable should be shielded

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Biosignal Source

Transducer

Conditioner

Radio Transmitter

Display

Conditioner

Radio Receiver

Block Diagram of a Typical Single Channel Radio Telemetry System

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A miniature battery operated radio transmitter is connected to the

electrodes of the patients

This transmitter broadcasts the biopotential over a limited range to

remotely located receiver

This detects the radio signals and recovers them for furtherprocessing

There is negligible connections or stray capacitance between the

electrode circuit and the rest of the system

So the receiving system can even be located in a room separate from

the patients

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Types of measurements made

Active

Passive

Types of Transmitters used

Tunnel diode FM transmitter

Harley type FM transmitter

Pulsed Hartley Oscillator

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L

TD

BD

R

1.5 V

Bio signalSource d

d

Single Channel FM Transmitter

S

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Tunnel diodes are higher active devices (TD, BD)

The circuit has higher fidelity and sensitivityCircuit Details

Radio Frequency used 100 to 250 MHz

Frequency response 0.01 Hz to 20kHz

Input Impedance 300 Kilo Ohms to Mega Ohms

Temperature Stability of Carrier Frequency 0.05% / o C

Varactor diodes d are used for frequency modulation

The signal is transmitted through the inductor L which is also one

of the components in the tank circuit of R.F. Oscillator

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Advantages

All the signals can be transmitted from the surface of the subject to a

receiver in a normal hospital environment

No shield room is needed

Interference is greatly reduced

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o

o

SignalInput

C2

C2

R2

C2

C1

R1

R3

R4

R5

T2T1

E

Hartley Type F.M. Transmitter

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The capacitorC1 and inductor L form the tank Circuit components of

Hartley Oscillator

The Capacitors C2 are coupling capacitors

T1 is the driver amplifier transistor and T2 is the oscillator transistor

The fact that the capacitance between emitter and base of a

transistor is voltage sensitive is used to frequency modulate the

carrier

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o oX X

C1

R1

1.3 V

15 turns 10 turns

47pF

0.1 uF

MCore

Physiological Parameters Telemetering Transmitter

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To measure temperature, a thermistor is placed in the place of R1

To measure pressure, the pressure changes should be given to move

the core M

To measure pH or any change in voltage, suitable electrodes are

connected across the voltage input XX1

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Bio Signal

20 kHzCarrier

100 MHzCarrier

AmplitudeModulator

FrequencyModulator

Amplifier Transmitter ReceiverFirst Stage

Demodulator

Biotelemetry System with a Subcarrier

Filter

Amplifier

Display

Second StageDemodulator

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To avoid the loading effect a sub carrier system is used

The signal is modulated on a sub carrier to convert the signal

frequency to the neighbourhood of the sub carrier frequency

Then the R.F. carrier is modulated by the sub carrier carrying the

signal

The receiver detects the R.F. and recovers the sub carrier carrying

the signal

Since the sub carrier frequency is quite different from all noise

interference and loading effect, it can be separated by filters

An additional stage of demodulation is needed to convert the signal

from the modulated sub carrier back to its real frequency and

amplitude

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Multiple Channel Telemetry Systems

Types

Frequency Division Multiplex System

Time Division Multiplex System


Each signal is frequency modulated o a sub carrier frequency Then these modulated sub carrier frequencies are combined to modulate

the main R.F. carrier

At the receiver side, the modulated sub carriers will be separated by the

proper band pass filters after the first discrimination

The individual signals are received from these modulated sub carriers by

the second set of discriminators

The low pass filters are used to extract the signals without any noisewww.eeecube.com

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InputChannel I

Input

Channel II

InputChannel III

Output

Channel Io

Output

Channel III

OutputChannel II

o

o

Amplifier

Amplifier

AmplifierSub Carrier

FM

Sub CarrierFM

Sub CarrierFM

Main FMTransmitter

FM ReceiverDemodulator

BP Filter

BP Filter

BP Filter

Sub CarrierDemodulator



f1

f1f2

f2f3

f3


LP Filter

LP Filter

LP Filter

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The transmission channel is connected to each signal - channel input for a

short time to sample and transmit that signal Then the transmitter is switched to the next signal channel in a definite

sequence

When all the channels have been scanned once a cycle is completed and the

next cycle will start

At the receiver end the process is reversed

The sequentially arranged signal pulses are distributed to the individual

channels by a synchronized switching circuit

If the number of scanning cycles per second in each signal is large and if

the transmitter and the receiver are synchronized, the signal in each channel

at the receiver side can be recovered without noticeable distortion

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InputChannel I

Input

Channel II

InputChannel III

Amplifier

Amplifier

AmplifierFM

TransmitterFM

Receiver

Gate

Gate

Gate

Gate

Gate

Gate

OutputChannel I

o

OutputChannel III

Output

Channel IIo

o

LP Filter

LP Filter

LP Filter

Gating SignalGenerator

Gating SignalGenerator

SynchronizationSignal

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bmi Unit 4_opt

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