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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
Power Supply Arrangement
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Power Supply Arrangement
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
Frequency 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
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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
Sub CarrierDemodulator
Sub CarrierDemodulator
f1
f1f2
f2f3
f3
Frequency Division Multiplex System
LP Filter
LP Filter
LP Filter
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Time Division Multiplex System
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
Time Division Multiplex System
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