biomedical engineering lecture sheet for khulna university

BIOMEDICAL ENGINEERING

Reference:

1.L. Cromwell, F.J. Weibell and E.A. Pfeiffer: Biomedical Instrumentation and Measurements, 2nd Edition.

2.R S Khandpur: Handbook of Biomedical Instrumentation, 2nd Edition.

Biotelemetry or Biomedical Telemetry

Biotelemetry is a technique, used for monitoring, recording & measuring the biological parameters over a distance.

Application:1. Wireless -telemetry.2. Telemedicine surveillance.

Physiological parameters adaptable to biotelemetry: Blood pressure Blood flow Respiration Gastrointestinal pressure

Biotelemetry System Components

Transmitter:

Subject

Exciter

Transducer

Direct Bio-potential

Carrier

Modulator

Processor

Amplifier

Biotelemetry System Components

Receiver:

Tuner

Tape Recorder

Demodulator Chart Recorder or

Oscilloscope

Block Diagram of ECG Telemetry

Transmitter & Receiver:

Subcarrier Modulator

Transmitter

ECGAmplifier

Battery Cardioscope

RF Amplifier

Demodulator

Heart Rate Monitor

Graphic Recorder

Tape Recorder

ReceiverAntenna

TransmitterAntenna

ECGElectrodes

Analog Physiological Signal Transmission

Transmission Over Telephone Line:

Pre amplifierFrequency Modulator

To Telephone

lines

FromTelephone

lines

Audio Amplifier

DemodulatorLow pass Integrator

Medical Transmitting Frequency

Frequencies used for medical telemetry are 37,102,153,159,220& 450MHz.

Reason:1.Radio waves hindered.2.Poor signal quality.3.Crosstalk or interference.

Blood Cell Counter

Blood cell counter count the size & number of cell within the blood.

Packed Cell Volume: The percentage of cells in the blood is called PCV.

Elements of blood:1.Plasma(55%)2.Blood cells(45%)

Types of Blood Cell:1.RBC or Erythrocyte(5.5 million per cubic mm)2.WBC or Leucocytes(5-10 thousand per cubic mm)3.Platelets or Thrombocytes(250-750 thousand per cubic mm)

Disease

Anemia : Anemia is the reduction of oxygen carrying capacity of blood.

Bone marrow dysfunction.Poor production rate of RBC.Change in number, volume or Hb concentration of

RBCIdentified by measurement of packed cell volume.

Dengue Fever: Dengue fever causes the reduction of platelet in the blood.

Identified by the number of platelet count.

Cell Size Calculation

Red cell count : The number of red cell per litter of blood.

Mean Cell Volume : MCV=PCV ÷red cell count.Unit : Femolitres. Normal value (86 ± 10)fl, disease(50-150)fl.

MCH : MCH=amount of Hb per litre ÷ red cell count.Unit:Picogram. Normal value(29.5 ± 2.5)pg, disease(15-50)pg.

MCHC: MCHC=amount of Hb per dl ÷ PCV.Unit: g/dl.

Contd.

Cell Size Calculation

MPV: MPV= Integrated platelet volume ÷ PLT.Unit : Femolitres.

Plateletcrit (PCT): Percentage of total specimen volume occupied by the platelet.

PCT%=MPV× PLT ×100.

Red cell distribution width: The width of the size distribution of red cell.

RDW=(20th-80th )percentile volume×100×k/(20th+80th)percentile volume.

Platelet distribution width: Represents the size distribution of platelets.

Blood Cell Counting Method

There are 3 method1.Microscopic Method:Principle : Diluted sample of blood is visually examined by

microscope & cells are count. Simple and suitable for small laboratories. Provide accuracy of ±20%.

2.Automatic optical method:Principle : In this method light scattered from blood cell is

collected & converted to electrical signal for rapid counting. Instrument required 1 ml sample & 30 s to cell count. Provide accuracy 2%.

3.Electrical conductivity method.

Electrical Conductivity Method

1.Coulter Counter:Principle: Coulter counter operate on the principle of conductivity

change when a cell passes through an orifice.Block Diagram:

A B

Electrical Conductivity Method

2. Picoscale Counter:Principle: It operates on the same principle of detecting the

change in conductivity in the presence of a cell within the orifice.

Block Diagram:

X-rays

Definition :X-rays are the electromagnetic radiation located at the low wavelength end of electromagnetic spectrum.

Electromagnetic Spectrum: Frequency: 30 petahertz to 30 exahertz . Wavelength: 0.01 to 10 nanometer. Energy : 120 eV to 120 keV. Speed: 3×108 m/s.

Relation between λ, E, f & V: Wave. Particle. Radiation.

Types & Unit of X-ray

Types:1. Soft X-ray: 0.12 to 12 keV (10 to 0.10 nm wavelength) .2. Hard X-ray: 12 to 120 keV (0.10 to 0.01 nm wavelength).

Exposure.

Units: Coulomb per kilogram. Rontgen: 1R=2.58 × 104 C/Kg RAD: D=fR. REM: REM=RAD×QF.

X-ray Tubes

Production of X-ray: When fast moving electron suddenly decelerated.

Operation of an X-ray Tube:

Internal Elements Anode material Target Voltage

Instrumentation for Diagnostic X-Ray

X-Ray to Visualize Inner Part of Body: Different components of body has different densities. Internal structure of body absorb Varying radiation. Leaving radiation show the desired image with spatial intensity

variation. Shadow image represent the X-Ray density of the organs.

Visualization of X-Ray

X-Ray can be visualized by producing an image of the intensity distribution after passing through body.

There are 3 techniques:

1.Fluoroscopy.

2.X-Ray films.

3. Image Intensifiers.

Fluoroscopy

Fluoroscopy: An imaging technique to obtain a real time moving image of the internal structures of patient with fluoroscope.

Component & Operating Principle:

X-ray source & Fluorescent screen.

A plastic base coated with thin layer of fluorescent material.

Glass plate viewed the optical image.

Image function based on X-ray intensity.

At high intensity it is harmful to eye.

At poor intensity, image can be viewed on dark room.

Eye adaption required 10 to 20 minute in dark.

X-ray Film

X-ray film are sandwiched between two screen & available in cassette.

Component & Operating Principle: One side is thin transparent plastic easily penetrate by X-rays. Other side is coated with photosensitive material. X-rays affect the photographic film as like as light. The film is immersed in a developing solution. After processing an shadow image of X-ray intensity produced.

Image Intensifiers

The image intensifiers can be used to brighten faint image on fluoroscopic screen.

Component & Operating Principle: Contains a fluorescent screen behave like photocathode. Electron image shift from fluorescent to phosphor screen. Lens & mirror system project image on phosphor screen. Finally, X-ray image is produced and appear on output screen. Video camera is used to record the image & to observe on TV monitor.

X-ray Machine

Block Diagram of X-ray Machine:

Timer

Exposure Switch

KV Selector

Voltage Compensator

Filament Supply and Temperature

Control

High Tension Supply

mA Control

Rectifier

mA Meter

Mains X-ray Tube

KV Meter

Voltmeter

Different Control of X-ray Machine

There are 3 different control of X-ray machine.1.Filament Heat Control (mA): It is determined by the mA setting. The hotter filament result emission of more electron. Larger mA current increases the cathode electron emission. More electron crossing X-ray tube, increase number of X-ray. No change in maximum and average energy.

Different Control of X-ray Machine

2. Kilovolt Control(kV):Voltage between (-) charged cathode & (+)charged anode is called peak kV.

Higher kVp increases speed of electron that strike the target. Maximum & average energy of X-ray beam increases. X-ray beam pass through more dense tissue produce better

radiographic image. Increasing penetrating ability increase X-ray production &

reduce exposure time.

Different Control of X-ray Machine

3. Timing Control: A timer on X-ray tube controls electron production from cathode. Increase in exposure time, increase number of X-ray. Doubling exposure time doubles the number of X-ray. It has no effect on average and maximum energy of X-ray beam.

Cooling Process.

Computed Tomography(CT)

CT is a powerful nondestructive technique to produce 3D cross-sectional image from flat X-ray image.

Basic Principle: The Greek word tomos means slice or section & graphe means drawing.

CT produces cross-sectional images or slices of anatomy.

Picture is made by viewing the patient via X-ray imaging from numerous angles.

By combining the series of X-ray the detailed structure is reconstructed.

Finally, reconstructing structure is displayed on Video monitor.

Limitation of X-ray

There are some limitations of using conventional X-ray. Two-dimensional picturization. Overlapping. Less shades of grey. Less resolution. No real time imaging. The X-ray photographic film has a limited dynamic range. Exposure of ionizing radiation is harmful to human body. Relatively low information compared with other imaging

method.

Now-a-days CT scan are used to overcome these limitation.

Use of CT Scanner

The CT scanner used for following purposes To produce 3D image of internal structure of the body. To observe the structures of brain and head. To observe the structures of chest and abdomen. To identify diseases. To evaluate multiple organ injury in case of trauma. To confirm the presence of lesions such as cysts & solid

tumors. To detect the problem of spinal cord such as osteoporosis. To plan radiation treatments for tumors & biopsies of

particular organ.

CT Image Producing Technique

Block Diagram: The basic block diagram for producing CT image is given below.

System Components

The CT system consists of the following 4 major sub-system.

Scanning System: It takes suitable reading for picture reconstruction. It includes X-ray source & detector.

Processing Unit: It converts these readings into intelligible picture information.

Viewing Part: It presents information in visual form for diagnosis.

Storage Unit: Store information for subsequent analysis.

Historical Development of Scanner

1.First Generation Scanner. Single x-ray tube & Detector. Single projection obtained by straight line motion. Frame rotate 1° for next projection. Translation & rotation repeated until 180°projection. Simplicity, flexible, detector match & wide range object. Scan time 4.5 minute.

2.Second Generation Scanner. Same translate & rotate geometry. Fan beam & multiple detector. Series of views during each translation. Rotation angle increased. Scan time 20 to 80 seconds.

Historical Development of Scanner

3.Third Generation Scanner. Rotate-rotate geometry. Fan shaped x-ray beam & arc shaped detector. Different projection obtained by high sampling rate . Transitional motion is converted to rotational motion. Scanning time reduced to few second or less.

4.Fourth Generation Scanner. Rotate- stationary system. Fan shaped x-ray beam & circular detector. Test specimen irradiated by wide fan beam. Number of view equals to number of detector. Combine artifact resistance of 2nd & speed of 3rd . Scan time 1-10 seconds.

Methods of CT Scanning

There are 2 methods of CT scanning1.Slice-by-slice method or conventional CT Dynamic incremental scanning. It generates by directing x-ray beam several different angles &

levels of abdomen. Contrast dye visible the organ on x-ray film. Computer process x-ray information and produces CT image. Provides higher ionizing radiation than chest radiographs &

easy to read. Very expensive to produce & may cause lung cancer.

Methods of CT Scanning

2. Volume acquisition method or spiral CT Involves simultaneous movement of patient table & x-ray tube. Volume acquisition of data reconstruct individual tomographic

image. Excellent multiplaner reformation are possible for thin image

slice. Provide greater visualization of blood vessels & internal

tissues. Reduces scanning time from 2 minutes of conventional CT to

20-30 sec. Widely used for the evaluation of severe trauma injuries such

as automobile accidents.

Fan Beam

The beam which is used to reduce scanning time is called fan beam.

It produce by the higher output rotating anode x-ray sources. It measure the density across the wider portion of the slice. It cover the entire width of the slice. Time for complete scanning is 2.5 second or less.

Advantages of CT

It provide axial, coronal and sagittal view of the tissue.

It shows automatically precise location of the lesion and extent.

It provides greater geometric precision.

It allows reconstruction of cross-sectional image of the entire maxilla or mandible or both.

The structure of the soft tissues both normal & pathological are clearly displayed.

Due to inherent high contrast resolution difference between tissue that differs less than 1% can be made.

Due to high sensitivity of detector large information is obtained from small exposure radiation to the patient.

As the image stored in computer so it can be viewed & manipulated in absence of patient.

Combining consecutive CT scan, a 3D image of the object can be accurately reconstructed.

Disadvantages of CT

Although CT is a relatively accurate test, it has some disadvantages.

CT scan is sophisticated, costly and difficult to maintain. Very thin contiguous or overlapping slice may result in a high dose of

radiation. There is an inherent risk associated with the contrast medium. Very high density materials like metal bullets & dental restorations

produce some severe artifact on CT scan, which produce interpretation difficult.

1. Streak artifact. Appear around material that block x-ray. Undersampling, photon starvation, beam hardening or scatter Commonly occur in posterior fossa of brain. Remove by newer reconstruction technique.

Artifacts

2.Partial volume effect. Appear as blurring over sharp edge. Caused when scanner unable to differentiate high & low density

tissue. Overcome by scanning using thinner slice.

3.Ring artifact. Mechanical artifact. Image of one or more ring appear within an image. Occur due to detector fault.

4.Motion artifact. Caused by movement of object. Reduced by IFT(Incompressible flow tomography).

5.Noise artifact. Caused by low signal to noise ratio. Also due to insufficient power to penetrate anatomy.

Magnetic Resonance Imaging(MRI)

MRI tomography is powerful medical imaging technique used in radiology, which uses magnetic fields and radio frequency signal to obtain anatomical information of human body.

Basic Principle: When certain material placed in MRI machine 2 things happen. Powerful magnetic field align the magnetization of atomic nuclei in the

body. Radio frequency field systematically alter the alignment of this

magnetization. The nuclei within this tissue produce a rotating magnetic field. Tissue take resonant characteristics & become magnetized. The nuclei can absorbed and re-radiate RF radiation at specific

frequency. This phenomena is called NMR. The RF signals produced by NMR can be displayed in the form of

image.

Comparison Between CAT & NMRI

A CAT scanner produce image only at right angles to body axis but an NMR scanner can produce at any desired cross-section.

Unlike CAT, NMRI imaging requires no moving parts, gantries or sophisticated crystal detector.

Unlike CAT, NMRI use no severe ionizing radiation & has minimal hazards for operators & patient.

The resolution of NMRI imaging is worse than the x-ray CAT scanner.

NMRI takes much longer time to reconstruct image than CAT scanner.

Compared to the CAT, NMRI signal is inherent to very low sensitivity.

Unlike CAT, NMRI based on very weak, non-ionizing radio-frequency phenomenon.

Explanation of Some Basic Concept

Magnetic moment: Nuclei of the material contain odd number of proton, neutron or

the combination of both. It has nuclear spin & magnetic moment with magnitude &

direction. Magnetic moment align the tissue randomly with zero

magnetization. Material under magnetic field Bo , nuclei experience an external

magnetic torque. It align the individual parallel or anti-parallel magnetic moments

in the direction of magnetic field. Slight excess nuclei aligned parallel & gives the tissue a net

magnetic field Mo .

Explanation of Some Basic Concept

Free induction decay: In NMR, at room temperature more protons in lower energy

state than higher. The excited protons tends to returns or relax to its low-energy

state. It performs spontaneous decay & re-emission of energy at a

time t in the form of radio wave. This decay is exponential in nature & produces a free induction

decay signal. It is the fundamental form of nuclear signal obtainable from

NMR system.

Explanation of Some Basic Concept

Excitation: If the material is now subjected to another magnetic field. A bar magnet is placed along the Y-axis. This cause the slight shift in net magnetization from Z-axis

through angle α. The same result can be obtained by applying a RF pulse at

resonant frequency of protons in the tissue. The angle α depends on the amplitude but primarily on the length

of RF pulse. The net magnetic moment M precesses with the same

characteristics frequency ωo .

Explanation of Some Basic Concept

Emission: When RF pulse is turned off, the net magnetization swing back

to Z-axis. It induces an NMR signal in the receiver coil. The individual magnetic moments begin to de-phase with one

another by rotating slower & faster. M in X-Y plane disappears when individual magnetic moment

cancel out each other.

Image Reconstruction Techniques

There are 4 image reconstruction techniques. In all cases Z-axis is coincidental with cylindrical axis of sample tube.

1.Sequential point method: 3 orthogonal linear field gradient each modulated with different

gradient applied to sample. A single point on the specimen which is unmodulated is taken as

reference signal. Sample volume is divided into nx,ny & nz volume elements along 3 axes. By moving the center of field gradients sensitive point move arbitrarily

through sample.

These NMR signal is used to reconstruct the image within this volume. This method utilize steady state free precession(SSFP) technique.

Image Reconstruction Techniques

2.Sequential line method: 2 modulated time varying & one static gradient are applied on the

sample. The modulated time varying gradient operate along X and Z axes. A single line of points is selected as a sensitive line. By moving this sensitive line across the sample some NMR signal is

obtained. These signal reconstruct the image.

3.Sequential plane method: It permits the simultaneous observation of an entire imaging

plane. Simultaneous observation & resolution of entire plane requires a

dynamic range of nx & ny pixels .

Image Reconstruction Techniques

4.Simultaneous volume measurement: In this case the image are reconstructed from a sufficient number of

projection of nuclear spin density. To obtain a projection of 3D spin density along straight line a strong

magnetic field is applied in chosen direction. Nuclear spin in a plane perpendicular to this direction, contribute to

resonance at same frequency. This signal intensity is the measure of the projected spin density. The NMR signal strength projection of spin density distribution for 3

different field is given below.

Basic NMR Component

The basic component of NMR imaging system is shown below.

A Magnet: It provides strong uniform, steady magnetic field Bo .

An RF transmitter: It delivers RF frequency magnetic field to the sample.

Basic NMR Component

A gradient system: It produces time varying magnetic fields of controlled spatial non-uniformity.

A detection system: This system yields the output signal.

An imaging system: Including computer, it reconstructs and displays the images.

Computer: It provides the imaging sequence in the system. Gates & envelopes for NMR pulse, blanking for pre & RF power

amplifier, voltage waveform of gradient magnetic field all under software control.

It also perform Fourier transformation, image reconstruction, data filtering, image display & storage function.

The computer in this purposes must have sufficient memory & speed to handle large image array.

Biological Effect of NMRI

There are 3 aspects of NMRI, which may cause health hazard.

1.Heating due to RF power: NMRI produce a temperature increase in head about 0.3˚c. This may cause due to RF energy absorption, which depends on tissue

properties, RF pulse & frequency of MRI signal. It may produce less amount of hazard for patient.

2.Static magnetic field: The static magnetic field in NMRI may produce some side effects. It may slight decrease in cognitive skill, mitotic increase in slime moulds

& delayed in wound healing.

3.Strong electric current induction: Oscillating magnetic field gradients may induce strong electric current. This may cause ventricular fibrillation. To avoid this field should not vary faster than 3 tesla/s.

Applications of NMRI

1.Brain & spinal cord: NMRI can produce very detailed structure of the brain & spinal cord. It can easily diagnosis brain tumors, stroke, dementia, multiple

sclerosis, motor neuron disease, meningitis and encephalitis.

2.Bones & joints: It is very effective of checking for damage soft tissue in bones & joints

such as cartilage, tendon, muscle & ligaments. Easily diagnosis bone & joint infection such as arthritis, osteomyelitis.

3.Cancer detection: NMRI are often used for the diagnosis of cancer. It can check how much of the organ is affected by the cancer.

4.Heart & blood vessel: It observe the function of myocardium of heart. This may identify the excessive fat deposition in the major blood

vessels. It can measure blood flow.

Ultrasonic Imaging

Ultrasound: It is a sonic energy at frequencies above the audible range.

Properties of ultrasound:1.Frequency: Ultrasonic's follow the general relationship of V=fλ. For diagnostic purposes ultrasound used frequencies of (1-15) MHz.

2.Propagation: Velocity of sound propagation through medium varies with the density

of medium & temperature. It also varies with its elastic properties. The velocity of sound through bone is much higher than 3360 m/sec.

3. Characteristic Impedance: The characteristics impedance of a material is the product of its

density & velocity of sound such as Z=ρV.

Properties of Ultrasound

4.Attenuation of ultrasonic energy: When ultrasound travels certain amount of the wave is attenuated for

each cm. Amount of attenuation is a function of both frequency of ultrasound &

characteristics of material. Occur in 2 ways absorption & redirection. Unit of attenuation constant α is dB/cm.

5.Half value layer: Half value layer is the depth of penetration at which the ultrasound

energy is attenuated to half of applied amount.

6.Doppler Effect: It is an well known characteristic of ultrasound. It is normally used to measure the velocity of blood. The frequency of reflected ultrasonic energy is increased or decreased

by moving interface. The amount of frequency shift can be found by Δf=2V/λ.

Properties & Production Method of Ultrasound

7.Beamwidth: Ultrasonic waves are transmitted through medium as a beam. The spatial distribution of energy in this beam split into near & far

fields. Near fields extended from transducer to a distance d=r2 /λ –λ/4. The semi angle of divergence about central axis is

θ=0.61λ/r=0.61V/rf=1.22V/fD, where D=diameter of the transducer.

Production method of ultrasound: There are 3 method for producing ultrasound.

1.Piezo-electric effect.2.Magneto striction method.3.Electro striction method.

Within these 3 method piezo-electric is generally used to generate & detect ultrasound waves at modern technology.

Detection Method of Ultrasound

There are 5 method for the detection of ultrasound.1.Kundit’s tube method.2.Conductive funnel method.3.Heated microphone method.4.Thermal detector method.5.Crystal detector.

Within this 5 method crystal detector is mostly used for the detection of ultrasound.

Ultrasonic imaging: The technique of producing image of internal organ by using ultrasound is called ultrasonic imaging.

Ultrasonography: The machine which is used for ultrasonic imaging is called ultrasonography or ultrasound scanner.

Display Mode of Ultrasonography

There are 3 display mode to observe the inside of the body.

1.A scan display modePrinciple: Each transmitted pulse from ultrasonography triggers the sweep of

oscilloscope. Pulse & returning echoes are displayed as vertical deflection. The height of the vertical blip correspond to echo strength. The sweep is calibrated in units of distance. In most cases transducer is stationary. Any movement of echo will be the result of moving targets. Display image in one dimensional form.

Application: In echoencephalogram to obtain record of brain. In echoopthalmoscope.

Display Mode of Ultrasonography

2.B scan display mode.Principle: It presents two-dimensional image of stationary organ. Transducer is moved with respect to the body. Vertical deflection of oscilloscope is made correspond to movement of

transducer. The movement may be linear, circular or combination of both. If the orientation is circular, sweep must be made to compensate for

the variations. This compensation provide true 2D image.

Application: To observe tumors, stone in kidney & gall bladder. To observe the fetus in mother womb.

Display Mode of Ultrasonography

3.M scan display mode.Principle: As A scan each transmitted pulse triggers the oscilloscope sweep. Received pulse brighten the trace rather than vertical deflection

control. Transducer is held stationary. Movement of dot along the sweep represent movement of received

targets. A stationary target will trace a straight line. Moving target will trace the pattern of movement with respect to

time. A light pen recorder is used to produce a chart record of the

movement.Application: To examine the activity of heart & valves. To produce image of non-stationary part of body. In echocardiogram.