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MEDICAL ELECTRONICS LECTURE NOTES © Ms.V.Ezhilya, AP/ECE

VSA SCHOOL OF ENGINEERING

DEPARTMENT OF ECE

MEDICAL ELECTRONICS

UNIT – 5: RECENT TRENDS IN MEDICAL INSTRUMENTATION

Thermograph, endoscopy unit, Laser in medicine, Diathermy units, Electrical safety in

medical equipment.

CLASS – 1

TOPIC: LASER

LASER – Light Amplification by Stimulated Emission of Radiation.

Fig: Laser Principle.

When an excited atom is impinged by a photon, the atom is brought to ground stage

emitting a photon identical to the incident one. If a large number of such coherent photons

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were emitted, the intensity of such photonic beam would be very high. Such “Light

Amplification” will be achieved by this “Stimulated Emission of Radiation” if a “population

inversion” can be achieved.

“Population inversion” means having a material with more number of atoms is the

excited state than in the ground state. When the excited atoms in a material, which is in the

population inversion, are brought to the ground state simultaneously either an enormous

amount of heat or a beam of coherent photons is produced. Materials with later emission are

known as “laser medium”.

Population inversion in a lasing medium can be achieved by an external energy source

such as a light source or an electric discharge. The process of obtaining population inversion is

known as “pumping” and the respective external source as “pumping source”.

The partially or fully reflecting mirrors enhance the process of stimulation by

reflecting the photons back and forth. The photons that are incident on the partially reflecting

mirror at a particular angle are sent out.

Types of lasers:

Classification based on physical status of lasing medium:

(1) solid lasers, e.g., Ruby laser

(2) gas lasers, e.g., CO2 laser

(3) liquid lasers e.g., Acridine red in ethyl alcohol.

Classification based on mode of emission:

(1) pulsed mode lasers e.g., Ruby laser

(2) Continuous wave lasers, e.g., CO2 laser.

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Examples of lasers:

Ruby laser:

1. Lasing medium: ruby crystal (AlO3 dopped with Cr3-).

2. Pumping source: Xenon flash lamp

3. Wave length (λ): (i) 0.55 μm(Green), (ii) 0.42 μm (Violet)

4. Uses: (i) tattoo and ports-wine removal, (ii) ophthalmology

CO2 laser:

1. Lasing medium: CO2 + N2 + He

2. Pumping source: electrical discharge

3. Wave length (λ): 10.6 μm (IR) - Invisible

4. Uses: Surgery

Acridine red in ethyl alcohol:

1. Lasing medium: Acridine red in ethyl alcohol

2. Pumping source: flash lamp

Laser applications in medicine:

(1) Surgery with minimal or no loss of blood and with greater precision, e.g., CO2

laser with 50 – 500W output power.

(2) Removal of tattoo and port-swine, e.g., pulsed ruby laser with 55-100 J/cm2

(3) Treating tumors, e.g., pulsed ruby laser with 1500-2000cm2

(4) Photocoagulation by red ruby laser or argon laser; “Photocoagulation” – process of

clotting blood by laser beam, e.g., pulsed ruby laser.

(5) Treatment of retinal holes/tears, retinal detachment, diabetic retinopathy, cataract,

e.g., argon and NdYAG lasers.

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(6) Treatment of glaucoma (increase in eye-ball pressure due to a block)

(7) Photodynamic therapy (PDT) – a treatment with a combination of a photosensistor

and a light beam in the presence of molecular oxygen causing biological

destruction

(8) Would healing and pain relief using cold lasers (cold lasers-lasers of very low

power in the range W)

Books Reffered:

1. Medical Electronics – R.L.Rekha

2. Handbook of biomedical instrumentation – R.S.Khandpur

HINTS:

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POSSIBLE QUESTIONS:

1. Define Defibrillator. [2m]

2. Write a detail note on defribillator. [16m]

3. Explain in detail about use of LASER in medicine. [ 8m]

4. Classify pacing modes. [2m]

CLASS – 2

TOPIC: Surgical Diathermy

Surgical diathermy:

Electrosurgical unit: The electronic device used to assist the surgical procedures by

providing cutting & hemostasis (stopping bleeding) is known as the electrosurgical unit.

Principle:

The electrosurgical unit consists of two electrodes one being called the active

electrode and other being called the passive or dispersive electrode or patient plate.

The active electrode has a very small cross-sectional area whereas the passive electrode

has a large surface area. A high-frequency electrical current is passed through these

electrodes. Due to far smaller cross-sectional area, the current density at the active

electrode is far greater than that at the passive electrode. As a result of this, the tissue

underneath the active electrode is heated up to destruction.

Electrotomy:

Process of cutting the tissues through application of high-frequency current.

Fulguration:

Process of destructing the superficial tissues through application of high-frequency

current without affecting the deep-seated tissues.

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Coagulation:

Clotting of blood through application of high-frequency current.

Desiccation:

Localized destruction of the deep-seated tissues through application of high-frequency

current. Different current waveforms are used for different applications such as coagulation,

desiccation, cutting & „bloodless‟ cutting.

The desiccation & coagulation are achieved by damped sinusoidal pulses of frequency

from 250 to 2000 kHz and power from 50 to 200 W shown in the following figure.

The cutting is achieved by a continuous sine wave of frequency from 500 to 2500 kHz and

power 100 to 750 W shown in the following figure.

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The bloodless cutting is achieved by combining the above two waveforms. The

resulting waveform is known as blended waveform shown in the following figure.

Diathermy:

Diathermy means „through heating‟ or producing deep heating directly in the

tissues of the body. This is achieved by the application of electrical energy through

electrodes at high frequencies in order to avoid stimulation of motor or sensory nerves.

Advantages of diathermy:

1. Selective treatment is possible i.e., affected tissues can alone be treated without

affecting the neighbouring tissues.

2. Precise control over the heat produced is possible i.e., the treatment can be

controlled precisely.

3. As the body becomes part of the electrical circuit, the heat is not transferred through

the skin.

4. As the high frequency alternating current is used, there will be no stimulation of motor

or sensory nerves and hence no discomfort to the patient.

Short wave diathermy:

Alternating current of frequency 27.12 MHz and wavelength 11 m is used. The following

figure shows the block diagram of a short wave diathermy unit.

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The transformer T1 provides EHT to anode & heating current to the cathode. The anode

is driven at 4000 V. A LC tuned circuit formed by the coil AB along with the capacitor C1 is used

to generate the short wave of desired frequency. The coil CD generates the positive feedback

for the oscillations to occur. The coil EF along with the capacitor C2 forms the patient tuning

circuit for coupling.

The circuit of a typical short wave diathermy unit is shown in the following figure.

The intensity of the current applied to the patient can be controlled by (i) controlling the

anode voltage or (ii) controlling the filament heating current or (iii) controlling the grid bias.

The intensity of the current applied to the patient is shown on an ammeter. Upto 500 W of

electrical energy is available from this circuit.

Auto tuning: Maximum electrical energy is delivered to the patient only if the unit is

correctly tuned to the electrical values of the object (part of the body).

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Detuning may happen due to unavoidable & involuntary movements of the patient.

An electronic circuit is used to measure the polarity & magnitude of the detuning & to

adjust the tuning capacitor accordingly.

The current through the patient is used to charge a capacitor to a voltage which is a

measure of the detuning. This voltage operates a servomotor to adjust the tuning capacitor

accordingly.

Application techniques:

1. Condenser type: The part of the body to be treated is placed between the electrodes

called the pads without touching the skin. This forms a capacitor. Due to dielectric

loss, heat is produced in the intervening tissues.

2. Inductor type: A flexible cable is wound around the part of the body to be treated.

When a RF current is passed through the cable, an electric field is set up at its ends

and a magnetic field at the center. Deep heating achieved via electrostatic field and

superficial heating is achieved via magnetic field.

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Microwave diathermy:

The tissues of the body are irradiated with very short wireless waves of frequency in the

microwave region. Heating is produced due to the absorption of microwaves by the tissues.

Typical frequency used is 2450 MHz corresponding to a wavelength of 12.25 cm. The

microwaves are transmitted in wireless fashion towards the portion of the body to be treated.

Thus no tuning is required.

The following figure shows the block diagram of a microwave diathermy.

The microwaves are generated by a microwave oscillator like magnetron. The

magnetron requires (i) a delay circuit to incorporate a delay for the initial warm-up (ii) cooling

facility using water or air for the anode & (iii) fuses to avoid damage due to excessive current

flow (> 500 mA).

The reflector antenna is used to direct the microwaves towards the portion of the body to

be treated. Typical duration of irradiation is 15-20 min. Much longer duration of irradiation may

cause some discomfort such as skin burns.

Ultrasonic diathermy:

In ultrasonic diathermy, heating is produced due to absorption of ultrasounds by the

tissues. The following figure shows the block diagram of ultrasonic diathermy.

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The conventional oscillator produces sinusoids of frequency 800 kHz to 1 MHz. These

electrical oscillations are then converted into ultrasounds by piezoelectric crystal.

Dosage: The dosage is controlled by varying any of the following parameters: (i)

frequency of ultrasound, (ii) intensity of ultrasound and (iii) duration of exposure.

At 1 MHz, the ultrasonic energy is reduced to 50 % at a depth of 5 cm in the soft tissues

while, at 3 MHz, the ultrasonic energy is reduced to 50 % at a depth of 1.5 cm. But at

frequencies less than 1 MHz, the ultrasonic energy tends to diffuse and no efficient treatment

can be done.

The ultrasonic diathermy can be operated either in continuous or pulsed mode. In the

continuous mode of operation, continuous ultrasonic waveform is used while in the pulsed

mode of operation, ultrasonic pulses are used.

Application techniques: Ultrasounds require medium to transmit. Air or bone

completely obstructs the transmission of ultrasounds. Gel-like medium or water is used to

transmit the ultrasounds through the tissues.

POSSIBLE QUESTIONS:

1. Define fulguration in diathermy.[2m]

2. Mention the advantages of performing surgery using LASER. [2m]

3. Distinguish defribillator from pacemaker. [2m]

4. Define diathermy. List its types. [2m]

5. Name the four valves of heart and define it. [2m]

6. Write a short notes on Surgical diathermy. [8m]

7. Describe in detail about diathermy and its types with neat diagram. [16m]

HINTS:

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CLASS – 3

TOPIC: Latest trends in diagnosis and therapy – Role of Expert system.

Key trends driving the medical electronics market are aging populations, rising

healthcare costs around the globe and the need for access to medical diagnosis and

treatment in remote and emerging regions and in our own homes.

The different world economies will continue to drive trends in these areas and

others for years to come.

Consequently, some of the key concerns medical electronics manufacturers face

today lie in the areas of portability and miniaturization, connectivity, safety, data

security and quality, and reliability.

Miniaturization & Integration

Ultrasound is a medical imaging market segment seeing high levels of innovation in

portable equipment.

Manufacturers of today‟s advanced portable or handheld ultrasound systems

require highly integrated, scalable solutions. This allows medical professionals to

move beyond the lab or office to reach clients in remote settings or emergency

situations around the world.

Integration continues to enable this trend of portability, as well as cost savings. A

good example of this is illustrated in the ultrasound imaging space. While

efficiently maximizing memory usage and power consumption, embedded

processors play a key role in balancing computational power, flexibility, battery

life and system size in medical imaging devices.

For example, today‟s highperformance DSPs have enough horsepower to efficiently

tackle the back-end digital processing on an ultrasound system. At the same time

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the DSP‟s programmability provides the ability to implement the newest software

algorithms available without changing system hardware. OEM development teams

benefit from increased system performance and reduced time-to-market provided

by the high level of system integration found on DSP system-on-chips (SOCs).

Figure 1 – Portable ultrasound system block diagram.

EXPERT SYSTEM:

In artificial intelligence, an expert system is a computer system that emulates the

decision-making ability of a human expert.

Expert systems are designed to solve complex problems by reasoning about

knowledge, like an expert, and not by following the procedure of a developer as is

the case in conventional programming.

The first expert systems were created in the 1970s and then proliferated in the 1980s.

Expert systems were among the first truly successful forms of AI software.

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An expert system has a unique structure, different from traditional programs. It is

divided into two parts, one fixed, independent of the expert system: the inference

engine, and one variable: the knowledge base.

To run an expert system, the engine reasons about the knowledge base like a human.

In the 80s a third part appeared: a dialog interface to communicate with users. This

ability to conduct a conversation with users was later called "conversational"

Software architecture:

1. The rule base or knowledge base

In expert system technology, the knowledge base is expressed with natural language

rules IF ... THEN ... For examples :

"IF it is living THEN it is mortal"

"IF his age = known THEN his year of birth = date of today - his age in years"

"IF the identity of the germ is not known with certainty AND the germ is gram-positive

AND the morphology of the organism is "rod" AND the germ is aerobic THEN there is a

strong probability (0.8) that the germ is of type enterobacteriacae"

This formulation has the advantage of speaking in everyday language which is very rare

in computer science (a classic program is coded). Rules express the knowledge to be

exploited by the expert system. There exist other formulations of rules, which are not in

everyday language, understandable only to computer scientists. Each rule style is

adapted to an engine style.

2. The inference engine

The inference engine is a computer program designed to produce a reasoning on

rules. In order to produce a reasoning, it should be based on logic. There are several

kinds of logic: propositional logic, predicates of order 1 or more, epistemic logic, modal

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logic, temporal logic, fuzzy logic, etc. Except for propositional logic, all are complex and

can only be understood by mathematicians, logicians or computer scientists.

Propositional logic is the basic human logic, that is expressed in syllogisms. The expert

system that uses that logic is also called a zeroth-order expert system. With logic, the

engine is able to generate new information from the knowledge contained in the rule

base and data to be processed.

The engine has two ways to run: batch or conversational. In batch, the expert

system has all the necessary data to process from the beginning. For the user, the

program works as a classical program: he provides data and receives results

immediately. Reasoning is invisible. The conversational method becomes necessary

when the developer knows he cannot ask the user for all the necessary data at the start,

the problem being too complex. The software must "invent" the way to solve the

problem, request the missing data from the user, gradually approaching the goal as

quickly as possible. The result gives the impression of a dialogue led by an expert. To

guide a dialogue, the engine may have several levels of sophistication: "forward

chaining", "backward chaining" and "mixed chaining". Forward chaining is the

questioning of an expert who has no idea of the solution and investigates progressively

(e.g. fault diagnosis). In backward chaining, the engine has an idea of the target (e.g. is it

okay or not? Or: there is danger but what is the level?). It starts from the goal in hopes of

finding the solution as soon as possible. In mixed chaining the engine has an idea of the

goal but it is not enough: it deduces in forward chaining from previous user responses all

that is possible before asking the next question. So quite often he deduces the answer to

the next question before asking it.

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A strong interest in using logic is that this kind of software is able to give the user

clear explanation of what it is doing (the "Why?") and what it has deduced (the "How?" ).

Better yet, thanks to logic, the most sophisticated expert systems are able to detect

contradictions in user information or in the knowledge and can explain them clearly,

revealing at the same time the expert's knowledge and way of thinking.

CLASS – 4

TOPIC: Pattern Recognition System & e-Health

In a pattern recognition method the provider uses experience to recognize a pattern of

clinical characteristics.

It is mainly based on certain symptoms or signs being associated with certain diseases

or conditions, not necessarily involving the more cognitive processing involved in a

differential diagnosis.

This may be the primary method used in cases where diseases are "obvious", or the

provider's experience may enable him or her to recognize the condition quickly.

Theoretically, a certain pattern of signs or symptoms can be directly associated with a

certain therapy, even without a definite decision regarding what is the actual disease,

but such a compromise carries a substantial risk of missing a diagnosis which actually

has a different therapy so it may be limited to cases where no diagnosis can be made.

In machine learning, pattern recognition is the assignment of a label to a given input

value.

An example of pattern recognition is classification, which attempts to assign each input

value to one of a given set of classes (for example, determine whether a given email is

"spam" or "non-spam").

However, pattern recognition is a more general problem that encompasses other types

of output as well. Other examples are regression, which assigns a real-valued output to

each input; sequence labeling, which assigns a class to each member of a sequence of

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values (for example, part of speech tagging, which assigns a part of speech to each word

in an input sentence); and parsing, which assigns a parse tree to an input sentence,

describing the syntactic structure of the sentence.

Pattern recognition algorithms generally aim to provide a reasonable answer for all

possible inputs and to perform "most likely" matching of the inputs, taking into account

their statistical variation.

This is opposed to pattern matching algorithms, which look for exact matches in the

input with pre-existing patterns.

A common example of a pattern-matching algorithm is regular expression matching,

which looks for patterns of a given sort in textual data and is included in the search

capabilities of many text editors and word processors. In contrast to pattern recognition,

pattern matching is generally not considered a type of machine learning, although

pattern-matching algorithms (especially with fairly general, carefully tailored patterns)

can sometimes succeed in providing similar-quality output to the sort provided by

pattern-recognition algorithms.

e – Health:

eHealth (also written e-health) is a relatively recent term for healthcare practice

supported by electronic processes and communication, dating back to at least 1999.

Usage of the term varies: some would argue it is interchangeable with health informatics

with a broad definition covering electronic/digital processes in health while others use

it in the narrower sense of healthcare practice using the Internet.

Forms of e-health:

The term can encompass a range of services or systems that are at the edge of

medicine/healthcare and information technology, including:

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Electronic health records: enabling the communication of patient data between different

healthcare professionals (GPs, specialists etc.);

Telemedicine: physical and psychological treatments at a distance;

Consumer health informatics: use of electronic resources on medical topics by healthy

individuals or patients;

Health knowledge management: e.g. in an overview of latest medical journals, best

practice guidelines or epidemiological tracking (examples include physician resources

such as Medscape and MDLinx);

Virtual healthcare teams: consisting of healthcare professionals who collaborate and

share information on patients through digital equipment (for transmural care);

mHealth or m-Health: includes the use of mobile devices in collecting aggregate and

patient level health data, providing healthcare information to practitioners, researchers,

and patients, real-time monitoring of patient vitals, and direct provision of care (via

mobile telemedicine);

Medical research using Grids: powerful computing and data management capabilities to

handle large amounts of heterogeneous data.

Healthcare Information Systems: also often refer to software solutions for appointment

scheduling, patient data management, work schedule management and other

administrative tasks surrounding health.

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E-Health data exchange

One of the factors blocking the use of e-Health tools from widespread acceptance is the

concern about privacy issues regarding patient records, most specifically the EPR

(Electronic patient record).

This main concern has to do with the confidentiality of the data. There is also concern

about non-confidential data however.

Each medical practise has its own jargon and diagnostic tools. To standardize the

exchange of information, various coding schemes may be used in combination with

international medical standards. Of the forms of e-Health already mentioned, there are

roughly two types; front-end data exchange and back-end exchange.

Front-end exchange typically involves the patient, while back-end exchange does not. A

common example of a rather simple front-end exchange is a patient sending a photo

taken by mobile phone of a healing wound and sending it by email to the family doctor

for control. Such an actions may avoid the cost of an expensive visit to the hospital.

A common example of a back-end exchange is when a patient on vacation visits a doctor

who then may request access to the patient's health records, such as medicine

prescriptions, x-ray photographs, or blood test results. Such an action may reveal

allergies or other prior conditions that are relevant to the visit.

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Books Reffered:

1. Medical Electronics – R.L.Rekha

2. Handbook of biomedical instrumentation – R.S.Khandpur

POSSIBLE QUESTIONS:

1. Define ehealth. [2m]

2. Write a detail note on role of expert system. [16m]

3. Explain in detail about ehealth. [ 8m]

4. Define pattern recognition system. [2m]

HINTS:

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CLASS – 4

TOPIC: Remote Arrhythmia monitoring system

A client-server model based on Internet protocols was used. ECG data was transmitted

from the remote handheld client to a centralized server, where the QRS and premature

ventricular contraction detection algorithms were implemented and graded depending on the

number and pattern of PVCs present.

The QRS sensitivity and specificity on ECG records from Physionet archives in absence

of arrhythmia was 100% and 99.62%, while in presence of arrhythmia was 99.34% and 99.31%.

The average 'negative time' measured on ventricular tachyarrhythmia records was 92 seconds.

The RCAM can provide remote detection of cardiac abnormalities and give specific diagnosis

and recommendations of actions to be taken immediately.

The limitation due to the inability of the PDA to perform complex computations was

overcome by the use of the remote server.

HINTS:

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POSSIBLE QUESTIONS:

1. Describe in detail about remote arrhythmia. [16m]

Books Reffered:

1. Medical Electronics – R.L.Rekha

2. Handbook of biomedical instrumentation – R.S.Khandpur