BME 353E – Biomedical Instrumentation & Measurements

BME 353E – Biomedical Instrumentation & Measurements
2 hrs lecture and 2 hrs practical / lab 3 credit-hours, 5 ECTS Instructor: Bahattin Karagözoğlu Assistant: Mahmud Esad Arar

Syllabus and Goal of the Course
Syllabus: Basic concepts of instrumentation. Biomedical sensors. Origins of biopotentials and electrodes. Biopotential amplifiers and other signal processors. Electrocardiography (ECG), analog and digital processing of ECG signals. Term project. Goal of the Course: This course is designed to introduce the instrumentation and measurement concepts and to illustrate their implementations in the biomedical field with examples. Eventually, it will develop the ability of biomedical engineering students to identify components of a biomedical instrument, from the human body to the display, and analyze principles and problems related to each section. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

BME 353 - Biomedical Instrumentation and Measurement
Prerequisites Prerequisites: BLM 208 – Electronic Circuits Prerequisite by Topic: Calculus, linear algebra and differential equations Linear system theory related to signal and system descriptions Electronic devices and circuits Biopotential signals and physiology of cardiovascular system. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Textbook and References
Textbook: Webster, J. G. (ed); "Medical Instrumentation: Application and design," 4th ed. John Wiley, 2009; References: Enderle J.D. and Bronzino J.D. Introduction to Biomedical Engineering, 3rd ed. Academic Press; 2011; Carr, J.J. and Brown J.M.; "Introduction to Biomedical Equipment Technology," Prentice-Hall, 4th ed. 2001; Karagözoğlu, B. “Elektronik Ölçme ve Görüntüleme Teknikleri,” Nobel, 2015. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Course Learning Objectives
By completion of the course, the students should be able to: Recognize the basic requirements of medical instruments, Describe the instrument functions and define terms related to electrical measurements Identify sensors and the critical issues for sensor choice, placement, and circuit implementation, Measure signals in medical environment and evaluate the quality of effect of measuring instruments on the measured data, Select protection schemes and devices for safe operations of electrically operated devices. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Course Content Week Subject 1 What is an instrument? What is special about BM instruments? Brief history of developments 2 Measurable medical quantities and their properties 3 Sensors and transducers; resistive and inductive sensors, bridge circuit 4 Capacitive and piezo electric sensors, and temperature measurement 5 Power sources for medical instruments: batteries and power supplies 6 Biopotential s and biopotential electrodes 7 Biopotential amplifiers 8 Midterm week, biopotential amplifiers (cont.) 9 ECG measurements and recording 10 Biopotential signal processors 11 Blood pressure an sound 12 Respiratory parameters and their measurements 13 Clinical laboratory instrumentation 14 Electrical safety in the medical environment B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Practical / Laboratory
Week Subject 1 Measurement principles; error, tolerance, accuracy, precision, linearity etc. instrument loading 2 Experiment design through a case study; measuring the heart rate through palpation and comparing the results to rate meter readings 3 Obtaining characteristic of a sensor 4 Special lab session 5 Electrodes and ECG measurements 6 EMG measurements 7 Design and implementation of an ECG amplifier 8 ECG amplifier (cont.) 9 Clinical ECG 10 11 Blood pressure measurement 12 Respiratory measurements 13 Project 14 B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Grading Assessment type Number Contribution Midterm exam (1 hour) 1 20 Quizzes (8 minutes) 6 12 Practical (preliminary work, lab work and report) 8 Lab projects 3 Project Final exam (2 hours) 40 Total 100 Bonuses Homework and active learning 9 Design of new experiments Preparing exemplary problems and solutions B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Biomedical Engineering
Metaphorical bridge Rehearsal: Engineers help in developing medicine and medical technology contributes to furthering the engineering in many fronts. Give two examples for each one of them. Engineering Medicine B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Biomedical Engineering (BME)
Application of electrical, mechanical, chemical, optical, and other engineering principles to understand, modify, or control biologic (i.e., human and animal) systems, as well as design and manufacture products that can monitor physiologic functions and assist in the diagnosis and treatment of patients. When biomedical engineers work within a hospital or clinic, they are more properly called clinical engineers. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Bioengineering Usually defined as a basic research-oriented activity closely related to biotechnology and genetic engineering, that is, the modification of animal or plant cells, or parts of cells, to improve plants or animals or to develop new microorganisms for beneficial ends. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Specific activities by BME
Artificial organs Automated patient monitoring Blood chemistry sensors Advanced therapeutic and surgical devices Application of expert systems and artificial intelligence to clinical decision making Design of optimal clinical laboratories Medical imaging systems Computer modeling of physiologic systems Biomaterials design Biomechanics of injury and wound healing Sports medicine Artificial organs (hearing aids, cardiac pacemakers, artificial kidneys and hearts, blood oxygenators, synthetic blood vessels, joints, arms, and legs). Automated patient monitoring (during surgery or in intensive care, healthy persons in unusual environments, such as astronauts in space or underwater divers at great depth). Blood chemistry sensors (potassium, sodium, O2, CO2, and pH). Advanced therapeutic and surgical devices (laser system for eye surgery, automated delivery of insulin, etc.). Application of expert systems and artificial intelligence to clinical decision making (computer-based systems for diagnosing diseases). Design of optimal clinical laboratories (computerized analyzer for blood samples, cardiac catheterization laboratory, etc.). Medical imaging systems (ultrasound, computer assisted tomography, magnetic resonance imaging, positron emission tomography, etc.). Computer modeling of physiologic systems (blood pressure control, renal function, visual and auditory nervous circuits, etc.). Biomaterials design (mechanical, transport and biocompatibility properties of implantable artificial materials). Biomechanics of injury and wound healing (gait analysis, application of growth factors, etc.). Sports medicine (rehabilitation, external support devices, etc.) B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Specialty areas in BME Bioinstrumentation; biomaterials; biomechanics; cellular, tissue and genetic engineering; clinical engineering; medical imaging; orthopedic surgery; rehabilitation engineering; and systems physiology. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Definition of a medical instrument
A medical instrument or device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery. The most important medical devices are those that save the most lives or alleviate the most pain. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Diagnosing a disease The physician obtains the history, examines the patient, performs tests to determine the diagnosis and prescribes treatment. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Historical Background - Early
1816 stethoscope 1850 clinical thermometers 1850 ophthalmoscopes 1857 laryngoscopes 1860 scopes for the rectum and vagina 1877 cystocopes for the urinary bladder 1895 x-rays 1896 sphygmomanometers 1901 ECG devices 1918 arthroscopes 1927 iron lung 1929 cardiac catheter 1929 EEG instruments 1931 Electrosurgery 1944 artificial kidney 1950s fiber optic imaging bundles 1951 cardiopulmonary bypass unit 1951 PET 1952 mechanical heart valves Historical Background - Early B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Historical development of medical instruments
Before 1900, medicine had little to offer the typical citizen because its resources were mainly the education and little black bag of the physician. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Will to Discover First blood pressure measurement setup B. Karagözoğlu BME Biomedical Instrumentation and Measurement

X-ray (roentgen) in 1895 ECG in 1903 EEG in 1929 1st CAD machine, 1st microprocessor in 1972 1st implantable pacemaker In 1961 IBM PC in 1981 B. Karagözoğlu BME Biomedical Instrumentation and Measurement

A typical IV infusion system B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Historical Background - Recent
1954 donor-organ transplants of the kidney 1957 synthetic arterial grafts 1959 artificial kidney chronic use 1959 implantable pacemakers 1960 cemented total artificial hips 1960 laser 1961 intra-aortic balloon pump 1963 donor-organ transplants of the liver 1963 pulsatile ventricular assist devices 1964 artificial kidney home use 1965 xenograft bioprosthetic heart valves 1967 donor-organ transplants of the heart 1968 balloon angioplasty 1968 ultrasonography 1969 artificial hearts 1971 CT 1980s MRI 1983 laparoscopic appendectomy 1987 laparoscopic cholecystectomy 1990s donor-organ transplants of the intestines & pancreas Historical Background - Recent B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Robotics a robot's design, manufacture, application, and structural disposition. It is related to electronics, mechanics, and software. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Rehabilitation The process of helping an individual achieve the highest level of independence and quality of life possible - physically, emotionally, socially, and spiritually. Rehabilitation engineering is to develop tools and facilities for the disabled people to help them in recovery and gain independence in their activities. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Biomechanics Application of mechanical principles to biological and medical systems, such as humans, animals, plants, organs, and cells. Study of the structure and function of biological systems by means of the methods of mechanics. Numerical methods are hence applied in almost every biomechanical study. Research is done in a iterative process of hypothesis and verification, including several steps of modeling, computer simulation and experimental measurements. Microprocessor controlled prosthetic leg B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Clinical Engineering The application of technology for health care in hospitals. The clinical engineer is a member of the health care team along with physicians, nurses and other hospital staff. They are responsible for developing and maintaining computer databases of medical instrumentation and equipment records and for the purchase and use of sophisticated medical instruments. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Clinical Engineers in the Hospital
They may also work with physicians on projects to adapt instrumentation to the specific needs of the physician and the hospital. This often involves the interface of instruments with computer systems and customized software for instrument control and data analysis. Clinical engineers feel the excitement of applying the latest technology to health care. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Interactions of a biomedical engineer in a hospital setting
B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Rehearsels Who is a bioengineer? Who is a clinical engineer? Why clinical engineers must be very literate in information technology? Why the patient history is taken in diagnosing a disease? What is the main reason for the speedy development in medical technology after 1950’s? Magnetic resonance imaging has been in use since 1940’s. Yet, its medical use as a diagnostic tool started after What is the basic reason behind this delay? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Interaction Between Specialties
These specialty areas frequently depend on each other. Often the biomedical engineer who works in an applied field will use knowledge gathered by biomedical engineers working in more basic areas. For example, the design of an artificial hip is greatly aided by a biomechanical study of the hip. The forces which are applied to the hip can be considered in the design and material selection for the prosthesis. Similarly, the design of systems to electrically stimulate paralyzed muscle to move in a controlled way uses knowledge of the behavior of the human musculoskeletal system. The selection of appropriate materials used in these devices falls within the realm of the biomaterials engineer. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

The future of medical device technologies
Computer-related technologies, molecular medicine, home- and self-care, minimally invasive procedures, device/drug hybrid products, and organ replacement/assist devices using both hardware and tissue-engineered components. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

1 Computer-related technologies
Computer-aided diagnosis, intelligent devices, biosensors and robotics, and networks of devices. Specific product-types integrated patient medical information systems, patient smart-cards, clinical lab robotics, computer-aided clinical lab systems, biosensors, and robotic surgery. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Future trends in computer-related technologies
All of the technologies encompassed by this category likely to experience significant development within the next five (and ten) years that would result in new products for clinical use. On a 'systems' level, very significant developments regarding integrated patient medical data bases (including patient 'smart cards'). Divided expectations regarding the future of computers in clinical decision making. Clinicians' projections were generally more conservative than engineers'. Generally anticipated an increasing trend toward reliance on automated analysis in the clinical laboratory. An escalating trend toward microprocessor-based intelligent devices is generally anticipated. Commonly cited examples are cardiac and drug-delivery implants, as well as 'smart' robotics used in minimally invasive surgery. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

3. Home- and Self-Care Generic technology areas included in this trend are home/self monitoring and diagnosis, home/self therapy, and telemedicine. Specific product examples encompassed by this category are home diagnostics and telemedicine for patients in the home. Expectation for significant developments leading to new products in each of the technologies in this category in both 5 – 10 year intervals. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Telemedicine and e-health
Healthcare practice supported by electronic processes and communication B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Future trends in Home- and Self-Care
Important but unlikely to produce significant technical advances: due to considerations of cost and, to a lesser extent, convenience. The types of home diagnostics commonly envisioned are tests involving urine and blood chemistry, as well as drug concentrations -- particularly for elderly patients. Improved monitoring of glucose levels for diabetics is frequently mentioned. The most common form of home therapy cited is drug administration using simplified delivery techniques. The prospect of using home-based intelligent devices to modulate therapies and to "coach" patients. The possible use of relatively simple forms of telemedicine for home care, especially within the confines of a local or regional medical system. Interestingly, anticipated greater significance for this "low-technology" telemedicine application than for some other "high-end" versions. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

4. Minimally Invasive Procedures
Technology groups related to this category include minimally invasive devices, medical imaging, microminiaturized devices, laser diagnosis and therapy, robotic surgical devices and non-implanted sensory aids. Specific examples are minimally invasive cardiovascular and neurosurgery, laser surgery, robotic surgery, nanotechnology, endoscopy, functional and multimodality imaging, MRI, PET, and image contrast agents. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Future trends in Minimally Invasive Procedures
Every technology in this category will experience significant new developments during the next five and ten year periods leading to new clinical products. Substantial developments were anticipated for microminiaturized devices, but only on a ten-year time scale. For non-implanted sensory devices, generally envisioned only a modest chance for major innovations throughout the next decade (except for the specific example of hearing aids). Expectation of continuing advancements in endoscopic procedures including fiber optic laser surgery and optical diagnosis, smart miniaturized robotic devices, and a range of miniaturized devices. Clinically, expected an emphasis on minimally invasive cardiovascular surgery and minimally invasive neurosurgery. Continuing advances in noninvasive medical imaging, including a trend to image-guided procedures. The most pronounced expectations are for developments in functional and multimodality imaging. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Where do they Work? Biomedical engineers are employed in Industry Government Clinical institutions Academic research They often serve a coordinating or interfacing function, using their background in both the engineering and medical fields. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Career Preparation The biomedical engineer should plan first and foremost to be a good engineer. Beyond this, he or she should have a working understanding of life science systems and terminology. Good communications skills are also important, because the biomedical engineer provides a link among professionals with medical, technical, and other backgrounds. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

A Top-Quality Biomedical Engineer Must Have
An excellent knowledge of physiology so that he/she can make sound judgments in solving biomedical problems. When working in a specific area of biomedicine, it is also necessary to know how disease alters functions; this is the field of pathophysiology. With such knowledge, the biomedical engineer does not have to rely on others for information about living organisms. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Block diagram of a generalized instrumentation system

Rehearsals Why the computer related medical technologies will experience a high rate of development in the next decade? What are the major contributing technologies for home-care? What are the industries where the biomedical engineers can work and what will be their responsibilities? What type of medical knowledge will be needed mostly by biomedical engineers? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Questions to Answer for Measurement
Why measure? What to measure? How to measure? How to establish conditions for measurement? How to verify the data? How to convert data into information? How to present the results? How to interpret the results? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Activities in Acquiring Knowledge

A simplified measurement system
A typical measurement system uses sensors to measure the variable, has signal processing and display, and may provide feedback. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Measurement with or without a clinician
(b) (a) Without the clinician, the patient may be operating in an ineffective closed loop system. (b) The clinician provides knowledge to provide an effective closed loop system. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Reporting abnormalities
In some situations, a patient may monitor vital signs and notify a clinician if abnormalities occur. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

What the Physician Wants?
O2 and nutrient concentrations in the cells Not possible in a direct way Blood flow and changes in the volume Cardiac output = stroke volume x heart rate Not easy to do Blood pressure Direct - requires invasive methods to be used Indirect - noninvasive, but full waveform is not easy to obtain Electrocardiogram and heart rate - noninvasive B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Rehearsals What is metabolism? What is homeostasis? Why a clinician is an essential element for an effective clinical instrument? Why the physician’s primary interest is in determining “O2 and nutrient concentrations in the cells”? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Medically important measurands
Biopotentials Pressure Flow Dimensions (imaging) Displacement (velocity, acceleration and force) Impedance Temperature Chemical concentrations B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Alternative operational modes
Direct-indirect modes Sampling and continuous modes Generating and modulating sensors Analog and digital modes Real-time and delayed-time modes B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Analog and digital signals
Time Amplitude Amplitude Time Analog signals can have any amplitude value Digital signals have a limited number of amplitude values B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Continuous and discrete-time signals
Amplitude Amplitude Time Continuous signals have values at every instant of time Discrete-time signals are sampled periodically and do not provide values between these sampling times B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Example to sampled data
Laboratory test Typical value Hemoglobin 13.5 to 18 g/dL Hematocrit 40 to 54% Erythrocyte count 4.6 to 6.2  106/ L Leukocyte count 4500 to 11000/ L Differential count Neutrophil 35 to 71% Band 0 to 6% Lymphocyte 1 to 10% Monocyte 1 to 10% Eosinophil 0 to 4% Basophil 0 to 2% Complete blood count for a male subject. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Origins of common biological signal
Type of signal Name of organ in Latin Type of presenting prefix+ name + suffix Electro Mechano Pnemo Cardio Encepha Myo Gram Graph Graphy B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Voltage and freq. ranges of some common biopot. signals

Medical measurement constraints
Range Frequency, Hz Method Blood flow 1 to 300 mL/s 0 to 20 Electromagnetic or ultrasonic Blood pressure 0 to 400 mmHg 0 to 50 Cuff or strain gage Cardiac output 4 to 25 L/min Fick, dye dilution Electrocardiography 0.5 to 4 mV 0.05 to 150 Skin electrodes Electroencephalography 5 to 300  V 0.5 to 150 Scalp electrodes Electromyography 0.1 to 5 mV 0 to 10000 Needle electrodes Electroretinography 0 to 900  V Contact lens electrodes pH 3 to 13 pH units 0 to 1 pH electrode pCO2 40 to 100 mmHg 0 to 2 pCO2 electrode pO2 30 to 100 mmHg pO2 electrode Pneumotachography 0 to 600 L/min 0 to 40 Pneumotachometer Respiratory rate 2 to 50 breaths/min 0.1 to 10 Impedance Temperature 32 to 40 °C 0 to 0.1 Thermistor B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Setting sensor specifications
Value Pressure range –30 to +300 mmHg Overpressure without damage –400 to mmHg Maximum unbalance ±75 mmHg Linearity and hysteresis ± 2% of reading or ± 1 mmHg Risk current at 120 V 10 A Defibrillator withstand 360 J into 50  Sensor specifications for a blood pressure sensor are determined by a committee composed of individuals from academia, industry, hospitals, and government. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Specifications for ECG
Value Input signal dynamic range ±5 mV Dc offset voltage ±300 mV Slew rate 320 mV/s Frequency response 0.05 to 150 Hz Input impedance at 10 Hz 2.5 M Dc lead current 0.1 A Return time after lead switch 1 s Overload voltage without damage 5000 V Risk current at 120 V 10 A Specification values for an electrocardiograph are agreed upon by a committee. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Classification of biomedical instruments
Quantity sensed: pressure, flow, temperature etc. Principle of transduction: resistive, inductive, capacitive, ultrasonic or electrochemical Organ system studied: cardiovascular, pulmonary, nervous, and endocrine systems. Clinical medical specialties: pediatrics, obstetrics, cardiology, or radiology. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Interfering and modifying inputs
An interfering input may shift the baseline Original waveform A modifying input may change the gain B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Simplified Electrocardiographic recording system

Compensation Techniques
Inherent insensitivity Negative feedback Signal filtering Opposing inputs B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Negative feedback y + Gd xd - Hf B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Signal filtering Signals without noise are uncorrupted
Interference superimposed on signals causes error. Frequency filters can be used to reduce noise and interference B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Opposing inputs Differential amplifier: v0 = Gd(vA- vB) DC cancellation (bucking) An input signal with dc offset An input signal without dc offset B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Generalized Static Characteristics
Error Accuracy Tolerance Precision and reproducibility Resolution Statistical control Static sensitivity Zero drift Sensitivity drift Linearity Input ranges Input impedance B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Measurement Errors

Errors in Analog Readings

Errors in Digital Readings

Accuracy Data points with Accuracy: closeness with which an instrument reading approaches the true or accepted value of the variable (quantity) being measured. It is considered to be an indicator of the total error in the measurement without looking into the sources of errors. low accuracy Accuracy is often expressed in percentage high accuracy B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Accuracy B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Precision Data points with A measure of the reproducibility of the measurements; i.e., given a fixed value of a variable, precision is a measure of the degree to which successive measurements differ from one another. low precision Number of distinguishable alternatives V is more precise than 2.43 V. high precision B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Resolution The smallest change in measured value to which the instrument will respond. Statistical control: random variations in measured quantities are tolerable, Coulter counter example B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Significant Figures

Question Two resistors, R1 and R2, are connected in series. Individual resistance measurements using a digital multimeter, yield R1 = 18.7  and R2 = . Calculate the total resistance to the appropriate number of significant figures. What would be the result for R1 = 18.7  and R2 = ? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Tolerance Maximum deviation allowed from the conventional true value. It is not possible to built a perfect system or make an exact measurement. All devices deviate from their ideal (design) characteristics and all measurements include uncertainties (doubts). Hence, all devices include tolerances in their specifications. If the instrument is used for high-precision applications, the design tolerances must be small. However, if a low degree of accuracy is acceptable, it is not economical to use expensive sensors and precise sensing components. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Static sensitivity Sensor signal Measurand Sensor signal Measurand A low-sensitivity sensor has low gain A high sensitivity sensor has high gain B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Static sensitivity constant over a limited range

Zero and sensitivity drifts

Linearity Output Input Output Input A nonlinear system does not fit a straight line A linear system fits the equation y = mx + b. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Calibration for linearity
Output Input Output Input The one-point calibration may miss nonlinearity The two-point calibration may also miss nonlinearity Measuring instruments should be calibrated against a standard that has an accuracy 3 to 10 times better than the desired calibration accuracy B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Hysteresis A hysteresis loop. The output curve obtained when increasing the measurand is different from the output obtained when decreasing the measurand. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Independent onlinearity

Input ranges An input signal which exceeds the dynamic range The resulting amplified signal is saturated at 1 V B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Input impedance Xd1 : effort variable System Output Xd2 : flow variable B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Frequency range Frequency response of the electrocardiograph B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Time delay Log scale w K x(t) 1 t y(t) Log scale w 1 td t B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Engineering Design Imagine Deliver Criticize Realize Contemplate Imagine: Tahayyül Contemplate: Tasavvur Realize: Tahakkuk Criticize: Tenkit Deliver: Teslim Design is the innovative process of identifying needs and then devising a product to fill those needs. It is a problem solving using the existing knowledge and technology: integration of knowledge. It considers alternative solutions for selecting the optimal solution with a fixed goal or specifications in mind. B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Design criteria Initial instrument design Signal factors Prototype tests Environmental factors Final instrument design Measurand Medical factors FDA, BMD approval Economical factors Production B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Design criteria Specificity Signal-to-noise ratio Stability Temperature Humidity Pressure Acceleration Shock Vibration Radiation Power requirements Mounting size, shape Initial instrument design Sensitivity Range Differential or absolute input Input impedance Transient and frequency response Accuracy Linearity Reliability Signal factors Prototype tests Environmental factors Final instrument design Measurand Invasive or non-invasive Tissue-transducer interface requirements Material toxicity Electrical safety Radiation and heat dissipation Patient discomfort Cost Availability Warranty Consumable requirements Compatibility with existing equipment Medical factors FDA, BMD approval Economical factors Production B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Signal factors Sensitivity Range Differential or absolute input Input impedance Transient and frequency response Accuracy Linearity Reliability B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Environmental factors
Specificity Signal-to-noise ratio Stability Temperature Humidity Pressure Acceleration Shock Vibration Radiation Power requirements Mounting size, shape B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Medical factors Invasive or non-invasive Tissue-transducer interface requirements Material toxicity Electrical safety Radiation and heat dissipation Patient discomfort B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Economic factors Cost Availability Warranty Consumable requirements Compatibility with existing equipment B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Rehearsals What is the function of a sensor? What is the difference between sensor and transducer? Why do we need a calibration signal? Why we need an external power source? What are the frequently used external power sources? What are the means for displaying the output? B. Karagözoğlu BME Biomedical Instrumentation and Measurement

Measurand B. Karagözoğlu BME Biomedical Instrumentation and Measurement

BME 353E – Biomedical Instrumentation & Measurements

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