Biomedical Instrumentation

Biomedical Instrumentation Biomedical instrumentation

Text Books & References • Introduction to biomedical equipment technology; J.J. Carr • Medical Instrumentation; Webster • Electronic devices; Boylestad Biomedical instrumentation

Syllabus • Introduction to biomedical instrumentation & measurement • Basic theories of measurement • Signals & noise • Electrodes, sensors and transducers Pp 26-125 Biomedical instrumentation

What is biomendical engineering • It is a cross-disciplinary field that incorporates • Engineering • Biology • Chemistry • Medicine • Biomedical instrumentation is used to take measurements that are used in • Monitoring • Diagnostic means • Therapy Biomedical instrumentation

Fields of biomedical engineering • Bioinstrumentation • Applies the fundamentals of measurement science to biomedical instrumentation • Emphasizes the common principles with making measurements in living cells • Biomaterials • Application of engineering materials in production of medical devices • Biomechanics • Behavior of biological tissues and fluids • Ergonomics (design principles) • Biosignals • The mechanisms of signal production • Fundamental origins in of the variability in the signal • Rehabilitation engineering • Design of equipments for disabled individuals Biomedical instrumentation

Scientific Notation The form of a number in scientific notation: N X 10x {Unit} • N: Numbers • 10: Base • x: Exponent • Never forget to write the UNIT ……if it exists • 10-x 1/10x • Prefixes: • Nano-, micro-, milli-, centi-, …, kilo-, mega-, giga-, tera- 10-9 …………………………………………………………………………………..1012 Biomedical instrumentation

Metric Prefixes Biomedical instrumentation

Units and physical constants Biomedical instrumentation

SI Units • The standard unit system for medical, engineering and scientific practice is taken from the SI (Systeme Internationale) CGS or MKS (also called metric system) • SI depends on multiplying prefixes in the basic units (see metric prefixes table) Biomedical instrumentation

Conversion to SI units Biomedical instrumentation

Conversion from SI units Biomedical instrumentation

standard physical units Biomedical instrumentation

Physical constants Biomedical instrumentation

Definitions • Measurand (Physical quantities): • Position, displacement • Temperature • Force • Pressure,… • Concentrations, chemicals,…, • Sensor: • is a device that detects a change in a physical stimulus and turns it into a signal which can be measured or recorded • Signal conditioning: • Amplifying, waveshaping, filtering, rectifying,… • A Transducer • is a device that transfers power from one system to another in the same or in a different form. Biomedical instrumentation

Common medical measurands The measurand is the measured quantity Biomedical instrumentation

Generalized Instrumentation system Biomedical instrumentation

Instrumentation System Output Input Display Signal conditioner Sensor Recorder Measurand • A Measuring system is required to compare a quantity with a standard or to provide an output that can be related to the quantity being measured • The quantity to be measured is detected by an input transducer or sensor. • The detected quantity may be converted to a mechanical or electrical form of energy Biomedical instrumentation

surface electrodepressuretransducerphotocoupler temperature sensorpressure gauge strain gauge ： Clinical Instrument A/DConverter LCD Sensor ProcessCircuit ．．．．．． ECGInstrument EMGInstrument Blood PressureInstrument Oscilloscope Medical Measurement Chain Biomedical instrumentation

Generalized Instrumentation System Dashed lines are optional for some application Biomedical instrumentation

“Averages”in Biomedical Engineering Biomedical instrumentation

Types of Averages • Definition • Most typical value or most expected value in a collection of numerical data • Different kinds of average • Mean (arithmetic mean): • The sum of all values xn divided by the number n of different values Ex.: mean average??? sum=125, n=28  Xmean=125/28=4.46 Biomedical instrumentation

Types of Averages • Median: • The middle value in a data set • Mode: • The most frequently occurring value in a data set • If data is perfectly symmetrical  ?? Biomedical instrumentation

Which average is the best to use for which kind of data?? • If data is symmetrical  use mean average • If data is highly asymm. (outliers)  median • If you need an answer to a question  mode • Ex.: most common cause of death, or most popular TV show on Friday,… • Other types of averages: • Geometric average biological studies • Harmonic mean (H.M.) when data are expressed in ratios (miles/hr, riyal/dozen,…) Biomedical instrumentation

Geometric average • Ex.: if you have 48$, spend half of your available money each day for 5 days. • Arithm. Mean= (48+24+..)/5=18.6 Biomedical instrumentation

Geometric average • To find the Geometric average • To straighten the curve  semilog paper Biomedical instrumentation

Harmonic mean (H.M.) • Is used when data is expressed in ratios (miles/hrs, riyals/dozen,…) • The expression of H.M. Biomedical instrumentation

Harmonic mean: example Biomedical instrumentation

Integrated Average V T 0 t1 t2 t • This average is applied often in RC circuits • The area under the curve of a time dependent function divided by the segment of the range over which the average is taken • The output of the circuit ~ time average of the input signal V1 Biomedical instrumentation

Root-mean-square “rms” • Used in electrical circuits and other technologies e.g.when comparing AC sine wave current with DC current the AC should be expressed in an equivalent value which is the rms. • Definition of rms: Vrms: is the rms value T: is the time interval t1 to t2 V(t): is the time-varying voltage function • Special case: the rms value of a sine wave voltage is Vp/√2 or 0.707 Vp (Vp is the peak voltage) Biomedical instrumentation

Root sum sqaure “rss” Biomedical instrumentation

Logarithmic Representation of signal Levels“Decible Notation dB” • Original unit was “bel” • The prefix “deci” means one tenth • Hence, the “decible” is one tenth of a “bel” • dB expresses logarithmically the ratio between two signal levels (ex.: Vo/Vi = Gain) • dB is dimensionless For voltage or current measurements For power measurements Review table 3-8 page 37 in IBET Biomedical instrumentation

Common dB scales in electronicsdBm, dBmV • dBm: 0 dBm refers to an input power of 1mW dissipated in 50Ω resistive load • What is the signal level 9mW as expressed in dBm? • dBm = 10 log (9mV/1mW) = 9.54 dBm • Express a signal level of 800 μV in dBm Use P=V2/R =0.00000064V/50Ω =0.0000128mW  dBm = 10log(P/1mW)= -48.9 Review dBmV and examples page 38,39 in IBET Biomedical instrumentation

The basic equations to calculate decibels (Logarithm) Io Iin Vin Vo Pin Po Biomedical instrumentation

Calculation of the overall strength of a system and calculating the system gain Biomedical instrumentation

For dB = 20 log (Vo/Vin) if it is needed to convert from dB to output-input ratio i.e. Vo/Vin Vo = Vin 10dB/20 or Vo = Vin EXP(dB/20) Ex: calculate the output voltage Vo if the input voltage Vin=1mV and an amplifier of +20 dB is used: Vo=(0.001V) 10(20/20) =(0.001) (10) = 0.01V Converting between dB and Gain notation Vin Av=20dB Vo ? 1 mV Biomedical instrumentation

Special decibel scales: dBm • dBm: used in reference frequency measurements (RF) • 0 dBm is defined as 1 mW of RF signal dissipated in 50-Ω resistive load • dBm = 10 log (P/1 mW) • EX: What is the signal level 9 mW as expressed in dBm? • dBm = 10 log (P/1 mW) dBm = 10 log (9 mW/1 mW) = 9.54 dBm Biomedical instrumentation

Data Classes • Qualitive • Nonnumerical or categorical (includes the presence or nonpresence of some factor, good or bad, defective or not defective, gender …) • Not inherently with numbers • Can be given a numerical flavor (1 or 0, yes or no) • Sometimes we assign some kind of scale Biomedical instrumentation

Data Classes • Quantitive • Naturally result in some number to represent a factor (amount of money, length, temperature, voltage, pressure, weight …) • Interval: referenced to a selected standard zero point (ex.: calendar is referred to date of birth of Christ or Hijra, temperature C is referred to the freezing or boiling point of water) note: centigrade: centi=100 (0-100 divisions from the arbitrarily set 0C to 100C) • Ratio: fixed to a natural zero point, such as weights, pressure, temperature (Kelvin) referred to the absolute zero (0 K) at which molecular motion ceases (-273.16C) Biomedical instrumentation

Variation and error • Variations (or random variation) are caused by certain errors in the measurement process. • Caused by type of meter used • Caused by variation in the process being measured • Random variation causes data obtained to disperse how to represent this dispersion? Histogram, normal distribution Biomedical instrumentation

Variation and error: Histograms & Normal distribution (Gaussian curve) • Data represented in fig.a  Histogram • Data represented in fig.b  normal distribution (Gaussian) • Set of data: Biomedical instrumentation

Variance & Standard deviation • The normal distribution gives a measure of data dispersion • Dispersion of data is summed up as variance and standard deviation of the data • Variance: • Standard deviation: In case of small data sets : the mean Biomedical instrumentation

X0 Accuracy of a measurement is indicated by the size of ΔX • Xi: true value • X0: central value of successive measurements • ΔX: Error • As ΔX  0 then X0  Xi ΔX Y X Xi Biomedical instrumentation

Basics of measurements Before we begin our look at biomedical instrumentation, we need to study some general characteristics of instrumentation Biomedical instrumentation

System Characteristics Specific ch/cs General ch/cs Biomedical instrumentation

Specific Characteristics for a system Specs for specific biomedical instrumentation as determined by the committee ………… ex: ECG ECG specifications Biomedical instrumentation

Some specific Characteristics For example • Dynamic range: • Given is the input dynamic range -5mV to +5mV • If input signal exceeds the dynamic range so it will cause an error • The amplified signal is then called to be saturated Biomedical instrumentation

Some specific Characteristics • DC offset • Is the amount the signal may be moved from its baseline and still be amplified properly by the system Without DC offset With DC offset Biomedical instrumentation

Some specific Characteristics • Slew rate • Maximum rate at which the system can observe a changing voltage per unit time • If the input signal exceed the given slew rate the output will be distorted • Frequency response • The range of frequencies of the measurand the system can handle Biomedical instrumentation

General characteristics These are characteristics all systems share • Linearity • Analog or digital system Biomedical instrumentation

Significant factors in measurements Biomedical instrumentation

Biomedical Instrumentation