Introduction to Biomedical Equipment Technology Dr. T. Elsarnagawy

Text Books & References Introduction to biomedical equipment technology; J.J. Carr Medical Instrumentation; Webster Electronic devices; Boylestad Dr. T. Elsarnagawy

Syllabus Introduction to biomedical instrumentation & measurement Basic theories of measurement Signals & noise Electrodes, sensors and transducers Pp 26-125 Dr. T. Elsarnagawy

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 Dr. T. Elsarnagawy

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 Dr. T. Elsarnagawy

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 Dr. T. Elsarnagawy

Metric Prefixes Symbol Name Multiplication p pico 1 x 10-12 n nano μ micro 1 x 10-6 m milli 1 x 10-3 k kilo 1 x 103 M Mega 1 x 106 G Giga 1 x 109 T Tera 1 x 1012 Dr. T. Elsarnagawy

Units and physical constants Dr. T. Elsarnagawy

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) Dr. T. Elsarnagawy

Conversion to SI units Dr. T. Elsarnagawy

Conversion from SI units Dr. T. Elsarnagawy

standard physical units

Physical constants Dr. T. Elsarnagawy

Definitions Measurand (Physical quantities): Sensor: 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. Dr. T. Elsarnagawy

Common medical measurands The measurand is the measured quantity Dr. T. Elsarnagawy

Generalized Instrumentation system Dr. T. Elsarnagawy

Instrumentation System 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 Display Recorder Signal conditioner Measurand Sensor Input Output Dr. T. Elsarnagawy

Medical Measurement Chain A/D Converter Oscilloscope LCD Process Circuit Sensor surface electrode pressure transducer photocoupler temperature sensor pressure gauge strain gauge ： EMG Instrument ECG Instrument Blood Pressure Instrument ．．．．．． Clinical Instrument Dr. T. Elsarnagawy

Generalized Instrumentation System Dashed lines are optional for some application Dr. T. Elsarnagawy

“Averages” in Biomedical Engineering Dr. T. Elsarnagawy

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 Dr. T. Elsarnagawy

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

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,…)

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

Geometric average To find the Geometric average To straighten the curve  semilog paper

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

Harmonic mean: example

Integrated Average 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 V t t1 t2 T V1 Dr. T. Elsarnagawy

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) Dr. T. Elsarnagawy

Root sum sqaure “rss”

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 Dr. T. Elsarnagawy

Common dB scales in electronics dBm, 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 Dr. T. Elsarnagawy

The basic equations to calculate decibels (Logarithm) Iin Io Vo Po Vin Pin Dr. T. Elsarnagawy

Calculation of the overall strength of a system and calculating the system gain Dr. T. Elsarnagawy

Converting between dB and Gain notation 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 Vin Av=20dB Vo ? 1 mV Dr. T. Elsarnagawy

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 (9 mW/1 mW) = 9.54 dBm Dr. T. Elsarnagawy

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

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)

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 

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:

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

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 Y ΔX X0 X Xi Dr. T. Elsarnagawy

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

System Characteristics Specific ch/cs General ch/cs

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

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

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

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

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

Significant factors in measurements

Measured/ Calibration curve O/p Max deviation Idealized curve (linear fit) I/p Dr. T. Elsarnagawy

Closeness to the true value of measurand Accuracy Closeness to the true value of measurand Dr. T. Elsarnagawy

Results have Low scatter  excellent precision a measure of the degree of agreement within a group of measurements – repeatability of a system- (however no guarantee of accuracy) Results have Low scatter  excellent precision Dr. T. Elsarnagawy

The relation may be linear or nonlinear 3. Sensitivity Relation between change in output for a given change in input (scale factor, magnification). The relation may be linear or nonlinear Dr. T. Elsarnagawy

How to calculate Sensitivity (S) Non-linear linear O/p O/p I/p I/p S:sensitivity=ΔO/p/ΔI/p Inverse Sens.=1/S Dr. T. Elsarnagawy

(i.e. Output in lin. prop to the input) Linearity: An instr. is said to be linear when incremental changes in input and output are constant over the specified range (i.e. Output in lin. prop to the input) Dr. T. Elsarnagawy

Smallest i/p increment change that gives some change in the o/p Resolution Smallest i/p increment change that gives some change in the o/p Example: Voltmeter scale with 100 divisions FS=200V, 1/10 of scale division can be estimated  determine the resolution? Solution: 1 division=200/100=2V Resolution=1/10 scale division=1/10x2=0.2V Dr. T. Elsarnagawy

Minimum input value below which no output can be detected. Threshold Minimum input value below which no output can be detected. 7. Hystresis Tendency for indications on an upward cycle to differ from the same points on the downward cycle Causes: Friction, relaxation Numeric value of Hyster.: % of full scale Dr. T. Elsarnagawy

Variation in output without change in input 8.Drift: Variation in output without change in input (...Temp. Changes or component instability) 9. Zero Stability Ability to return to zero when measurand = 0 Dr. T. Elsarnagawy

All together Dr. T. Elsarnagawy

10. Dynamic range: Rdyn=Ymax-Ymin Given is the input dynamic range -5mV to +5mV If input signal exceeds the dynamic range so it will cause an error in the output The amplified signal is then called to be saturated Dr. T. Elsarnagawy

11. 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 Dr. T. Elsarnagawy

13. Frequency response characteristics The range of frequencies of the measurand the system can handle Wideband Band-pass --- Phase distortion Typical for sensors Dr. T. Elsarnagawy

12. 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 Dr. T. Elsarnagawy

Measurements for calibration means المعـــايره Measurements for calibration means - قياسات الإنحراف عن المنحنى الخطى Creep - قياسات الحراره Temperature Hystresis - الإنحراف عن الصفر Zero drift - خطأ الرجوع إلى الصفر (نقطه البدايه) Zero error - خطأ تكرار القياسات Reproducability

Calibration procedure Calibration is used to detect the errors in a sensor  Correction if possible Sensor Transducer Calibration measurements Reference standard

Assignment for next week Measurement errors Describe the four general categories of error Dealing with measurement errors

Signals

Sinusoidal waveform Dr. T. Elsarnagawy

                                                                                                    Dr. T. Elsarnagawy

Types of signal Static: dc Quasistatic Periodic: sine, square,… v(t)=v(t+T) d. Repetitive: quasiperiodic e. Single event transient signal f. Repetitive single event Dr. T. Elsarnagawy

Waveform symmetry Dr. T. Elsarnagawy

Signal sampling Most instrumentation transducers have analog output At the interface between analog transducers and digital computers the signal must be digitized So the signal is sampled at regular intervals Each sample voltage is then converted into an equivalent digital value The next sample cannot be taken until the conversion of the last sample is to digital form is completed Dr. T. Elsarnagawy

Sampled signals Dr. T. Elsarnagawy

Effect of the sampling rate 12 sample/sec 1 Sample/sec If fsampling > fsignal  o.k. Ideally fsampling = 2 fsignal If fsampling < fsignal  aliasing Dr. T. Elsarnagawy

Sampling is used to form To reconstruct the original signal after sampling  pass the sampled waveform through a low-pass filter that blocks fs Sampling is used to form AM, PM, Some applications don’t accept fsampling=2fsignal as in ECG  =5fsignal Dr. T. Elsarnagawy

Essential Electronics Formula Dr. T. Elsarnagawy

Essential Electronics Formula Ohm's Law The first of these is Ohm's Law, which states that a voltage of 1V across a resistance of 1 Ohm will cause a current of 1 Amp to flow. The formula is R = V / I    (where R = resistance in Ohms, V = Voltage in Volts, and I = current in Amps) V = R * I   I = V / R  Dr. T. Elsarnagawy

Reactance The impedance (reactance) of a capacitor, which varies inversely with frequency (as frequency is increased, the reactance falls and vice versa). XC = 1 / (2  Π f C) where Xc is capacitive reactance in Ohms,  (Π pi) is 3.14159, f is frequency in Hz, and C is capacitance in Farads. Inductive reactance, being the reactance of an inductor. This is proportional to frequency. XL = 2 Π f L where XL is inductive reactance in Ohms, and L is inductance in Henrys Dr. T. Elsarnagawy

Either way, a drop of 3dB represents half the power and vice versa. Decibels (dB) dB = 20 log (V1 / V2) dB = 20 log (I1 / I2) dB = 10 log (P1 / P2) Either way, a drop of 3dB represents half the power and vice versa. Dr. T. Elsarnagawy

When resistance and inductance are combined, the formula is Frequency There are many different calculations for this, depending on the combination of components. The -3dB frequency for resistance and capacitance (the most common in amplifier design) is determined by fo = 1 / (2 Π R C)    where fo is the -3dB frequency When resistance and inductance are combined, the formula is fo = R / (2 Π L) Dr. T. Elsarnagawy

Power Power in any form can be calculated by a number of means: P = V I P = V2 / R P = I2 R where P is power in watts, V is voltage in Volts, and I is current in Amps. Dr. T. Elsarnagawy