Biomedical Instrumentation

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Ophelia Hampton
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1 Biomedical Instrumentation Michael R. Neuman, PhD, MD Memphis Joint Program in Biomedical Engineering Orhan Soykan, PhD Medtronic, Inc. and Michigan Tech Heidi Niska, BSEE Graduate student, Michigan Tech

2 General Information on the Course Instructors Textbook: J. Webster, Medical Instrumentation: Application and Design Lab: No lab this and next week! (Withhold Cheers!) Recitation sessions Office hours

3 Instrumentation Devices that can be used to make a measurement and give quantititave (or sometimes qualititative) results

4 Biomedical Instrumentation Devices that can be used to make measurements of biologic or medical quantities and give quantititave (or sometimes qualititative) results

5 Examples of Familiar Biomedical Instrumentation Clinical Thermometer Stethoscope

6 Neonatal Intensive Care Unit

7 Future Biomedical Instrument Tricorder (Star Trek) Completely non-invasive Internal and external measurements Imaging Internal intelligence to make diagnosis and suggest therapy

8 Home Glucose Monitoring Requires blood sample (<10µL) Must use microlancet Colorimetric or electrochemical determination Newer units have software instructions and memory

9 Basic Biomedical Instrument Physiologic System Sensor Processor Display Storage Observer

10 Fundamental Rules of Biomedical Instrumentation Minimum disturbance to physiologic system Sensor must be at physiologic variable value Maintain simplicity

11 Important Instrumentation Terms Sensitivity - Change in output as a function of a change in input Stability - Consistency in output for a constant input Specificity - Ability to distinguish desired variable from other competing variables Accuracy - Difference between true value and measured value divided by the true value Precision - Number of distinguishable alternatives from which a given result is selected Resolution - Smallest increment that can be measured with certainty Reproducibility - Same output for the same input

12 Transfer Characteristic Signal In U i (t) (Physiologic Variable) Operation, f Signal Out U o (t) U o (t) U o (t) = f(u i (t)) U i (t)

13 Instrument Output For an instrument with a linear transfer characteristic, the sensitivity is the slope of this curve Variable Measured Sensitivity - Change in output as a function of a change in input

14 Variable Time Stability - Consistency in output for a constant input

15 Instrument Output Variable Measured Specificity - Ability to distinguish desired variable from other competing variables

16 Instrument Output Variable Measured Accuracy - Difference between true value and measured value divided by the true value

17 Instrument Output Variable Measured Precision - Number of distinguishable alternatives from which a given result is selected. In other words: the smallest change in a variable that can be correctly measured

18 Instrument Output Variable Measured Resolution - Smallest increment that can be measured with certainty

19 Instrument Output Calibration 1 Calibration 3 Calibration 2 Variable Measured Reproducibility - Same output for the same input

20 Basic Biomedical Instrument Physiologic System Sensor Processor Display Storage Observer

21 Possible Types of Transducers Mechanical Electrical Thermal Optical Chemical Acoustic Hydraulic

22 Possible Types of Transducers Mechanical Electrical Optical Microphone Loud Speaker Thermal Chemical Acoustic Hydraulic

23 Types of Sensors Physical Chemical Bioanalytical

24 Types of Sensors Physical Strain gauge Accelerometer Load cell (force) Pressure sensor Chemical Oxygen electrode Glass electrode (ph) Bioanalytical Glucose sensor Lactate sensor Velocimeter Thermistor Metal resistance thermometer Flow sensor Ion-selective electrode CO 2 sensor And so on.

25 Single Conversion Sensor Physiologic Variable Sensor Electrical Signal Body Temperature Thermistor Electrical Resistance Partial Pressure Of Oxygen Clark Electrode Electrical Current

26 Multiple Conversion Sensor Physiologic Variable Intermediate Variable Sensor Electrical Signal Blood Pressure Diaphragm Displacement Displacement Sensor Electrical Signal Serum Glucose Hydrogen Peroxide H 2 O 2 Sensor Electrical Signal

27 Thin-Film Gold Temperature Sensor Nasal Oral/Nasal In place on an infant R ( + ( T )) = R0 1 α T 0 R 0 is the resistance at temperature T 0 α Is the temperature coefficient of resistance

28 Thermistor (Temperature Sensor) Semiconductor Oxides Insulation High sensitivity Inexpensive Non-linear Moderate stability R = R 0 Lead Wires 1 exp β T 1 T 0 R 0 is the resistance at absolute temperature T 0 β Is a constant

29 Capacitance Force Sensor A Force d C = A ε d ε is the dielectric constant

30 Capacitance Force Sensor Cut-away structure of 64-element force sensor Micrograph of thickfilm silicone dielectric strips Assembled sensor

Substrate Single thin-film basis ion-selective electrode Ion-selective electrodes

31 Ion-Selective Electrodes Hydrogel Inner Solution Ion-Selective Membrane Substrate Thick-film Wall Hydrogel Inner Solution Ion-Selective Membrane Reference Electrode Substrate Single thin-film basis ion-selective electrode Ion-selective electrodes on a ceramic substrate with the inner chamber defined by 100 µm thick glaze films.

I m. R s. Digital. R x. OhmmetersxSeries Shunt Digital. R m

I m. R s. Digital. R x. OhmmetersxSeries Shunt Digital. R m µa Meter I I s I m s E Digital x I Voltmeter x x E µa Meter m Is OhmmetersxSeries Shunt Digital EIx= = ()E sm x mxvi= x Shunt Ohmmeter Shunt s x E µa Meter I m I m V m E ) ( v I E ) ( E v E v E I When