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Medical instrumentation Basic concepts of instrumentation

measureand Primary sensing device

Variable conversion element

Calibrationsignal

RadiationElectric current

Or other applied energy

Power source

Signal processing

Data storgae

Control & feedback

Outputdisplay

Data transmission

Medical instrumentsDiagnosisTreatmentMonitorFunction compensationReplacement

Medicine domainsObject for medicine• From crowd to single molecule

Process for medicine• Remove, maintain, recovery, improvement

Utilities for medicine• Acute chemical treatment, chronic physical

therapy, life-long bio-regulation

MeasurandBiopotential: ECG,EMG, EEG Pressure: BPFlow: BF, AF Displacement: Joint operationImpedance: EICT, ultrasoundTemperature: body temperatureChemical concentration• Composite, concentration, activity

Biosignals

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Various signals for cardio system Bioelectric signalsSystem action• Relative to source, conduct path,

responseExample• ECG (electrocardiograph)• EEG (electroencephalograph)• EMG (electromyography)• Other bioelectric signals

Example ECG Bioimpedance signalsConcerning compositionActive stimulation

• 20µA-20mA;50kHz-1Mhz• Less polarization, minimal damage

Example• EICT• Concentration measurement• Bioimpedance for acupuncture• Safety control for electrosurgical unit

Bioacoustic signalsTissue property & actionAction or active stimulationExample• Ultrasound application• Heart sound• Muscle action

Biomechanic signalsSystem mechanical functionSignal less propagationExample• Blood pressure• Blood flow• Musclosketetal force• Respiratory vibration

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Biochemical signalsConcerning • Concentration• Activity

Low frequencyExample

• Ionic concentration• Ph value• Blood gas saturation

Other signalsBiomagnetic signals• Dipole action• MCG, MEG

Biooptical signals• Absorption• Emission infrared, Far infrared• Auto-fluoresce

Biosignal characteristicsLow frequency, low level• micro- to mil- level• less then 2000Hz

Contaminating with noise• Internal noise vs. external noise• Periodic vs. nonperiodic noise• Physiology vs. physical noise

Biosignal characteristicsVarying with different factors

• Individual variation • Environment: physiological vs. mechanic

Compensating by system• Relation between system• Feedback automatic regulation

Variety of physiology• In vitro vs. in vivo• Exciting of transducer• Anesthesia & exercise

Requirements of biosensorsSafety• In vitro vs. in vivo• Long term vs. short term

Sensitvity• Long term vs. short term• Decay vs. stability• S/N

Response• Frequency vs. amplitude• Linear vs. nonlinear• Log vs. non log

Requirements of biosensorsSignals/noise ratioImpedance match• With biosystem• With physical circuit

Reproducibility• With methods• With time• With products

Stability• With time• With environment

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Requirements of biosensorsSpecification• Single action• Multiple action

Compatibility• Immunology• Local biotissue

Distortion

Classification of biomedical sensor

Physical sensorsElectric:electrodesGeometric:strain gaugeMechanical:LVDTThermal:thermistorHydraulic:magnetic field Optical:photo diode

Chemical sensorsGas:CO2, SO2 sensorElectrochemical: ionic sensorPhotometric:glucose sensorBioanalytic• Component pair-reaction

Surface electrodes Blood pressure sensors

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Flow sensor Temperature measurementClinical temperature

• Disease relation• Hypo- & hyperthermic treatment• Thermograph

Sensors• Thermocouple• Thermistor• Thermal diode• Optic fiber• RTD

Temperature measurement Moisture sensorsConductive filmCapacitor gateCrystalStretch-fiber

Level sensors Immunologically field-effect sensor

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Integrated optical sensor Glucose sensor

葡萄聚糖

Antigen-antibody sensor Optical sensor

Clark sensor Cantilevers

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Signal processing of Instrument

Stage 1Core:• Signal amplifying• Impedance matching• Signal converting

Peripheral• Bias or driving• Calibrating• Isolating

Stage 2Core:• Amplifying• Signal separating

Peripheral• Stabilizing• Synchronizing• Multiplexing• Demultiplexing

Biosignal frequency distribution

(ERG)(EMG)

(ECG)

(EEG)

Filter (time-domain)

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Filter effect Stage 3Core• Feature extractingPeripheral• Rectifying• Synchronizing• Converting

Stage 4Core• Signal reducing• ModulatingPeripheral• Triggering• Timing• Displaying

Life cycleProblem identificationSystem designAnimal testSafety verifcationClinical evaluationCertificationMarketing

Design processing Problem identifyRequirements definitionSpecification confirmationBlock diagram drawingDetail designSystem testUser testMarketing monitoring

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Problem identificationProblemPurposeFunction• Monitoring/therapy• Assistance/replacement

Processing objects• Vivo/Vitro• Human body/sample• Chemical/physical

Problem identificationPossible resolution• Technology• Human ability• Cost efficiency

– economic/human being benefit

Users/environment• Patient/physician• Hospital/Home• General/special environment

Requirement definitionInput/output form• Type/range• Limitation/practices

User interface• Type• Response time

Display/record• Temporal/long term• Real-time/off-line

System view• Size/weight• Stand alone/communication

Specification confirmationInput specification• Form• Range/limitation

Output specification• Form• Loading

Environment specification• Temperature/humidity• Noise

Interface specification• Human/machine• Form

Block diagram drawingSystem diagramFunction diagramSignal flow diagramManpower diagramTime scheme diagramCost diagram

Detail designFunction evaluationRough system designPart selection/evaluationBlock establishment/testBlock linkage/testSystem assemblyPrototype establishment

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System testFunction testTolerance test• Sample/total test• Long-term/accelerated test

Environment testInterface testSafety testLife time test

User testFunction testInterface/friendship testError operation testTraining test

MarketingUser identificationCost evaluationPrice strategyMarketing channelService systemReport system

Certification of instrumentSafety verificationClinical testCertificationMarketing evaluation

Electricity safetyHeatingStimulationElectrochemical burn

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Physiological effects of electricity Physiological effects of electricityThreshold of perception(0.5mA 60Hz; 2-10mA DC)Let-go-current (9.5mA)Respiratory paralysis (18-22mA)Ventricular fibrillation (75-400mA)Sustained myocardial contraction (1-6A)Burn & physical injury (>10A)

Important susceptibility parameters

SexFrequencyDurationBody weightPoint of entry: macroshock vs microshock

Sex factor

Frequency factor Duration factor

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Body weight factor Point of entry

Distribution of electric power Power distribution

Chassis leakage Macroshock

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Microshock Microshock

Microshock Microshock

Electrical safety standardNational Fire Protection Association(NFPA)Association for the Advancement of Medical Instrumentation (AAMI SCL-P 10.75)National Electrical Manufacturer Association (NEMA)FAD-MDS-201-0035IEEE 711-2ISO-60601~12

Protection by equipment designReduction leakage current: lead & layoutDouble-insulated equipmentOperation at low voltageCurrent limitersElectrical isolation

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Electrical isolation Test of electrical appliancesGround-pin-to-chassis resistance• < 0.15Ω

Chassis leakage current• <100µA (500µA), dc~1KHz, 1000Ω

Leakage current of patient lead• <10µA (50µA)

AC isolation current• <20µA

Ground-pin-to-chassis resistance Chassis leakage current

Leakage current of patient lead Leakage current of patient lead

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AC isolation current Patient electrical environmentNEC (national electric code) 517-80,81, frequency <1000 Hz, 1000Ω resistorGeneral-care area• <500mV, 4 single or 2 duplex receptacles• 2 branch electrical circuit• Equalpotential grounding

Critical-care area• <100mV, 6 single or 3 duplex receptacles• 2 branch electrical circuit• Equalpotential grounding

Protection against shockIsolating patient from electrical conductorEqualpotential of all conductor surfaceEqualpotential grounding• Connection resistance< 0.1Ω• Receptacle ground < 20mV• Receptacle to conductor <100mV

Equipotential grounding

Certification Medical device regulation

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History1976;94th Congress 1996, FDA's Center for Devices and Radiological Health (CDRH) 510(k) Process Reengineering Team • Representatives from CDRH• Center for Biologics Evaluation and Research (CBER) • FDA's Office of Chief Counsel.

1997, the 105th Congress: FDA Modernization Act of 1997 (FDAMA)

RegulationDevices pose the least amount of risk• General controls

More complex and riskier devices• Performance standards

Most complicated and riskiest devices• Premarket approval

Regulation of medical deviceDefinition

• Medical purpose not rely on chemical actionLaw

• Medical Device Amendments (94-295, 1976)• Safe Medical Devices Act (1990)

Medical devices classification• Potential hazards: Class I, II, III• Preamendment, Postamendment• Substantially equivalent, Implant, Custom

Regulation of medical deviceClass I

• Perform registration, premarketing notification, record keeping, labeling, reporting of adverse experiences, good manufacturing practices.

Class II• 510k

Class III• Safety & effectiveness prior to market release

New 510(k) paradigmSpecial 510k (Design control activity)• As submission for substantial equivalence (SE)

determination • 26 days vs 111 days (traditional 510K)

Abbreviated 510(k) (Special controls) • Performance standards• Postmarket surveillance• Patient registries• Device-specific guidance documents• Labeling recommendations.

Regulation gap (European Union )Medical Devices Directive (MDD; 93/42/EEC) (European Union )

• Four different routes to quality assurance for a Class IIb device, three for a Class III product.

• Annexes III, IV, V, and VI of the MDD for separating design control from manufacturing or production control (not accepted by USA)

• Class I sterile and measuring devices, (Annex V, production quality assurance) with a self-declaration by the manufacturer

EN ISO 9001 and EN 46001Comparison

• ISO 9001; ISO 13486--EN ISO 9001 and EN 46001• ISO 9002 and ISO 13488-- EN 46002

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Regulation gap (Union States)Current Good Manufacturing Practices (CGMP) and quality system regulation (QSR). (FDA)Premarket notification 510(k) evaluation and premarket approval (PMA) review. Final Design Control Inspectional Strategy.The quality assurance system in both the European Union and the United States must cover both production and design control for Class II (both IIa and IIb) and Class III products.(ISO 9001; ISO 13486)

• Class I without design control requirements, and with manufacturers to satisfy the QSR by meeting ISO 9002 and ISO 13488

Global Harmonization & Mutual Recognition

Moving ahead quickly regarding an MRA with the EU, particularly on quality systems. The acceptance of a universal data set for clinical trials. The recognition of international performance standards.(GMP, ISO 13485/88, ISO 9000) Steady progress toward an MRA according to accredited third partiesThe acceptance by regulatory authorities in Asia of a common dossier.

Development trend for medical instrumentation

Evolution keysDisease profileHealthcare flowMedical demandsTechnique trend

Disease profileMedical developmentEnvironment developmentResource availabilityHuman right development

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Disease profileInfection disease

• Plague• Influenza• Enterovirus/SARS

Acute disease• Inflection• Accident• Temporal myofunction

Chronic disease (civilized disease)• Age disease• Civilized disease--HIV• Genetic disease• Sequela of acute disease

Healthcare flowKnowledge de-noblesParamedical developmentHealthcare insureSocial structure

Healthcare flow (traditional) Healthcare flow (trend)

Internet

ITC platform Web-based inspectorsMobile promulgators

Treatment vs monitoring

Manpower & devicesLocalization & remote access

For motion disable

For CV disease

For metabolism disease

For respiratory disease

Internet & telecom networking

Hospital & homecare application

Bed monitorOxygen treatment

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Hospital & homecare application Hospital & homecare application

Support vs replace

Artificial organs Cardio-lung machineDialysis machine

Support vs replace

Technique trendMiniature & wearableBiocompatibleDe-professionalWeb- & telecomCustomized

Miniature (pacemaker)

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Bio-compatible (stain) Bio-compatible (tissue engineering)

De-professional (defibrillator) De-professional (defibrillator)

Networking healthcare

For motion disable

For CV disease

For metabolism disease

For respiratory disease

Internet & telecom networking

ITC Server

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Mobile promulgators

Customized Healthcare

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Multiple technique