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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