医学仪器的基本概念.ppt

Medical Instrumentation -Application and Design Basic Concepts of Medical Instrumentation Generalized Medical Instrumentation System1MeasurandvBiopotentialvpressurevFlowvdimensions(imaging)vdisplacement(velocity,acceleration and force)vImpedancevtemperaturevChemical concentrationGeneralized Medical Instrumentation SystemSensorsSensor:converts a physical measurand to an electric outputTransducer:converts one form of energy to anotherIn general,sensor=transducer+variable conversion elementVariable-conversion elements need external electric power to obtain a sensor outputGeneralized Medical Instrumentation SystemSuch as:A diaphragm converts pressure to displacement(transducer)A strain gage converts displacement to an electric voltage(variable-conversion element)Generalized Medical Instrumentation SystemlSignal conditioninglAmplify and filter the signallMatch the impedance of the sensor to the displaylAnalog to digital convertslSignal filtering:-reduce undesirable sensor signals -convert information from the time domain to the frequency domain -average repetitive signals to reduce noiseGeneralized Medical Instrumentation SystemvOutput displayNumerical or graphicalDiscrete or continuousPermanent or temporaryGeneralized Medical Instrumentation SystemAuxiliary elementCalibration signalControl and feedback(automatic or manual)Data storageDate transmissionRadiation electric current or other applied energyAlternative Operational ModesDirect-indirect modesvDirect mode:measurand can be interfaced directly to sensor.(ECG,body temperature)vIndirect mode:measurand is not accessible.Use another measurand that bears a known relation to the desired measurand.Alternative Operational ModesExample:Cardiac output determined from measurements of respiration and blood gas concentration Morphology of internal organs determined from X-ray shadowsAlternative Operational ModesSampling and continuous modesSampling modes:Body temperature changes so slowly that it may be sampled infrequentlyContinuous modes:ECG or respiratory gas flow requires continuous monitoringAlternative Operational ModeskGenerating and Modulating sensorskGenerating sensors:produce signal output from energy taken directly from the measurand.(photovoltaic cell)kModulating sensors:use the measurand to alter the flow of energy from an external source that affects the sensor output(example:photoconductive cell)Alternative Operational ModesAnalog and Digital modesAnalog modes:continuous measurements in any timeDigital modes:discrete and take on only a finite number of different valuesAdvantages:greater accuracy,repeatability,immunity to noiseAlternative Operational ModesReal-time and Delayed-time modesReal-time mode:Sensor must acquire signals in real time as the signals occur.(ECG)Delayed-time mode:Several days may be required before an output is obtained.(cell cultures)Medical measurement constraintsThe medical instrumentation is designed to measure various medical and physiological parametersMeasurement range and frequency range are two major factors.(Tab1.1)Many crucial variables in living systems are inaccessible(cardiac output)Medical measurement constraintsParameter or Measuring TechniquePrincipal Measurement Range of ParameterSignal Frequency Range,HZStandard Sensor or MethodBlood pressure,arterialDirectindirect10-400mm Hg25-400mm HgDc-50Dc-60Strain-gage manometerCuff,auscultationElectrocardiography(ECG)0.5-4mV0.01-250Skin electrodeElectroencephalography(EEG)5-300uVDc-150Scalp electrodesElectromyography(EMG)0.1-5mVDC-10,000Needle electrodesRespiratory rate2-50 breaths/min0.1-10Strain gage on chest impedance.nasal thermistorTemperature of body32-40 90-104Dc-0.1Thermistor,thermocoupleMedical measurement constraintsVariables measured are seldom deterministic,vary with time(body temperature,blood pressure)Many medical measurements vary widely among normal patient(blood pressure,heart rate)Many feedback loops exist among physiological systems and many of the interrelationships are poorly understoodMedical measurement constraintsDepend either on some form of energy being applied to the living tissue or on some energy being applied as an incidental consequence of sensor operation (example:X-ray,Ultrasonic imaging techniques and electromagnetic or Doppler ultrasonic blood flow-meters depend on externally applied energy)Medical measurement constraintsqSome important additional constraints:Reliable,easy to operate,withstanding physical abuse and exposure to corrosive chemicalsTo minimize electric-shock hazardsTo consider the safety of patients and medical personnelClassifications of Biomedical InstrumentsAccording to the quantity:bPressure,flow,temperature.According to the principle of transductionbResistive,inductive capacitive,ultrasonic electrochemical.Classifications of Biomedical InstrumentsAccording to each organ systembCardiovascular,pulmonary,nervous,endocrine.According to the clinical medicine specialtiesbPediatrics,obstetrics,cardiology radiology.Interfering and Modifying inputsInterfering inputs:affect the instrument as a consequence of the principles used to acquire and process the desired inputsModifying inputs:Undesired quantities that indirectly affect the output by altering the performance of the instrument itselfInterfering and Modifying inputsgSome undesirable quantities can act as both a modifying input and an interfering input.Figure1.2 Simplified electrocardiography recording Figure1.2 Simplified electrocardiography recording systemsystemInterfering and Modifying inputsvThe desired input is the ECG voltage VecgvTwo possible interfering inputs:stray magnetic fields and capacitively coupled noisevTwo possible modifying inputs:Orientation of patient cablesChanges in electrode-skin impedanceCompensation TechniquesSeveral compensation methods for eliminating the effects of interfering and modifying inputsInherent Insensitivity:if all instrument components are inherently sensitive only to desired inputs,then interfering and modifying inputs have no effect.Compensation TechniquesNegative feedback:Xd:input Y:outputGd:amplification Hi:feedback elementCompensation TechniquesNegative feedbackCompensation TechniquesIf 1 then Only the feedback element Hi determines the output for a given input Compensation TechniquesSignal filtering a device or program that separates data,signals or material in accordance with specified criteria.Filtering may be inserted:at the instrument inputat some point within the instrument at the output of the instrumentCompensation TechniquesoOpposing inputs Additional interfering inputs can be used to cancel undesired output componentsCommercial medical instrumentation development processMany factors affect the design of biomedical instrumentsSignal factorEnvironmental factorMedical factorEconomic factorCommercial medical instrumentation development processMeasurandSignal factorsEnvironmentalfactorsMedical factorsEconomic factorsSensitivity Range Differential or absolute inputInput impedanceTransient and frequency responseAccuracy linearity ReliabilitySpecificity Signal-to-noise ratioStability;temperature,humidityPressure,acceleration,shockVibration,radiation Power requirementsMounting size,shapeInvasive or non-invasiveTissue-sensor interface requirementsMaterial toxicity Electric safetyRadiation and heat dissipationPatient discomfortCost Availability Warranty Consumable requirementsCompatibility with existing equipmentInitial instrumentdesignPrototype testsFinal instrumentdesignFDA BMD approvalProductionCommercial medical instrumentation development processIdeas:physicians,nurses,clinical engineers,and sales personnel are good sources of ideasAnalysis:bmarketing search and analysisbTechnical feasibility analysisbManufacturing feasibility analysis:personnel,standards,manufacturing requirements,sales and services requirements,time schedule for the project.Commercial medical instrumentation development process1A detailed product specification describe all the product features，Include:Numerical values for performance Internal testing requirements User interface requirements Environmental testing requirementsSize,weight,colorCommercial medical instrumentation development processThe product specification is used by:Design and development engineersTest equipment design engineersQuality assurance engineersManufacturing engineersCommercial medical instrumentation development processvManufacturable prototype:tested on animals or humanvFinal design review should include:Test results,clinical results(including user feedback)detailed cost estimates