Aula Teorica 1 Instrumentação Biomédica

Instrumentação BiomédicaInstrumentação Biomédica

Conceitos FundamentaisConceitos Fundamentais

JCMetrôlho, Out. 07JCMetrôlho, Out. 07

Instrumentação BiomédicaInstrumentação Biomédica 22

Biomedical engineers work in a variety of fields

•Bioinstrumentation•Biomaterials •Biomechanics•Biosignals•Biosystems•Biotransport•Cellular engineering•Clinical engineering•Tissue engineering•Rehabilitation engineering


Biomedical engineers work in a variety of disciplines

•Agriculture - Soil monitoring

•Botany - Measurements of metabolism

•Genetics - Human genome project

•Medicine - Anesthesiology

•Microbiology - Tissue analysis

•Pharmacology - Chemical reaction monitoring

•Veterinary science - Neutering of animals

•Zoology - Organ modeling


Biomedical engineers may work in a variety of environments

•IndustryIndustry

•GovernmentGovernment

•Clinical InstitutionsClinical Institutions

•AcademicResearchAcademicResearch


Problemstatem ent

R eviewprior work

S tatehypothesis

Performexperim ents

D esign furtherexperim ents

Analyzedata

F ina lconclusions

M oreexperim entsnecessary

Problemsolved

In the scientific method, a hypothesis is tested by experiment to determine its validity


C hiefcom pla int

O bta inh is tory

L is t thed ifferentia ld iagnosis

Exam inationand tests

Select furthertests

U se datato narrow the

d iagnosis

F ina ld iagnosis

M ore thanone like ly

O nly onelike ly

T reatm entand

evaluation

The physician obtains the history, examines the patient, performs tests to determine the diagnosis and prescribes treatment.


Sensor

D atacom m unication

D atad isp lays

E ffector

M easurand

S ignalcondition ing

S ignalprocessing

D atastorage

Feedback

O utputs

A typical measurement system uses sensors to measure the variable, has signal processing and display, and may provide feedback.


InstrumentPatient

InstrumentPatient

Clinician

Without the clinician, the patient may be operating in an ineffective closed loop system. (b) The clinician provides knowledge to provide an effective closed loop system.

(a) (b)


Instrum entPatientC lin ic ian

Abnorm alreadings

In some situations, a patient may monitor vital signs and notify a clinician if abnormalities occur.


MeasurementMeasurement RangeRange Frequency, HzFrequency, Hz MethodMethod

Blood flowBlood flow 1 to 300 mL/s1 to 300 mL/s 0 to 200 to 20 Electromagnetic or ultrasonicElectromagnetic or ultrasonic

Blood pressureBlood pressure 0 to 400 mmHg0 to 400 mmHg 0 to 500 to 50 Cuff or strain gageCuff or strain gage

Cardiac outputCardiac output 4 to 25 L/min4 to 25 L/min 0 to 200 to 20 Fick, dye dilutionFick, dye dilution

ElectrocardiographyElectrocardiography 0.5 to 4 mV0.5 to 4 mV 0.05 to 1500.05 to 150 Skin electrodesSkin electrodes

ElectroencephalographyElectroencephalography 5 to 300 5 to 300 VV 0.5 to 150 0.5 to 150 Scalp electrodesScalp electrodes

ElectromyographyElectromyography 0.1 to 5 mV0.1 to 5 mV 0 to 100000 to 10000 Needle electrodesNeedle electrodes

ElectroretinographyElectroretinography 0 to 900 0 to 900 V V 0 to 500 to 50 Contact lens electrodesContact lens electrodes

pHpH 3 to 13 pH units3 to 13 pH units 0 to 10 to 1 pH electrodepH electrode

ppCOCO22 40 to 100 mmHg40 to 100 mmHg 0 to 20 to 2 ppCOCO22 electrode electrode

ppOO22 30 to 100 mmHg30 to 100 mmHg 0 to 20 to 2 ppOO22 electrode electrode

PneumotachographyPneumotachography 0 to 600 L/min0 to 600 L/min 0 to 400 to 40 PneumotachometerPneumotachometer

Respiratory rateRespiratory rate 2 to 50 2 to 50 breaths/minbreaths/min 0.1 to 100.1 to 10 ImpedanceImpedance

TemperatureTemperature 32 to 40 °C32 to 40 °C 0 to 0.10 to 0.1 ThermistorThermistor

Common medical measurands


SpecificationSpecification ValueValue

Pressure rangePressure range ––30 to +300 mmHg30 to +300 mmHg

Overpressure without damageOverpressure without damage ––400 to +4000 mmHg400 to +4000 mmHg

Maximum unbalanceMaximum unbalance ±75 mmHg±75 mmHg

Linearity and hysteresisLinearity and hysteresis ± 2% of reading or ± 1 mmHg± 2% of reading or ± 1 mmHg

Risk current at 120 VRisk current at 120 V 10 10 AA

Defibrillator withstandDefibrillator withstand 360 J into 50 360 J into 50

Sensor specifications for a blood pressure sensor are determined by a committee composed of individuals from academia, industry, hospitals, and government.


Figure 1.1 Generalized instrumentation systemFigure 1.1 Generalized instrumentation system The sensor converts The sensor converts energy or information from the measurand to another form (usually energy or information from the measurand to another form (usually

electric). This signal is the processed and displayed so that humans can electric). This signal is the processed and displayed so that humans can perceive the information. Elements and connections shown by dashed lines perceive the information. Elements and connections shown by dashed lines

are optional for some applications.are optional for some applications.

PerceptibleoutputOutput

display

ControlAndfeedback

Signalprocessing

Datatransmission

Datastorage

VariableConversionelement

Sensor

PrimarySensingelement

Measurand

Calibrationsignal

Radiation,electric current,or other appliedenergy

Powersource

© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.


Mensuranda: quantidade física, propriedade Mensuranda: quantidade física, propriedade ou condição que se pretende medirou condição que se pretende medir

biopotencialbiopotencial temperaturatemperatura impedânciaimpedância pressão, fluxopressão, fluxo concentração químicaconcentração química força, aceleração, velocidade, deslocamentoforça, aceleração, velocidade, deslocamento dimensões (imagiologia)dimensões (imagiologia)


SensoresSensores Transdutor: dispositivo que converte uma Transdutor: dispositivo que converte uma

forma de energia noutra forma de energia noutra Sensor: converte uma mensuranda (valor Sensor: converte uma mensuranda (valor

de entrada) para grandeza eléctrica (valor de entrada) para grandeza eléctrica (valor de saída)de saída) responder apenas à forma de energia da responder apenas à forma de energia da

mensurandamensuranda interface com o tecido vivo, extraindo a menor interface com o tecido vivo, extraindo a menor

energia possível energia possível minimamente invasivominimamente invasivo


Condicionamento de sinalCondicionamento de sinal

AmplificarAmplificar o sinal eléctrico relevante o sinal eléctrico relevante FiltrarFiltrar ruído ou outros sinais ruído ou outros sinais

indesejáveisindesejáveis LimitarLimitar amplitudes máximas amplitudes máximas AdaptarAdaptar impedâncias entre os impedâncias entre os

diferentes componentesdiferentes componentes ConverterConverter entre diferentes grandezas entre diferentes grandezas

eléctricaseléctricas


VisualizaçãoVisualização

Resultado do processo de medição Resultado do processo de medição em formato adequado para fácil em formato adequado para fácil percepçãopercepção numériconumérico gráficográfico contínuo ou intermitentecontínuo ou intermitente permanente ou temporáriopermanente ou temporário visual, acústico, …visual, acústico, …


Componentes auxiliaresComponentes auxiliares

sinal de calibração o mais a montante sinal de calibração o mais a montante possível na cadeia de mediçãopossível na cadeia de medição

controlo e realimentação para ajuste de controlo e realimentação para ajuste de sensor, condicionamento e visualizaçãosensor, condicionamento e visualização automático ou manualautomático ou manual

armazenamentoarmazenamento temporário ou de arquivotemporário ou de arquivo

comunicaçãocomunicação local ou remotalocal ou remota


Modos de funcionamentoModos de funcionamento

directo ou indirectodirecto ou indirecto a grandeza que se pretende conhecer não está a grandeza que se pretende conhecer não está

acessívelacessível escolhe-se mensuranda com relação conhecida escolhe-se mensuranda com relação conhecida

contínuo ou por amostragemcontínuo ou por amostragem variações rápida (frequência cardiaca) ou lenta variações rápida (frequência cardiaca) ou lenta

(temperatura do corpo)(temperatura do corpo) sensoressensores

geradores: retiram energia da mensurandageradores: retiram energia da mensuranda moduladores: mensuranda controla fluxo de moduladores: mensuranda controla fluxo de

energia de fonte auxiliarenergia de fonte auxiliar


Modos de funcionamentoModos de funcionamento

analógico ou digitalanalógico ou digital exactidãoexactidão repetibilidaderepetibilidade fiabilidadefiabilidade imunidade ao ruídoimunidade ao ruído processamento e visualizaçãoprocessamento e visualização

tempo real ou diferidotempo real ou diferido necessidade de processar sinal pode atrasar a necessidade de processar sinal pode atrasar a

disponibilidade dos resultadosdisponibilidade dos resultados


MeasurementMeasurement RangeRange Frequency, HzFrequency, Hz MethodMethod

Blood flowBlood flow 1 to 300 mL/s1 to 300 mL/s 0 to 200 to 20 Electromagnetic or ultrasonicElectromagnetic or ultrasonic

Blood pressureBlood pressure 0 to 400 mmHg0 to 400 mmHg 0 to 500 to 50 Cuff or strain gageCuff or strain gage

Cardiac outputCardiac output 4 to 25 L/min4 to 25 L/min 0 to 200 to 20 Fick, dye dilutionFick, dye dilution

ElectrocardiographyElectrocardiography 0.5 to 4 mV0.5 to 4 mV 0.05 to 1500.05 to 150 Skin electrodesSkin electrodes

ElectroencephalographyElectroencephalography 5 to 300 5 to 300 VV 0.5 to 150 0.5 to 150 Scalp electrodesScalp electrodes

ElectromyographyElectromyography 0.1 to 5 mV0.1 to 5 mV 0 to 100000 to 10000 Needle electrodesNeedle electrodes

ElectroretinographyElectroretinography 0 to 900 0 to 900 V V 0 to 500 to 50 Contact lens electrodesContact lens electrodes

pHpH 3 to 13 pH units3 to 13 pH units 0 to 10 to 1 pH electrodepH electrode

ppCOCO22 40 to 100 mmHg40 to 100 mmHg 0 to 20 to 2 ppCOCO22 electrode electrode

ppOO22 30 to 100 mmHg30 to 100 mmHg 0 to 20 to 2 ppOO22 electrode electrode

PneumotachographyPneumotachography 0 to 600 L/min0 to 600 L/min 0 to 400 to 40 PneumotachometerPneumotachometer

Respiratory rateRespiratory rate 2 to 50 2 to 50 breaths/minbreaths/min 0.1 to 100.1 to 10 ImpedanceImpedance

TemperatureTemperature 32 to 40 °C32 to 40 °C 0 to 0.10 to 0.1 ThermistorThermistor

Table 1.1 Medical and physiological parameters.


SpecificationSpecification ValueValue

Pressure rangePressure range ––30 to +300 mmHg30 to +300 mmHg

Overpressure without damageOverpressure without damage ––400 to +4000 mmHg400 to +4000 mmHg

Maximum unbalanceMaximum unbalance ±75 mmHg±75 mmHg

Linearity and hysteresisLinearity and hysteresis ± 2% of reading or ± 1 mmHg± 2% of reading or ± 1 mmHg

Risk current at 120 VRisk current at 120 V 10 10 AA

Defibrillator withstandDefibrillator withstand 360 J into 50 360 J into 50

Sensor specifications for a blood pressure sensor are determined by a committee composed of individuals from academia, industry, hospitals, and government.


Figure 1.2 Simplified electrocardiographic recording systemFigure 1.2 Simplified electrocardiographic recording system Two Two possible interfering inputs are stray magnetic fields and capacitively coupled possible interfering inputs are stray magnetic fields and capacitively coupled noise. Orientation of patient cables and changes in electrode-skin impedance noise. Orientation of patient cables and changes in electrode-skin impedance

are two possible modifying inputs. are two possible modifying inputs. ZZ11 and and ZZ22 represent the electrode-skin represent the electrode-skin

interface impedances.interface impedances.

Electrodes

50-Hzac magneticfield

Displacementcurrents

Differentialamplifier

+

+Vcc

Vcc

Z1

Zbody Z2

vo

vecg



Características estáticasCaracterísticas estáticas

ExactidãoExactidão PrecisãoPrecisão ResoluçãoResolução ReprodutibilidadeReprodutibilidade Controlo estatísticoControlo estatístico Sensibilidade estáticaSensibilidade estática


Figure 1.3 Figure 1.3 (a) Static-sensitivity curve that relates desired input (a) Static-sensitivity curve that relates desired input xxdd to output to output

yy. Static sensitivity may be constant for only a limited range of inputs. (b) . Static sensitivity may be constant for only a limited range of inputs. (b) Static sensitivity: zero drift and sensitivity drift. Dotted lines indicate that zero Static sensitivity: zero drift and sensitivity drift. Dotted lines indicate that zero

drift and sensitivity drift can be negative. [Part (b) modified from drift and sensitivity drift can be negative. [Part (b) modified from Measurement Systems: Application and DesignMeasurement Systems: Application and Design, by E. O. Doebelin. Copyright , by E. O. Doebelin. Copyright

1990 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Co.]1990 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Co.]

Intercept b xd

y

x'd

y'

y (Output)

y = mxd + b

xd (Input)

(a)

Slope m =y

xd

Total error due to drift

Characteristic with zero and sensitivity drift

+ Zerodrift

+ Sensitivitydrift

Sensitivity drift

Zero drift

(b)

y (Output)

xd (Input)



Figure 1.4 Figure 1.4 (a) Basic definition (a) Basic definition of linearity for a system or of linearity for a system or element. The same linear element. The same linear

system or element is shown system or element is shown four times for different inputs. four times for different inputs. (b) A graphical illustration of (b) A graphical illustration of

independent nonlinearity independent nonlinearity equals equals A% of the reading, or A% of the reading, or B% of full scale, whichever is B% of full scale, whichever is

greater (that is, whichever greater (that is, whichever permits the larger error). [Part permits the larger error). [Part

(b) modified from (b) modified from Measurement Measurement Systems: Application and Systems: Application and

DesignDesign, by E. O. Doebelin. , by E. O. Doebelin. Copyright Copyright 1990 by McGraw- 1990 by McGraw-Hill, Inc. Used with permission Hill, Inc. Used with permission

of McGraw-Hill Book Co.] of McGraw-Hill Book Co.] xd (Input)

B% of full scale

A% of reading

Overall tolerance band

Least-squaresstraight line

(a)

(b)

Point at whichA% of reading = B% of full scale

y (Output)

x1(x1 + y2)y1

x2Kx1 Ky1y2Linear

system

Linearsystem

Linearsystem

Linearsystem

and and

(y1 + y2)


Figure 1.6 Figure 1.6 (a) A (a) A low-pass low-pass RCRC filter, an filter, an

example of a first-example of a first-order instrument. (b) order instrument. (b) Static sensitivity for Static sensitivity for constant inputs. (c) constant inputs. (c) Step response for Step response for

larger time constants larger time constants ((LL) and small time ) and small time

constants (constants (SS). (d) ). (d)

Sinusoidal frequency Sinusoidal frequency response for large response for large

and small time and small time constants.constants.

t

1

(c)

(a)

C

+

+

y(t)

Output y(t)

Input x(t)

Slope = K = 1

(b)

Y (jX (j

Logscale

1.00.707

Log scale (d)

0°

45°

90°

Log scale

t

1

0.63

LS

L

S

SL

L

S

y(t)

x(t)

x(t)

y(t)

R


Figure 1.7 Figure 1.7 (a) Force-(a) Force-measuring spring measuring spring

scale, an example of a scale, an example of a second-order second-order

instrument. (b) Static instrument. (b) Static sensitivity. (c) Step sensitivity. (c) Step

response for response for overdamped case overdamped case

= 2, critically = 2, critically damped case damped case

= 1, underdamped = 1, underdamped case case = 0.5. (d) = 0.5. (d)

Sinusoidal steady-state Sinusoidal steady-state frequency response, frequency response, = 2, = 2, = 1, = 1, = 0.5. = 0.5.

[Part (a) modified from [Part (a) modified from Measurement Systems: Measurement Systems:

Application and Application and DesignDesign, by E. O. , by E. O.

Doebelin. Copyright Doebelin. Copyright 1990 by McGraw-Hill, 1990 by McGraw-Hill,

Inc. Used with Inc. Used with permission of McGraw-permission of McGraw-

Hill Book Co.]Hill Book Co.]

Outputdisplacement

Output y(t)

(b)(a)

(d)(c)

1Ks

x(t)

y(t)yn yn + 1

Resonance

2

Logscale

1

2

-90°

0.51

2 -180°

1

0.5

0.5

Log scale

Log scale

K1

t

t

Input x(t)

Slope K =1

Ks

InputForce x(t)

0

0°

n

n

Y (jX (j

y(t)


Figure 1.8 Design Figure 1.8 Design process for medical process for medical

instruments instruments Choice and Choice and design of instruments are design of instruments are affected by signal factors, affected by signal factors,

and also by environmental, and also by environmental, medical, and economic medical, and economic factors. (Revised from factors. (Revised from

Transducers for Biomedical Transducers for Biomedical Measurements: Application Measurements: Application

and Design, and Design, by R. S. C. by R. S. C. Cobbold. Copyright Cobbold. Copyright 1974, 1974,

John Wiley and Sons, Inc. John Wiley and Sons, Inc. Used by permission of John Used by permission of John

Wiley and Sons, Inc.)Wiley and Sons, Inc.)

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Aula Teorica 1 Instrumentação Biomédica