basic concepts bmt. instrumentation design and development is a creative process involving an idea...
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Basic Concepts
BMT
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Instrumentation design and development is a creative process involving an idea and then taking it to
the implementation level (prototype => product). Key deliverable is also a patent. Medical Instrumentation development has more exacting demands since human health depends on the performance of the device. The key regulatory barriers are: animal/clinical protocol approval, investigational device examination/clinical engineering certification, FDA approval. The prototype to the medical product is a long, expensive, and highly regulated process.
• The key concerns of the FDA are: safety and efficacy• The key categories of FDA regulation are: Class I (General
controls=>labelling), Class II (Performance standards; grand-fathering before 1976), Class III (Premarketing approval).
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• You should be familiar with the issue of• Patents• University/medical center regulations (animal,
clinical)• FDA• In the development of the device, you should be
familiar with• Measurement factors (instrumentation)• Environmental factors, social Medical factors;
aesthetics, history, tradition, liability…• Economic factors: cost-benefit, profit,
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Food and Drug Administration (FDA)
Government body entrusted with the responsibility to regulated medical devices, drugs, etc.
Primary task: certify safety and efficacy
FDA regulates through FDA Instrumentation Categories
Design Control Class I
Process Control Class II
Good Manufacturing Practices Class III
What FDA Categories do the Instruments in the Previous Slide Belong to?
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FDA Device Regulations
• Class I – General Controls– Required to perform registration, labeling, and good
manufacturing practices and to report adverse effects
• Class II – Performance Standards– Required to prove “substantial equivalence” via the
510(k) process
• Class III – Pre-market Approval (PMA)– Requires extensive testing and expert scrutiny– PMA is necessary for devices used in supporting or
sustaining human life
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General Medical Instrumentation System
Measurand(e.g. blood pressure, ECG potential, etc.)
SensingElement
SignalProcessing
OutputDisplay
• Sensors such as electrodes, pressure transducer• Instrumentation: amplifier, filter, signal conditioning• Microprocessor, telemetry, Internet interface• Case study (student project): Wireless heart rate alarm via
cell phone
http://www.qubitsystems.com/electro.html
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System Block Diagram
Signal source
Inter-ference
“Induced”
InputOutput
Transfer Function
• Accuracy, Precision
• Linearity, nonlinearity
• Response function (1st, 2nd order)
• Step response, transient response
• Stability, temperature response
• Noise, interference rejection
System PropertiesInternal interference
(added)
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Sources of Signal Interference
• Any measurement includes signal+noise
• Signal sources: ECG. EEG, blood pressure, temperature…
• Noise sources– External: 60 Hz, radio
frequency (RF), magnetic…
– Internal: muscle noise, motion artifact, eye blink artifact… Taken from http://www.temple.edu/biomed/
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Principles of Measurements I
• Linearity, Accuracy, Stability… => apply to real problems, applications
• First order, second order systems…=> apply to real problems, applications
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System Linearity
• Properties required for a linear system– If y1 and y2 are the
responses to x1 and x2, respectively, then y1 + y2 is the response to x1 + x2 and Ky1 is the response to Kx1, where K is a constant.
• Linearity is necessary for a system that has a linear calibration curve.
LinearSystem
x1 y1
LinearSystem
x2 y2
LinearSystem
x1 + x2y1 + y2
LinearSystem
Kx1 Ky1
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Dynamic System Characteristics
• General Form of Input-Output Relationship
– Time-Domain
– Transfer Function
• Most instruments are of zero, first or second order– n = 0,1, or 2; m = 0.
• Input is typically transient (step function), periodic (sinusoid), or random (bounded white noise)
)(...)(... 0101 txbdt
dxb
dt
xdbtya
dt
dya
dt
yda
m
m
mn
n
n
01
01
)(...)(
)(...)(
)(
)((
ajaja
bjbjb
jX
jYjH
nn
mm
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Zero-Order System
• Expression of the input-output relationship– Time-domain
Relationship
– Transfer Function
• Example– Linear potentiometer
)()( 00 txbtya
0
0)(a
bjH
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First-Order System
• System contains a single energy-storage element
• Time-domain relationship
• Transfer Function
• Example– RC Low-pass or High-pass Filters
)()( 001 txbtyadt
dya
01
0
)()(
aja
bjH
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Simple First-Order Circuits
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/filcap2.html
• Properties: attenuation, delay, transient response, loss of frequency (low or high)
• Think of the examples of first order systems?
x(t)
-
+y(t)
-
+
Low-pass Filter
x(t)
-
+
y(t)
-
+
High-pass Filter
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Second-Order System
• Second-order system can approximate higher-order systems
• Time-domain Relationship
• Transfer Function
• Example– Mechanical force-measuring instrument– Pressure transducer
)()( 0012
2
2 txbtyadt
dya
dt
yda
012
2
0
)()()(
ajaja
bjH
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Second-Order System
• Over-damped
• Critically-damped
• Under-damped
12 20
1 aa
a
12 20
1 aa
a
12 20
1 aa
a
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Practice Questions
• Who do you file patent with? What is the basic style of a patent?
• What regulations are followed to do animal/clinical studies?
• Give several examples of each of the FDA categories.• Give examples of negative feedback and positive
feedback in medical sensors and instruments• Pressure sensor may be modeled as a second order
system. How does over/under/critically damped measurement affect Pressure reading?