Bioinstrumentation
Medical Instrumentation: Application and Design Third Edition
John G. Webster, Editor
Kuo-Sheng Cheng, Ph.D.
Department of Biomedical Engineering
National Cheng Kung University
Medical Imaging &
Instrumentation Laboratory
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The Importance of Medical
Instrumentation
• Diagnosis and therapy depend heavily on
the use of medical instrumentation.
• Medical procedures:
Medicine can be defined as a multistep procedure
on an individual by a physician, group of
physician, or an institute, repeated until the
symptoms disappear.
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The Importance of Medical
Instrumentation
• Medical procedure
– 1) Collection of data - qualitative and/or
quantitative
– 2) Analysis of data
– 3) Decision making
– 4) Treatment planning based on the decision
– 5) Repeat
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A Story of New Medical Device
• The invention, prototype design, product
development, clinical testing, regulatory
approval, manufacturing, marketing, and
sale of a new medical instrument add up a
complex, expensive, and lengthy process.
• A success story - Technicon’s Auto
Analyzer
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Development of Technicon’s Auto
Analyzer
• The inventor - Leonard Skeggs,
• Chair of Department of Pathology at Case
Western Reserve University - Dr. Alan
Moritz
• Technicon Corporation founders - Edwin C.
Whitehead, and his father
• a four-page confidential disclosure form
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Development of Technicon’s Auto
Analyzer
• Two key persons to recall the invention Technicon’s only salesman, Ray Roesch,
and the doctor at the Cleveland Veterans
Adminstration Hospital, Joseph Kahn.
• Patent application and protection
• Marketing strategy
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Development of Technicon’s Auto
Analyzer
• Factors affected the success
– it allows an enormous improvement in quality
of laboratory test results, and an enormous
reduction in the cost of doing chemical analysis.
– accurate laboratory data are useful in diagnosis.
– reimbursement policies increase the availability
of health care.
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• Evolutionary product v.s. Revolutionary
product
• Generalized medical instrumentation system
–
–
–
–
–
measurand
sensor
signal conditioning
output display
auxiliary elements
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Control
And
feedback
Power
source
Sensor
Measurand
Primary
Sensing
element
Calibration
signal
Variable
Conversion
element
Signal
processing
Output
display
Data
storage
Data
transmission
Perceptible
output
Radiation,
electric current,
or other applied
energy
Figure 1.1 Generalized instrumentation
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Alternative Operational Modes
•
•
•
•
•
Direct-Indirect modes
Sampling and Continuous modes
Generating and Modulating sensors
Analog and Digital Modes
Real-time and Delayed-time Modes
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Medical Measurement Constraints
• Many crucial variables in living systems are
inaccessible.
• Variables measured are seldom
deterministic.
• Nearly all biomedical measurements depend
on the energy.
• Operation of instruments in the medical
environment imposes important additional
constraints.
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Classifications of Biomedical
Instruments
•
•
•
•
The sensed quantity
The principle of transduction
The organ system for measurement
The clinical medicine specialities
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Classifications of Biomedical
Instruments
• Based on the activities involved in the
medical care, medical instrumentation may
be divided into three categories:
– diagnostic devices
– therapeutic devices
– monitoring devices
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Generalized Static Characteristics
•
•
•
•
•
•
•
•
Accuracy
Precision
Resolution
Reproducibility
Statistical control
Static sensitivity, Sensitivity drift
Zero drift
Linearity
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Characteristic with zero and sensitivity drift
Total error due to drift
y (Output)
y (Output)
D x'd
+ Sensitivity
drift
D y'
-
Dy
Intercept b
Slope m =
Dxd
Dy
Dxd
+ Zero
drift
Zero drift
-
Sensitivity drift
y = mxd + b
xd (Input)
(a)
xd (Input)
(b)
Figure 1.3 (a) Static-sensitivity curve that relates desired input xd to output y.
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 drift
and sensitivity drift can be negative.
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Generalized Static Characteristics
• Input ranges
• Input impedance
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Generalized Dynamic Characteristics
• Differential or Integral equations
• Transfer functions
• Time delay
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Figure 1.8 Design
process for medical
instruments Choice
and design of
instruments are
affected by signal
factors, and also by
environmental,
medical, and
economic factors.
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Regulation of Medical Devices
• 1976 - Medical Device Amendments to the
Federal Food, Drug, and Cosmetics Act
• 1990 - Safe Medical Devices Act
Medical Device: any item promoted for a
medical purpose that does not rely on
chemical action to achieve its intended
effect
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Regulation of Medical Devices
• Medical devices were classified in two
ways:
– Class I (general controls), Class II
(performance standards), and Class III
(premarketing approval)
– Preamendment, Postamendment, Substantially
equivalent, implant, custom, investigation, and
transitional.
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Biomedical Transducer
Measuring is the key to understand, and transducer plays
an important role in measurement.
Kuo-Sheng Cheng, Ph.D.
Institute of Biomedical Engineering
National Cheng Kung University
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What is the Transducers?
• In principle, Transducers are devices that
convert signals in one form of energy into
signals in another form of energy.
• Sensors
• Actuator
• Conventional v.s. Intelligent Transducers
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What are the Transduers, Sensors, and
Actuators?
• Transducer - A device that converts energy
of one form to another.
• Sensor - A device that converts a physical
parameter to an electric output.
• Actuator - A device that converts an electric
signal to a physical output.
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Conventional v.s. Intelligent
Transducer
• Conventional transducer
Physical
or
Chemical
Parameters
Sensor
Transmission
Link
Signal
Processing
Display
Storage
Actuator
...
Further
Processing
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Conventional v.s. Intelligent
Transducer
• Intelligent transducer
Physical
or
Chemical
Parameters
Sensing Element
&
Signal Processing
Transmission
Link
Signal
Processing
Display
Storage
Actuator
...
Further
Processing
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Transducer Categories
• By application
• By physical or chemical principles used
• By the process used to convert the signal
energy into an electrical signal
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Three types of output signal
• Self-generating (active) transducers:
– The electrical signal output of transducer is
generated from another form of input energy.
e.g.
Light
in
~
I
Electrical
RL Signal
Output
Photovoltaic cell
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Three types of output signal
• Modulating (passive) transducer:
– The input signal energy of transducer is used to
modulate the electrical energy flow from the
power supply to the transducer output.
e.g.
Light
in
I
Photoconductive cell
Electrical
RL Signal
Output
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Three types of output signal
• Tandem transducers:
– The original input signal energy is converted to
a final output of electrical energy through two
or three effects or conversions in tandem.
e.g.
Light in
Photoconductive cell
I
Modulated
light
Y-position
Electrical
RL Signal
Output
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1. Sensor characteristics
2. Physical Sensors
• Displacement measurements
• Resistive
• Capacitive
• Inductive
• Piezoelectric
• Temperature measurements
• Optical measurements
3. Chemical Sensors
• Biochemical
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Electronic Sphygmomanometer
The System Design & Analysis
Student: Cheng-Yu Chen
Advisor: Kuo-Sheng Cheng
Biomedical Imaging & Instrumentation Lab
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Introduction
• The blood pressure measurement
-Invasive method
Stephen Hales placed a glass tube in the artery of horse for blood
pressure measurement in 1733.
The measurement of blood pressure with a mercury sphygmomanometer
was first invented by J. M. Poiseuille in 1828.
-Noninvasive method
Limb-occluding device that contained an arm cuff was first invented by
S. Riva-Rocci in 1896.
L. Hill and H. Barnard published a modified sphygmomanometer with
cuff in 1898.
N. S. Korotkov invented an auscultatory measurement of systolic and
diastolic blood pressure in 1905.
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Introduction (cont.)
• Stephen Hales demonstrated the
blood pressure in horse in 1733.
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Introduction (cont.)
• Riva-Rocci’s
sphygmomanometer, 1896
• Blood pressure
measurement using
Korotkov’s method, 1905
*E. O’Brien and D. Fitzgerald, “The history of indirect blood
pressure measurement,” Handbook of Hypertension, Vol. 14: Blood
Pressure Measurement
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Introduction (cont.)
• Korotkov’s method
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Introduction (cont.)
• The oscillometric method
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System Description
RS-232 Data
transmission
Analog signal
processing Circuits
Display unit
Pressure
Low-Pass Filter
High-Pass Filter
Microprocessor
with A/D converter
Signal
Air pump & valve
control circuit
Cuff
Instrumentation
Amplifier
Pressure
Sensor
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Hardware Design
• The system circuits
Display Unit
Pressure
Sensor
Microprocessor
With A/D
Converter
Analog Signal
Processing Circuit
RS-232 Data
Transmission
Air Pump & Valve
Control Circuit
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