Biomedical Instrumentation
BME-301
Lecture -2
Dr. Muhammad Umair Ahmad Khan
umair.ahmad@uet.edu.pk
04-09-2024
Medical instrumentation
q Definition: instrument for sensing, diagnostics,
therapeutics or surgery of human being.
q The global medical device market is
expected to reach an
estimated $350+ billion by 2025.
q Total cost of health care in the U.S. currently
stands at $2.7 trillion.
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Medical instrumentation classification
q Diagnostic instrumentation
q Therapeutic instrumentation
q Clinical laboratory instrumentation
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Medical instrumentation classification
Diagnostic Instrumentation:
Diagnostic instruments are tools/devices used to determine
the nature and cause of a patient’s ailment.
Imaging Systems: MRI (Magnetic Resonance Imaging), CT
(Computed Tomography) scanners, X-ray machines, and
ultrasound devices.
Endoscopes: For visualizing the internal parts of the body,
like the gastrointestinal tract.
Electrocardiographs (ECGs)To measure the electrical
activity of the heart.
Spirometers: To measure lung function and volume.
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Medical instrumentation classification
Therapeutic Instrumentation:
Therapeutic instruments are used to treat diseases and medical
conditions
Dialysis Machines: Used to filter the blood for patients with kidney
failure.
•Lasers: Used in surgeries to cut, remove, or modify tissue with
precision.
•Defibrillators: Deliver electrical shocks to restore the heart's normal
rhythm.
•Ventilators: Assist or replace spontaneous breathing.
•Infusion Pumps: For controlled delivery of medications or nutrients.
•Radiation Therapy Machines: To treat certain cancers by directing
high-energy particles or waves to destroy or damage cancer cells.
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Medical instrumentation classification
Clinical Laboratory Instrumentation:
These are instruments found in a clinical laboratory setting used to
analyze patient specimens, such as blood, urine, or tissues. The results
obtained from these instruments aid clinicians in the diagnosis,
prognosis, and treatment of diseases. Blood Analyzers: Used to
measure different components of the blood, such as cells, glucose,
electrolytes, and more.
1. Microscopes: For examining tissues, cells, and other specimens
at a microscopic level.
2. Hematology Analyzers: For counting blood cells, measuring
hemoglobin, and other related tests.
3. Centrifuges: Used to separate different components of a sample,
such as plasma from blood cells.
4. Molecular Diagnostic Instruments: To detect and measure DNA
or RNA of pathogens or genetic conditions.
5. Mass Spectrometers: For identifying and quantifying the 6
chemical composition of samples.
Diagnostic instrumentation
q Definition: a device that gathers information
leading to the identification of a disease or
disorder.
Stethoscope CT
(invented in 1819) (X-ray computed tomography )
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Generalized composition of
diagnostic instrument
Signal Output
Measurand Sensor
processing display
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Generalized composition of
diagnostic instrument
Signal Output
Measurand Sensor
processing display
q Measurand: physical quantity, property, or
condition that the system measures.
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Measurand
q Examples:
n Blood oxygen saturation
n Electrical activity of the heart
n Tumor
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Measurand
q Examples:
n Blood oxygen saturation
n Electrical activity of the heart
n Tumor
Normal ECG Abnormal ECG
(Electrocardiography)
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Measurand
q Examples:
n Blood oxygen saturation
n Electrical activity of the heart
n Tumor
Tumor
Liver
Ultrasound image of tumor in liver
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Measurand
q Constrains:
n Accessibility
n Vary with time and among patients
n Safety
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Measurand
q Constrains:
n Accessibility
n Vary with time and among patients
n Safety
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Measurand
q Constrains:
n Accessibility
n Vary with time and among patients
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Measurand
q Constrains:
n Accessibility
n Vary with time and among patients
n Safety:
q Limitation of external applied signals
q Electrical safety
Radiation hazard
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Generalized composition of
diagnostic instrument
Signal Output
Measurand Sensor
processing display
q Sensor: a device that converts the measurand
into a signal carrying information.
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Sensor
q Classification: according to the quantities to be
measured
n Thermal quantities
n Mechanical quantities
n Chemical quantities
n Radiation intensity
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Sensor
q Classification: according to the quantities to be
measured
n Thermal quantities
n Mechanical quantities
n Chemical quantities
n Radiation intensity
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Sensor
q Classification: according to the quantity to be
measured
n Thermal quantities
n Mechanical quantities
n Chemical quantities
n Radiation intensity
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Sensor
q Classification: according to the quantity to be
measured
n Thermal quantities
n Mechanical quantities
n Chemical quantities
n Radiation intensity
Blood glucose meter
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Sensor
q Classification: according to the quantity to be
measured
n Thermal quantities
n Mechanical quantities
n Chemical quantities
n Radiation intensity
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Sensor
q Static characteristics: the relationship between the
output signal and the measurand.
q Limit of detection: the lowest value of measurand
that can be detected by the sensor.
q Sensitivity: the smallest change it can detect in
the quantity that it is measuring.
q Repeatability: ability of a sensor to reproduce
output readings under the same input.
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Sensor
q Requirements:
n Sensitive to the measured property
n Accurate
n Stable and reliable
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Generalized composition of
diagnostic instrument
Signal Output
Measurand Sensor
processing display
n Signal processing: amplifies, filters, or in any
other way changes the output of the sensor to
prepare signals suitable for display.
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Signal Processing
n Challenges:
q Biological signal magnitudes are low
q Any measurement includes noise
Parameter Range
ECG 0.5 – 4 mV
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Signal Processing
n Challenges:
q Biological signal magnitudes are low
q Any measurement includes noise
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Signal Processing
n Noise sources:
q External: power lines, radio broadcast, cell phone …
q Internal: muscle noise, motion artifact…
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Signal Processing
n Eliminate noise:
q Signal filtering: separate noise from the desired
signal using their distinct property. e.g. separate
high frequency noise from low frequency signal.
q Opposing inputs: if noise is known, it can be
removed from the signal by subtracting the noise
from the signal.
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Generalized composition of
diagnostic instrument
Signal Output
Measurand Sensor
processing display
n Output display: convey the information obtained
by the measurement in a meaningful way
(visual, audible)
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Generalized Biomedical
Instrumentation System
o Main difference of medical
instrumentation systems and
conventioanl ones is that source of
signals is living tissue or energy
applied to living tissue.
o The sensor converts energy or information from the measurand to an electric
signal. This signal is processed and displayed so that humans can percieve the
information.Dashed lines show optional elements and connections for some
applications.
Generalized Biomedical
Instrumentation System
o Measurand is defined as physical quantity,
property, or condition that the system measures.
o The accessibility of measurand may be
n internal (blood pressure),
n body surface (electrocardiogram potential),
n emanation from the body, or tissue sample (infrared
radiation)
n derived from a tissue sample (blood or biopsy)
o Measurands can be grouped into:
n biopotential,
n pressure,
n flow,
n imaging,
n displacement,
n impedance,
n temperature,
n chemical concentration
Sensor
o Sensor is a device that converts physical measurand
to an electric signal. (Sensor is a type of transducer
but transducer is not necessarily a transducer such
as an actuator.)
o Sensor should
n respond only to the form energy present in the
Power measurand and exclude others.
Source n Minimize the energy extracted
n Be minimally invasive.
o Primary sensing element gives an output (mostly
linear) that is a function of measurand. Mercury-in-
glass thermometer outputs temperature reading in
terms of the level of the mercury.
o Variable conversion elements are needed where the
output variable of a primary sensing element is in an
inconvenient form and has to be converted to a more
convenient form.
o For instance, the displacement-measuring strain
gauge has an output in the form of a varying
resistance. The resistance change cannot be easily
measured and so it is converted to a change in
voltage by a bridge circuit, which is a typical
example of a variable conversion element.
o Many variable conversion elements need an external
electric power to obtain a sensor output.
Sensor
Sensor:
A sensor is a device that detects and measures changes in a physical
quantity and converts it into a readable form. Sensors are used to monitor
various parameters and provide data that can be used for analysis, control,
or display. Sensors typically don't directly provide an electrical output;
instead, they produce some sort of physical change that can be converted
into an electrical signal by external circuitry.
Example of sensors:
Temperature Sensor: Measures temperature and provides a change in
resistance, capacitance, or voltage.
Light Sensor (Photodetector): Measures light intensity and produces a
change in current or voltage.
Pressure Sensor: Measures pressure and might produce a change in
resistance or capacitance.
Sensor
1.Electrocardiogram (ECG) Electrodes: These sensors are used
to measure the electrical activity of the heart. They detect the
electrical signals generated by the heart's contractions and
provide data for diagnosing conditions like arrhythmias.
2.Pulse Oximeter: This sensor measures the oxygen saturation
of a patient's blood by shining light through a finger or earlobe
and detecting the amount of light absorbed by oxygenated and
deoxygenated blood.
3.Temperature Sensor (Thermistor): Used to monitor a
patient's body temperature. Thermistors change resistance
with temperature, and this change is measured to determine
the patient's temperature.
Transducer
Transducer:
A transducer, on the other hand, is a device that converts one form of
energy into another. In the context of sensors, transducers convert physical
quantities into electrical signals. Transducers are a broader category that
includes sensors. All sensors are transducers, but not all transducers are
sensors. Transducers can also convert other forms of energy, such as
mechanical or acoustic energy, into electrical signals.
Examples of transducers
Microphone: Converts sound waves (acoustic energy) into electrical
signals.
Piezoelectric Transducer: Converts mechanical vibrations into electrical
signals and vice versa.
Transducer
1.Ultrasound Transducer: Converts electrical signals into sound
waves (ultrasound) and vice versa. Used in medical imaging to create
images of internal structures like organs and tissues.
2.Piezoelectric Transducer for Imaging: Used in medical ultrasound
imaging systems to convert electrical signals into ultrasound waves
and vice versa. These transducers emit and receive ultrasound
signals for imaging purposes.
3.Pressure Transducer: Converts the pressure exerted by fluids or
gases in the body into electrical signals. These are used in invasive
procedures like measuring intracranial pressure or intra-arterial
blood pressure.
Output Display
o The results of the measurement process must be displayed in a
form that the human operator can recieve.
o The best form may be for visual sense
n Numerical or graphical
n Discrete or continuous
n Permanent (print out) or temporary (LCD screen)
o Auditory sense (Doppler ultrasound signal)
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Auxiliary Elements
o Calibration according to the properties of the measurand
should be applied to the sensor input or as early in the
signal processing chain as possible.
o Control and feedback is required to elicit the measurand,
to adjust the sensor and signal conditioner and to direct
the flow of output for display, storage and signal
conditioner.
o Data Storage may be necessary for signal conditioning
and signal processing and to enable the operator to
examine data that precede alarm conditions.
o Data Transmission may be required for remote deisplay
at nurses’s statins, medical centers, or medical data-
processing facillities.
Medical Measurement
Constraints
o Typical medical parameter magnitude and frequency ranges: Table 1.1
o Most of the parameter measurement ranges are quite low compared with nonmedical
parameters
n Small amplitude. Most voltages are in microvolt range
n Low frequency. Signals are in the audio-frequency range (20*20000Hz) or below.
o Frequent inaccessibility due to the lack of proper measurand-sensor interface. Cardiac output.
o To isolate measurand from other systems of body, it is not possible to turn it off or remove a
part of it during measurements.
o Inherent variability with time and among subjects.Body temperature changes between 36.5
and 37.5 degrees. Temperature depends on time of the day, person
o Many feedback loops among physiological systems exist and it is seldom feasible to control or
neutralize the effects of these systems on the measurand. The most common method of
coping with this variablility is to assume empirical statistical and probalistic distribution
functions.
o It is difficult to establish safety level of the externally applied energy. X-ray, ultrasonic
imaging. The heating of tissue is one effect that must be limited.
o Additional constraints of a medical equipment
n Reliability
n Easy to use
n Must withstand physical abuse and exposure to corrosive chemicals
n Minimized electric-shock hazards
Table 1.1: Examples of medical and physological paramaters
Accuracy
o Accuracy is defined as the degree of conformity of a
measured value to the true (conventional true value –
CTV) or accepted value of the variable being measured.
It is a measure of the total error in the measurement
without looking into the sources of the errors.
o Mathematically it is expressed as the maximum absolute
deviation of the readings from the CTV. This is called the
absolute accuracy.
absoluteAccuracy = maximum DeviationFromCTV
AbsoluteAccuracy
RelativeAccuracy =
CTV
PercentageAccuracy =100xRelativeAccuracy
Example
o A voltmeter is used for reading on a
standard value of 50 volts, the
following readings are obtained: 47,
52, 51, 48. What are the
n absolue acccuracy,
n relative accuracy and
n percentage accuracy?
Answer
Resolution
o Resolution is the smallest
increment a tool can detect and
display.
o Resolution of an digital multimeter
is the smallest value the Least
Significant Digit (LSD) can display
for each range.
o The resolution of an analog meter
corresponds to the smallest scale
subdivision for a particular range.
Precision
o Precision is too often confused with Accuracy
o Precision is a measure of repetability of an measurement. The average value of
a set of readings is found by averaging the measurements taken repeatedly with
the same measuring device in the same conditions. The deviation of the
readings from the mean (average) value determines the precision of the
instrument. The figure below illustrates this:
o Bias
o The difference between CTV and average value (VAV) is called the bias. Ideally,
the bias should be zero. For a high quality digital voltmeter, the loading error is
negligible yielding bias very close to zero.
Bias
Example
o A voltmeter is used for reading on a
standard value of 50 volts, the
following readings are obtained: 47,
52, 51, 48. What are the
n Precision and
n bias?
Solution
o Bias = CTV – VAV
o average (VAV) = (47+48+51+52)/4 =
49.5 V
o Pr = max {(49.5 – 47), (52 – 49.5)}
= 2.5 volts
o Bias = 50 – 49.5 = 0.5 volt
Example
o A digital thermometer is used to
measure the boiling point of water
(100.0°C). The measurement is
repeated 5 times and following
readings are obtained: 99.9, 101.2,
100.5, 100.8, 100.1.
o Determine the accuracy, the precision
and the bias of the thermometer.
o TCTV = 100.0°C;
o TAV =( 99.9 + 101.2 + 100.5 + 100.8 +
100.1)/5 = 100.5°C.
o Absolute Accuracy = max of [(101.2 – 100.0),
(100.0 – 99.9)] = 1.2°C;
o Relative Accuracy=0.012
o Percentage Accuracy % acc. = 1.2%
o Pr = max of [(101.2 – 100.5), (100.5 – 99.9)]
= 0.7°C
o Bias = TCTV - TAV = -0.5°C.
Precision:
Repeatability and Reproducibility
o Repeatability and reproducibility are ways of measuring precision.
o For repeatability to be established, the following conditions must
be in place:
n the same location;
n the same measurement procedure;
n the same observer;
n the same measuring instrument,
used under the same conditions; and repetition over a short
period of time.
o Reproducibility refers to the degree of agreement between the
results of experiments conducted by
n different individuals,
n at different locations,
n with different instruments.
