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Biomedical Signal Analysis > Measurement > Flashcards

Measurement Flashcards

1
Q

What is measurement?

A

Measurement is the collection of quantitative data.
A measurement is made by comparing a quantity with a standard unit. Since this comparison cannot be perfect, measurements inherently include error.

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2
Q

What do we normally want to measure?

A
  • Target: physical/electrical / chemical / biological quantities
    *Things we may want to measure: dimensional/ mechanical changes, chemical changes, electrical changes, thermal changes
    e.g. biopotentials: electrical changes
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3
Q

What is a biopotential electrode?

A

Electrodes provide the interface between the electronic changes in the body and the recording /measuring device.
Biopotential electrodes have a transducer function that conducts a small current across the interface between the body and the measuring circuit.

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4
Q

Describe the charge transfer at the electrode-electrolyte interface. ( * How does the transfer function of the biopotential electrode look schematically?)

A
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5
Q

Describe the equivalent circuit for a biopotential electrode in contact with an electrolyte.

A
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6
Q

What is a movement artifact? give several examples of movement artifacts related to the biopotential electrodes.

A

Artifact generated by movement.
e.g. coughing or breathing with a large movement of the chest
–>1. low-frequency artifacts
–>2. baseline drift
in chest-lead ECG signals
e.g. arm or leg is moved in the case of limb-lead ECG acquisition

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7
Q

How do non-polarizable electrodes (Ag/AgCl) help against motion artifacts?

A

using non-polarizable electrodes (Ag/AgCl) reduces the low-frequency noise created by motion artifacts
⟹ECG, and EEG should use such electrodes (it can be filtered out of EMG)

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8
Q

List three electrode types, which are used in biomedical signal analysis.

A
  1. metal plate electrodes which are disposable foam-pads –> cheap, minimum prep time for hospitals, used in ECG)
  2. suction electrodes e.g. precordial (chest) ECG
  3. implantable electrodes e.g. microelectrode array for cardiac pace maker
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9
Q

What is an artifact in biomedical signal?

A

Any signal other than that of interest could be termed interference, artifact, or simply noise.

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10
Q

What are the sources of noise/artifacts?

A

physiological
the instrument used
the environment of the experiment

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11
Q

Give several examples of measurement error sources

A
  • movement artifacts
  • maternal ECG superimposed in fetal ECG
  • physiological artifacts and interference (EGG)
  • 50 Hz (60 Hz) power line artifact
  • low frequency (drift) artifact from circuitry
  • amplifier noise
  • quantization errors
  • choice of incorrect sampling rate
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12
Q

Where do you place the electrodes on the body for a 12-leads ECG?

A

4 electrodes on limbs:
* LA = left arm
* RA = right arm
* LL = left leg
* RL/N = right leg (neutral electrode)
6 electrodes on the chest:
* V1: Fourth intercostal space, on the right sternal border
* V2 : Opposite V1, on the left sternal border
* V3 : Between V2 and V4
* V4 : Fifth intercostal space, on the mid-clavicular line
* V5 : Same level as V4, anterior axillary line
* V6 :Same level as V4, mid-axillary line

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13
Q

What are the lead systems that make up the standard 12-leads ECG?

A

3 lead systems:
* Standard Limb Leads (Bipolar): I, II & III
* Augmented Limb Leads (Unipolar): aVR, aVL & aVF
* Precordial Leads (Chest leads): V1- V6

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14
Q

What is Wilson´s central terminal?

A

-used as the reference for chest leads
-central of an imagined triangle (Einthoven´s triangle) formed by combining the left arm, right arm, and left leg leads.

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15
Q

What is Einthoven’s triangle?

A
  • hypothetical equilateral triangle formed by leads I, II, and III (left arm, right arm, and left leg leads)
    • center of the triangle: Wilson’s central terminal
    • schematically, the heart is at the center of the triangle
      Lead I: RA–>LA
      Lead II: RA–>LL
      Lead III: LA–>LL
      (vector travels towards the lead - positive lead
      vector travels away from the lead - negative lead)
  • facilitate viewing and analysis of the electrical activity of the heart from different perspectives in the frontal plane
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16
Q

From Einthoven’s triangle, derive the formulas for the leads / show the lead interrelationships

A

Lead I is the voltage difference between the LA and RA electrodes (LA – RA)
I = LA - RA
II = LL - RA
III = LL - LA
Interrelationships
II = I + III
aVL = LA - (RA+LL) /2 or = (I-III)/2
aVF = LL - (RA+LA) /2 or = (II+III)/2
avR = RA - (LL+LA) /2 or = - (I+II)/2

17
Q

What are the important features of standard clinical ECG?

A
  • ECG signal peak value normally about 1 mV
  • amplifier gain: 1000
  • recommended sampling rate: 500 Hz for diagnostic ECG
  • normally filtered to 0.05 - 100 Hz bandwidth
  • ECG for HR monitoring: reduced bandwidth, 0.5 - 50 Hz
  • high-resolution ECG: greater bandwidth, 0.05 - 500 Hz
18
Q

What does the power spectrum of an ECG including a power line artifact look like?

A

The spectrum illustrates peaks at the fundamental frequency of 60Hz as well as the
third & fifth harmonics at
180Hz and 300Hz respectively.

19
Q

Managing noise and artifacts starts with the experimental design, not with the data. Brainstorm a couple of general ideas on how to prevent/handle noise in typical biosignal measurements.
For example, think about how to prevent movement artifacts during ECG, why we use reference electrodes, etc.

A
  • 50 Hz (60 Hz) power line artifact
    - –>simple EM shielding of cables and grounding of the chassis of equipment reduce EM and power-supply interference in most cases.
    ERPs and EEGs may require a wire-mesh-shielded (Farraday) cage to contain the subject and the instruments.
  • Amplifier noise from instrumentation amplifiers
    –> reduce the thermal components of the noise by cooling the devices to low temperature (not practical, high cost)
    –> use low-noise power supplies
    —> use specialized electronic amplifiers with high input impedance
    —> high common-mode rejection ratio and high power-supply rejection ratio
20
Q

What is 3D Motion capture?

A
  • also known as motion capture or mocap,
  • a technique used to record and analyze the movement of objects or people.
  • measured using a system of (infrared) cameras that capture the position of (active or passive) markers at anatomical landmarks
21
Q

Why is human movement an important source of information?

A

Important information of
- injuries
- pathologic changes
for
- study and analyze complex movement patterns
- understand how the body or object moves in different conditions such as injuries or pathological changes

22
Q

What is the difference between passive marker systems and active marker systems?

A

Markers:
- in the passive system:
+ do not have any internal power source
+ do not emit any signals themselves.
- in the active system:
+ have an internal power source
+ emit light
–>allows the markers to be detected even when they are out of the range of the sensors or when they are occluded by other objects.
+ individual markers work at defined frequencies

23
Q

What are some applications of 3D motion capture in biomedical signal analysis?

A
  • biomechanics: movement pattern, kinematics of body
  • rehabilitation: assess and monitor the progress of patients undergoing physical therapy or rehabilitation
  • clinical gait analysis: study the way a person walks –> identify abnormalities or problems
  • sport science: movement pattern of athletes
  • orthopedic surgery
24
Q

What is IMU? (inertial measurement unit)

A
  • allow the continuous recording of movement in order to obtain information about activities of daily living or disease detection
    -recorded using micro-electrical mechanical systems (MEMS) that capture movement-related information
25
Q

List three types of sensors, which are used in inertial-magnetic measurement systems.

A
  • Accelerometers:
    +measure acceleration –> position and orientation of an object
    + provide info abt linear and angular motion
  • Gyroscopes:
    + measure angular rate of change –> orientation of an object
    + provide info abt the rotational motion
  • Magnetometers:
    + measure the position of the sensor relative to the earth’s magnetic field
    + used in combination with accelerometers and gyroscopes

Biomedical Signal Analysis (7 decks)

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