Week 3: signal processing

Question 1

Define a medical device

Answer 1

An instrument, apparatus, appliance, material or other article, when used alone or in combination, together with any other software necessary for its proper application, intended by the manufacturer to be used for human beings for: diagnosis, prevention, monitoring, treatment or for the alleviation of disease

e.g., ECG machine, MRI, Echo

Question 2

Describe intended purposes of use

Answer 2

This defines what the manufacturer states that the device should be used for, according to the manufacturer’s data, labelling & instructions

If a device is used outside of its intended purpose, then it breaches legal & safety regulations

Question 3

Define a transducer

Answer 3

A device that converts one form of energy to another

Question 4

Define a pressure transducer

Answer 4

A pressure transducer converts blood pressure (mechanical energy) into electrical energy, as the ECG electrode converts electrical energy in a tissue into electrical energy in a circuit

Question 5

Describe the use of the Edwards TruWave Disposable Pressure Transducer

Answer 5

Used to measure arterial or venous pressure, Output voltage is proportional to the pressure.
It has; Ports for patient and atmosphere connection, Saline pressurised to 300 mmHg (flush system) & Electrical cable to send the signal to the monitor.

Question 6

Define sensitivity

Answer 6

Defined as the ratio of the change of the output to the change of the input
sensitivity=change in output/change in input

Question 7

Define linearity

Answer 7

It measures how closely a device output follows a straight line when the input is increased
Input Vs output should ideally be linear

Linearity= (max deviation from ideal)/ (full scale output) x100

Question 8

Define hysteresis

Answer 8

Refers to how a sensor’s output differs as the input increases from the value when it decreases

Hysteresis: (max hysteresis error)/ (full scale output) x100=

Question 9

Describe the range and the dynamic range

Answer 9

Dynamic range: the ratio of the largest to the smallest input values that a system can detect
e.g., ECG amplifier can detect from 0.5 microV to 10mV

Range: The largest input value a system can measure

e.g., a BP device might be able to be reliably used up to a maximum pressure of 265mmHg

Question 10

Define resolution

Answer 10

The smallest input change that can be processed by a system, it produces a measurable change in output

Question 11

Define calibration

Answer 11

The comparison of a test instrument with a more accurate standard (as close to the truth as possible)

Question 12

Describe the importance of calibrating equipment

Answer 12

1. Ensures that measurements are accurate & consistent
2. Results from different locations or time periods can be compared
3. Equipment remains safe & reliable for use

Question 13

Describe the process of calibration

Answer 13

1. Compare your device to a known standard
2. Measure how close your readings are to the known standard
3. Adjust if necessary until it matches the standard value

Example: A calibrated volume syringe tests a spirometer.

Question 14

Define traceability

Answer 14

refers to the fact that every measurement is able to be traced back to a national standard

Question 15

Define a single point calibration

Answer 15

Is where it is checked at only 1 value, this can be accurate up to a point

Question 16

Define a multipoint calibration

Answer 16

Where the device is checked at several intervals across the normal range, this ensures accuracy across all conditions.
E.g., spirometry is calibrated at low, medium & high flow rates

The further you deviate from the standard the greater the chance of error

Question 17

Define quality assurance

Answer 17

Part of the quality management, it provides assurance that the quality requirements of a device will be fulfilled
A systematic process that ensures that everything we do meets quality standards, a preventative technique

Question 18

Define quality control

Answer 18

Detects whether the output meets standards
e.g., daily equipment checks

Question 19

Define SI units

Answer 19

SI stands for Système International d’Unités — the International System of Units, used worldwide for scientific and medical measurement.
It ensures consistency, traceability,

All physical quantities are based of 7 fundamental units, other units are derived from these

Question 20

State the name and management of relevant cardiac physiology department

Answer 20

QMS & CQC

which cover:
1. Leadership & management
2. Clinical
3. patient experience
4. Safety & risk management
5. Facilities & resources

Question 21

Define the difference between a fundamental and a derived unit

Answer 21

Fundamental unit:
A fundamental (base) unit is an independent unit used to measure a basic physical quantity. It cannot be expressed in terms of other units.
e.g., metre (m) for length, kilogram (kg) for mass,

Derived unit:
A derived unit is a unit obtained by combining fundamental units according to a physical relationship. It depends on base units.
E.g., metre per second (m/s) for velocity, newton (kg·m/s²) for force,

Key difference:
Fundamental units are basic and independent, while derived units are formed from combinations of fundamental units.

Question 22

Define prefix and list common ones

Answer 22

A prefix is a word part or symbol placed before a unit to indicate a multiple or sub-multiple of that unit, usually based on powers of ten.

e.g., Milli, Mega, Kilo