Lesson Notes By Weeks and Term v4 - SHS 3
DIAGNOSTIC DEVICE
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DIAGNOSTIC DEVICE
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Subject: Biomedical Science
Class: SHS 3
Term: 2nd Term
Week: 4
Grade code: 2.3.1.LI.3
Strand code: 3
Sub-strand code: 1
Content standard code: 2.3.1.CS.1
Indicator code: 2.3.1.LI.3
Theme: BIOMEDICAL INTERVENTION
Subtheme: DIAGNOSTIC DEVICE
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This lesson introduces the fundamental principles of bioinstrumentation that underpin the design and construction of every medical diagnostic device we see and use. From the simple thermometer used at home to the complex MRI machine in a major hospital, these devices are built on a common set of engineering and biological principles. Understanding these principles is crucial for appreciating how doctors can "see" inside our bodies, detect diseases like malaria or diabetes early, and monitor our health. In Ghana, where access to timely and accurate diagnosis can save countless lives, understanding the technology behind these tools is more important than ever.
This section breaks down the core ideas you need to understand the principles behind diagnostic devices. A. What is Bioinstrumentation?
Bioinstrumentation is the application of engineering principles and techniques to the fields of biology and medicine for the purpose of measurement, diagnosis, and therapy. In simple terms, it's the science of creating tools and devices to measure biological signals and diagnose medical conditions.
Every diagnostic device, no matter how simple or complex, can be understood using a Generalised Medical Instrumentation System. This system has four main parts that work together: Measurand: This is the physical quantity, property, or condition that the system measures. It's the "what" we are trying to detect in the body. *Examples:* Body temperature, blood glucose level, blood pressure, electrical activity of the heart (ECG), presence of malaria parasites. Sensor/Transducer: This is the part of the device that comes into contact with the patient (directly or indirectly) and detects the measurand. Its crucial job is to convert one form of energy into another, usually into an electrical signal. *Example:* In a digital thermometer, the *thermistor* at the tip is the sensor. It converts heat (thermal energy) into a change in electrical resistance (electrical signal). *Example:* In a glucose meter test strip, an enzyme (glucose oxidase) acts as a biological sensor. It reacts with glucose, producing an electrical current. Signal Conditioning Unit: The electrical signal from the sensor is often very weak, noisy, or not in a useful format. This unit's job is to "clean up" and boost the signal. *Functions:* Amplification: Making the signal stronger. Filtering: Removing unwanted noise or interference (e.g., from muscle movements during an ECG). Conversion: Changing the signal type (e.g., from analogue to digital for a computer to process). Output Display/Processing Unit: This is the final stage where the processed signal is presented to the user (doctor, nurse, or patient) in a readable format. *Examples:* A number on an LCD screen (digital thermometer, blood pressure monitor), a graph on a monitor (ECG machine), a coloured line on a test strip (pregnancy test, malaria RDT).
Example: A Digital Blood Pressure Monitor Measurand: Blood pressure in the brachial artery. Sensor: A pressure sensor inside the cuff detects the vibrations in the artery wall as the cuff deflates. It converts this pressure/vibration into an electrical signal. Signal Conditioning: The weak electrical signal is amplified and filtered to remove noise. An Analogue-to-Digital Converter (ADC) changes it into a digital format. Output Display: A microprocessor calculates the systolic and diastolic pressures and displays the numbers (e.g., "120/80 mmHg") on an LCD screen. B. Key Performance Characteristics of Diagnostic Devices