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: 16
Grade code: 3.3.1.LI.2
Strand code: 3
Sub-strand code: 1
Content standard code: 3.3.1.CS.1
Indicator code: 3.3.1.LI.2
Theme: BIOMEDICAL INTERVENTION
Subtheme: DIAGNOSTIC DEVICE
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In Ghana today, from the smallest Community-based Health Planning and Services (CHPS) compound in a rural village to the largest teaching hospital like Korle-Bu, diagnostic devices are essential tools for healthcare. A simple Malaria Rapid Diagnostic Test (RDT) can save a life by confirming a diagnosis quickly. A blood pressure monitor helps manage hypertension, a growing problem in our communities. Understanding how these devices work is not just an academic exercise; it is the first step towards innovating, repairing, and creating new solutions for our own healthcare challenges.
2.1 What is a Diagnostic Device?
A diagnostic device is any tool, instrument, or system used to detect, measure, and monitor a person's health condition to help in the diagnosis, treatment, or prevention of disease. Its primary purpose is to provide information about a patient's body. Key Distinction: Diagnostic: Gathers information (e.g., Glucometer, Thermometer, Malaria RDT). Therapeutic: Actively treats a condition (e.g., Nebulizer for asthma, Dialysis machine). Assistive: Helps a person with a disability perform a task (e.g., Hearing aid, Prosthetic limb).
Ghanaian Examples: Digital Blood Pressure Monitor: Widely used in clinics and homes to diagnose and monitor hypertension. Malaria RDT Kit: A common tool in CHPS compounds to quickly diagnose malaria from a drop of blood without a microscope. 2.2 The Fundamental Building Blocks of a Diagnostic Device
Almost every diagnostic device, from a simple thermometer to a complex MRI machine, can be understood by breaking it down into four core functional units or "blocks". Sensor / Transducer: Function: This is the part that directly interacts with the body. It "senses" a physical or chemical property and converts it into a signal, usually an electrical signal. A device that converts one form of energy to another is called a transducer. Examples: Thermistor (in a digital thermometer): Its electrical resistance changes with temperature. LED and Photodiode (in a pulse oximeter): The LED shines light through your finger, and the photodiode detects how much light passes through. The amount of light changes with your blood pulse. Enzyme-coated strip (in a glucometer): Reacts chemically with glucose in the blood to produce a small electrical current. Microphone (in a digital stethoscope): Converts sound waves from the heart/lungs into an electrical signal. Signal Processing Unit: Function: The raw signal from the sensor is often weak, noisy, or not in a useful format. The signal processor's job is to "clean up" and interpret this signal. It may involve: Amplification: Making a weak signal stronger. Filtering: Removing unwanted noise (e.g., from movement). Calculation: Performing mathematical operations to get a final value (e.g., converting a resistance change into a temperature in °C, or counting electrical pulses to calculate beats per minute). Examples: This can be a simple electronic circuit with operational amplifiers (op-amps) or, more commonly today, a tiny computer called a microcontroller (like a tiny brain). Output / Display Unit: Function: This unit presents the processed information to the user (doctor, nurse, or patient) in a human-readable format. Examples: LCD/LED Screen: Shows numbers (e.g., "37.5 °C" or "120/80 mmHg"). Buzzer or Beeper: Makes a sound (e.g., when a thermometer has finished measuring). Indicator Light (LED): Can blink with a heartbeat or show a positive/negative result. Printed Lines: On a Malaria RDT, a coloured line appears to indicate a positive result. Power Source: Function: Provides the electrical energy needed for all the other components to work. Examples: Batteries: (AA, AAA, button cells) for portable devices. Mains Electricity: (AC power) for larger, stationary devices in hospitals. 2.3 Worked Example: A Simple Pulse Monitor