X-rays and Ultrasound Flashcards
Why do x-rays cause ionisation?
They are high frequency, high energy waves
What materials are x-rays absorbed by?
Dense materials like bone or metal
What materials do x-rays pass through?
Less dense materials like healthy tissue
Why do x-rays produce shadow images?
The x-rays not absorbed by bone pass through to the detectors
What happens during an x-ray?
The x-rays are produced in an x-ray tube when fast moving electrons hit a target and the energy from the collision is released as x-rays. The x-rays are then directed at the patient.
What does a flat panel detector do?
Collects x-rays that are not absorbed by the body
What does a flat panel detector contain and what does it do?
CCD. The sensors in a CCD are covered by a layer that converts x-rays to light.
The denser an object is, how does it appear on an x-ray?
Brighter
How do x-rays ionise substances?
They knock electrons off cell’s atoms
What can high doses of x-rays do?
Kill living cells
What can low doses of x-rays do?
Cause cell mutation that leads to cancer
What is radiotherapy?
When x-ray beams kill or slow the growth of cancer cells
How are x-rays detected?
Photographic film or electronic detectors that produce an electronic image to be seen on a screen
How do people working with x-rays protect themselves?
Lead lined suits, stand behind lead screens, wear film badges to monitor their exposure to x-rays
What do CT scanners do?
Use x-rays and computers to combine x-rays from different positions to produce 3D images of the body
How are x-ray machines similar to CT scanners?
They distinguish between bone and soft tissue
How are x-ray machines different to CT scanners?
CT scanners distinguish between soft tissue types, produce 3D images and use a higher radiation dose
What medical instrument uses refraction and total internal reflection?
Endoscope
What is total internal reflection?
Light travels from a high to low density, so the incident substance has a larger refractive index. The angle of incidence exceeds the critical angle and light is reflected back on itself
What is the critical angle?
The angle at which light is reflected back upon itself
What angle is the critical angle about?
42 degrees
Why do we clad optic fibres?
- To keep the signal secure
- To maintain the signal quality
- To keep light rays within the core
- To provide strength to the signal
How do we use an ultrasound probe on the body?
The probe detects echoes as they bounce back to the scanner, so the scanner can map out the boundary of the object.
How can we use ultrasound to work out how fast blood cells move?
Ultrasound reflects off the cells and causes a Doppler shift
What is ultrasound?
A sound wave with frequency above 20,000Hz that travels at different speeds through different materials
Why can we use pulses of ultrasound to measure distance inside materials?
It partially reflects off boundaries
How do you work out the distance inside a material from an ultrasound reflection?
(speed X time) / 2
How do you calculate the time taken for an ultrasound pulse from an oscilloscope trace?
Number of squares between pulses X time per square
What are the two main medical uses of ultrasound?
Scanning fetus’ and detecting and treating kidney stones
How does visible light travel through optic fibres?
Total internal reflection - repeatedly reflecting off the inside surface of the fibre
How do endoscopes work?
Use optic fibres and a camera to examine inside patients. Visible light sent down the fibre reflects off internal organs to the camera.
