Diagnostic Imaging Techniques Flashcards
(23 cards)
What is an endoscope?
An endoscope is a flexible tube that allows you to look inside the body, in many cases there is no need to perform surgery and in other cases only a small incision is required
What is endoscopes designed to do?
To provide a direct view of an internal part of the body
Possibly remove samples from body
What are some areas that you can get images of?
Oesophagus Stomach Intestines Heart Lungs
What happens when waves go from a dense medium to a less dense medium?
They speed up at the boundary, this causes light rays to bend, this is kmow an as refraction
What is total internal reflection?
When it goes beyond a certain angle, called the critical angle, all the waves reflect back into the glass
When is the only time total internal reflection occurs?
When a ray of light is going from a high to a low refractive index
What is an optical fibre?
An optical fibre is a thin rod of high-quality glass
What happens in optical fibres?
Very little light is absorbed by the glass, light getting in at one end undergoes repeated total internal reflection even when the fibre is bent, and emerges at the other end
What is a coherent bundle?
A coherent bundle is when a bundle of fibres is placed together in an orderly manner along its length, with the posititions remaining unchanged, this allows actual images to be transmitted along the fibres
Why can coherent bundles transmit images?
It transmits light independently of its neighbour fibres
What doe coherent bundles consist of?
Fibres of a very small diameter, about 10mm.
The ends of each bundle are cut square and polished smooth to prevent distortions.
What does each fibre transmit in an optical fibre?
Each fibre transmits a small element of the image which is seen at the other end as a mosaic
How are incoherent bundles arranged?
This is when the bundle of fibres are arranged at random (or sometimes a light guide)
What is incoherent suitable for transmission of?
Only night, not images
What size are the fibres in a incoherant bundle?
Relatively large, 50-100mm
How is an image formed using an endoscope?
Light is shone down the incoherant bundle so that the site under examination is illuminated. Clear images can then be transmitted back to the eyepiece using a coherent bundle
What happens if the fibres in a endoscope touch?
The light leaks from one fibre to another
What is used to prevent light leaking from one fibre to another in endoscopes?
The fibres are coated with a second layer of glass of slightly lower refractive index
Why do u use cladding in endoscopes?
This increases the critical angle at the edge of the fibre
It also serves to protect the core from the surface scratches, this would lead to loss of light
What is the long flexible shaft of the endoscope usually made of?
A crush resistant covering of bronze or steel spiral.
What are some applications of endoscopy?
Visual evidence of upsets, tumours and intestinal bleeding
Remove foreign bodies from the oesophagus
Carry out biopsies
Is ultrasound ionising?
No
How does ultrasound work?
Low intensity ultrasonic waves pass through tissues without causing them harm. They are reflected at the boundaries between biological structures. These reflections are then created by and ultrasound scanner
