P3 - Medical Imaging Flashcards
Describe how X-ray scans work
X-rays are transmitted by healthy tissue but are absorbed by denser material like bone and metal
This means that when X-rays pass through a person with an X-ray imaging method behind them, only the X-rays that have passed through healthy tissue will actually hit the imaging method
What are X-rays?
High frequency, short wavelength electromagnetic waves with a diameter the same size as an atom
What are the 2 methods of X-ray imaging and how do they work?
When photographic film is hit by X-rays, it goes from clear to dark and cloudy until it turns black so if it is placed behind the patient, only the film behind the bones will stay colourless giving an image of the bone structure
The same can be done except charge couple devices (CCDs) which are tiny silicon chips are placed behind the patient. When hit by an X-ray, a CCD will send a signal to a computer so that a computerised image can be formed
Describe CT scans
Computerised axial tomography uses X-rays to produce high resolution images of hard and soft tissue
The patient is put inside a cylindrical scanner and an X-ray is sent from an X-ray tube on one side and picked up by a detector on the other side
The tube and detector are rotated during the scan
A computer interprets the signals from the detectors to form an image of 2D slice through the body
Multiple scans can be done to compile a 3D image of the body
Why can X-rays be used for treating cancer?
They cause ionisation meaning that they can kill living cells
Describe how X-rays are used to treat cancer
X-rays are focused on the tumour using a wide beam
The bean is rotated round the patient with the tumour at the centre
This minimises the exposure of normal cells to radiation reducing the chances of damaging the rest of the body
What 3 things do radiographers do to minimise exposure to X-rays?
Wear lead aprons
Stand behind a lead screen
Leave the room while scans are being done
X-ray radiation can’t penetrate lead
What is ultrasound?
Sound with a higher frequency than humans can hear (above 20000Hz)
Describe how ultrasound imaging works
Partial reflection means that when a wave passes from one medium to another, some is refracted and some is reflected
A pulse of ultrasound is pointed at an object and a detector is used to detect the reflected pulse (the time from when the ultrasound is emitted to when it is detected is measured)
Since we know the time and speed of the pulse of ultrasound, we can calculate the distance to the change in media
Describe the main 2 uses of ultrasound
It can be used to destroy kidney stones which are hard masses that block the urinary tract. Ultrasound is directed at the kidney stone and it turns to sand-like particles that pass out of the body in urine
They can scan for a foetus because ultrasound is partially reflected by the boundary between the womb fluid and skin of the foetus
What is the formula for calculating distance in an ultrasound scan?
Distance there and back (m) = wave speed (m/s) * time there and back (s)
Compare the safety of the 3 methods of medical imaging
Ultrasound waves are non-ionising abs completely safe
X-ray scans do cause ionisation and can cause cancer if the dose is too high (can’t be used on developing babies)
CT scans use a lot more X-ray radiation than regular X-ray scans meaning there is more ionisation so use of this machine is minimised
Compare the image quality of the 3 methods of medical imaging
Ultrasound images are quite fuzzy so some conditions can’t be diagnosed using these images
X-rays produce clear images of bone and metal but not much else
CT scans produce very high quality images to diagnose complicated illnesses. Hard and soft tissue are differentiated. Multiple scans can be used to produce 3D images
