P3 - Medical Applications Flashcards
Give two ways in which X-Rays are used in hospitals.
- To make images and CT scans.
- To destroy tumours at or near the body surface.
Why are X-rays dangerous?
X-rays damage living tissue when they pass through.
What is the absorption of X-rays like when passing through the body?
X-rays are absorbed more by bones and teeth (ie. dense materials) than softer tissues.
What is a CT scan?
CT scans distinguish between different types of soft tissue as well as between bone and soft tissue.
What are X-rays?
Electromagnetic waves with a short wavelength.
How are X-rays produced?
- A focused beam of electrons is made using a cathode.
- The electrons are fired at a high voltage to make them move quickly towards a positive metal plate.
- The high energy electrons excite the metal plate causing the release of an X-ray.
How are radiographs produced?
- X-rays are directed at the patient with a flat-panel detector on the other side.
- The X-rays pass through the designated area.
- X-rays pass through the soft tissue but are absorbed by bone.
- The parts of the detector hit by X-rays becomes darker producing a negative image.
How is a radiograph of an organ produced?
-The patient consumes a contrast medium such as barium which absorbs X-rays easily.
How are patients protected from the X-rays?
The parts not being scanned are covered by lead plates meaning X-rays only pass to the necessary area.
How are digital X-ray images produced?
- The flat-panel contains a CCD which is covered in a substance which converts X-rays into light.
- The light rays are converted into electrical signals which are sent to the computer.
How are X-rays dangerous?
- X-radiation ionises substances.
- High doses kill living cells/
- Low doses cause cell mutations and cancerous growth.
What is used to warn workers of X-rays?
Film badges show when the worker has been overexposed to radiation. A dosimeter.
How does a CT scanner work?
- The X-ray tube automatically moves around the ring.
- At each position, X-rays pass through the patient to the detector ring.
- Electronic signals from the detector are recorded by the computer so a 3D image can be produced.
Give three advantages of CT scanners.
- CT scanners can distinguish between bone and soft tissue.
- The image can distinguish between different types of soft tissue.
- CT scanners produce a 3D image.
Give two disadvantages of CT scanners.
- They give a high dose of ionising radiation.
- CT equipment is very expensive.
Give three advantages of X-ray machines.
- They can distinguish between bone and soft tissue.
- They give a lower dose of ionising radiation.
- They are relatively cheap.
What are ultrasound waves?
Sound waves above 20,000Hz.
What are ultrasound waves used for in medicine?
Ultrasonic scanning and destroying kidney stones.
Why can ultrasound waves be used to scan the body?
Ultrasound waves are partially reflected at a boundary between two different types of tissue.
Why is an ultrasound scan safer than X-ray?
An ultrasound scan is non-ionising.
What is a transducer?
The part of the ultrasound machine that produces and detects ultrasound waves.
What happens each pulse from the transducer?
- It is partially deflected at each boundary between tissues in its path.
- It returns to the transducer as a sequence of reflected pulses arriving at different times.
Give two advantages of using ultrasound.
- It is non-ionising.
- It can be used to scan organs and soft tissue.
What is an A-scan?
Measuring the length of an eyeball using ultrasound.
How does an A-scan happen?
- A transducer at the front of the eye sends ultrasound pulses into the eye.
- The reflected pulses are detected by a transducer and displayed on an oscilloscope.
How is the distance travelled by an ultrasound pulse.
speed of ultrasound waves in body tissue x transit time
How is the depth of a boundary below a surface calculated?
1/2 x speed of ultrasound wave x transit time
What is ultrasound therapy?
Breaking up kidney stones using an A-scan to determine their location.
What is the refractive index of a substance?
How much a substance can refract a light ray.
How is refractive index calculated?
n = sin(incidence) / sin(refraction)
What is the critical angle of a substance?
The angle of a light ray in a transparent substance that produces refraction along the boundary.
How is the critical angle related to the refractive index?
refractive index = 1 / sin(c) where c is the critical angle.
What is total internal reflection?
When the angle of incidence of a light ray is greater than the critical angle.
How are optical fibres used in medicine?
They are used to make endoscopes.
How do light and IR travel down an optical fibre?
At each boundary, the light is totally internally reflected.
What are the purposes of the two bundles of optical fibres in an endoscope?
- Shine light in the cavity.
- See internal surfaces of the cavity.
