P3 Topic 1 - Radiation And Treatment Flashcards
How are X-rays used in medical imaging?
High energy EM waves that are absorbed by dense materials such as bone or metal are shone through the body. They are used to take X-ray photographs which can be used to diagnose bone fractures.
What causes long- and short-sightedness?
Long - cornea becomes flatter so light rays focus behind the retina.
Short - cornea stretches so light rays focus in front of the retina.
How do CAT scans work?
Computerised Axial Tomography scans use X-rays to produce an image of a two-dimensional slice of the body. They use intense ionising beams of X-rays. CAT scans can also show soft tissue as well as bones.
How are endoscopes used to see inside the body?
Endoscopes use optical fibres and visible light to see inside a patient’s body. It is a non-invasive technique as no surgery is needed. Instead a camera is sent inside the body so that the doctors can see what is going on inside. Keyhole surgery (laparoscopy), where a small incision is made into the patient and then the endoscope is sent in, can also be used.
Which medical techniques use ultrasound and how?
Breaking down kidney stones:
Kidney stones that block the urinary tract can be removed using ultrasound. A concentrated beam is aimed at the stone which turns into sand-like particles, these pass out of the body as urine with very little discomfort to the patient.
Pre-natal Scans of a Foetus:
Ultrasound imaging can be used to diagnose soft tissue problems and to perform pre-natal scans of a foetus in the womb. The ultrasound reflect off the different tissue boundaries and the times and distributions of the echoes are processed by a computer to form an image on a screen.
Measuring Blood Flow Speed:
Ultrasound works in real time and can be used to show moving and changing things. This makes it useful for investigating blood problems, such as the speed of the blood and identifying blockages in the veins and arteries.
Define radiation.
Radiation is energy that originates from a source.
Define refraction.
Refraction is when radiation changes direction as it enters a different medium. This is caused by the change in density from one medium to the other - which changes the speed of the radiation.
When a wave slows down, it bends toward the normal. If a wave hits the boundary at 90 degrees, it will not change direction, but will still slow down.
Not all the light is refracted as some may reflect off the boundary, depending on the angle of incidence.
What are the two types of lenses and what kinds of images do they produce?
Converging:
Converges light rays at a focal point, produces a real image that can be projected onto a screen.
Diverging:
Diverges light rays so that they can be traced back behind the lens to a focal point. It causes a virtual image.
What are the three rules for refraction in a converging lens?
- A ray parallel to the axis refracts through the lens and passes through the focal point.
- An incident ray passing through the focal point before entering the lens will refract through the lens and travel parallel to the axis.
- A ray passing through the centre of the lens carries on in the same direction.
What are the three rules for refraction in a diverging lens?
- A ray parallel to the axis refracts through the lens and travels in line with the focal point so that it appears to have come from the focal point.
- An incident ray passing towards the focal point refracts through the lens and travels parallel to the axis.
- A ray passing through the centre of the centre of the lens carries on in the same direction.
How does the position of the object affect the image?
At 2F
Between F and 2F
Nearer than F
At 2F:
Real, inverted, same size as object, image at 2F
Between F and 2F:
Real, inverted, bigger than object, image beyond 2F
Nearer than F:
Virtual, right way up, bigger than object, same side of lens as object
How do you work out the power of a lens using the focal point?
Power of lens = 1 / Focal Length
What happens if the angle if incidence (i) is:
- LESS than the critical angle
- EQUAL to the critical angle
- GREATER then the critical angle
- Most of the light passes out and is refracted, but some is internally reflected.
- The emerging ray comes out along the surface. There is more internal reflection.
- No light comes. It is all internally reflected. Total internal reflection.
What is Snell’s Law?
n1 x Sin(i) = n2 x Sin(r)
n1 = refractive index of first medium n2 = refractive index of second medium i = Angle of Incidence r = Angle of Refraction
What is the equation to calculate intensity using power and area?
Intensity = Power / Area
W/m^2 = W / m^2
