Unit 3 - Medical Physics Flashcards
Give 4 properties of X Rays.
They are absorbed by bone and metal. They have a wavelength the diameter of an atom. They are transmitted through soft tissue/skin. They affect photographic film. They are transverse electromagnetic waves. They are ionising.
Why are The number of x Rays a person has monitored over time?
X rays are ionising and can kill healthy cells/cause damage to DNA/damage cells/cause cancer.
Give 2 examples of medical uses of X rays.
Imaging bones. Imaging dental problems. Imaging the body (CT scans). Killing cancer cells.
Give 2 precautions taken by professionals involved in using X rays.
Leave the room. Warning light above the door of a room when x rays are used. Wearing a lead apron to absorb x rays. Standing behind a screen.
What are the advantages of CT scans over X rays?
Clearer, more detail, 3D image. CT scans can take images of slices of body. The whole body can be imaged.
Describe ultrasound.
A longitudinal wave/vibration above 20 000Hz/ beyond upper range of human hearing. Sound humans can’t hear.
How is an image formed using ultrasound?
Ultrasound waves are partially reflected when they meet a boundary between two substances. The time taken for this reflection (echo) gives the distance of the boundary. Reflected waves are collected and processed into an image by a computer.
What is ultrasound used for?
Imaging babies in the womb (pre-natal scanning). Destroying kidney stones. Treating muscle damage, tendons, ligament damage. removing plaque from teeth
What is refraction?
The bending of light moving from one substance (medium) to another.
What is the name of the point which a convex lens makes light rays meet?
The focal point.
Why is an image formed from a lens virtual?
The real light rays do not meet to make the image, virtual light rays meet instead.
Why are some people are short sighted?
Their eye ball is too long or the lens is unable to focus light rays onto the retina.
Why are some people long sighted?
Their eye ball is too short or the lens can not focus light rays onto the retina.
Give the near point and far point of our vision.
Near point = 20 cm. Far point = infinity
What is the power of a lens with a focal distance of 60cm?
1/0.6 = 1.67D (notice 0.6m not 60cm!)
The image is focused onto the retina in our eye. What is it focused on in a digital camera?
The CCD - charged coupled device
Which TWO parts of the eye refract light before it arrives at the retina?
The lens and the cornea.
Which part of the eye changes the shape of the lens to focus close by and far away objects?
The ciliary muscles.
How can a lens be made thinner and flatter but still have the power needed to refract light correctly?
The lens must have a higher refractive index.
Give Two factors affecting the power of a lens.
The refractive index of the lens and the thickness of the lens.
What is an X Ray?
A very high frequency electromagnetic wave.A transverse wave, vibrations are perpendicular to the direction of energy transfer.
Why is a charge coupled device CCD useful in medical imaging?
Images can be formed and stored electronically, so easily shared and manipulated.
How are ultrasound waves produced?
Electronic systems produce ultrasound, a longitudinal wave with vibrations parallel to the transfer of energy.
What is the distance from a lens to the principle focus or focal point called?
The focal length.
What does the power of a lens tell you?
How much the lens bends light rays. Greater the power the more it bends light.
Give one property of a lens that affects its power.
The thickness of the lens. The curvature of the lens (how much it bulges outwards or caves inwards. The refractive index of the lens.
What type of lens is found in a magnifying glass?
A convex lens or converging lens.
The nature of an image is describe in 3 ways. What are they?
Virtual or real. Inverted (upside down) or upright. Relative size compared to the object (smaller or larger)
Why does the shape of the lens in the eye need to be changed?
To allow light rays to focus/meet on the retina from objects close by (thick lens) and far away (thinner lens).
What is the equivalent part to our retina in a camera?
Digital camera = CCD, Traditional camera = photographic film.
Give two factors affecting the focal length of a lens.
The curvature of the two surfaces of the lensThe refractive index of the material the lens is made of.
Describe what happens to a light Ray in an endoscope.
Light is totally internally reflected because it reflects from the optical fibre at an angle larger than the critical angle.
Give a medical use for a laser.
It is an energy source used for cutting skin/tissue burning cells and sealing blood vessels. Lasers are also used in eye surgery to correct sight.
Describe why light totally internally reflects in an optical fibre.
The light hits the edge of the fibre at an angle bigger than the critical angle and reflects rather than refracts out of the fibre.
