P3- medical physics

x-rays

• part of electromagnetic spectrum
• high frequency and short wave length (about same diameter as an atom)
• they effect photographic film in the same way as light
• they are absorbed by metal and bone
• they are transmitted by healthy tissue
• they are ionising and can damage living tissue
• used to check for fractures or dental problems
• charged coupled devices make electronic images of x ray
• Ct scanner are xrays that produce a cross section of the body (3d) 
• soft tissue and organs do not show up so to make it show up you must drink a contrast medium that can be aborbed by the xray
• workers must wear film badges or stand behind a screen to protect themselves
• xrays can be used to treat cancerous tumours

ultrasound

• human ear can detect sound waves with frequencies between 20Hz and 20000Hz
• sound waves higher than 20000Hz are ultrasound waves
• when the wave meets a boundary between two different materials e.g. tissue and bone part of the wave is reflected and travels back to a detector, it can calculate how far away it is
• distance= speed x time
• it is non ionising
• used for scanning
• used to shatter kidney stones
• can detect soft tissue

refractive index

• refraction is the change of direction of light as passes from one substance into another
• it happens because waves change speed as they cross a boundary
• no change if light is travelling along the normal
• refractive index of a substance is the measure of how much of the substance  can refract a light ray
• refractive index= sin i / sin r

the endoscope

• critical angle is the angle of insidence of a light ray in a transparent substance which produces refraction along the boundary
• refractive index= 1/sin c
• an endoscope is a device used to look inside a patients body without cutting it open
• endoscope contains bundles of optical fibres
• optical fibres are very thin, flexible glass fibres- visible light can be sent…