Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Welcome To The P3 Overview P3 1.1 X-rays X-Rays X-rays and Gamma rays are the electromagnetic waves with the shortest wavelength and highest energy. X-rays have wavelengths about the width of an atom, and gamma rays about the width of a nucleus In an X-ray machine, VERY FAST ELECTRONS are fired in a beam at a metal target. Some of their kinetic energy is converted into Xrays X-Ray Photography X-Rays have enough energy to pass through lots of solid materials such as skin, muscle and fat, but are absorbed by denser materials like bone. Most metals absorb X-rays almost completely. Sheet of photographic film X-rays passing through blacken the film, bones cast a shadow (looks white) “Barium Meal” Lead lined apron Metal is opaque to long wavelength 9low energy) X-rays Soft tissue casts a weak shadow if the x-ray wavelength is long enough What are the risks from having an X-Ray? Radiographers use the lowest energy X-rays for the shortest time possible to get a clear picture. This reduces the radiation risk to the patient to the minimum. Radiographers themselves wear lead lined protective clothing and operate the machine from a distance. Safety ! SECURITY Airport baggage scanners make use of false colour images. Operators must be trained to check each image in a few seconds. Body scanners These use ‘scattered’ (ie reflected) low energy X-rays to see beneath clothing Coming soon to an airport near you! Computerised Axial Tomography ‘ (CAT scan or CT scan). In the 1970s a method was developed to give much higher quality images including a 3D view of the patient. This method of scanning is called Computerised Axial Tomography (CAT or CT). Computerised axial tomography (CAT or CT) In the CT scanner there is one X ray source but a large number of detectors and the patient is placed inside this on a couch. Each detector records an image and the source and detectors are then rotated around the patient to give views from a variety of direction.. The couch and patient are then moved along the axis of the machine and another set of images is taken. few minutes or up to half an hour. This large number of images (many hundreds) are then combined by a computer to give a composite detailed 3D image of the organs under investigation. P3 1.2 Ultrasound • Have frequencies greater than 20000Hz. • Too high pitched for human hearing, • Non-ionising Medical images from ultrasound • The ultrasound is sent into the patients body. • At each boundary between different tissues or organs some of the ultrasound is reflected. • The depth of each layer is calculated using the time taken for each reflected wave to return. • The reflected waves (echoes) are usually processed to produce a picture of the inside of the body on a screen. In reality, the trace on a CRO will look more like this. Each pulse is a reflection off a different surface. To determine the time to receive any of the echoes… Pulses B and C indicate echoes from surfaces inside the patient. 1. Count the number of boxes to a certain pulse, Pulse A indicates when the pulse was sent. 2. Multiply by the given scale. Use Speed = Distance Time A BC D Breaking down kidney stones and stones elsewhere in the body • A high powered ultrasound wave is used to break down kidney stones and other stones in the body. • The stones vibrate until they shake themselves apart and are then easily passed out of the body via the urethra. Before After P3 1.3 Refractive index Refraction of light at a plane surface (a) Less to more optical dense transition (e.g. air to glass) AIR GLASS normal angle of incidence angle of refraction Light bends TOWARDS the normal. The angle of refraction is LESS than the angle of incidence. (b) More to less optical dense transition (e.g. water to air) angle of refraction normal angle of incidence WATER AIR Light bends AWAY FROM the normal. The angle of refraction is GREATER than the angle of incidence. refractive index n = sin i sin r Snell’s Law Refractive Index for a vacuum (and air ) = 1 air P3 1.4 Critical angle and Endoscope critical angle The critical angle is the angle of incidence in the denser medium that results in an angle of refraction of 90º n= 1 sin c where: n is the refractive index of the denser medium (glass in the example opposite). c is the critical angle. GLASS AIR NORMAL angle of refraction = 90º 3. Optical fibres Optical fibre consists of two concentric layers of different types of glass, core and cladding. Light entering the inner core always strikes the boundary of the two glasses at an angle that is greater than the critical angle. core cladding The Endoscope The medical endoscope contains two bundles of fibres. One set of fibres transmits light into a body cavity and the other is used to return an image for observation. Optical Fibres is guided by T.I.R . . . Light in at this end . . . and comes out here. Optical fibres are used in communications to carry signals. (The signals are pulses of laser light) Optical fibres are used in medicine to look inside the body. An endoscope is made of a bunch of optical fibres to carry light into and out of the body. P3 1.5 Lenses Convex FOCUS axis F PARALLEL rays from distant object focal length P=1 f dioptres Convex lenses bring the rays together (‘converge’) at a focus. Convex lenses are CONVERGING LENSES Converging lens images 1. Object more than twice the focal length distant from a converging lens object O 2F F Uses: Camera and Eye The image formed is: Smaller than the object (diminished) Between the F and 2F Inverted (upside down) Real F 2F image 3. Object nearer than the principal focus image F object F observer Uses: Magnifying glass The image formed is: Larger than the object On the same side of the lens as the object Upright Virtual Concave PARALLEL rays from distant object F F Concave lenses spread the rays out (‘diverge’). Concave lenses are DIVERGING LENSES Diverging lens images Objects at all distances from a diverging lens object F observer image Use: Correction of short sight The image formed is: Smaller than the object On the same side of the lens as the object Upright Virtual P3 1.7 The Eye Short sighted Causes: Shape of eyeball…………………….. Shape of lens………………………… Focal point……………………………. Short-sight Long sighted Causes: Shape of eyeball…………………….. Shape of lens………………………… Focal point……………………………. Long-sight Comparison of Eye and Camera Physics Clinic • Every Thursday from 3:00 pm in Lab 9 And Finally…… • Remember the motto And Finally…… • Remember the motto Physics is Fun!