- Created by: fern
- Created on: 08-04-13 20:03
Medical applications of physics- X-RAYS (1.1)
- Part of the electromagnetic spectrum
- X-rays have a high frequency & a very short wavelength (electromagnetic waves)
- can be used for medical diognosis, CT scans and Cancer precautions
- bone fractures and dental problems can be detected
Properties of an X-ray include:
- X-rays are transmitted by (pass through) healthy tissue
- absorbed by denser materials like metal and bone
- They can be used to take photographs because they affect photographic film in the same way as light.
Charge-coupled devices (CCSs)
- Electronically - small sillicon chips divided up into a grid of millions of identical pixels
- CCDs detect X-rays and produce electronic signals which form high resolution images
- Detect the brighter parts of image where fewer X-rays get through
- negative image produced (plate starts of white) Lightest areas appear darkest.
Medical applications of Physics - C.T SCANS (1.1)
Computerised axial tomography (CT)
- X-rays are used to produce a high resolution image of soft and hard tissues
- An X-ray beam is fired through the body from an X-ray tube and is picked up by detectors on the opposite side
- X-ray tubes & detectors are rotated throughout the scan
- computers interpret signals from the detectors and form an digital image of a 2D slice through the body (cross section)
- Multiple 2D CT scans can be put together to make a 3D image inside the body
- Body organs made of soft tissue (such as intestines) can be filled with a contrast medium so that they absorb X-rays and can be seen on an X-ray image
- C.T scans use 9x more X-rays than normal X-rays to find any tiny variations in tissue density.
Risks & Cancer
Medical applications of Physics- X-RAYS, CANCER & RISKS (1.1)
Treating cancerous tumors
- X-rays can cause ionisation
- using high does can kill living cells & can be used to treat cancers (like gamma rays)
- To treat cancers the X-rays are focused on a tumor using a wide beam which is rotated around the patient with a tumor at the centre.
- This will minimise radiation being exposed to normal cells which will reduce the chances of damaging the rest of the body
- Rays must be carefully focused/have the correct dosage in order to kill cancer cells.
- sometimes normal cells can be damaged in this process.
- Radiographers need to minimise their X-ray dosage
- They prevent harm to their cells by wearing lead apron and standing behind a lead screen or by leaving the room when scans are done.
- Lead aprons are used to shield areas which are not being scanned so that the exposure time of an X-ray is kept to a minimum.
Medical applications of physics-ULTRASOUND (1.2)
- Human ear can detect sound waves with frequencies between 20Hz & 20,000Hz
- Ultrasound is sound with higher frequency than humans can hear.
- electrical oscillations of any frequency can be made with electrical systems
- converted into mechanical vibrations to produce sound waves with high frequency than human upper limit.
How they work
- Sound waves pass from one medium to another
- When a wave meets a boundary part of the wave is relected off the boundary and some is refracted (change of direction of light)
- This is called partial reflection, it means you can point a pulse of ultrasound at an object and wherever there are boundaries between 2 substances some of the ultrasound gets reflected back to the derector
- The time this takes for the reflection to reach the detector can be used to measure the distance of the boundary.
Medical applications of Physics - OSCILLIOSCOPES (1.2)
- Oscilliscope traces show ultrasound pulses reflecting off two separate boundaries
- Oscilliscopes can beused to woek out the time between the pulses by measuring on the screen.
- If you know the speed of sound in the medium (a substance where energy can be transfered from one location to another) then the distance between the boundaries can be calculated.
This can be done using the equation: S = V X T
- S = Distance travelled in metres (m)
- V = Speed of the ultrasound wave in metres per second (m/s)
- T = Time taken in seconds (s)
In the time between the transmitter sending a pulse of ultrasound and it returning to the detector it has travelled from the transmitter to the boundary and back (twice the distance).
Medicine Advantages and Disadvantages
Medical applications of physics -
Medicine Advantages and disadvantages (1.1-1.2)
Advantages of ultrasound
- They are able to break down Kidney stones (hard masses that block the urinary tract)
- ultrasound beam concentrates high energy waves at the kidney stone to turns it into small particles
- The patient does not need surgery and it is a relitively painless process (particles pass out the body in urine)
- Can check fetal development by reflecting a wave once it reaches a boundary (fluid in womb/skin of fetus). The echos are processed by a computer to produce a video image of the fetus.
- Non- ionising and safe.
Disadvantages of ultrasound
- Ultrasound images are typically fuzzy.,
- It can be harder to diagnose some conditions with the images which are produced.
Medicine Advantages and Disadvantages
Medical applications of physics
Medicine advantages and disadvantages (1.1-1.2)
Disadvantages of X-rays
- X-rays are ionising (not safe to use on developing babies)
- Ionisation of cells can cause cancer if someone is exposed to a high enough dose
Advantages of X-rays
- They produce clear images of bones and metals
Disadvantages of CT scans
- use alot more X-ray radiation than standard X-rays, exposed to more ionisation.
Advantages of CT scans
- detailed 3D images to diagnose complicated illnesses and plan complicated surgery
Medical applications of physics-REFRACTIVE INDEX (1.3)
- Refraction is the change of direction of light when it passes from one transparent substance to another.
- it takes place because waves change speed when they cross a bounary
- The speed of light is determined by the material (medium) through which it is travelling
- Light travells faster in a vacum than it does in any other medium
- A light ray refracts when it passes from air to glass, it is refracted towards the normal
- a ray of light travelling along a normal is not refracted
- The frequency of light does not change during refraction
Refractive Index is a measure of how much a substance can refract a ray of light.
N = SIN I / SIN R
- N = the refractive index of the substance
- Sin I = the sine of the angle of incidence
- Sin R = the sine of the angle of refraction
- the bigger the refractive index, the slower the light travels in the material.
Total internal reflection
Medical applications of physics-TOTAL INTERNAL REFLECTION (1.4)
The critical angle
- The critical angle is known as the angle on incidence
- when light passes between one medium to another it changes speed
- when light speeds up from one material to another the angle of refraction is greater than the angle of incidence.
- rays of light refract when they cross from glass to air, it is refracted away from the notmal.
- if the angle of incidence in the glass is gradually increased , the angle of refraction increases until the refracted ray emerges along the boundary
Refractive index equation : N = 1/ SIN C
- N = The refractive index
- C= The critical angle
Total internal reflection
Medical applications of physics- TOTAL INTERNAL REFLECTION (1.4)
- Total because all of the energy is reflected.
- Internal because the energy stays inside the material.
- Reflection because the light is reflected.
- Total internal reflection can only take place when a wave travels through a more dense substance towards a less dense substance ( light passes - glass/water or water/air)
- occurs when angle of incidence is increased beyond the critical angle light ray
- light cannot pass throught the surface- it is reflected.
- A dense material with a high refractive index has a low critical angle
- high refractive index = totally internally reflect more light
- more light will be incident at an angle bigger than the critical angle.
- when total internal reflection occurs the angle of reflection is equal to the angle of incidence
Medical applications of physics-THE ENDOSCOPE (1.4)
- Endoscopes are thin tubes which contain optical fibres
- they allow surgeons to examine inside the body without cutting it open or to perform "keyhole surgery" (advantageous = only having to cut small holes in people)
- Endoscopes consist of two bundles of optical fibre (one carries light to an area and the other caries an image back so that it can be viewed
- the image can be seen through an eyepiece or displayed as a moving image on screen.
- Lazer lights can be used as an engery source in an endoscope during cutting, cauterising (burning tissue to stop bleeding.) and burning
- The colour of the lazer light is matched to the type of tissue to produce maximum absorbtion
- an optical fibre is a very thin, flexible glass fibre.
- can carry visible light over long distances.
- bounce waves off the sides of a thin inner core of glass or plastic.
- wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end.
- total internal reflection.
Medical applications of physics= LENSES (1.5)
Converging (convex) lenses
- Converging lenses are thicker in the middle
- rays of light that pass through the lens are brought closer together (they converge)
- parallel rays of light that pass through a converging lens are refracted so that they converge to a point
- this point is called the "principal focus" (focal point)
- The distance from the centre of the lens to the principal focus is the focal length
- light can pass through the lens in either direction so there is a principal focus on either side of the lens.
- An object further away from the lens than the principal focus produces an inverted, real image.
- The size of the image depends on the position of the object
- The nearer the object to the lens, the larger the image.
Uses of Converging lenses
Medical applications of physics- USES OF CONVERGING LENSES (1.5)
The Camera (camera lenses are CONVERGING)
- Rays of light from the person are converged by the convex lens
- This forms an image on the film or CCD in the case of a digital camera.
- an object close to the lens causes the light rays to enter at a sharper angle.
- this causes the rays to converge away from the lens.
- the lens can only bend the light to a certain degree, the image is focussed so that it can fit on the film
- this is done by moving the lens away from the film.
- if the object is away from the lens the rays enter at a wider angle
- the are rays being refracted at a sharper angle and the image forms closer to the lens.
- the lens needs to be positioned closer to the film to get a focused image.
- the real image of a closer object forms further away from the lens than the real image of a distant object
- the action of focusing is the moving of the lens to get the real image to fall on the film.
- The image formed is said to be real because the rays of light from the object pass through the film and are inverted (upside down).
Uses of converging lenses
Medical applications of physics- USES OF CONVERGING LENSES (1.5)
Magnifying glasses are converging (convex) lenses
- Magnifying glasses produce a magnified (larger( image of a particular object
- If the object is nearer to the lens than the principal focus then the image is magnified
- The distance between the object and the lens must be shorter than the focal length of the lens.
- The image produced is virual (produced with virtual rays of light) and upright
Magnification = image height/ object height.
Medical applications of physics-LENSES (1.5)
Diverging (concave) lenses
- Diverging lenses are thinner in the middle
- parallel rays of light pass through diverging lenses and refract so that they diverge away from a point.
- This point is called the "principal focus"
- the distance from the centre of the lens and the principal focus is called the focal length.
- light can pass through the lens in either direction so there is a pricipal focus on both sides of the lens.
- images produced by converging (concave lenses) are always VIRTUAL.
- images produced by converging lenses are diminishes (SMALLER)
Using and drawing lenses
Medical applications of physics- USING LENSES (1.6)
Drawing ray diagrams
use three construction rays from a single point on the OBJECT to locate the corresponding point on the IMAGE.
- 1). draw a straight line from the object to the lens, then draw a diagonal line from the lens through the focal point.
- 2). draw a diagonal line from the object and throught the lens.
- 3). draw a diagonal line from the object through the focal point to the lens and then a straight line from the lens to the image.
- 1). Draw a straight line from the object to the lens, then draw a diagonal line from the lens throught the focal point.
- 2). draw a diagonal line from the object through the lens.
the nature of an image
medical applications of physics- USING LENSES (1.6)
the line throught the centre of a lens and at right angles to it is called the PRINCIPAL AXIS
The nature of an image is:
- Is it real or virtual?
- Is it upright or inverted (upside down)
- has it changed size (larger/smaller)
- Virtual images are created with virtual rays of light (dotted lines)
- Real images are created with actual rays of light (solid lines)
Diagram of the eye
The human eye
Medical applications of physics-THE EYE (1.7)
- IRIS- coloured ring of muscle that conrols the amount of light that enters the eye
- CORNEA- transparent layer that protects the eye and helps to focus light onto the retina
- PUPIL- the central hole formed by the iris, light enters the eye through the pupil
- CILIARY MUSCLES- attatched to the lens by suspensory ligaments, the muscles change the thickness of the eye lens
- EYE LENS- focuses light onto the retina
- RETINA- the light sensitive cells around the inside of the eye.
- BLIND SPOT-region where the retina is not sensitive to light (no light sensitive cells present)
- OPTIC NERVE- carries nerve impulses from the retina to the brain
- AQUEOUS HUMOUR-transparent watery liquid that supports the front of the eye
- VITREOUS HUMOUR-transparent jelly like substance that supports the back of the eye
- EYE MUSCLES-move the eye in the socket
How we see
Medical applications of physics- THE EYE (1.7)
How the eye works
- Light enters the eye through a tough, transparent layer called the CORNEA.
- the CORNEA protects the eye and helps to focus light onto the RETINA.
- the "photo-receptors" or the RETINA are a layer of light sensitive cells around the inside of the eye (at the back)
- The IRIS controlls the amount of light which enters the eye, this determines and alters the size of the PUPIL.
- the PUPIL is thecircular opening at the centre of the IRIS (it is a small hole)
- the EYE LENS focuses light to give a sharp image on the RETINA.
- the image on the RETINA is inverted (upside down) but the brain interprets it so that you can see it the right way up.
Focusing on objects at different distances.
Medical applications of phsics-THE EYE (1.7)
How does the eye focus on objects at different distances?
- The CILIARY MUSCLES alter the thickness of the EYE LENS
- The EYE LENS is automatically designed to become thinner to keep what you see in focus
- They are attatched to the edge of the lens by the SUSPENSORY LIGAMENTS.
- the fibres if the CILIARY muscles are parallel to the circular edge of the EYE LENS
- when they contract they shorten and squeese the eye lens making it thicker
- relax = thinner
- thinner = focus
More about the eye
Medical applications of physics-MORE ABOUT THE EYE (1.8)
- Person with short sight can see close objects clearly but distant objects are blurred.
- The uncorrected image is formed at the front of the retina
- The eyeball is too long or the eye lens is too powerful
- can be corrected using a diverging lens
- Can see distant objects clearly but close objects are blurred
- uncorrected image is formed behind the retina
- the eyeball is too short or the eye lens is too weak
- can be corrected using a converging lens
Focal length of a lens is determined by
- the refractive index of the material it is made by
- the curvature (how much they deviate from straight line) of two surfaces of lens
More about the eye
Medical applications of physics- MORE ABOUT THE EYE (1.8)
- P = 1/F
- P= power of the lens in dioptres (D)
- F= focal length in metres (m)
DIOPTRES AND FOCAL LENGTH
- for a lens of a given focal length, the greater the refractive index of the lens material, the flatter and thinner the lens can be manufactured.
- Long sight (+D) converges light
- Short sight (-D) Diverges light