Physics Revision
- Created by: Théa
- Created on: 14-05-13 17:35
What are X-rays?
-X-rays are part of the electromagnetic spectrum
-Very short wavelength (about the width of an atom)
-Can cause ionisation (knock off electrons from cells)
-Ionisation of atoms in DNA can lead to cancer
-X-rays can be used to treat cancer
-Can affect photographic film in the same way light does
-Can be absorbed by metal and bone
-Can be therefore used to diagnose broken bones
Medical Uses of X-rays
-Diagnosis of chest conditions (e.g. Pneumonia)
-Detection of foreign objects
-Diagnose fractures
-Diagnose dislocations
-Diagnosis of bone or joint conditions (e.g. Arthritis)
-Surgical tool
CT Scans
-Can show a person through 360 degrees
-Connected to charge-coupled device (CCD) which converts X-rays into light, to produce a 3D digital image
CT Scanner vs. X-ray Machine
CT Scanner:
-3D image
-More expensive
-Distinguish between hard and soft tissue
-Higher dose of X-rays
X-ray Machine:
-Lower dose of X-rays
-2D image
-Cheaper
-Cannot distinguish between hard or soft tissue, only bones
Ultrasound
-Such a high frequency, humans cannot hear it. The human hearing range is 20Hz to 20,000Hz
-Speed of sound = wavelength x frequency
-Longitudinal waves (wave direction is same as wave motion, like a slinky, so it moves back and forth)
-Can be refracted, reflected and diffracted
-Requires a medium to travel through
-Speed of sound is affected by the medium. The higher the density, the higher the speed, as there are more particles.
-The shorter the wavelength of the wave on the oscilloscope, the higher the pitch and the longer the wavelength, the lower the pitch.
Uses of Ultrasound
-Scanning unborn babies
-Scanning the heart
-Finding and treating kidney stones
-Communication between animals
-Navigation in boats or submarines (SONAR)
Calculating distance using ultrasound:
- Distance = speed x time/2
Ultrasound Scans And Kidney Stones
Ultrasound Scans:
-The wave is partially reflected when it meets a boundary between two different media (e.g. muscle, bone, liquid, fat, etc.) These reflections are collected and interpreted as a picture.
-Use a frequency of between 2MHz and 20MHz
Kidney Stones:
-Ultrasound can also be used to treat kidney stones
-A high powered ultrasound is used for this
-Stones vibrate until they break apart and are easily passed out of the body via the urethra
-Advantageous as you do not have to have surgery and it is pain-free.
Advantages and Disadvantages of Ultrasound
Advantages:
-Non-invasive (no surgery)
-'Real time' video
-Image is available immediately
-Accurate
-Considered risk-free, as it doesn't damage cells
Disadvantages:
-Images from deeper into the body result in progressively poorer resolution
-Relies on expertise of sonographer
-After 18 weeks of pregnancy, scans aren't to show anything but major problems with the baby, so smaller, more minor problems are not always detected.
Ultrasound vs. X-rays
Ultrasound:
-Uses high frequecy sound waves
-Reflects off different tissues in the body and so can show soft and hard tissue and liquid
-The result is a 'real time' video
-Considered safe, as it uses non-ionising waves
X-rays:
-Uses high frequency electomagnetic waves
-It's blocked mainly be bone and is mainly used for looking at broken bones
-The result is an image developed later
-Too many X-rays could lead to cell damage as it is ionising radiation
-Image is made by a film on the other side of the object.
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