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Physics 3a
» X-Rays in Medicine
» Ultrasound
» Ultrasound Uses
» Refractive Index
» Lenses and Images
» Lenses
» Magnification and Power
» The Eye
» Correcting Vision
» Total Internal Reflection…read more

Slide 2

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X-Rays are waves of high frequencies and short wavelengths.
Their wavelength is about the same size of an atom.
X-Rays can pass through (are transmitted by) tissue and are
absorbed by dense materials. Because of this, they can be used
to take photographs.
Images can be formed electronically with charge-coupled devices
(CCDs), which are tiny silicon chips that are divided into grids of
millions of identical pixels. They detect X-Rays and send of
electronic signals, which form high resolution images.
The paper used in X-Rays starts of all white, and the white parts of an
X-Ray image show were fewer rays were able to pass through. Bones
are visible in X-Ray images because they're dense materials, that don't
allow the rays through. The black parts on the picture show soft tissue,
where rays were able to pass through and darken the paper.…read more

Slide 3

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CT Scans
Computerised Axial Tomography (CT) scans use X-Rays. They produce high
quality images of both soft and hard tissue.
The patient is passed through a cylindrical scanner, where X-Ray beams are
aimed at the body. These beams are picked up by detectors.
The X-Ray transmitters and detectors are rotated during the scan.
The whole thing is connected to a computer, that forms multiple images of 2D
slices through the body. These images are put together to make a 3D image of
the body.…read more

Slide 4

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Cancer Treatment
X-Rays can ionise cells. This means that they can strip electrons from their atoms and
break down chemical bonds, which releases highly reactive ions.
This makes them useful for treating cancers.
» The rays are focused on the tumour using a wide beam
» This beam is rotated around the tumour
» Rotating the beam reduces the exposure of healthy cells to the ionising rays. It
reduces the changes of damaging the rest of the body
» When carefully focused they can kill cancer cells. Though some normal cells are
still damaged, which is why people going through radiotherapy may feel unwell.…read more

Slide 5

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Safety Precautions
Constant exposure to the ionising radiation caused by X-Rays can be damaging to the
human body, so radiographers need to minimise their X-Ray dose.
They can do so by:
» Wearing lead Aprons
» Standing behind lead screens when X-Rays are
taking place
» Or leaving the room when they're taking place
Lead is useful at blocking radiation. Its used to shield areas of the
patients body that aren't being investigated. The exposure time for
X-Rays is always kept to a minimum to decrease the radiation
exposure…read more

Slide 6

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Ultrasound waves are waves that are higher then
the upper limit of human heating (Over 20
When their waves pass from one medium to another, some of the waves are
reflected off the boundary and some is transmitted (refracted). This is partial
Because of this, when ultrasound is directed at an object that has boundaries
between the substances, some ultrasound gets reflected back.
Detectors can be used to measure how far boundaries are (using the time taken
for it to be reflected) . This is how ultrasound images are formed.…read more

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