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Medical Physics

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Non-Invasive Methods in Diagnosis
Any non-invasive technique in diagnosis is any method which doesn't require an
The lack of operation means that there is a much lower risk of infection, lower
after-care costs but is often more expensive.
Most don't use ionising radiation (except from tracers & PET scans).
Many techniques (such as MRI) are time-consuming and have a low throughput
of patients.…read more

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X-Rays ­ Production
An X-ray tube is an evacuated tube with two electrodes.
Large voltage accelerates electrons towards anode.
Upon collision, electrons are rapidly decelerated and about 1% of energy loss is
converted into X-ray photons.
X-rays escape through the window of the X-ray casing.
More controllable than -rays as production can be controlled (electricity as
opposed radioactive decay).
X-ray beams are collimated ­ beams are parallel sided to minimise energy loss.…read more

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X-Rays ­ Energy & Spectra
Energy of X-rays vary.
Overall trend of Braking radiation with sharp peaks of characteristic radiation.
Caused when electrons change energy levels and emit photons of very specific
Known as the Compton effect.…read more

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X-Rays ­ Attenuation
Attenuation is the gradual decrease in intensity as X-rays pass through a
Three main methods of attenuation:
Photoelectric effect ­ low energy photons displace electrons.
Compton scattering ­ mid energy photons inelastically displaced by collision with
electron. Electron scattered and photon has reduced energy.
Pair production ­ high energy photon produces an electron-positron pair.…read more

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X-Rays - Image Enhancement
Photographic film or fluorescent plates are more sensitive than traditional X-ray
Image intensifiers are screens with tiny phosphor dots which glow when exposed
to X-rays.
This allows a high-quality camera to record the glowing of dots to show a moving
image of the X-rays.
Contrast media such as barium sulphate are ingested/injected to improve the
contrast of X-ray images.
The high attenuation coefficient means that soft tissues can easily be identified.…read more

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