Nuclear Magnetic resonance (NMR)

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Nuclear Magnetic resonance (NMR)
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Nuclear Magnetic Resonance

• NMR works by getting hydrogen nuclei in the body
  to emit radio waves. Analysis of this radiation
  enables a very detailed image to be built.

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Magnetic nuclei

• Nuclei are charged and spin. This means nuclei
  with an odd number of protons or neutrons behave
  like mini magnets.

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Magnetic nuclei

• This means in an applied magnetic field the
  nuclei will line up like compass needles but
  either with (low energy) or against (high energy)
  the field

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Magnetic nuclei

• The stronger the applied field, the bigger the
  difference between the two energy states

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Resonating

• Just like the compass needle in a field, the
  nuclei can oscillate

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Resonating

• If a hydrogen nuclei is placed in a strong
  magnetic field and is pushed by radio waves of
  the correct frequency (60 MHz) it will resonate

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Resonating

• The resonating hydrogen nuclei will emit radio
  waves as it resonates, which can be detected and
  used to build up an image.

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Magnetic resonance imaging (MRI)

• The radio waves emitted by the resonating nuclei
  are detected by a coil of wire and analysed by a
  computer. There are useful aspects of the
  radiation that can be used to build the image.

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MRI - Frequency

• The frequency of the resonance depends on the
  strength of the field (stronger field higher
  frequency) If the field is varied from one place
  to another, the position of the source can be
  found.

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MRI - Frequency

• The frequency of the resonance depends on the
  strength of the field (stronger field higher
  frequency) If the field is varied from one place
  to another, the position of the source can be
  found.

Radio transmitter
Radio receiver
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MRI Relaxation time

• The time taken for the oscillation to die away is
  different for different tissue. This can be added
  to the image.

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Use of lasers in medicine
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Light from a normal bulb

• Spreads out on all directions and is normally
  many wavelengths (and phases)

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Light from a normal bulb

• When focussed by a lens not all light hits the
  lens

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Light from a normal bulb

• The light is not parallel so it is not all
  focused on the same point a diffuse spot is
  formed

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Laser light

• The light from a laser IS parallel and consists
  of the same wavelength (and in phase). This is
  called coherent light.

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Laser light

• When focussed by a lens, laser light can produce
  a very intense point of light

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Laser light

• Energy from beam can be focused on a very small
  piece of matter, causing it to be vaporised.

Cloud of vaporised dog
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Advantages of cutting with a laser?

• Finer cut
• Vaporising action seals small blood vessels
  causing less bleeding

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Used with optical fibres

• The laser light can be fed along optical fibres
  enabling surgeon to performs operations inside
  the body without large incisions.

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Laser angioplasty

• An optical fibre is fed along a blood vessel from
  the arm to the heart where it is used to cut away
  unwanted material.

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Measuring oxygen content of blood
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Pulse oxiometer

• Laser light will pass through thin body parts
  like a finger of babys foot

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Pulse oximeter

• Two lasers are used, one giving out red light and
  the other infra red light.

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Pulse oximeter

• Red light is absorbed most by blood with no
  oxygen and IR most by blood with oxygen.

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Pulse oximeter

• By measuring the relative absorption of the two
  wavelengths it is possible to calculate the
  amount of oxygen in the blood (as well as
  monitoring the pulse.