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Medical Imaging The Physics Of Light Microscopes And Magnetic Resonance (Mri) Units

619 words - 2 pages

Medical PhysicsExtended Response TaskThe Physics of Medical ImagingBen Cotterill - 23/4/07Part 2 - Studying a medical imaging techniqueMagnetic Resonance ImagingMRIIntroduction The main components used in Magnetic Resonance Imaging (MRI) are a strong magnetic field and a certain radio frequency. The radio frequency tells the computer 'what it sees', allowing the computer to devise an image. The magnetic field is required to allow the radio frequency to do its job.MRI relies on tissue density and the unique 'magnetic' properties of a hydrogen atom.The "Magnetic" in MRIProbably the most crucial MRI component is the solid, but stable magnetic field and the magnet that produces it. MRI machines generally use between 0.5 and 2.0 Tesla.The magnet inside an MRI unit is usually a type of magnet called a "superconducting magnet". Magnets of this type can be turned on and off by sending a current through wires. The coils of the magnets are submerged in liquid helium (4.4K, about -269.11 oC) to reduce resistance in the wires. These magnets produce the required 0.5 - 2.0 Tesla.The "Resonance" in MRIThe second important element in an MRI scan requires a radio frequency (RF) signal.Inside the human body, there are billions of hydrogen atoms. These hydrogen atoms spin on their axis randomly when not in contact with strong magnetic fields (See below left)These hydrogen atoms, with one proton and one electron, act like 'bar magnets' with a north and a south pole. When a magnetic field passes through them, they align themselves with the field. However, this means that they can align facing in one of two possible ways: parallel or antiparallel to the field. (See right).When the hydrogen atoms align like this, the atoms that face opposite directions 'cancel' each other out. It is the atoms that do not cancel out that produce the MRI image. (See below left).When affected by the magnetic field, pulses of...

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