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MRI

How MRI's work, advantages/disadvantages and when MRI's are used

TermDefinition
advantages (4) can manipulate the patient and the gradient to get what you need. non-ionising no side effects no surgery involved/non invasive
disadvantages (6) costly/expensive to maintain time consuming claustrophobic no pregnant women due to unknown effects on developing fetus no metallic objects near the MRI sometimes inaccurate
when would you use it (7) they're frequently used to diagnose issues with your: joints brain ankles breasts heart blood vessels
stage 1 the patient lies on the table which slides into the horizontal tube known as the 'bore'
stage 2 surrounding the bore is a huge superconducting magnet made of many coils of wire that generate a large magnetic field as the electricity passes through it.
stage 3 maintenance of the magnetic field requires vast amounts of energy which can be maintained through the use of superconductivity (reducing resistance in the wires to almost absolute zero by constantly cooling with a substance such as liquid helium)
stage 4 once the patient is positioned correctly the scan can begin.
stage 5 the magnetic field causes protons in the hydrogen atoms which are precessing (spinning) on their axis to stop spinning and align with the magnetic field, pointing either towards the head or feet of the patient.
stage 6 approximately half of the protons end up pointing towards the head, and the other half towards the patients feet
stage 7 these very protons aligned in opposite direction are said to ' cancel each other out', leaving only very few unmatched protons pointing 'towards the patients head or feet.'
stage 8 a radio frequency (RF) pulse is then generated and directed towards the unmatched protons, which absorb the energy in pulse and start to spin again.
stage 9 at the same time the gradient magnets can be adjusted in order to focus the magnetic field on the exact 'slice' that medical staff want an image of
stage 10 when the RF pulse is switched off the protons which had absorbed the energy begin to return to their previous alignment with the magnetic field, releasing energy as they do so.
stage 11 this energy can be picked up by the coils inside the MRI machine and converted into an image on a computer.
stage 12 the density of different tissues means that they will have different amounts of hydrogen, leading to the tissues appearing different from each other on the image these differences can be further increased by using specific dyes helping identify anomaly's
Created by: Olivia_Huggett