TABLE OF CONTENT
MRI stands for “Magnetic Resonance Imaging”.
Originally know as “Nuclear Magnetic Resonance”(NMR)
Used in medical field to produce image of internal structures of living organism.
MAJOR COMPONENTS OF MRI
•Coils (gradient coils , RF coils , Shimming coils)
TYPES OF MAGNETS
•Permanent Magnet – 0.064 T to 0.3 T
•Resistive Magnet – up to 0.3 T
•Super conductive Magnet- up to 12 T
SUPER CONDUCTING MAGNETS
•Utilize the property of Zero electrical resistance exhibited by certain materials like (Niobium Titanium)
•Loop of wire is surrounded with coolant, such as liquid helium , liquid nitrogen (cryogen), to reduce the electric resistance of the wire .
•At 4 degree kelvin (-269 degree c) wire loses its resistance.
•High current (760 A) at low voltage is required to convert them into superconductive – Ramping
•Super conductivity under low temperature was first observed by Argentinean Alex Muller and German George Bednorz.
e)Prevention of accident
•A faraday cage or faraday shield is an enclosure used to block electromagnetic fields. A faraday shield may be formed by a continuous covering of conductive material or in the case of a faraday cage, by a mesh of such materials.
•Faraday cages come in all shapes and sizes, but all of them use a metal screen that conducts electricity, creating a shielding effect.
IDEAL MRI ROOM
•1)An outer shell for structural support
•2) A middle metallic rf-shield
•3)An interior layer made of finish materials.
•The floor is generally made of monolithic copper covered over with solid material.
•Door must not allow any rf leakage, being shield by a set of electrical contact strips or continuous metallic pneumatic tube.
•Window are laminated with blackened copper mesh between two pieces of glass.
•Virtually any metal can be used including aluminum and steel but copper is generally used because it is more conductive metal.
•2)Patient history (medical history, claustrophobia)
•4)Changing in hospital gown
•5)Use of MRI compatible devices .
•1st MRI accident occurred in New-York area hospital in 2001 July .
•A six year old boy , Michael Colombini lost his life when the machine’s powerful magnetic field jerked a metal oxygen tank across the room, crushing the child’s head.
•In India latest MRI accident that took a life of a person named Rajesh Maru happened in 2018 in Nair Hospital Mumbai.
WHAT WE DO IF ACCIDENT HAPPEN
a)Inform authority or higher level officer asap.
b)Switch off system and all electronic but remember switching system doesn’t mean magnate is off.
c) Find alternate of quenching.
d) Do not quench machine in hurry unless its life threatening situation.
•A quench is an event that occurs only in superconducting magnates and results in a loss of magnetic field of the MRI magnet.
•It is caused by a loss of superconductivity , a rapid increase in the resistivity of the magnet coil windings, which generates heat that results in rapid evaporation, or boil-off of the magnet coolant.
•There are two situation in which quench may occur:
a)Spontaneously due to some force or disruption to the magnate system.
b)The emergency “Magnet Stop” button is pressed during emergency situation.
•Emergency Magnet Rundown Unit: This initiates a controlled quench and turns off the magnetic field.
•It is typically a big red button located on the wall of the magnet room near the door.
•This button should only be used in a life threating situation.
•Pressing this button makes the scanner out of service costing heavily for replacing lost liquid helium.
Emergency shutdown :
Does not quench the magnet but turns off most electrical power in the scanner room and operator area, including the console ,computers , patient table , ups etc.
•It may be simple red button labeled or unlabeled
•This switch should be used when there is serious equipment fault or hazard ,such as fire , water in the vicinity of the MR scanner
“MRI CAN TURN INTO MONSTER ,IT IS IN OUR HAND TO STOP DISASTER”
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