MRI 4 Flashcards
superconducting magnets, gradient coils, radiofrequency coils, quench
What are superconducting magnets?
electromagnets made from coils of superconducting coils which are kept at low temp. The coils have no electrical resistance therefore allowing them to conduct much larger electric currents and produce greater magnetic fields
What are the advantages of superconducting magnets
They operate at greater field strengths allowing high signal to noise ratios, permitting good image resolution and image scanning
What ate the disadvantages of superconducting magnets
Expensive to run especially with an additional cost of cryogenic liquids
They cannot be turned off causing a lack of emergency shutdown procedures
What are the risk of the magnetic field in MRI and how are they minimised?
The magnet of the scanner will pull on all magnetic materials and this may cause unwanted movement of internal medical devices, or the radiofrequency energy may cause heating of the device and surround. Metal objects can become airborne projectiles. These are minimised by the implementation of safety rules
What do gradient coils do ?
These coils will produce a magnetic field which is strong on one side and weak on the other and this changes the precssional frequency of the hydrogen nuclei along the gradient coil
There are three sets of gradient coils at right angles to each other and each coil produces a magnetic gradient in a particular direction along the x, y and x axes.
What are the 3 gradient coils and what do the do?
The X gradient coil will produce sagittal images,
the Y gradient coil will produce coronal images
Z gradient coil will produce axial/transverse images
When all three are used together a gradient can be produced in any direction along the axes and images may be acquired from any plane.
What are the risks of the gradient magnetic fields in MRI and how can these be minimised?
The activation and deactivation of currents through gradient coils during image acquisition can produce a lot of noise and this may cause temporary hearing loss, this is minimized by providing patients with disposable earplugs.
What do radiofrequency coils do?
They provide the frequency and bring it closer to the body. They emit them into the patient and record the echos
What is meant by the term quench
Quenching is the stopping of the magnetic field by boiling the liquid helium to allow the coils to heat up eventually stopping the magnetic field. The quench button is pressed if a patient is trapped, and you cannot remove them.
