Learning Objective

(1) To be able to recognize the fundamental hardware essential to MRI operation
(2) To understand the contribution of each piece of hardware to the production of an MRI image

Summmary

Magnetic Resonance Imaging systems are typically composed of 3 main different types of magnets, as well as systems for control and maintenance.

The three types of magnet include :
(a) a main magnet;
(b) a set of radio frequency coils;
(c) a magnetic field gradient system,

B₀: The main magnet is typically a powerful, homogeneous, static magnetic field. This sets the stage that makes imaging possible by encouraging the nuclei in the hydrogen atoms to align with the field. These magnets are often superconducting and can produce main magnetic fields (B₀) on the order of Teslas (1.5 T, 3T, 7T, 10T…). To put that in context, a fridge magnet might be 0.01 T right up at the surface of the magnet, and an MRI system must produce a constant magnetic field over the field of view that we want to image, so 10’s of centimetres.
RF: The radio frequency (RF) coils send and receive signal at frequencies on the order of megahertz (MHZ), like a radio might. There may often be two RF coils one for transmission (Tx), used to excite the hydrogen nuclei that are aligned with the main field, and another one for reception (Tx). These electromagnets produce magnetic fields that oscillate in strength (or detect oscillations) at a frequency that is proportional the strength of the magnetic field that the hydrogen is experiencing.
G: The gradient coils (Gx, Gy, Gz) are used localize the signal, letting us figure out what the amplitude of the signal is from each part of our image. To do this they take advantage of the fact that that the oscillation is proportional the strength of the magnetic field. These coils oscillate on the order of kHz, which is similar to the frequency of sound. The oscillation of the gradient coils is why MRI’s can be so noisy.

Acknowledgements

No acknowledgement found.

References

No reference found.