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» System Architecture

The hardware components of an MRI scanner are displayed in this learning tool.

« System Architecture

Superconducting Magnet

Higher field strengths can be obtained with the superconducting design because a larger current is achievable. I have used a superconducting magnet as the example in the diagram, because these are the most common type. Superconducting coils sit in a cryogen bath (liquid helium, at less than 4.2K). A large current passes through the coils to create the magnetic field (it's basically a solenoid). This current draws no power because the coils offer no electrical resistance. The magnet, therefore, is always "on".

Answer this...

What procedure produces the highest risk of a quench?

When metal is in the scanner.

Pressing the big red STOP button.

When "ramping up" the main magnetic field (or ramping it down).


Try again.

INCORRECT. That's not what I was getting at. Let's rephase: an unexpected quench.

Try again.

CORRECT. The most risky time for a quench is when the magnetic field of a superconducting magnet is being "ramped up" (or down). Sudden boil-off of the cryogen is more likely.

Answer this...

How might you quote the homogeneity of a magnetic field?

In Gauss.

in milli-Tesla.

In parts-per-million.

INCORRECT. Homogeneity is not specified absolutely.

Try again.

INCORRECT. Homogeneity is not specified absolutely.

Try again.

CORRECT. In parts-par-million (ppm), and crucially, over a specific volume centred at the isocentre. E.g. 5 ppm over 50 cm diameter sphere at the isocentre.

Further reading on these topics:
Books: MRI From Picture to Proton p169, Q&A in MRI p56-58
Online: Basics of MRI

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