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QUESTIONS
» Image Creation

How is the MRI image created? This section explores slice selection, spatial encoding and the FFT.

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Phase Encoding Timing

Answer this...

Can the phase encoding gradient be applied at the same time as the frequency encoding gradient?

Yes.

No.

INCORRECT. Choose "No".


Phase encoding is now introduced, depicted as a series of possible gradient strengths for each time the pulse sequence is repeated. This pulse sequence will be modified further in subsequent questions.

CORRECT. Frequency encoding occurs during signal measurement, and so phase encoding must be finished before the frequency encoding gradient is applied.

The dephasing gradient applied in the frequency encoding direction (equal to half of the positive frequency encoding gradient in area) may be applied during phase encoding; the gradient which causes the deliberate dephasing of spins prior to signal measurement is orthogonal to the phase encoding gradient and they will not interfere with each other.

Further reading on this topic:
Books: Q&A in MRI p82, MRI From Picture to Proton p118f
Online: Basics of MRI

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