Lesson 4

Question 1

What is Fourier transform?

Answer 1

It tells you how many spins you have of a particular frequency in a particular area

Question 2

When is a y-axis gradient applied in the context of phasing encoding?

Answer 2

Briefly before signal collection, which changes the spins and causes them to start dephasing.
Gradient is then turned off, and the spins process at the Lamor frequency but the difference between phase angle of the spins remains/ will be remembered.
This is how phase encoding works.

Question 3

What goes into the FT to be analysed?

Answer 3

Sine wave of MR signal against time

Question 4

What is k space?

Answer 4

It is a computational database where frequency information is saved

Question 5

They y gradient can only be on for a short amount of time, how do you make the 2nd axsi experience the same progression of signal evolution?

Answer 5

Gy must be stepped up in amplitude in successive shots of the scan so that a spin echo is gradually formed along this 2nd axis.
This therefore allows us to build a sine wave (echo) that can be input into the FT

Question 6

What is TR?

Answer 6

Repetition time, is the amount of time between successive pulse sequences applied to the same slice.

Question 7

What is a disadvantage of 2DFT?

Answer 7

It uses phase encoding, which means that it is very motion sensitive

Question 8

What is the main method of FT acquisition?

Answer 8

2DFT

Question 9

What is TE?

Answer 9

Time to Echo (TE) is the time between the delivery of the RF pulse and the receipt of the echo signal.
Time between two 90 degree pulses