Commissioning

Question 1

How does increasing length:diameter ratio affect image quality?

Answer 1

Uniformity increases

Question 2

How does increasing diameter affect image quality?

Answer 2

fringe field increases, rise time increases => TEmin increases, max gradient strength increases

Question 3

What are the advantages of driving a birdcage coil in quadrature?

Answer 3

Single drive produces counter-rotating B field, which does not couple to spin system as rotation is against precession direction => ineffficient. Quadrature drive resolves this.

Question 4

What are the benefits of non-quadrature technology?

Answer 4

Dielectric resonance is a function of amplitude and phase of B1 => use these technologies to control it better and reduce dielectric effects on homogeneity.

Question 5

Explain two methods for non-quadrature transmission.

Answer 5

1) fixed non quadrature: single WF gen, RF amp, fixed non-90 degree phase shift
2) multi-transmit: two separate WF generators, with separate RF amps