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ProSet: suppress fat or water

White Paper
Janssen, Karen Philips Healthcare Philips Global

ProSet is a selective excitation technique that employs a frequency and spatially selective excitation pulse.  This excitation pulse is a slice-selective binomial RF pulse that suppresses either water or fat. The use of ProSet does not increase scan time. ProSet has been introduced with Intera systems and Intera upgrades.

 

ProSet exploits the difference between water and fat resonance frequencies. The binomial pulse in ProSet is designed to separate the magnetization components of water and fat, so that either the water or the fat alone is in the horizontal plane, and therefore the only component that yields signal. A binomial pulse consists of several separate pulses with a short time in between.

How ProSet works

A 121 binomial 90º pulse is composed of a 22.5º, a 45º, and a 22.5º pulse.

 

After the first 22.5º pulse the water and fat magnetization are in phase. Since they precess with a slightly different frequency, the phase difference will grow.

First 22.5º pulse Water and fat have opposite phases
First 22.5º pulse
Water and fat have opposite phases
The 45º pulse Wait until water and fat have opposed phase The last 22.5º pulse
The 45º pulse
Wait until water and fat have opposed phase
The last 22.5º pulse

 

When the water and fat magnetization have exactly opposite phases, the 45º pulse is applied. Its effect is that both the water and fat magnetization are in the same plane again and in phase, but they make a different angle with the vertical axis. Precession is left to continue until water and fat have opposite phases again.

 

The last 22.5º pulse brings the water magnetization to the horizontal plane and the fat magnetization on the vertical. Now water is contributing signal, but fat is not.

 

The waiting time between the two composing pulses of the binomial pulse depends on the frequency difference of water and fat, and therefore it depends on the field strength. By selecting to rotate forward or backward with the second pulse, either water or fat can be selected to yield signal, while the other one is suppressed.



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