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Resonance Frequency determination for 2D RF pulses (navigator beams)

IP.com Disclosure Number: IPCOM000126287D
Publication Date: 2005-Jul-12
Document File: 2 page(s) / 99K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID690940

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Resonance Frequency determination for 2D RF pulses (navigator beams)

Navigator beams (a.k.a. pencil beams) can be made with 2D RF pulses. The shape of the RF pulse and the underlying gradient waveform determine the shape of the excited volume. Usually this is a cylinder. In case of off-resonance (because the resonance frequency is not correctly determined), the size of the cylinder will increase and the

cylinder will become hollow. This is illustrated in the cross-sections below:

On the left, the excitation is on-resonance, on the right the excitations is off- resonance.

Currently, the resonance frequency is determined separately for navigator beams with a general-purpose sequence. This sequence is a volume excitation + frequency analysis of the echo signa l.

The invention is about a totally different way of determining the optimal resonance frequency, dedicated for 2D RF pulses.

In the normal use of a navigator excitation, the readout is orthogonal to the selection plane. For example is the selection gradients are in X and Y, the cross-section of the cylinder will be in the X-Y-plane and the cylinder will stretch out in the Z-direction. The read-out will also be in the Z-direction.

However when the read-out direction is changed to X or Y, we will image a projection (in X or Y) of the cross-section of the beam. The size of this projection can be used as a measure for optimizing the resonance frequency. After all, we know what size and where we expect the projecti...