Richard Edden

  MRS of Lactate

  Spinal Cord MRSI


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GABA can be detected in vivo using the MEGA-PRESS experiment to edit out overlying signals associated with creatine (CR). The MEGA-PRESS experiment suffers from bandwidth-related spatial effects, in the same way as the traditional PRESS experiment (See MRS of Lactate). Although the chemical shift separation of the GABA spin system is less severe than in lactate, significant losses of the order of 25% can still occur. Since GABA concentrations are low and the MEGA experiment only acquires the outer two peaks of te GABA triplet, optimising the sensitivity of the experiment is very important.

It is possible to predict the phase of the outer peaks of the GABA triplet in the two halves of the MEGA-PRESS experiment in each of the four regions of the PRESS volume. These can be shown figuratively (b and d represent the two experiments and f the difference):

The predictions stand up well against MRSI experiments.

The IVS method can be applied to saturate signal in regions where the phase is poorly behaved. This results in an increase of about 30% in the signal detected by the difference experiment(in both phantom and in vivo measurements).

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