Single-voxel technique

Fig. 12. Sequences for volume selective single voxel spectroscopy. Both techniques work with three slice-selective RF-pulses. (a) The Point RESolved Spectroscopy (PRESS) sequence generates a volume selective double spin-echo. The entire time delay between the initial 90° excitation and the echo is sensitive to transverse relaxation, (b) The Stimulated Echo Acquisition Mode (STEAM) sequence generates a stimulated echo. Maximal signal intensity (without relaxation effects) is only half the signal intensity of PRESS under comparable conditions, but slice profiles are often better (only 90° pulses instead of 180° pulses) and the TM interval is not susceptible to transverse relaxation, (c) The recorded echo signal is only generated in a volume corresponding to the intersection of all three slices.

Although ECVT is a promising non-intrusive technique, this system is limited to measuring bubbles greater than the voxel resolution. A bubble smaller than the voxel resolution cannot be measured by the ECVT. A potential solution to this issue is to increase the number of sensor electrodes and modify the related sensitivity which could increase the resolution to track the smaller, single bubble. 

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