A method for characterising localisation techniques in volume selected nuclear magnetic resonance spectroscopy

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Abstract
A number of techniques now exist for the collection of in vivo magnetic resonance spectra from a restricted volume of interest. These should ideally achieve complete suppression of signal from tissues extraneous to the sample region without loss of signal from within that region. The extent to which this ideal is realised is an important consideration in the comprehension and quantification of localised spectra. The authors have defined three parameters for the objective characterisation of volumes of interest and designed a test object with which they can be measured. The test object is constructed of Perspex and susceptibility mapping was used to ensure that this material did not appreciably disturb the magnetic field. The authors' method has been used to characterise volumes of interest of various sizes selected using the ISIS technique. Deviations from ideal behaviour were found and have been attributed to various signal loss and contamination mechanisms. One important conclusion is that less contamination is obtained by selecting a large volume of interest enclosing the sample region than a small volume entirely within that region.