Extraneous lipid contamination in single-volume proton MR spectroscopy: phantom and human studies.

PURPOSE To determine the degree of extraneous lipid contamination in defined volumes of interest studied with single-volume proton MR spectroscopy.

METHODS Single-volume proton MR spectroscopy was performed on a fat/water phantom and in three volunteers using the stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) localization methods. Three different volumes of interest (8, 27, and 64 cm3) were examined at echo times of 20, 135, and 270 for the STEAM sequences and 135 and 270 for the PRESS acquisitions in both the phantom and the volunteers (volumes of interest were placed adjacent to but not encompassing fat-containing structures, such as the scalp and retroorbital fat). The degree of lipid contamination was then correlated with measurements of the section profiles.

RESULTS The PRESS method resulted in less extraneous lipid contamination in both phantom and volunteer studies. The STEAM method had the highest level of lipid contamination signal in phantom and human studies. In the volunteers, volumes of interest abutting fat-containing structures obtained with PRESS or STEAM sequences showed no lipid contamination. However, the STEAM sequences showed lipid signal in the volume of interest adjacent to orbital fat whereas the PRESS sequences did not. These observations are supported by the section profile studies, which showed that the actual volume excited by the STEAM sequence was 7% to 32% larger than that originally selected, while with PRESS the actual excited volume was 12% to 16% smaller than that originally selected.

CONCLUSION In our MR unit, short-echo-time STEAM sequences (< or = 135 milliseconds) resulted in extraneous lipid contamination in phantom and human studies adjacent to the orbits. PRESS sequences showed no lipid contamination in volumes abutting fat structures in phantoms or humans. These results correlated closely with the configuration of the section profiles. Although these findings might be dependent on the MR unit used, our study could help determine extraneous lipid contamination for other MR units.