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 spect roscopy. METHODS: Single-volume proton MR spectroscopy was performed o n a fat/water phantom and in three volunteers using the stimulated-ech o acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) loc alization methods. Three different Volumes of interest (8, 27, and 64 cm(3)) were examined at echo rimes of 20, 135, and 270 for the STEAM s equences and 135 and 270 for the PRESS acquisitions in both the phanto m and the volunteers (volumes of interest were placed adjacent to but not encompassing fat-containing structures, such as the scalp and retr oorbital fat). The degree of lipid contamination was then correlated w ith measurements of the section profiles. RESULTS: The PRESS method re sulted in less extraneous lipid contamination in both phantom and volu nteer studies. The STEAM method had the highest level of lipid contami nation 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 seq uences showed lipid signal in the Volume of interest adjacent to orbit al fat whereas the PRESS sequences did not. These observations are sup ported by the section profile studies, which showed that the actual vo lume excited by the STEAM sequence was 7% to 32% larger than that orig inally 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 (less than or equal to 135 milliseco nds) resulted in extra neous lipid contamination in phantom and human studies adjacent to the orbits. PRESS sequences showed no lipid contam ination in volumes abutting fat structures in phantoms or humans. Thes e results correlated closely with the configuration of the section pro files. Although these findings might be dependent on the MR unit used, our study could help determine extraneous lipid contamination for oth er MR units.