Quality assessment of localization technique performance in small volume in vivo 1H MR spectroscopy

A new phantom and evaluation method for experimental evaluation of 1H-magnetic resonance spectroscopy single volume localization techniques regarding signal contamination (C), defined as the part of the signal originating outside the volume of interest, is presented. The quality assessment method is based on a spherical phantom with an oil/water interface in order to reduce susceptibility effects, and applied for stimulated-echo acquisition method (STEAM) and spin-echo (SE) sequences, echo times of 270, 135, and 10 ms, and cubic volumes of interest (VOI) of 1(3), 1.5(3), 2(3), 2.5(3), and 3(3) cm3. To be able to mimic measurements of the contamination in three dimensions the physical gradients representing the three orthogonal directions for slice selection were shifted in the pulse sequences. Contamination values in one dimension differed between 6.5% and 8.4% in SE sequences, and between 0.7% and 13.8% in STEAM sequences. In STEAM sequences a decrease of C with increasing VOI size was observed while SE sequences showed comparable C values for the different VOI sizes tested. The total contamination in three dimensions were 19% and 18% in SE and STEAM sequences with a TE of 270 ms, and 7% in a STEAM sequence with a TE of 10 ms, respectively. The presented evaluation method is easily applied to the new phantom and showed high reproducibility.