Extended ISIS sequences insensitive to T-1 smearing

Image selected in vivo spectroscopy (ISIS) is a volume selection method oft en used for in vivo P-31 MRS, since it is suitable for measurements of subs tances with short T-2. However, ISIS can suffer from significant signal con tributions caused by T-1 smearing from regions outside the VOI, A computer model was developed to simulate this contamination. The simulation results for the ISIS experiment order implemented in our MR system (ISIS-0) were in agreement with results obtained from phantom measurements. A new extended ISIS experiment order (E-ISIS) was developed, consisting of four "optimal" ISIS experiment orders (ISIS-1 to ISIS-4) performed consecutively with dumm y ISIS experiments in between. The simulation results show that contaminati on due to T-1 smearing is, effectively, eliminated with E-ISIS and is signi ficantly lower than for ISIS-0 and ISIS-1, E-ISIS offers increased accuracy for quantitative and qualitative determination of substances studied using in vivo MRS. Hence, E-ISIS can be valuable for both clinical and research applications, (C) 2000 Wiley-Liss, Inc.