[Shortening of the measurement time by 1H-MR turbo spectroscopic imaging of the brain]

Abstract

Purpose: Development of a new technique for reduction of measurement time in 1H-MR spectroscopic imaging of the brain. Optimisation of the sequence parameters in volunteer and in patient examinations and comparison to the results obtained with conventional 2 D-SI.

Methods: Examination of 20 healthy volunteers and 5 patients in a 1.5 T whole-body MR system. In "turbo-spectroscopic imaging" (TSI) sequences, a train of spin-echo signals with different phase encoding is acquired after each 90 degrees excitation. 32 x 32 matrix elements covered a field of view of 20 cm, and additional volume selection was performed by double spin echo excitation. Measurement duration 9 min with acquisition of four phase encoding steps per TR interval, whereas the corresponding 2 D-SI sequence (TR/TE 2000/272 ms) took 30 min.

Results: The TSI data sets yielded maps of the regional distribution of metabolite concentrations with a quality comparable to the 2 D-SI results. Signal homogeneity and delineation of brain lesions, however, were superior in conventional spectroscopic imaging. The T2 relaxation of the metabolites required a reduced sampling interval for each phase-encoded echo, and hence the frequency resolution of the corresponding TSI spectra was not always sufficient for separating choline and creatine signals.

Conclusion: With measurement durations < 10 min the TSI technique allows in clinical studies a combination with single-voxel MRS for accurate quantification and with a diagnostic MRI within a total examination time of less than one hour.