Nagarajan Rajakumar PhD, Abstract Co-Author: Nothing to Disclose

Yutaka Natsuaki, Abstract Co-Author: Researcher, Siemens AG

Margaret Keller, Abstract Co-Author: Nothing to Disclose

Tim DeVito, Abstract Co-Author: Nothing to Disclose

Michael Albert Thomas PhD, Presenter: Nothing to Disclose

Two-dimensional (2D) correlated spectroscopy (L-COSY) enables converting a crowded overlapping 1D MR spectrum to a better resolved 2D spectrum through the addition of a spectral dimension. However, to acquire high-quality MR spectra, reliable localized shimming is an essential prerequisite and Fast automatic shimming technique by mapping along projections (FASTMAP) may serve that purpose with better efficiency than the default auto shim. A major goal of this work was to evaluate the overall performance of 2D L-COSY combined with FASTMAP on 3T MRI/MRS scanner; for comparison, 2D L-COSY spectra were also recorded using the conventional auto-shim.

12 healthy human subjects were scanned on a 3T Magnetom Trio MRI/MRS scanner (Siemens Healthcare, Erlangen, Germany) equipped with phased array head coils after obtaining informed consent. 2D L-COSY parameters were: TR/TE =2s/30ms, 64Δt1 increments (Δt1), 8averages per Δt1, and total acquisition time of 17mins. The 2D raw matrix consisted of 2048 complex points along first dimension and 64 points along second dimension. Matrices were zero filled to 4096x256 and processed by Felix software (Felix NMR Inc, SanDiego, CA). The unsuppressed water signal was used to evaluate the field homogeneity. Typically, 3-5 iterations were used to complete the FASTMAP shimming procedure (VB15A WIP#479: FASTMAP).

The line width of approximately 15Hz was obtained at 3T in the frontal lobe of human brain after shimming with FASTMAP and more than 20Hz were obtained by using auto shim by using 2D L-COSY spectra. The following metabolites have been quantified (N-Acetylaspartate (NAA),Creatine (Cr), Choline (Cho), Phosphocholine (PCh), Aspartate (Asp), GABA, Glutamine/Glutamate (Glx), Threonine-Lactate (Lac), Myo-inositol (mI), N-Acetylaspartate glutamate (NAAG), Myo-inositol Choline (mICh), Phosphoethanolomine (PE), Taurine (Tau),) ) and the coefficient of variance (CV) of various metabolites ratios recorded by FASTMAP and auto shim were calculated. Entire shimming procedure was completed in less than a minute compared to auto shim (3mins.) with better coefficient of variance (<20%) obtained using FASTMAP.

The quality of the FASTMAP based 2D L-COSY spectra was improved significantly compared to that with auto shim.

Improved static field homogeneity achieved by FASTMAP will facilitate better metabolite quantitation in different brain pathologies.

Rajakumar, N, Natsuaki, Y, Keller, M, DeVito, T, Thomas, M, Evaluation of FASTMAP Combined 2D Correlated Spectroscopy in Human Brain at 3T  .  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013621.html