Using Peak-Enhanced 2D-Capon Analysis with Single Voxel Magnetic Resonance Spectroscopy to Estimate T2* for Metabolites. Fred J. Frigo 1, James A. Heinen 2, Thoralf Niendorf 1, Jeffrey A. Hopkins 1, and Bryan J. Mock 1 1. GE Healthcare, Milwaukee, WI USA 2. Marquette University, Milwaukee, WI USA

Introduction Fig. 1. MR image of human brain. Fig. 2. MRS absorption spectrum of region indicated in Fig. 1. Single voxel proton magnetic resonance spectroscopy (MRS) is typically used in a clinical setting to quantify metabolites in the human brain. MRS absorption spectrum as shown in Fig. 2 shows key metabolites, such as NAA, creatine, choline and others. 2D Capon analysis can be used for MRS (1) to estimate frequency and damping. Damping information determined from 2D Capon analysis is related to T2*, the total transverse relaxation time, for each metabolite.

Methods Fig. 3. Phase-corrected water-suppressed raw data with residual water removed. Hardware: GE 1.5 T Signa scanner, 40mT/m gradient coil, single channel head coil. PRESS/p: TE=35ms, TR=1500ms, 8 cm 3 voxel, 16 reference frames, 128 water-suppressed frames, scan time = 3 minutes 48 seconds. Water-suppressed data is phase corrected, and residual water is removed. Fourier transformation of data from Fig. 3 results in MRS absorption spectrum shown in Fig. 2. 2D Capon analysis can also be performed on the raw data shown in Fig. 3 to estimate frequency and damping.

Methods Summary of 2D Capon analysis

Results 2D Capon analysis of MRS data from Fig. 3 is shown in Fig. 4 Peak-enhanced 2D Capon analysis shown in in Fig. 5 simplifies interpretation of results Damping characteristics which are related to T2* for each metabolite can be seen easily in Fig. 6 Fig. 4. 2D-Capon analysis surface. Fig. 5. 2D-Capon analysis peak-enhanced surface.Fig. 6. 2D-Capon analysis peak-enhanced contour.

Conclusions References 1. Stocia P, Sundin T, “Nonparametric NMR Spectroscopy”, JMR, 152:57-69, Hurd RE, Sailasuta N, Srinivansan R, Vigneron DB, Nelson S, “3T Brain Spectroscopy: Repeatability and Inter-subject Variability”, Proc. of ISMRM, 11:1145, Michaeli S, et al., “Proton T2 Relaxation Study of Water, N-acetylaspartate, and Creatine in Human Brain using Hahn and Carr-Purcell Spin Echoes at 4T and 7T”, MRM, 47: , Opstad KS, Griffiths JR, Bell BA, Howe FA, “In vivo lipid T2 relaxation time measurements in high-grade tumors: differentiation of glioblastomas and metastases”, Proc. of ISMRM, 11:754, Determination of T2* for metabolites has been studied (2),(3) and has been shown to have clinical value for certain pathologies including cancer (4). Peak-enhanced 2D Capon analysis facilitates determining damping factors,, for each metabolite which are related to T2*. 2D Capon analysis can be performed on the same data used to create conventional MRS absorption spectra. Computational processing requirements for 2D Capon analysis should not prohibit practical implementation for clinical settings. Using 2D Capon analysis in conjunction with single voxel proton MRS studies provides an effective method for estimating T2* for each metabolite. The authors would like to thank Dr. Thomas Raidy of Duke University and Dr. Jason A. Polzin and David H. Gurr of GE Healthcare for their helpful comments and ideas. Acknowledgments