Ningzhi Li1, Li An1, Christopher Johnson1, Jun Shen1. 1. Molecular Imaging Branch, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
Abstract
BACKGROUND: Due to imperfect slice profiles, unwanted signals from outside the selected voxel may significantly contaminate metabolite signals acquired using in vivo magnetic resonance spectroscopy (MRS). The use of outer volume suppression may exceed the SAR threshold, especially at high field. OBJECTIVE: We propose using phase-encoding gradients after radiofrequency (RF) excitation to spatially encode unwanted signals originating from outside of the selected single voxel. METHODS: Phase-encoding gradients were added to a standard single voxel point-resolved spectroscopy (PRESS) sequence which selects a 2 × 2 × 2 cm3 voxel. Subsequent spatial Fourier transform was used to encode outer volume signals. Phantom and in vivo experiments were performed using both phase-encoded PRESS and standard PRESS at 7 Tesla. Quantification was performed using fitting software developed in-house. RESULTS: Both phantom and in vivo studies showed that spectra from the phase-encoded PRESS sequence were relatively immune from contamination by oil signals and have more accurate quantification results than spectra from standard PRESS spectra of the same voxel. CONCLUSION: The proposed phase-encoded single-voxel PRESS method can significantly suppress outer volume signals that may appear in the spectra of standard PRESS without increasing RF power deposition.
BACKGROUND: Due to imperfect slice profiles, unwanted signals from outside the selected voxel may significantly contaminate metabolite signals acquired using in vivo magnetic resonance spectroscopy (MRS). The use of outer volume suppression may exceed the SAR threshold, especially at high field. OBJECTIVE: We propose using phase-encoding gradients after radiofrequency (RF) excitation to spatially encode unwanted signals originating from outside of the selected single voxel. METHODS: Phase-encoding gradients were added to a standard single voxel point-resolved spectroscopy (PRESS) sequence which selects a 2 × 2 × 2 cm3 voxel. Subsequent spatial Fourier transform was used to encode outer volume signals. Phantom and in vivo experiments were performed using both phase-encoded PRESS and standard PRESS at 7 Tesla. Quantification was performed using fitting software developed in-house. RESULTS: Both phantom and in vivo studies showed that spectra from the phase-encoded PRESS sequence were relatively immune from contamination by oil signals and have more accurate quantification results than spectra from standard PRESS spectra of the same voxel. CONCLUSION: The proposed phase-encoded single-voxel PRESS method can significantly suppress outer volume signals that may appear in the spectra of standard PRESS without increasing RF power deposition.
Authors: Níall Lally; Li An; Dipavo Banerjee; Mark J Niciu; David A Luckenbaugh; Erica M Richards; Jonathan P Roiser; Jun Shen; Carlos A Zarate; Allison C Nugent Journal: J Magn Reson Imaging Date: 2015-06-07 Impact factor: 4.813
Authors: E R Danielsen; T V Elberling; A K Rasmussen; J Dock; M Hørding; H Perrild; G Waldemar; U Feldt-Rasmussen; C Thomsen Journal: J Clin Endocrinol Metab Date: 2008-05-20 Impact factor: 5.958