Original contributions High-resolution 3D MR spectroscopic imaging of the prostate at 3 T with the MLEV-PRESS sequence Albert P. Chen a , Charles H. Cunningham b , John Kurhanewicz a , Duan Xu a , Ralph E. Hurd c , John M. Pauly b , Lucas Carvajal a , Kostas Karpodinis a , Daniel B. Vigneron a, 4 a Department of Radiology, University of California at San Francisco, San Francisco, CA 94143-2512, USA b Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA c GE Health Care Technologies, Menlo Park, CA 94025, USA Received 9 December 2005; accepted 2 March 2006 Abstract A 3 T MLEV-point-resolved spectroscopy (PRESS) sequence employing optimized spectral– spatial and very selective outer-voxel suppression pulses was tested in 25 prostate cancer patients. At an echo time of 85 ms, the MLEV-PRESS sequence resulted in maximally upright inner resonances and minimal outer resonances of the citrate doublet of doublets. Magnetic resonance spectroscopic imaging (MRSI) exams performed at both 3 and 1.5 T for 10 patients demonstrated a 2.08F0.36-fold increase in signal-to-noise ratio (SNR) at 3 T as compared with 1.5 T for the center citrate resonances. This permitted the acquisition of MRSI data with a nominal spatial resolution of 0.16 cm 3 at 3 T with similar SNR as the 0.34-cm 3 data acquired at 1.5 T. Due to the twofold increase in spectral resolution at 3 T and the improved magnetic field homogeneity provided by susceptibility-matched endorectal coils, the choline resonance was better resolved from polyamine and creatine resonances as compared with 1.5 T spectra. In prostate cancer patients, the elevation of choline and the reduction of polyamines were more clearly observed at 3 T, as compared with 1.5 T MRSI. The increased SNR and corresponding spatial resolution obtainable at 3 T reduced partial volume effects and allowed improved detection of the presence and extent of abnormal metabolite levels in prostate cancer patients, as compared with 1.5 T MRSI. D 2006 Elsevier Inc. All rights reserved. Keywords: Spectroscopic imaging; Prostate cancer; High field; MLEV-PRESS 1. Introduction Magnetic resonance spectroscopic imaging (MRSI) in conjunction with high-resolution anatomical MR imaging of the prostate has become a routine clinical examination for staging, treatment planning and monitoring of prostate cancer patients [1– 4]. To date, virtually all MRI/MRSI studies have been acquired using 1.5 T MR systems. The typical spatial resolution of MRSI at 1.5 T has been ~0.3 cc or a voxel with 7 mm on a side [1– 4]. Due to the complex zonal anatomy of the prostate and the often small multifocal nature of prostate cancer, partial volume effects remain a problem in some MRSI studies even at 0.3 cc spatial resolution. With the recent availability of 3 T whole-body systems, the potential exists for improving spectral signal- to-noise ratio (SNR) and resolution for prostate MRSI using these high-field MR scanners. The theoretical two-fold increase in SNR from 1.5 to 3 T may allow the MRSI data to be acquired with half the voxel size at 3 T without compromising the spectral quality. The increase in spectral resolution at 3 T also may offer better separation of the choline, polyamine and creatine resonances that overlap considerably at 1.5 T. There have been a few recent studies investigating prostate MRSI at 3 T [5–14]; however, none has demon- strated the theoretical doubling in SNR possible at 3 T as compared with 1.5 T. In addition, these studies have reported major challenges in obtaining and quantifying 3 T prostate MRSI due to differences in J-modulation of the citrate resonance, magnetic-susceptibility-induced magnetic field inhomogeneities and chemical-shift misregistration as compared with 1.5 T studies. One of the challenges for prostate MRSI at 3 T is accurate quantification of citrate at a reasonable echo time (TE) to allow the decay of macromolecules and to avoid T2 0730-725X/$ – see front matter D 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2006.03.002 4 Corresponding author. Tel.: +1 415 476 3343; fax: +1 415 514 4451. E-mail address: vigneron@mrsc.ucsf.edu (D.B. Vigneron). Magnetic Resonance Imaging 24 (2006) 825 – 832