Fast multi-voxel two-dimensional spectroscopic imaging at 3T

Department of Radiology, University of California-San Francisco, San Francisco, CA, USA.
Magnetic Resonance Imaging (Impact Factor: 2.09). 11/2007; 25(8):1155-61. DOI: 10.1016/j.mri.2007.01.118
Source: PubMed


The utility of multivoxel two-dimensional chemical shift imaging in the clinical environment will ultimately be determined by the imaging time and the metabolite peaks that can be detected. Different k-space sampling schemes can be characterized by their minimum required imaging time. The use of spiral-based readout gradients effectively reduces the minimum scan time required due to simultaneous data acquisition in three k-space dimensions (k(x), k(y) and k(f(2))). A 3-T spiral-based multivoxel two-dimensional spectroscopic imaging sequence using the PRESS excitation scheme was implemented. Good performance was demonstrated by acquiring preliminary in vivo data for applications, including brain glutamate imaging, metabolite T(2) quantification and high-spatial-resolution prostate spectroscopic imaging. All protocols were designed to acquire data within a 17-min scan time at a field strength of 3 T.

Download full-text


Available from: Daniel M Spielman, Oct 01, 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: After more than 10 years of use, clinical neuroimaging spectroscopy has proven to be invaluable in the MRI assessment of several brain diseases. The metabolic characterization of diverse brain lesions and pathological conditions is well established by spectroscopy studies at 1.5 T, but recently, an increase in the number of 3T magnets has noticeably improved routine neuroimaging in general. For brain proton spectroscopy, the use of higher magnetic fields has been promising in terms of increasing the signal/noise ratio across the spectrum and widening the frequency bandwidth to allow clearer separation of peaks that are otherwise too close to each other at 1.5 T, especially glutamate, glutamine and gamma-aminobutyric acid (GABA). The individual detection and quantification of these metabolites will add more details to the characterization of brain diseases, and allow the inclusion of more brain pathologies. Moreover, the ongoing advances in dedicated hardware and integrated software have led to more accurate and automated postprocessing, offering neuroradiologists a more user-friendly interface. This is an up to date review of the main clinical applications of brain proton MR spectroscopy that are potentially improved at 3T, taking into account the peculiarities of higher magnetic fields. It is based on both the literature and our own clinical experience, starting from July 2005 and including more than 250 scans at 3T (unpublished material), and emphasizes, for every indication, a practical approach to brain MRS to achieve the optimal clinical impact.
    Journal of Neuroradiology 07/2008; 36(1):24-40. DOI:10.1016/j.neurad.2008.04.001 · 1.75 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Exploiting the speed benefits of echo-planar imaging (EPI), the echo-planar spectroscopic imaging (EPSI) sequence facilitates recording of one spectral and two to three spatial dimensions faster than the conventional magnetic resonance spectroscopic imaging (MRSI). A novel four dimensional (4D) echo-planar correlated spectroscopic imaging (EP-COSI) was implemented on a whole body 3 T MRI scanner combining two spectral with two spatial encodings. Similar to EPSI, the EP-COSI sequence used a bipolar spatial read-out train facilitating simultaneous spatial and spectral encoding, and the conventional phase and spectral encodings for the other spatial and indirect spectral dimensions, respectively. Multiple 2D correlated spectroscopy (COSY) spectra were recorded over the spatially resolved volume of interest (VOI) localized by a train of three slice-selective radiofrequency (RF) pulses (90°-180°-90°). After the initial optimization using phantom solutions, the EP-COSI data were recorded from the lower leg of eight healthy volunteers including one endurance trained volunteer. Pilot results showed acceptable spatial and spectral quality achievable using the EP-COSI sequence. There was a detectable separation of cross peaks arising from the skeletal muscle intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) saturated and unsaturated pools. Residual dipolar interaction between the N-methylene and N-methyl protons of creatine/phosphocreatine (Cr/PCr) was also observed in the tibialis anterior region.
    Magnetic Resonance in Medicine 10/2010; 64(4):947-56. DOI:10.1002/mrm.22499 · 3.57 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: One of the drawbacks of scanning patients using multiple-voxel spectroscopic imaging is the long acquisition time. This is especially true when one is interested in obtaining absolute metabolite concentrations which requires acquisition of unsuppressed water spectra in addition to the suppressed spectra. In our experiment, turbo spectroscopic imaging (TSI) method with acquisition of three echoes per excitation was applied to reduce scanning time without lowering the spatial resolution. In 15 relapsing-remitting multiple sclerosis patients (mean age 37.07years, mean disease duration 7.67years), an MRSI scan at the level of centrum semiovale was obtained. The scan time was approximately 7min including the unsuppressed spectra. Tissue water was used as an internal concentration reference to obtain absolute metabolite concentrations of N-acetyl-aspartate (NAA), creatine (Cr), and choline (Cho). The peak areas were corrected for differences in transversal and longitudinal relaxation times and a water concentration of 55.5M was assumed. A three-dimensional high-resolution T 1 scan was acquired and used to segment tissue in gray matter (GM), white matter (WM), and cerebrospinal fluid using FSL’S FAST segmentation method (a software library of the automated segmentation tool by the Center of Functional MRI of the Brain, Oxford, UK). Finally, a regression analysis was employed to address the metabolite concentrations and ratios in GM and WM, respectively. Our study shows that the metabolite concentrations (NAA, Cho, Cr) and metabolite ratios (NAA/Cr and Cho/Cr) in GM and WM obtained using the methods discussed earlier are comparable to the results found in other studies of similar patient groups. It also shows that TSI method can be used to obtain the absolute metabolite ratios in a reasonable scan time.
    Applied Magnetic Resonance 10/2010; 39(3):251-260. DOI:10.1007/s00723-010-0153-9 · 1.17 Impact Factor
Show more