Abstract
Attempts have been made to reduce the total scan time in multi-dimensional J-resolved spectroscopic imaging (JRESI) using an echo-planar (EP) readout gradient, but acquisition duration remains a limitation for routine clinical use in the brain. We present here a significant acceleration achieved with a 4D EP-JRESI sequence that collects dual phase encoded lines within a single repetition time (TR) using two bipolar read-out trains. The performance and reliability of this novel 4D sequence, called Multi-Echo based Echo-Planar J-resolved Spectroscopic Imaging (ME-EP-JRESI), was evaluated in 10 healthy controls and a brain phantom using a 3 T MRI/MRS scanner. The prior knowledge fitting (ProFit) algorithm, with a new simulated basis set consisting of macromolecules and lipids apart from metabolites of interest, was used for quantitation. Both phantom and in-vivo data demonstrated that localization and spatial/spectral profiles of metabolites from the ME-EP-JRESI sequence were in good agreement with that of the EP-JRESI sequence. Both in the occipital and temporal lobe, metabolites with higher physiological concentrations including Glx (Glu+Gln), tNAA (NAA+NAAG), mI all had coefficient of variations between 9–25%. In summary, we have implemented, validated and tested the ME-EP-JRESI sequence, demonstrating that multi-echo acquisition can successfully reduce the total scan duration for EP-JRESI sequences.
Highlights
Better separation of the resonance lines by adding an extra spectral dimension as accomplished in localized correlated spectroscopy (L-COSY)[9] and J-resolved spectroscopy (JPRESS)[10, 11], spectral overcrowding can be reduced which helps in accurate quantification of several low concentration metabolites
Phantom scans are presented here from a gray matter brain phantom to study the acceleration of scan time compared with EP-J-resolved spectroscopic imaging (JRESI) and to show that quantitation results using the prior knowledge fitting (ProFit) algorithm are not affected by the multi echo readout
Two bipolar echo-planar spectroscopic imaging (EPSI) read-out trains differently phase-encoded along the spatial dimension and separated by a slice selective refocusing 180° pulse were included in the Multi echo (ME)-EP-JRESI technique to accelerate the acquisition by collecting two k-space lines per TR
Summary
Better separation of the resonance lines by adding an extra spectral dimension as accomplished in localized correlated spectroscopy (L-COSY)[9] and J-resolved spectroscopy (JPRESS)[10, 11], spectral overcrowding can be reduced which helps in accurate quantification of several low concentration metabolites. One of the major hurdles in clinical implementation of these multi-dimensional MRSI sequences is longer scan time. In EPSI, a time varying readout-gradient train encodes one spatial and one spectral (temporal) dimension during a single readout, leaving the remaining spatial dimensions to be incrementally phase encoded sequentially resulting in an acceleration of Nx or Ny times. Such an acceleration in scan time makes it feasible to acquire spatially resolved multi-dimensional spectral data in a clinical setting[21], increase spatial resolution, or collect 3D data sets[20]. In-vivo scans from healthy controls are presented to show that spatial and spectral quality is maintained despite the loss of spectral resolution
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