Evaluation of two‐dimensional L‐COSY and JPRESS using a 3 T MRI scanner: from phantoms to human brain in vivo

Abstract

Localized versions of two-dimensional (2D) magnetic resonance spectroscopic (MRS) sequences, namely JPRESS and L-COSY, have been implemented on a whole-body 3T MRI/MRS scanner. Volume selection was achieved using three slice-selective radio-frequency (RF) pulses: 90 degrees-180 degrees-180 degrees in JPRESS and 90 degrees-180 degrees-90 degrees in L-COSY with a CHESS sequence prior to voxel localization for global water suppression. The last 180 degrees RF pulse was used for resolving the J-coupled cross peaks in JPRESS, whereas the last 90 degrees RF pulse was used for coherence transfer between J-coupled metabolites in L-COSY. A head MRI coil for 'transmission' and a 4 inch receive surface coil for 'reception' or a head coil transmit/receive were used. A total of 16 healthy volunteers were investigated using these 2D MRS sequences. Voxel sizes of 18 and 27 ml were localized in the occipito-parietal gray and white matter regions and the total duration for each 2D signal acquisition was typically 35 min. Compared with 2D L-COSY, reduced spectral width along the second spectral dimension and shorter 2D spectral acquisition were the major advantages of 2D JPRESS. In contrast, increased spectral width along the new spectral dimension in L-COSY resulted in an improved spectral dispersion enabling the detection of several brain metabolites at low concentrations that have not been resolved using the conventional one-dimensional (1D) MRS techniques. Due to increased sampling rate, severe loss of metabolite signals due to T2 during t1 was a major drawback of 2D JPRESS in vivo.

On the use of Cramér–Rao minimum variance bounds for the design of magnetic resonance spectroscopy experiments

“…The one-dimensional case corresponds to the clinically most frequently used localization sequence, PRESS (Point RESolved Spectroscopy (Bottomley, 1984)), with the echo time as an optimizable parameter and with a linear combination model of basis sets as evaluation tool. Simultaneous evaluation of multiple spectra with differing echo times corresponds to 2D J-separation spectroscopy (2DJ MRS or J-PRESS) (Aue et al, 1976;Kreis and Boesch, 1994;Thomas et al, 1996;Thomas et al, 2003), where a series of PRESS scans is acquired with TE incremented by a fixed step size, thus obtaining a two-dimensional dataset, which is usually Fourier transformed in both dimensions before evaluation. 2DJ-MRS has been recommended (Roussel et al, 2010; for simultaneous quantification of brain metabolites, and it has been claimed previously (Gonenc et al, 2010) that in particular the quantification of coupled metabolites is improved with 2DJ compared to 1D experiments.…”

In vivo 2D magnetic resonance spectroscopy of small animals

“…Brain spectra of a 27-cm 3 VOI have been recorded at 1.5 T and 3 T with these two sequences over 35 min. It appears that the resolution power of this 2D method is considerably greater at 3 T [33]. The reliability of this experiment has been proved by an in vivo study of human brains at 1.5 T [73], and it has also been applied to evaluating the water-to-fat ratio in human breast cancer [74].…”

“…The intensity of the peaks depends on the T 2 value of the protons and on the coupling patterns. For a given pulse scheme, the sensitivity and the spectral power of resolution did not increase as expected between 1.5 and 3 T, because the decrease of the T2 relaxation time of the metabolite protons results in a significant loss of signal at long echo times [33]. At higher field values, the effect of strong coupling is limited, and 2D J-resolved spectroscopy can be used to investigate efficiently metabolic processes in small animals [27,28,31].…”

Two-dimensional MR spectroscopy of healthy and cancerous prostates in vivo

“…The 2D cross peaks due to different choline groups (namely free choline, phosphocholine and ethanolamine) and myo-inositol were resolved recently in the human brain [99,107]. The 2D L-COSY spectra of human prostates did not detect these cross peaks due to the smaller voxel size and lower resolution along F 1 compared to the 2D L-COSY spectrum of the brain.…”