Investigating the regional effect of the chemical shift displacement artefact on the J‐modulated lactate signal at ultra high‐field. (2nd November 2020)

• Record Type: Journal Article
• Authors: Fernandes, Carolina C.; Lanz, Bernard; Chen, Chen; Morris, Peter G.; Salmon, Carlos G.
• Is Part Of: NMR in biomedicine. Volume 34:Number 2(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-11-02
• Subjects: chemical shift displacement artefact -- J‐modulation -- lactate -- MR spectroscopy -- product operator formalism -- STEAM; Nuclear magnetic resonance -- Periodicals; Magnetic Resonance Spectroscopy -- Periodicals; 574
• DOI: 10.1002/nbm.4440
• Languages: English
• ISSNs: 0952-3480

Abstract

Abstract : The present work aims to show the applicability of an analytical model for the optimisation of the STEAM sequence timing parameters for lactate detection at ultra high‐field. The effects of the chemical shift displacement artefact on the J‐modulated signal for a weakly‐coupled spin system were considered in the three applied directions of field gradients and the product operator formalism was used to obtain expressions for the signal modulation in each compartment of the excited volume. The validity of this model was demonstrated experimentally at 7 T in a phantom and acquisitions with optimised parameters were performed on a healthy volunteer. The spectra acquired with TE = 144 ms with the optimised mixing time and TE = 288 ms showed easily detectable lactate peaks in the normal human brain. Additionally, the acquisition with the longer TE resulted in a spectrum with less lipid/macromolecular contamination. The simulations shown here demonstrated that the proposed analytical model is suitable for correctly predicting the resulting lactate signal. With the optimised parameters, it was possible to use a simple sequence with sufficient signal‐to‐noise ratio to reliably distinguish lactate from overlapping resonances in a healthy brain. Abstract : The applicability of an analytical model for predicting the resulting lactate signal, as well as determining the localisation of the signal throughout the excited region is shown for the STEAM sequence. This three‐dimensional model is particularly useful in the case of an inhomogeneously distributed metabolite and allows for the optimisation of the sequence timing parameters. This work demonstrates that it is possible to use a standard sequence for detecting lactate with sufficient SNR and minimal contamination from lipids and macromolecules, in a healthy brain at ultra high‐field.