Restoration of motion‐related signal loss and line‐shape deterioration of proton MR spectra using the residual water as intrinsic reference

Quantification of non–water‐suppressed MR spectra with correction for motion‐induced signal reduction

“…Inevitable subject motions during successive data acquisition in magnetic resonance spectroscopy (MRS) may cause signal loss because of two major mechanisms (1)(2)(3)(4). First, motion-induced magnetic field drifts may lead to frequency shift over multiple MRS acquisition frames.…”

“…In conventional MRS studies, data from all acquisition frames are simply averaged, and therefore the destructively averaged spectrum would be affected by signal-to-noise ratio (SNR) attenuation and spectral shape distortion because of frame-to-frame phase/ frequency variations. It has been shown that, by performing frame-by-frame corrections for the intrascan phase/ frequency variations, the constructively averaged MRS data exhibit significantly improved SNR and spectral quality (1)(2)(3)(4)(5)(6)(7)(8). The search for an effective intrascan phase/frequency correction method is thus an active field of research for in vivo MRS.…”

“…Over the past decades, several methods have been proposed to measure the intrascan phase/frequency variations in MRS scans in order to perform constructive averaging (1,2,(4)(5)(6). In one of these methods, the non-water-suppressed (NWS) free induction decay and water-suppressed (WS) MRS data were acquired in an interleaved manner (2).…”

“…Alternatively, the phase variations induced by intrascan motion could be measured on a frame-by-frame basis directly from the residual water signals of WS MRS data (1,4). However, even though the information estimated directly from the WS MRS data better reflects the instant phase variation in comparison to the interleaved free induction decay-based measurements, this approach has two main limitations: First, the residual water signals in WS MRS data have low SNR that limits the accuracy of frameby-frame phase estimation (1).…”

T2-based segmentation of periventricular volumes for quantification of proton magnetic resonance spectra of multiple sclerosis lesions

“…7) on absolute quantification of proton MR spectra, 21 periventricular MS lesions filling more than 50% of the VOI were selected from a previous MRS study (11). The spectra were acquired at short echo time (30 ms) and long repetition time (6 s), individually phase corrected for motion effects (12) prior to averaging, and evaluated using a linear combination of model spectra (LCModel, [13,14]). Absolute tissue concentrations of the main metabolites were estimated using s long and the corrected s CSF for the CSF partial volume.…”