Non‐water‐suppressed 1 H FID‐MRSI at 3T and 9.4T

Purpose In this study, we demonstrate the first combination of 3D FID proton MRSI and spatial encoding via concentric‐ring trajectories (CRTs) at 3T. FID‐MRSI has many benefits including high detection sensitivity, in particular for J‐coupled metabolites (e.g., glutamate/glutamine). This makes it highly attractive, not only for clinical, but also for, potentially, functional MRSI. However, this requires excellent reliability and temporal stability. We have, therefore, augmented this 3D‐FID‐MRSI sequence with single‐echo, imaging‐based volumetric navigators (se‐vNavs) for real‐time motion/shim‐correction (SHMOCO), which is 2× quicker than the original double‐echo navigators (de‐vNavs), hence allowing more efficient integration also in short‐TR sequences. Methods The tracking accuracy (position and B0‐field) of our proposed se‐vNavs was compared to the original de‐vNavs in phantoms (rest and translation) and in vivo (voluntary head rotation). Finally, the intra‐session stability of a 5:40 min 3D‐FID‐MRSI scan was evaluated with SHMOCO and no correction (NOCO) in 5 resting subjects. Intra/inter‐subject coefficients of variation (CV) and intra‐class correlations (ICC) over the whole 3D volume and in selected regions of interest ROI were assessed. Results Phantom and in vivo scans showed highly consistent tracking performance for se‐vNavs compared to the original de‐vNavs, but lower frequency drift. Up to ~30% better intra‐subject CVs were obtained for SHMOCO (P < 0.05), with values of 9.3/6.9/6.5/7.8% over the full VOI for Glx/tNAA/tCho/m‐Ins ratios to tCr. ICCs were good‐to‐high (91% for Glx/tCr in motor cortex), whereas the inter‐subject variability was ~11–19%. Conclusion Real‐time motion/shim corrected 3D‐FID‐MRSI with time‐efficient CRT‐sampling at 3T allows reliable, high‐resolution metabolic imaging that is fast enough for clinical use and even, potentially, for functional MRSI.

Section: Discussionmentioning

confidence: 68%

Intra‐session and inter‐subject variability of 3D‐FID‐MRSI using single‐echo volumetric EPI navigators at 3T

Moser

Eckstein

Hingerl

et al. 2019

“…A next step toward clinical translation could be to combine metabolite cycling with cardiac echo‐planar spectroscopic imaging . Metabolite cycling has already been combined with spectroscopic imaging for brain applications, but the transition to the heart has not yet been made.…”

Section: Discussionmentioning

confidence: 99%

Navigator‐free metabolite‐cycled proton spectroscopy of the heart

Peereboom

Gastl

Füetterer

et al. 2019

Twitter: @CMR_ZurichPurpose: Respiratory gating in cardiac water-suppressed (WS) proton spectroscopy leads to long and unpredictable scan times. Metabolite cycling allows to perform frequency and phase correction on the water signal and, hence, offers an approach to navigator-free cardiac spectroscopy with fixed scan time. The objective of the present study was to develop and implement navigator-free metabolite-cycled cardiac proton spectroscopy (MC nonav) and compare it with standard navigator-gated WS (WS nav) and navigator-free WS (WS nonav) measurements for the assessment of triglyceride-to-water ratios (TG/W) and creatine-to-water ratios (CR/W) in the intraventricular septum of the in vivo heart. Methods: Navigator-free metabolite-cycled spectroscopy was implemented on a clinical 1.5T system. In vivo measurements were performed on 10 young and 5 older healthy volunteers to assess signal-to-noise ratio efficiency as well as TG/W and CR/W and the relative Cramér-Rao lower bounds for CR. The performance of the metabolite-cycled sequence was verified using simulations. Results: On average, scan times of MC nonav were 3.4 times shorter compared with WS nav, while no significant bias for TG/W was observed (coefficient of variation = 14.0%). signal-to-noise ratio efficiency of both TG and CR increased for MC nonav compared with WS nav. Relative Cramér-Rao lower bounds of CR decreased for MC nonav. Overall spectral quality was found comparable between MC nonav and WS nav, while it was inferior for WS nonav. Conclusion: Navigator-free metabolite-cycled cardiac proton spectroscopy offers 3.4-fold accelerated assessment of TG/W and CR/W in the heart with preserved spectral quality when compared with navigator-gated WS scans. K E Y W O R D S1 H-MRS, cardiac spectroscopy, creatine, metabolite cycling, respiratory motion compensation, triglyceride 1 | INTRODUCTION Proton MR spectroscopy (MRS) has proven a valuable tool to study cardiac metabolism. 1 It has been shown that myocardial triglyceride (TG) levels are dependent on age, 2 diet, 3 and circadian rhythm 4 in healthy subjects. Both fatty acid usage and total creatine (CR) levels tend to decrease as a function of heart failure severity, 5 where distinctions can be made between different types of cardiomyopathy. 6 Other diseases such as diabetes type 2 7 and aortic stenosis 8 also show effects on myocardial TG levels.Although proton MRS is not a new method for cardiac research, its transition to the clinic has not succeeded so far. The lack of clinical translation is partly related to motion effects 796 | PEEREBOOM Et al.

“…The L2 method was shown to allow reconstruction of metabolic images even from the LTE‐NWS‐MRSI data with metabolic images generally close to those from the LTE‐WS‐MRSI. Several previous studies have demonstrated the feasibility of in vivo non‐water‐suppression MRSI with metabolite and water signals measured simultaneously . Advantages of this approach include the availability of the full water signal for eddy current correction and use an internal reference for metabolite quantification.…”

Section: Discussionmentioning

confidence: 99%

“…Several previous studies have demonstrated the feasibility of in vivo non-water-suppression MRSI with metabolite and water signals measured simultaneously. [37][38][39][40][41][42] Advantages of this approach include the availability of the The limits of agreement are calculated as mean ± 1.96 standard deviation and shown on each plot (dashed lines). The solid line represents the mean of the measurement differences full water signal for eddy current correction and use an internal reference for metabolite quantification.…”

Section: Discussionmentioning

confidence: 99%

Water removal in MR spectroscopic imaging with L2 regularization

Lin

Považan

Berrington

et al. 2019

Purpose An L2‐regularization based postprocessing method is proposed and tested for removal of residual or unsuppressed water signals in proton MR spectroscopic imaging (MRSI) data recorded from the human brain at 3T. Methods Water signals are removed by implementation of the L2 regularization using a synthesized water‐basis matrix that is orthogonal to metabolite signals of interest in the spectral dimension. Simulated spectra with variable water amplitude and in vivo brain MRSI datasets were used to demonstrate the proposed method. Results were compared with two commonly‐used postprocessing methods for removing water signals. Results The L2 method yielded metabolite signals that were close to true values for the simulated spectra. Residual/unsuppressed water signals in human brain short‐ and long‐echo time MRSI datasets were efficiently removed by the proposed method allowing good quality metabolite maps to be reconstructed with minimized contamination from water signals. Significant differences of the creatine signal were observed between brain long‐echo time MRSI without and with water saturation, attributable to the previously described magnetization transfer effect. Conclusions With usage of a synthesized water matrix generated based on reasonable prior knowledge about water and metabolite resonances, the L2 method is shown to be an effective way to remove water signals from MRSI of the human brain.