The purpose of this work is to validate a simple and versatile integrated variable flip angle (VFA) method for mapping B1 in hyperpolarized MRI, which can be used to correct signal variations due to coil inhomogeneity. Simulations were run to assess performance of the VFA B1 mapping method compared to the currently used constant flip angle (CFA) approach. Simulation results were used to inform the design of VFA sequences, validated in four volunteers for hyperpolarized xenon-129 imaging of the lungs and another four volunteers for hyperpolarized carbon-13 imaging of the human brain. B1 maps obtained were used to correct transmit and receive inhomogeneity in the images. Simulations showed improved performance of the VFA approach over the CFA approach with reduced sensitivity to T1. For xenon-129, the B1 maps accurately reflected the variation of signal depolarization, but in some cases could not be used to correct for coil receive inhomogeneity due to a lack of transmit-receive reciprocity resulting from suboptimal coil positioning. For carbon-13, the B1 maps showed good agreement with a separately acquired B1 map of a phantom and were effectively used to correct coil-induced signal inhomogeneity. A simple, versatile, and effective VFA B1 mapping method was implemented and evaluated. Inclusion of the B1 mapping method in hyperpolarized imaging studies can enable more robust signal quantification.
Abstract Background Magnetic resonance (MR) imaging of deuterated glucose, termed deuterium metabolic imaging (DMI), is emerging as a biomarker of pathway-specific glucose metabolism in tumors. DMI is being studied as a useful marker of treatment response in a scan-rescan scenario. This study aims to evaluate the repeatability of brain DMI. Methods A repeatability study was performed in healthy volunteers from December 2022 to March 2023. The participants consumed 75 g of [6,6′ 2 H 2 ]glucose. The delivery of 2 H-glucose to the brain and its conversion to 2 H-glutamine + glutamate, 2 H-lactate, and 2 H-water DMI was imaged at baseline and at 30, 70, and 120 min. DMI was performed using MR spectroscopic imaging on a 3-T system equipped with a 1 H/ 2 H-tuned head coil. Coefficients of variation (CoV) were computed for estimation of repeatability and between-subject variability. In a set of exploratory analyses, the variability effects of region, processing, and normalization were estimated. Results Six male participants were recruited, aged 34 ± 6.5 years (mean ± standard deviation). There was 42 ± 2.7 days between sessions. Whole-brain levels of glutamine + glutamate, lactate, and glucose increased to 3.22 ± 0.4 mM, 1.55 ± 0.3 mM, and 3 ± 0.7 mM, respectively. The best signal-to-noise ratio and repeatability was obtained at the 120-min timepoint. Here, the within-subject whole-brain CoVs were -10% for all metabolites, while the between-subject CoVs were -20%. Conclusions DMI of glucose and its downstream metabolites is feasible and repeatable on a clinical 3 T system. Trial registration ClinicalTrials.gov, NCT05402566 , registered the 25th of May 2022. Relevance statement Brain deuterium metabolic imaging of healthy volunteers is repeatable and feasible at clinical field strengths, enabling the study of shifts in tumor metabolism associated with treatment response. Key points • Deuterium metabolic imaging is an emerging tumor biomarker with unknown repeatability. • The repeatability of deuterium metabolic imaging is on par with FDG-PET. • The study of deuterium metabolic imaging in clinical populations is feasible. Graphical Abstract
Purpose The aim of the study was to investigate whether incorrectly compensated eddy currents are the source of persistent X‐nuclear spectroscopy and imaging artifacts, as well as methods to correct this. Methods Pulse‐acquire spectra were collected for 1 H and X‐nuclei ( 23 Na or 31 P) using the minimum TR permitted on a 3T clinical MRI system. Data were collected in 3 orientations (axial, sagittal, and coronal) with the spoiler gradient at the end of the TR applied along the slice direction for each. Modifications to system calibration files to tailor eddy current compensation for each X‐nucleus were developed and applied, and data were compared with and without these corrections for: slice‐selective MRS (for 23 Na and 31 P), 2D spiral trajectories (for 13 C), and 3D cones trajectories (for 23 Na). Results Line‐shape distortions characteristic of eddy currents were demonstrated for X‐nuclei, which were not seen for 1 H. The severity of these correlated with the amplitude of the eddy current frequency compensation term applied by the system along the axis of the applied spoiler gradient. A proposed correction to eddy current compensation, taking account of the gyromagnetic ratio, was shown to dramatically reduce these distortions. The same correction was also shown to improve data quality of non‐Cartesian imaging (2D spiral and 3D cones trajectories). Conclusion A simple adaptation of the default compensation for eddy currents was shown to eliminate a range of artifacts detected on X‐nuclear spectroscopy and imaging.
Purpose Imaging of the different resonances of dissolved hyperpolarized xenon‐129 ( 129 Xe) in the lung is performed using a four‐echo flyback 3D radial spectroscopic imaging technique and is evaluated in healthy volunteers (HV) and subjects with idiopathic pulmonary fibrosis (IPF). Theory and Methods 10 HV and 25 subjects with IPF underwent dissolved 129 Xe MRI at 1.5T. IPF subjects underwent same day pulmonary function tests to measure forced vital capacity and the diffusion capacity of the lung for carbon monoxide (DL CO ). A four‐point echo time technique with k‐space chemical‐shift modeling of gas, dissolved 129 Xe in lung tissue/plasma (TP) and red blood cells (RBC) combined with a 3D radial trajectory was implemented within a 14‐s breath‐hold. Results Results show an excellent chemical shift separation of the dissolved 129 Xe compartments and gas contamination removal, confirmed by a strong agreement between average imaging and global spectroscopy RBC/TP ratio measurements. Subjects with IPF exhibited reduced imaging gas transfer when compared to HV. A significant increase of the amplitude of RBC signal cardiogenic oscillation was also observed. In IPF subjects, DL CO % predicted was significantly correlated with RBC/TP and RBC/GAS ratios and the correlations were stronger in the inferior and periphery sections of the lungs. Conclusion Lung MRI of dissolved 129 Xe was performed with a four‐echo spectroscopic imaging method. Subjects with IPF demonstrated reduced xenon imaging gas transfer and increased cardiogenic modulation of dissolved xenon signal in the RBCs when compared to HV.
MRI with hyperpolarised 13C represents a promising modality for in-vivo spectroscopy and provides a unique opportunity for non-invasive assessment of cardiac regional metabolism.
Figures sources for "Kurzawski, JW, Cencini, M, Peretti, L, et al. Retrospective rigid motion correction of three‐dimensional magnetic resonance fingerprinting of the human brain. Magn Reson Med. 2020; 84: 2606– 2615. https://doi.org/10.1002/mrm.28301"
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