Comparison of hyperpolarized 13 C and non-hyperpolarized deuterium MRI approaches for imaging cerebral glucose metabolism at 4.7 T

Advances and prospects in deuterium metabolic imaging (DMI): a systematic review of in vivo studies

BACKGROUND

Deuterium metabolic imaging (DMI) has emerged as a promising non-invasive technique for studying metabolism in vivo. This review aims to summarize the current developments and discuss the futures in DMI technique in vivo.

METHODS

A systematic literature review was conducted based on the PRISMA 2020 statement by two authors. Specific technical details and potential applications of DMI in vivo were summarized, including strategies of deuterated metabolites detection, deuterium-labeled tracers and corresponding metabolic pathways in vivo, potential clinical applications, routes of tracer administration, quantitative evaluations of metabolisms, and spatial resolution.

RESULTS

Of the 2,248 articles initially retrieved, 34 were finally included, highlighting 2 strategies for detecting deuterated metabolites: direct and indirect DMI. Various deuterated tracers (e.g., [6,6'-2H2]glucose, [2,2,2'-2H3]acetate) were utilized in DMI to detect and quantify different metabolic pathways such as glycolysis, tricarboxylic acid cycle, and fatty acid oxidation. The quantifications (e.g., lactate level, lactate/glutamine and glutamate ratio) hold promise for diagnosing malignancies and assessing early anti-tumor treatment responses. Tracers can be administered orally, intravenously, or intraperitoneally, either through bolus administration or continuous infusion. For metabolic quantification, both serial time point methods (including kinetic analysis and calculation of area under the curves) and single time point quantifications are viable. However, insufficient spatial resolution remains a major challenge in DMI (e.g., 3.3-mL spatial resolution with 10-min acquisition at 3 T).

CONCLUSIONS

Enhancing spatial resolution can facilitate the clinical translation of DMI. Furthermore, optimizing tracer synthesis, administration protocols, and quantification methodologies will further enhance their clinical applicability.

RELEVANCE STATEMENT

Deuterium metabolic imaging, a promising non-invasive technique, is systematically discussed in this review for its current progression, limitations, and future directions in studying in vivo energetic metabolism, displaying a relevant clinical potential.

KEY POINTS

• Deuterium metabolic imaging (DMI) shows promise for studying in vivo energetic metabolism. • This review explores DMI's current state, limits, and future research directions comprehensively. • The clinical translation of DMI is mainly impeded by limitations in spatial resolution.

Dual-Tuned Coaxial-Transmission-Line RF Coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields

OBJECTIVE

Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging (13C-HPMRI) and deuterium metabolic imaging (2H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios (ɣ13C = 10.7 MHz/T; ɣ2H = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil.

METHODS

Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters.

RESULTS

Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the 13C and 2H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned 1H/13C and 1H/2H CTLs RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained.

CONCLUSION

The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging.

SIGNIFICANCE

The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.

A proton birdcage coil integrated with interchangeable single loops for multi-nuclear MRI/MRS

Energy metabolism is fundamental for life. It encompasses the utilization of carbohydrates, lipids, and proteins for internal processes, while aberrant energy metabolism is implicated in many diseases. In the present study, using three-dimensional (3D) printing from polycarbonate via fused deposition modeling, we propose a multi-nuclear radiofrequency (RF) coil design with integrated 1H birdcage and interchangeable X-nuclei (2H, 13C, 23Na, and 31P) single-loop coils for magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS). The single-loop coil for each nucleus attaches to an arc bracket that slides unrestrictedly along the birdcage coil inner surface, enabling convenient switching among various nuclei and animal handling. Compared to a commercial 1H birdcage coil, the proposed 1H birdcage coil exhibited superior signal-excitation homogeneity and imaging signal-to-noise ratio (SNR). For X-nuclei study, prominent peaks in spectroscopy for phantom solutions showed excellent SNR, and the static and dynamic peaks of in vivo spectroscopy validated the efficacy of the coil design in structural imaging and energy metabolism detection simultaneously.

Subcutaneous deuterated substrate administration in mice: An alternative to tail vein infusion

PURPOSE

Tail-vein catheterization and subsequent in-magnet infusion is a common route of administration of deuterium (2 H)-labeled substrates in small-animal deuterium (D) MR studies. With mice, because of the tail vein's small diameter, this procedure is challenging. It requires considerable personnel training and practice, is prone to failure, and may preclude serial studies. Motivated by the need for an alternative, the time courses for common small-molecule deuterated substrates and downstream metabolites in brain following subcutaneous infusion were determined in mice and are presented herein.

METHODS

Three 2 H-labeled substrates-[6,6-2 H2 ]glucose, [2 H3 ]acetate, and [3,4,4,4-2 H4 ]beta-hydroxybutyrate-and 2 H2 O were administered to mice in-magnet via subcutaneous catheter. Brain time courses of the substrates and downstream metabolites (and semi-heavy water) were determined via single-voxel DMRS.

RESULTS

Subcutaneous catheter placement and substrate administration was readily accomplished with limited personnel training. Substrates reached pseudo-steady state in brain within ∼30-40 min of bolus infusion. Time constants characterizing the appearance in brain of deuterated substrates or semi-heavy water following 2 H2 O administration were similar (∼15 min).

CONCLUSION

Administration of deuterated substrates via subcutaneous catheter for in vivo DMRS experiments with mice is robust, requires limited personnel training, and enables substantial dosing. It is suitable for metabolic studies where pseudo-steady state substrate administration/accumulation is sufficient. It is particularly advantageous for serial longitudinal studies over an extended period because it avoids inevitable damage to the tail vein following multiple catheterizations.

Deuterium Magnetic Resonance Spectroscopy Quantifies Tumor Fraction in a Mouse Model of a Mixed Radiation Necrosis / GL261-Glioblastoma Lesion

PURPOSE

Distinguishing recurrent brain tumor from treatment effects, including late time-to-onset radiation necrosis (RN), presents an on-going challenge in post-treatment imaging of neuro-oncology patients. Experiments were performed in a novel mouse model that recapitulates the relevant clinical histologic features of recurrent glioblastoma growing in a RN environment, the mixed tumor/RN model. The goal of this work was to apply single-voxel deuterium (2H) magnetic resonance spectroscopy (MRS), in concert with administration of deuterated glucose, to determine if the metabolic signature of aerobic glycolysis (Warburg effect: glucose → lactate in the presence of O2), a distinguishing characteristic of proliferating tumor, provides a quantitative readout of the tumor fraction (percent) in a mixed tumor/RN lesion.

PROCEDURES

2H MRS employed the SPin-ECho full-Intensity Acquired Localized (SPECIAL) MRS pulse sequence and outer volume suppression at 11.74 T. For each subject, a single 2H MRS voxel was placed over the mixed lesion as defined by contrast enhanced (CE) 1H T1-weighted MRI. Following intravenous administration of [6,6-2H2]glucose (Glc), 2H MRS monitored the glycolytic conversion to [3,3-2H2]lactate (Lac) and glutamate + glutamine (Glu + Gln = Glx).

RESULTS

Based on previous work, the tumor fraction of the mixed lesion was quantified as the ratio of tumor volume, defined by 1H magnetization transfer experiments, vs. the total mixed-lesion volume. Metabolite 2H MR spectral-amplitude values were converted to metabolite concentrations using the natural-abundance semi-heavy water (1HO2H) resonance as an internal concentration standard. The 2H MR-determined [Lac] / [Glx] ratio was strongly linearly correlated with tumor fraction in the mixed lesion (n = 9), Pearson's r = 0.87, and 77% of the variation in the [Lac] / [Glx] ratio was due to tumor percent r2 = 0.77.

CONCLUSIONS

This preclinical study supports the proposal that 2H MR could occupy a well-defined secondary role when standard-of-care 1H imaging is non-diagnostic regarding tumor presence and/or response to therapy.

Dual-tuned Coaxial-transmission-line RF coils for Hyperpolarized 13C and Deuterium 2H Metabolic MRS Imaging at Ultrahigh Fields

Objective

Information on the metabolism of tissues in healthy and diseased states plays a significant role in the detection and understanding of tumors, neurodegenerative diseases, diabetes, and other metabolic disorders. Hyperpolarized carbon-13 magnetic resonance imaging (13C-HPMRI) and deuterium metabolic imaging (2H-DMI) are two emerging X-nuclei used as practical imaging tools to investigate tissue metabolism. However due to their low gyromagnetic ratios (ɣ13C = 10.7 MHz/T; ɣ 2H = 6.5 MHz/T) and natural abundance, such method required a sophisticated dual-tuned radiofrequency (RF) coil.

Methods

Here, we report a dual-tuned coaxial transmission line (CTL) RF coil agile for metabolite information operating at 7T with independent tuning capability. The design analysis has demonstrated how both resonant frequencies can be individually controlled by simply varying the constituent of the design parameters.

Results

Numerical results have demonstrated a broadband tuning range capability, covering most of the X-nucleus signal, especially the 13C and 2H spectra at 7T. Furthermore, in order to validate the feasibility of the proposed design, both dual-tuned 1H/13C and 1H/2H CTLs RF coils are fabricated using a semi-flexible RG-405 .086" coaxial cable and bench test results (scattering parameters and magnetic field efficiency/distribution) are successfully obtained.

Conclusion

The proposed dual-tuned RF coils reveal highly effective magnetic field obtained from both proton and heteronuclear signal which is crucial for accurate and detailed imaging.

Significance

The successful development of this new dual-tuned RF coil technique would provide a tangible and efficient tool for ultrahigh field metabolic MR imaging.

Noninvasive assessment of metabolic turnover during inflammation by in vivo deuterium magnetic resonance spectroscopy

Background

Inflammation and metabolism exhibit a complex interplay, where inflammation influences metabolic pathways, and in turn, metabolism shapes the quality of immune responses. Here, glucose turnover is of special interest, as proinflammatory immune cells mainly utilize glycolysis to meet their energy needs. Noninvasive approaches to monitor both processes would help elucidate this interwoven relationship to identify new therapeutic targets and diagnostic opportunities.

Methods

For induction of defined inflammatory hotspots, LPS-doped Matrigel plugs were implanted into the neck of C57BL/6J mice. Subsequently, 1H/19F magnetic resonance imaging (MRI) was used to track the recruitment of 19F-loaded immune cells to the inflammatory focus and deuterium (2H) magnetic resonance spectroscopy (MRS) was used to monitor the metabolic fate of [6,6-2H2]glucose within the affected tissue. Histology and flow cytometry were used to validate the in vivo data.

Results

After plug implantation and intravenous administration of the 19F-containing contrast agent, 1H/19F MRI confirmed the infiltration of 19F-labeled immune cells into LPS-doped plugs while no 19F signal was observed in PBS-containing control plugs. Identification of the inflammatory focus was followed by i.p. bolus injection of deuterated glucose and continuous 2H MRS. Inflammation-induced alterations in metabolic fluxes could be tracked with an excellent temporal resolution of 2 min up to approximately 60 min after injection and demonstrated a more anaerobic glucose utilization in the initial phase of immune cell recruitment.

Conclusion

1H/2H/19F MRI/MRS was successfully employed for noninvasive monitoring of metabolic alterations in an inflammatory environment, paving the way for simultaneous in vivo registration of immunometabolic data in basic research and patients.

Deuterium brain imaging at 7T during D2 O dosing

PURPOSE

To characterize the (2 H) deuterium MR signal measured from human brain at 7T in participants loading with D2 O to ˜1.5% enrichment over a six-week period.

METHODS

2 H spectroscopy and imaging measurements were used to track the time-course of 2 H enrichment within the brain during the initial eight-hour loading period in two participants. Multi-echo gradient echo (MEGE) images were acquired at a range of TR values from four participants during the steady-state loading period and used for mapping 2 H T1 and T2 * relaxation times. Co-registration to higher resolution 1 H images allowed T1 and T2 * relaxation times of deuterium in HDO in cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM) to be estimated.

RESULTS

2 H concentrations measured during the eight-hour loading were consistent with values estimated from cumulative D2 O dose and body mass. Signal changes measured from three different regions of the brain during loading showed similar time-courses. After summing over echoes, gradient echo brain images acquired in 7.5 minutes with a voxel volume of 0.36 ml showed an SNR of ˜16 in subjects loaded to 1.5%. T1 -values for deuterium in HDO were significantly shorter than corresponding values for 1 H in H2 O, while T2 * values were similar. 2 H relaxation times in CSF were significantly longer than in GM or WM.

CONCLUSION

Deuterium MR Measurements at 7T were used to track the increase in concentration of 2 H in brain during heavy water loading. 2 H T1 and T2 * relaxation times from water in GM, WM, and CSF are reported.

Metabolic imaging with deuterium labeled substrates

Deuterium metabolic imaging (DMI) is an emerging clinically-applicable technique for the non-invasive investigation of tissue metabolism. The generally short T1 values of 2H-labeled metabolites in vivo can compensate for the relatively low sensitivity of detection by allowing rapid signal acquisition in the absence of significant signal saturation. Studies with deuterated substrates, including [6,6'-2H2]glucose, [2H3]acetate, [2H9]choline and [2,3-2H2]fumarate have demonstrated the considerable potential of DMI for imaging tissue metabolism and cell death in vivo. The technique is evaluated here in comparison with established metabolic imaging techniques, including PET measurements of 2-deoxy-2-[18F]fluoro-d-glucose (FDG) uptake and 13C MR imaging of the metabolism of hyperpolarized 13C-labeled substrates.

Deuterium metabolic imaging and hyperpolarized 13C-MRI of the normal human brain at clinical field strength reveals differential cerebral metabolism

Deuterium metabolic imaging (DMI) and hyperpolarized 13C-pyruvate MRI (13C-HPMRI) are two emerging methods for non-invasive and non-ionizing imaging of tissue metabolism. Imaging cerebral metabolism has potential applications in cancer, neurodegeneration, multiple sclerosis, traumatic brain injury, stroke, and inborn errors of metabolism. Here we directly compare these two non-invasive methods at 3 T for the first time in humans and show how they simultaneously probe both oxidative and non-oxidative metabolism. DMI was undertaken 1-2 h after oral administration of [6,6'-2H2]glucose, and 13C-MRI was performed immediately following intravenous injection of hyperpolarized [1-13C]pyruvate in ten and nine normal volunteers within each arm respectively. DMI was used to generate maps of deuterium-labelled water, glucose, lactate, and glutamate/glutamine (Glx) and the spectral separation demonstrated that DMI is feasible at 3 T. 13C-HPMRI generated maps of hyperpolarized carbon-13 labelled pyruvate, lactate, and bicarbonate. The ratio of 13C-lactate/13C-bicarbonate (mean 3.7 ± 1.2) acquired with 13C-HPMRI was higher than the equivalent 2H-lactate/2H-Glx ratio (mean 0.18 ± 0.09) acquired using DMI. These differences can be explained by the route of administering each probe, the timing of imaging after ingestion or injection, as well as the biological differences in cerebral uptake and cellular physiology between the two molecules. The results demonstrate these two metabolic imaging methods provide different yet complementary readouts of oxidative and reductive metabolism within a clinically feasible timescale. Furthermore, as DMI was undertaken at a clinical field strength within a ten-minute scan time, it demonstrates its potential as a routine clinical tool in the future.

Emerging methods and applications of ultra-high field MR spectroscopic imaging in the human brain

Magnetic Resonance Spectroscopic Imaging (MRSI) of the brain enables insights into the metabolic changes and fluxes in diseases such as tumors, multiple sclerosis, epilepsy, or hepatic encephalopathy, as well as insights into general brain functionality. However, the routine application of MRSI is mostly hampered by very low signal-to-noise ratios (SNR) due to the low concentrations of metabolites, about 10000 times lower than water. Furthermore, MRSI spectra have a dense information content with many overlapping metabolite resonances, especially for proton MRSI. MRI scanners at ultra-high field strengths, like 7 T or above, offer the opportunity to increase SNR, as well as the separation between resonances, thus promising to solve both challenges. Yet, MRSI at ultra-high field strengths is challenged by decreased B0- and B1-homogeneity, shorter T2 relaxation times, stronger chemical shift displacement errors, and aggravated lipid contamination. Therefore, to capitalize on the advantages of ultra-high field strengths, these challenges must be overcome. This review focuses on the challenges MRSI of the human brain faces at ultra-high field strength, as well as the possible applications to this date.

Proton/Deuterium Magnetic Resonance Imaging of Rodents at 9.4T Using Birdcage Coils

The purpose of the present study was to fabricate a volume coil for proton/deuterium magnetic resonance imaging (MRI) in rodents at 9.4 T. Two birdcage radiofrequency (RF) coils have been designed for proton/deuterium MRI: the rungs of two concentric birdcages were azimuthally interleaved with each other for better decoupling, and the two coils were tuned to 400.3 and 61.4 MHz for ¹ H/² H resonance at 9.4 T. Compared to a commercially available coil, the proposed ¹ H/² H RF coil provides reasonable transmission efficiency and imaging signal-to-noise ratio (SNR); the relationships among imaging parameters such as SNR, voxel size, and deuterium oxide concentrations have been quantitatively studied, and the linear correlation results together with the spectroscopic data in vivo indicate its feasibility in deuterium metabolic imaging (DMI) in vivo. Our study indicates that using the birdcage design for MRI signal excitation combined with surface coil array for signal reception can facilitate DMI investigations more effectively towards future pre-clinical and clinical applications. As a noninvasive method by measuring nonhydrogen nuclear deuterium signals to reflect metabolite information, DMI will feature prominently in future precision medicine through the whole process of diagnosis, treatment, and prognosis. © 2021 Bioelectromagnetics Society.

Residual quadrupolar couplings observed in 7 Tesla deuterium MR spectra of skeletal muscle

Purpose

Deuterium metabolic imaging could potentially be used to investigate metabolism in skeletal muscle noninvasively. However, skeletal muscle is a tissue with a high degree of spatial organization. In this study, we investigated the effect of incomplete motional averaging on the naturally abundant deuterated water signal in 7 Tesla deuterium spectra of the lower leg muscles and the dependence on the angle between the muscle fibers and the main magnetic field B₀, as determined by DTI.

Methods

Natural abundance deuterium MRSI measurements of the right lower leg muscles were performed at 7 Tesla. Three subjects were scanned in a supine position, with the right leg parallel with the B₀ field. One subject was scanned twice; during the second scan, the subject was laying on his right side and the right knee was bent such that the angle between the right lower leg and B₀ was approximately 45°. DTI was performed in the same subjects in the same positions at 3 Tesla to determine muscle fiber angles.

Results

We observed splittings in the natural abundance deuterated water signal. The size of the splittings varied between different muscles in the lower leg but were mostly similar among subjects for each muscle. The splittings depended on the orientation of the muscle fibers with respect to the main magnetic field B₀.

Conclusion

Partial molecular alignment in skeletal muscle leads to residual deuteron quadrupolar couplings in deuterated water, the size of which depends on the angle between the muscle fibers and B₀.

Deuterium MRSI characterizations of glucose metabolism in orthotopic pancreatic cancer mouse models

Detecting and mapping metabolism in tissues represents a major step in detecting, characterizing, treating and understanding cancers. Recently introduced deuterium metabolic imaging techniques could offer a noninvasive route for the metabolic imaging of animals and humans, based on using ² H magnetic resonance spectroscopic imaging (MRSI) to detect the uptake of deuterated glucose and the fate of its metabolic products. In this study, ² H_6,6' -glucose was administered to mice cohorts that had been orthotopically implanted with two different models of pancreatic ductal adenocarcinoma (PDAC), involving PAN-02 and KPC cell lines. As the tumors grew, ² H_6,6' -glucose was administered as bolii into the animals' tail veins, and ² H MRSI images were recorded at 15.2 T. 2D phase-encoded chemical shift imaging experiments could detect a signal from this deuterated glucose immediately after the bolus injection for both the PDAC models, reaching a maximum in the animals' tumors ~ 20 min following administration, and nearly total decay after ~ 40 min. The main metabolic reporter of the cancers was the ² H_3,3' -lactate signal, which MRSI could detect and localize on the tumors when these were 5 mm or more in diameter. Lactate production time traces varied slightly with the animal and tumor model, but in general lactate peaked at times of 60 min or longer following injection, reaching concentrations that were ~ 10-fold lower than those of the initial glucose injection. This ² H_3,3' -lactate signal was only visible inside the tumors. ² H-water could also be detected as deuterated glucose's metabolic product, increasing throughout the entire time course of the experiment from its ≈10 mM natural abundance background. This water resonance could be imaged throughout the entire abdomen of the animals, including an enhanced presence in the tumor, but also in other organs like the kidney and bladder. These results suggest that deuterium MRSI may serve as a robust, minimally invasive tool for the monitoring of metabolic activity in pancreatic tumors, capable of undergoing clinical translation and supporting decisions concerning treatment strategies. Comparisons with in vivo metabolic MRI experiments that have been carried out in other animal models are presented and their differences/similarities are discussed.

Deuterium Metabolic Imaging-Rediscovery of a Spectroscopic Tool

The growing demand for metabolism-specific imaging techniques has rekindled interest in Deuterium (2H) Metabolic Imaging (DMI), a robust method based on administration of a substrate (glucose, acetate, fumarate, etc.) labeled with the stable isotope of hydrogen and the observation of its metabolic fate in three-dimensions. This technique allows the investigation of multiple metabolic processes in both healthy and diseased states. Despite its low natural abundance, the short relaxation time of deuterium allows for rapid radiofrequency (RF) pulses without saturation and efficient image acquisition. In this review, we provide a comprehensive picture of the evolution of DMI over the course of recent decades, with a special focus on its potential clinical applications.

Improving deuterium metabolic imaging (DMI) signal-to-noise ratio by spectroscopic multi-echo bSSFP: A pancreatic cancer investigation

PURPOSE

Deuterium metabolic imaging (DMI) maps the uptake of deuterated precursors and their conversion into lactate and other markers of tumor metabolism. Even after leveraging ² H's short T₁ s, DMI's signal-to-noise ratio (SNR) is limited. We hypothesize that a multi-echo balanced steady-state free precession (ME-bSSFP) approach would increase SNR compared to chemical shift imaging (CSI), while achieving spectral isolation of the metabolic precursors and products.

METHODS

Suitably tuned ² H ME-bSSFP (five echo times [TEs], ΔTE = 2.2 ms, repetition time [TR]/flip-angle = 12 ms/60°) was implemented at 15.2T and compared to CSI (TR/flip-angle = 95 ms/90°) regarding SNR and spectral isolation, in simulations, in deuterated phantoms and for the in vivo diagnosis of a mouse tumor model of pancreatic adenocarcinoma (N = 10).

RESULTS

Simulations predicted an SNR increase vs. CSI of 3-5, and that the peaks of ² H-water, ² H_6,6' -glucose, and ² H_3,3' -lactate can be well isolated by ME-bSSFP; phantoms confirmed this. In vivo, at equal spatial resolution (1.25 × 1.25 mm² ) and scan time (10 min), ² H_6,6' -glucose's and ² H_3,3' -lactate's SNR were indeed higher for bSSFP than for CSI, three-fold for glucose (57 ± 30 vs. 19 ± 11, P < .001), doubled for water (13 ± 5 vs. 7 ± 3, P = .005). The time courses and overall localization of all metabolites agreed well, comparing CSI against ME-bSSFP. However, a clearer localization of glucose in kidneys and bladder, the detection of glucose-avid rims in certain tumors, and a heterogeneous pattern of intra-tumor lactate production could only be observed using ME-bSSFP's higher resolution.

CONCLUSIONS

ME-bSSFP provides greater SNR per unit time than CSI, providing for higher spatial resolution mapping of glucose uptake and lactate production in tumors.

Deuterium Magnetic Resonance Imaging and the Discrimination of Fetoplacental Metabolism in Normal and L-NAME-Induced Preeclamptic Mice

Recent magnetic resonance studies in healthy and cancerous organs have concluded that deuterated metabolites possess highly desirable properties for mapping non-invasively and, as they happen, characterizing glycolysis and other biochemical processes in animals and humans. A promising avenue of this deuterium metabolic imaging (DMI) approach involves looking at the fate of externally administered ²H_6,6′-glucose, as it is taken up and metabolized into different products as a function of time. This study employs deuterium magnetic resonance to follow the metabolism of wildtype and preeclamptic pregnant mice models, focusing on maternal and fetoplacental organs over ≈2 h post-injection. ²H_6,6′-glucose uptake was observed in the placenta and in specific downstream organs such as the fetal heart and liver. Main metabolic products included ²H_3,3′-lactate and ²H-water, which were produced in individual fetoplacental organs with distinct time traces. Glucose uptake in the organs of most preeclamptic animals appeared more elevated than in the control mice (p = 0.02); also higher was the production of ²H-water arising from this glucose. However, the most notable differences arose in the ²H_3,3′-lactate concentration, which was ca. two-fold more abundant in the placenta (p = 0.005) and in the fetal (p = 0.01) organs of preeclamptic-like animals, than in control mice. This is consistent with literature reports about hypoxic conditions arising in preeclamptic and growth-restricted pregnancies, which could lead to an enhancement in anaerobic glycolysis. Overall, the present measurements suggest that DMI, a minimally invasive approach, may offer new ways of studying and characterizing health and disease in mammalian pregnancies, including humans.

Deuterium metabolic imaging - Back to the future

Deuterium metabolic spectroscopy (DMS) and imaging (DMI) have recently been described as simple and robust MR-based methods to map metabolism with high temporal and/or spatial resolution. The metabolic fate of a wide range of suitable deuterated substrates, including glucose and acetate, can be monitored with deuterium MR methods in which the favorable MR characteristics of deuterium prevent many of the complications that hamper other techniques. The short T₁ relaxation times lead to good MR sensitivity, while the low natural abundance prevents the need for water or lipid suppression. The sparsity of the deuterium spectra in combination with the low resonance frequency provides relative immunity to magnetic field inhomogeneity. Taken together, these features combine into a highly robust metabolic imaging method that has strong potential to become a dominant MR research tool and a viable clinical imaging modality. This perspective reviews the history of deuterium as a metabolic tracer, the use of NMR as a detection method for deuterium in vitro and in vivo and the recent development of DMS and DMI. Following a review of the NMR characteristics and the biological effects of deuterium, the promising future of DMI is outlined.