Deuterium body array for the simultaneous measurement of hepatic and renal glucose metabolism and gastric emptying with dynamic 3D deuterium metabolic imaging at 7 T

3D deuterium metabolic imaging (DMI) of the human liver at 7 T using low-rank and subspace model-based reconstruction

PURPOSE

To implement a low-rank and subspace model-based reconstruction for 3D deuterium metabolic imaging (DMI) and compare its performance against Fourier transform-based (FFT) reconstruction in terms of spectral fitting reliability.

METHODS

Both reconstruction methods were applied on simulated and experimental DMI data. Numerical simulations were performed to evaluate the effect of increasing acceleration factors. The impact on spectral fitting results, SNR, and the overall normalized root mean square error (NRMSE) compared to ground-truth data were calculated. A comparative analysis was performed on DMI data acquired from the human liver, including both natural abundance and post-deuterated glucose intake data at 7 T.

RESULTS

Simulation showed the Cramer-Rao lower bound [%] of water, glucose, sum of glutamate and glutamine (Glx), and lipid signals for the low-rank and subspace model-based reconstruction at R = 1.0 was 12.4, 14.7, 17.3, and 11.0 times lower than FFT. At R = 1.1, NRMSE was 1.4%, 1.3%, 0.8%, and 4.2% lower for the water, glucose, Glx, and lipid, respectively, compared to FFT. However, the NRMSE of the Glx and lipid increased by 0.4% and 3.2% at R = 1.3. For the in vivo DMI experiment, SNR was 2.5-3.0 times higher compared to FFT. The fitted amplitude of water and glucose peaks showed Cramer-Rao lower bound [%] values that were approximately 2.3 times lower than FFT.

CONCLUSION

Simulations and in vivo experiments on the human liver demonstrate that low-rank and subspace model-based reconstruction with undersampled data mitigates noise and enhances spectral fitting quality.

Deuterium MRS for In Vivo Measurement of Lipogenesis in the Liver

Hepatic de novo lipogenesis (DNL) plays a key role in the pathogenesis of several metabolic diseases that affect the liver. In humans, the detection of deuterium (2H) in triglycerides from very low density lipoprotein collected from blood after administration of deuterated water (D2O) is commonly used as an indirect estimate of hepatic DNL. Here, we tested in rats (1) the feasibility to detect 2H-labeling directly in liver lipids in vivo by using noninvasive 2H MRS and (2) to what extent these results correlated with the gold standard measurement of DNL in excised liver tissue. To increase hepatic DNL, half of the animals (n = 4) underwent a 7-week dietary intervention in which fructose was provided in drinking water. Deuterium MRS data were acquired from a single voxel placed in the liver. In vivo 2H MRS data showed 2H-labeling in the combined peak of methyl and methylene resonances after 1 week of administrati NBM_70014 on of 5% D2O as drinking water. DNL was calculated using 1H and 2H NMR data acquired from extracted lipids of excised liver tissue. The 2H lipid level measured in vivo correlated with the ex vivo estimates of hepatic DNL (r = 0.81, p = 0.016). These results demonstrate the feasibility of direct detection of deuterium labeling in liver lipids using localized 2H MRS in vivo and indicate the potential of this approach to measure hepatic DNL. These initial observations provide a basis for the method to be translated and to develop noninvasive, quantitative measurements of hepatic DNL in humans.

Deuterium Metabolic Imaging of the Human Abdomen at Clinical Field Strength

OBJECTIVES

The aim of the study was to translate abdominal deuterium metabolic imaging (DMI) to clinical field strength by optimizing the radiofrequency coil setup, the administered dose of deuterium (2H)-labeled glucose, and the data processing pipeline for quantitative characterization of DMI signals over time. This was assessed in the kidney and liver to establish a basis for routine clinical studies in the future.

MATERIALS AND METHODS

5 healthy volunteers were recruited and imaged on 2 or 3 separate occasions, with varying doses of 2H-glucose: 0.75 g/kg (high dose), 0.50 g/kg (medium dose), and 0.25 g/kg (low dose), resulting in a total of 13 DMI scan sessions. DMI was performed at 3 T using a flexible 20 × 30 cm2 2H-tuned transmit-receive surface coil. For quantitative comparisons across scans, the 2H-glucose signal was normalized against the sum of 2H-glucose and 2H-water (GGW ratio). To quantify the time course of GGW, 3 novel metrics of metabolism were defined and compared between doses and organs: the maximum value across the time course (GGWmax), the sum over the whole time course (GGWAUC), and the average signal across a defined plateau (GGWmean plateau). The 2H-lipid signal overlaps with 2H-lactate; hence, the 2 signals were measured as the combined 2H-lipid+lactate signal.

RESULTS

The careful positioning of a dedicated surface coil minimized unwanted gastric signals while maintaining excellent hepatic and renal measurements. The time courses derived from the liver and kidney were reproducible and comparable across different doses, showing the potential for dose reduction. The signal from the liver plateaued at approximately 30 minutes, and that from the kidney at approximately 40 minutes. The liver exhibited higher quantitative values for 2H-glucose uptake compared to the kidney, a trend consistent across all 3 quantitative metrics and doses, for example, for the highest dose: GGWAUC liver = 31 ± 3; GGWAUC kidney = 27 ± 3; P = 0.05. A trend toward lower quantitative measurements with decreasing dose was observed: this was significant between the high and the low dose for all 3 parameters and between the medium and low dose for GGWmean plateau and GGWAUC, but was not significant between the high and the medium dose for any of the 3 parameters. The hepatic 2H-lipid+lactate signal increased over 70-90 minutes in 12/13 cases (mean: 39 ± 24%), while the renal lipid+lactate signal increased in only 8/13 cases (mean: 5 ± 17%). The hepatic 2H-water signal increased in all 13 cases (mean: 18 ± 10%), and the renal 2H-water signal increased in only 10/13 cases (mean: 10 ± 13%).

CONCLUSIONS

DMI of the human abdomen is feasible using a clinical magnetic resonance imaging system and the signal changes measured in the kidney and liver can serve as a reference for future clinical studies. The 2H-glucose dose can be reduced from 0.75 to 0.50 g/kg to minimize gastric signal without substantially affecting the reliability of organ quantification. The increase in 2H-lipid+lactate or 2H-water signal over time could serve as direct and indirect measures of metabolism, respectively.

Development of a Double Tuned 2H/31P Whole-Body Birdcage Transmit Coil for 2H and 31P MR Applications From Head to Toe at 7 T

Deuterium (2H) and phosphorus (31P) magnetic resonance spectroscopy (MRS) are complementary methods for evaluating tissue metabolism noninvasively in vivo. Combined 2H and 31P MRS would therefore be of interest for various applications, from cancer to diabetes. Loop coils are commonly used in X-nuclei studies in the human body for both transmit and receive. However, loop coils suffer from limited penetration depth and inhomogeneous B1 + field. The purpose of this work is to develop a double tuned 2H/31P whole-body birdcage transmit coil for 7 T for 2H and 31P MRS imaging (MRSI) with homogeneous excitation over a large field-of-view. The performance of the 2H/31P birdcage coil was assessed on B1 + fields over a body-sized phantom at 2H and 31P frequencies using an 8-channel 2H/31P receive array. Using two elements of the 2H/31P receive array, natural abundance 2H and 31P 3D MRSI data at rest were acquired consecutively in the brain and lower leg muscles. Additionally, 2H and 31P 3D MRSI data were acquired from one volunteer 90 min after [6,6'-2H2]-glucose intake, using 8-channel 2H/31P receive array around the abdomen. The B1 + variation of the whole-body birdcage coil over the phantom was 12.1% for 2H and 19.2% for 31P. High-quality 2H and 31P 3D MRSI data were acquired from the brain and the lower leg. Whole liver coverage was achieved in both 2H and 31P 3D MRSI data. The developed 2H/31P whole-body birdcage transmit coil allows simultaneous 3D mapping of glucose and energy metabolism and membrane turnover throughout the human body.

Evaluation of Hepatic Glucose and Palmitic Acid Metabolism in Rodents on High-Fat Diet Using Deuterium Metabolic Imaging

BACKGROUND

One of the main features of several metabolic disorders is dysregulation of hepatic glucose and lipid metabolism. Deuterium metabolic imaging (DMI) allows for assessing the uptake and breakdown of 2H-labeled substrates, giving specific insight into nutrient processing in healthy and diseased organs. Thus, DMI could be a useful approach for analyzing the differences in liver metabolism of healthy and diseased subjects to gain a deeper understanding of the alterations related to metabolic disorders.

PURPOSE

Evaluating the feasibility of DMI as a tool for the assessment of metabolic differences in rodents with healthy and fatty livers (FLs).

STUDY TYPE

Animal Model.

POPULATION

18 male Sprague Dawley rats on standard (SD, n = 9, healthy) and high-fat diet (HFD, n = 9, FL disease).

FIELD STRENGTH/SEQUENCE

Phase-encoded 1D pulse-acquire sequence and anatomy co-registered phase-encoded 3D pulse-acquire chemical shift imaging for 2H at 9.4T.

ASSESSMENT

Localized and nonlocalized liver spectroscopy was applied at eight time points over 104 minutes post injection. The obtained spectra were preprocessed and quantified using jMRUI (v7.0) and the resulting amplitudes translated to absolute concentration (mM) according to the 2H natural abundance water peak.

STATISTICAL TESTS

Two-way repeated measures ANOVA were employed to assess between-group differences, with statistical significance at P < 0.05.

RESULTS

DMI measurements demonstrated no significant difference (P = 0.98) in the uptake of [6,6'-2H2]glucose between healthy and impaired animals (AUCSD = 1966.0 ± 151.5 mM - minutes vs. AUCHFD = 2027.0 ± 167.6 mM·minutes). In the diseased group, the intrahepatic uptake of palmitic acid d-31 was higher (AUCHFD = 57.4 ± 17.0 mM·minutes, AUCSD = 33.3 ± 10.5 mM·minutes), but without statistical significance owing to substantial in-group variation (P = 0.73).

DATA CONCLUSION

DMI revealed higher concentrations of palmitic acid in rats with FL disease and no difference in hepatic glucose concentration between healthy and impaired animals. Thus, DMI appears to be a useful tool for evaluating metabolism in rodents with FL disease.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Deuterium Metabolic Imaging Enables the Tracing of Substrate Fluxes Through the Tricarboxylic Acid Cycle in the Liver

Alterations in tricarboxylic acid (TCA) cycle metabolism are associated with hepatic metabolic disorders. Elevated hepatic acetate concentrations, often attributed to high caloric intake, are recognized as a pivotal factor in the etiology of obesity and metabolic syndrome. Therefore, the assessment of acetate breakdown and TCA cycle activity plays a central role in understanding the impact of diet-induced alterations on liver metabolism. Magnetic resonance-based deuterium metabolic imaging (DMI) could help to unravel the underlying mechanisms involved in disease development and progression, however, the application of conventional deuterated glucose does not lead to substantial enrichment in hepatic glutamine and glutamate. This study aimed to demonstrate the feasibility of DMI for tracking deuterated acetate breakdown via the TCA cycle in lean and diet-induced fatty liver (FL) rats using 3D DMI after an intraperitoneal infusion of sodium acetate-d3 at 9.4T. Localized and nonlocalized liver spectra acquired at 10 time points post-injection over a 130-min study revealed similar intrahepatic acetate uptake in both animal groups (AUCFL = 717.9 ± 131.1 mM▯min-1, AUClean = 605.1 ± 119.9 mM▯min-1, p = 0.62). Metabolic breakdown could be observed in both groups with an emerging glutamine/glutamate (Glx) peak as a downstream metabolic product (AUCFL = 113.6 ± 23.8 mM▯min-1, AUClean = 136.7 ± 41.7 mM▯min-1, p = 0.68). This study showed the viability of DMI for tracking substrate flux through the TCA cycle, underscoring its methodological potential for imaging metabolic processes in the body.

Interleaved trinuclear MRS for single-session investigation of carbohydrate and lipid metabolism in human liver at 7T

The liver plays a central role in metabolic homeostasis, as exemplified by a variety of clinical disorders with hepatic and systemic metabolic disarrays. Of particular interest are the complex interactions between lipid and carbohydrate metabolism in highly prevalent conditions such as obesity, diabetes, and fatty liver disease. Limited accessibility and the need for invasive procedures challenge direct investigations in humans. Hence, noninvasive dynamic evaluations of glycolytic flux and steady-state assessments of lipid levels and composition are crucial for basic understanding and may open new avenues toward novel therapeutic targets. Here, three different MR spectroscopy (MRS) techniques that have been combined in a single interleaved examination in a 7T MR scanner are evaluated. 1H-MRS and 13C-MRS probe endogenous metabolites, while deuterium metabolic imaging (DMI) relies on administration of deuterated tracers, currently 2H-labelled glucose, to map the spatial and temporal evolution of their metabolic fate. All three techniques have been optimized for a robust single-session clinical investigation and applied in a preliminary study of healthy subjects. The use of a triple-channel 1H/2H/13C RF coil enables interleaved examinations with no need for repositioning. Short-echo-time STEAM spectroscopy provides well resolved spectra to quantify lipid content and composition. The relative benefits of using water saturation versus metabolite cycling and types of respiratory synchronization were evaluated. 2H-MR spectroscopic imaging allowed for registration of time- and space-resolved glucose levels following oral ingestion of 2H-glucose, while natural abundance 13C-MRS of glycogen provides a dynamic measure of hepatic glucose storage. For DMI and 13C-MRS, the measurement precision of the method was estimated to be about 0.2 and about 16 mM, respectively, for 5 min scanning periods. Excellent results were shown for the determination of dynamic uptake of glucose with DMI and lipid profiles with 1H-MRS, while the determination of changes in glycogen levels by 13C-MRS is also feasible but somewhat more limited by signal-to-noise ratio.

Glucose versus fructose metabolism in the liver measured with deuterium metabolic imaging

Chronic intake of high amounts of fructose has been linked to the development of metabolic disorders, which has been attributed to the almost complete clearance of fructose by the liver. However, direct measurement of hepatic fructose uptake is complicated by the fact that the portal vein is difficult to access. Here we present a new, non-invasive method to measure hepatic fructose uptake and metabolism with the use of deuterium metabolic imaging (DMI) upon administration of [6,6'-²H₂]fructose. Using both [6,6'-²H₂]glucose and [6,6'-²H₂]fructose, we determined differences in the uptake and metabolism of glucose and fructose in the mouse liver with dynamic DMI. The deuterated compounds were administered either by fast intravenous (IV) bolus injection or by slow IV infusion. Directly after IV bolus injection of [6,6'-²H₂]fructose, a more than two-fold higher initial uptake and subsequent 2.5-fold faster decay of fructose was observed in the mouse liver as compared to that of glucose after bolus injection of [6,6'-²H₂]glucose. In contrast, after slow IV infusion of fructose, the ²H fructose/glucose signal maximum in liver spectra was lower compared to the ²H glucose signal maximum after slow infusion of glucose. With both bolus injection and slow infusion protocols, deuterium labeling of water was faster with fructose than with glucose. These observations are in line with a higher extraction and faster turnover of fructose in the liver, as compared with glucose. DMI with [6,6'-²H₂]glucose and [6,6'-²H₂]fructose could potentially contribute to a better understanding of healthy human liver metabolism and aberrations in metabolic diseases.

Deuterium echo-planar spectroscopic imaging (EPSI) in the human liver in vivo at 7 T

PURPOSE

To demonstrate the feasibility of deuterium echo-planar spectroscopic imaging (EPSI) to accelerate 3D deuterium metabolic imaging in the human liver at 7 T.

METHODS

A deuterium EPSI sequence, featuring a Hamming-weighted k-space acquisition pattern for the phase-encoding directions, was implemented. Three-dimensional deuterium EPSI and conventional MRSI were performed on a water/acetone phantom and in vivo in the human liver at natural abundance. Moreover, in vivo deuterium EPSI measurements were acquired after oral administration of deuterated glucose. The effect of acquisition time on SNR was evaluated by retrospectively reducing the number of averages.

RESULTS

The SNR of natural abundance deuterated water signal in deuterium EPSI was 6.5% and 5.9% lower than that of MRSI in the phantom and in vivo experiments, respectively. In return, the acquisition time of in vivo EPSI data could be reduced retrospectively to 2 min, beyond the minimal acquisition time of conventional MRSI (of 20 min in this case), while still leaving sufficient SNR. Three-dimensional deuterium EPSI, after administration of deuterated glucose, enabled monitoring of hepatic glucose dynamics with full liver coverage, a spatial resolution of 20 mm isotropic, and a temporal resolution of 9 min 50 s, which could retrospectively be shortened to 2 min.

CONCLUSION

In this work, we demonstrate the feasibility of accelerated 3D deuterium metabolic imaging of the human liver using deuterium EPSI. The acceleration obtained with EPSI can be used to increase temporal and/or spatial resolution, which will be valuable to study tissue metabolism of deuterated compounds over time.