Frequency-specific SSFP for hyperpolarized C metabolic imaging at 14.1 T

Metabolic imaging of hyperpolarized [1-¹³C] pyruvate co-polarized with [¹³C]urea by dynamic nuclear polarization with rapid dissolution is a promising new method for assessing tumor metabolism and perfusion simultaneously in vivo. Novel pulse sequences are required to enable dynamic imaging of multiple ¹³C spectral lines with high spatiotemporal resolution. The goal of this study was to investigate a new frequency-specific approach for rapid metabolic imaging of multiple ¹³C resonances using the spectral selectivity of steady-state free precession pulse (SSFP) trains. Methods developed in simulations were implemented in a dynamic frequency-cycled balanced SSFP pulse sequence on a 14.1-T animal magnetic resonance imaging scanner. This acquisition was tested in thermal and hyperpolarized phantom imaging studies and in a transgenic mouse with prostate cancer.     

Pulse sequence for dynamic volumetric imaging of hyperpolarized metabolic products

Dynamic nuclear polarization and dissolution of a ¹³C-labeled substrate enables the dynamic imaging of cellular metabolism. Spectroscopic information is typically acquired, making the acquisition of dynamic volumetric data a challenge. To enable rapid volumetric imaging, a spectral-spatial excitation pulse was designed to excite a single line of the carbon spectrum. With only a single resonance present in the signal, an echo-planar readout trajectory could be used to resolve spatial information, giving full volume coverage of 32 × 32 × 16 voxels every 3.5 s. This high frame rate was used to measure the different lactate dynamics in different tissues in a normal rat model and a mouse model of prostate cancer.     

Fast volumetric spatial-spectral MR imaging of hyperpolarized C-labeled compounds using multiple echo 3D bSSFP

Purpose

The goal of this work was to develop a fast 3D chemical shift imaging technique for the noninvasive measurement of hyperpolarized ¹³C-labeled substrates and metabolic products at low concentration.

Materials and Methods

Multiple echo 3D balanced steady state magnetic resonance imaging (ME-3DbSSFP) was performed in vitro on a syringe containing hyperpolarized [1,3,3-2H3; 1-¹³C]2-hydroxyethylpropionate (HEP) adjacent to a ¹³C-enriched acetate phantom, and in vivo on a rat before and after intravenous injection of hyperpolarized HEP at 1.5 T. Chemical shift images of the hyperpolarized HEP were derived from the multiple echo data by Fourier transformation along the echoes on a voxel by voxel basis for each slice of the 3D data set.

Results

ME-3DbSSFP imaging was able to provide chemical shift images of hyperpolarized HEP in vitro, and in a rat with isotropic 7-mm spatial resolution, 93 Hz spectral resolution and 16-s temporal resolution for a period greater than 45 s.

Conclusion

Multiple echo 3D bSSFP imaging can provide chemical shift images of hyperpolarized ¹³C-labeled compounds in vivo with relatively high spatial resolution and moderate spectral resolution. The increased signal-to-noise ratio of this 3D technique will enable the detection of hyperpolarized ¹³C-labeled metabolites at lower concentrations as compared to a 2D technique.     

Analysis of hyperpolarized dynamic C lactate imaging in a transgenic mouse model of prostate cancer

This study investigated the application of an acquisition that selectively excites the [1-¹³C]lactate resonance and allows dynamic tracking of the conversion of ¹³C-lactate from hyperpolarized ¹³C-pyruvate at a high spatial resolution. In order to characterize metabolic processes occurring in a mouse model of prostate cancer, 20 sequential 3D images of ¹³C-lactate were acquired 5 s apart using a pulse sequence that incorporated a spectral–spatial excitation pulse and a flyback echo-planar readout to track the time course of newly converted ¹³C-lactate after injection of prepolarized ¹³C-pyruvate. The maximum lactate signal (MLS), full-width half-maximum (FWHM), time to the peak ¹³C-lactate signal (TTP) and area under the dynamic curve were calculated from the dynamic images of 10 TRAMP mice and two wild-type controls. The regional variation in ¹³C-lactate associated with the injected pyruvate was demonstrated by the peak of the ¹³C-lactate signal occurring earlier in the kidney than in the tumor region. The intensity of the dynamic ¹³C-lactate curves also varied spatially within the tumor, illustrating the heterogeneity in metabolism that was most prominent in more advanced stages of disease development. The MLS was significantly higher in TRAMP mice that had advanced disease.     

Feasibility of using hyperpolarized [1-13C]lactate as a substrate for in vivo metabolic 13C MRSI studies

The development of dynamic nuclear polarization in solution has enabled in vivo 13C MR studies at high signal-to-noise ratio following injection of prepolarized 13C substrates. While prior studies have demonstrated the ability to observe metabolism following injection of hyperpolarized 13C pyruvate, the goal of this study was to develop and test a new hyperpolarized agent for investigating in vivo metabolism, [1-13C]lactate. A preparation for prepolarized 13C lactate and the requisite dissolution media were developed to investigate the feasibility for in vivo 13C MRS/MRSI studies following injection of this hyperpolarized agent. This study demonstrated, for the first time, not only the ability to detect hyperpolarized [1-13C]lactate in vivo but also the metabolic products 13C pyruvate, 13C alanine and 13C bicarbonate following injection in normal rats. The use of 13C lactate as a substrate provided the opportunity to study the conversion of lactate to pyruvate in vivo and to detect the secondary conversions to alanine and bicarbonate through pyruvate. This study also demonstrated the potential value of this hyperpolarized agent to investigate in vivo lactate uptake and metabolism in preclinical animal models.     

Investigating tumor perfusion and metabolism using multiple hyperpolarized (13)C compounds: HP001, pyruvate and urea

The metabolically inactive hyperpolarized agents HP001 (bis-1,1-(hydroxymethyl)-[1-(13)C]cyclopropane-d(8)) and urea enable a new type of perfusion magnetic resonance imaging based on a direct signal source that is background-free. The addition of perfusion information to metabolic information obtained by spectroscopic imaging of hyperpolarized [1-(13)C]pyruvate would be of great value in exploring the relationship between perfusion and metabolism in cancer. In preclinical normal murine and cancer model studies, we performed both dynamic multislice imaging of the specialized hyperpolarized perfusion compound HP001 (T(1)=95 s ex vivo, 32 s in vivo at 3 T) using a pulse sequence with balanced steady-state free precession and ramped flip angle over time for efficient utilization of the hyperpolarized magnetization and three-dimensional echo-planar spectroscopic imaging of urea copolarized with [1-(13)C]pyruvate, with compressed sensing for resolution enhancement. For the dynamic data, peak signal maps and blood flow maps derived from perfusion modeling were generated. The spatial heterogeneity of perfusion was increased 2.9-fold in tumor tissues (P=.05), and slower washout was observed in the dynamic data. The results of separate dynamic HP001 imaging and copolarized pyruvate/urea imaging were compared. A strong and significant correlation (R=0.73, P=.02) detected between the urea and HP001 data confirmed the value of copolarizing urea with pyruvate for simultaneous assessment of perfusion and metabolism.     

Design of spectral-spatial outer volume suppression RF pulses for tissue specific metabolic characterization with hyperpolarized C pyruvate

[1-¹³C] pyruvate pre-polarized via DNP has been used in animal models to probe changes in metabolic enzyme activities in vivo. To more accurately assess the metabolic state and its change from disease progression or therapy in a specific region or tissue in vivo, it may be desirable to separate the downstream ¹³C metabolite signals resulting from the metabolic activity within the tissue of interest and those brought into the tissue by perfusion. In this study, a spectral-spatial saturation pulse that selectively saturates the signal from the metabolic products [1-¹³C] lactate and [1-¹³C] alanine was designed and implemented as outer volume suppression for localized MRSI acquisition. Preliminary in vivo results showed that the suppression pulse did not prevent the pre-polarized pyruvate from being delivered throughout the animal while it saturated the metabolites within the targeted saturation region.     

Application of double spin echo spiral chemical shift imaging to rapid metabolic mapping of hyperpolarized [1-¹³C]-pyruvate

Undersampled spiral CSI (spCSI) using a free induction decay (FID) acquisition allows sub-second metabolic imaging of hyperpolarized 13C. Phase correction of the FID acquisition can be difficult, especially with contributions from aliased out-of-phase peaks. This work extends the spCSI sequence by incorporating double spin echo radiofrequency (RF) pulses to eliminate the need for phase correction and obtain high quality spectra in magnitude mode. The sequence also provides an added benefit of attenuating signal from flowing spins, which can otherwise contaminate signal in the organ of interest. The refocusing pulses can potentially lead to a loss of hyperpolarized magnetization in dynamic imaging due to flow of spins through the fringe field of the RF coil, where the refocusing pulses fail to provide complete refocusing. Care must be taken for dynamic imaging to ensure that the spins remain within the B?-homogeneous sensitive volume of the RF coil.     

Time resolved spectroscopic NMR imaging using hyperpolarized Xe

We have visualized the melting and dissolution processes of xenon (Xe) ice into different solvents using the methods of nuclear magnetic resonance (NMR) spectroscopy, imaging, and time resolved spectroscopic imaging by means of hyperpolarized ¹²⁹Xe. Starting from the initial condition of a hyperpolarized solid Xe layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample, pieces of Xe ice first fall through the viscous ethanol to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The xenon atoms are trapped in this liquid layer up to room temperature and keep their magnetization over a time period of 11 min. In the ethanol/water mixture (80 vol%/20%), most of the polarized Xe liquid first stays on top of the ethanol/water ice block and then starts to penetrate into the pores and cracks of the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogeneous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe (about half of the density of liquid Xe) can be stored or delivered in pure ethanol.     

13C direct detected COCO-TOCSY: a tool for sequence specific assignment and structure determination in protonless NMR experiments

A novel experiment is proposed to provide inter-residue sequential correlations among carbonyl spins in (13)C detected, protonless NMR experiments. The COCO-TOCSY experiment connects, in proteins, two carbonyls separated from each other by three, four or even five bonds. The quantitative analysis provides structural information on backbone dihedral angles phi as well as on the side chain dihedral angles of Asx and Glx residues. This is the first dihedral angle constraint that can be obtained via a protonless approach. About 75% of backbone carbonyls in Calbindin D(9K), a 75 amino acid dicalcium protein, could be sequentially connected via a COCO-TOCSY spectrum. 49 [Formula: see text] values were measured and related to backbone phi angles. Structural information can be extended to the side chain orientation of aminoacids containing carbonyl groups. Additionally, long range homonuclear coupling constants, (4)J(CC) and (5)J(CC), could be measured. This constitutes an unprecedented case for proteins of medium and small size.     

13C/12C-Untersuchungen an Tumorzellen

Abstract

The metabolism of tumor-cells differs in many ways from normal (healthy) cells. One of the major differences is the high glycolytic activity in tumor-cells with the subsequent formation of lactate from glucose, even in the presence of oxygen. The question whether this high rate of glycolysis has any effect on the ¹³C/¹²C-relation of the cells is examined in experiments with a tumor-cell line (HT29) and in specimens of human breast cancer.

The HT29 cells show a clear decrease in ¹³C content compared to their culture medium (Δδ = 3.28‰).

Tissue from human breast cancer has more ¹³C than normal breast tissue taken from the same patient ((Δδ = 2.74‰). But the content of fat is much higher in the normal tissue and its δ-value is negatively correlated with its fat content. It is concluded that the difference between normal and tumor tissue is due to the heterogeneous composition of the normal tissue samples.     

13C NMR Chemical Shifts of Heterocycles: Empirical Substituent Effects in 5-Halomethylisoxazoles

Evaluation by empirically derived equations for the Substituent effect (α, β, γ, δ) on the ¹³C NMR chemical shifts for C-3, C-4. C-5 and halomethyl-substituent carbon (C-6) in isoxazoles 1-5 [where C-3 substituent (R¹) = H, alkyl or phenyl, C-4 Substituent (R²) = H, alkyl, and C-5 substituent (R³) = di-or trihalomethyl, methyl and H], taking as reference the compound la, is reported. From the calculated values for the α, β, γ, δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1–5. The ¹³ C chemical shifts of the C-3, C-4, C-5, C-6 of these compounds, can be estimated with good precision: 94% of the calculated chemical shifts are found to be within ±1.0ppm, and 100% are found to be within ±1.5ppm.     

[13C]Aminopyrine and [13C]Caffeine Breath Test: Influence of Gender,Cigarette Smoking and Oral Contraceptives Intake

Abstract

The [¹³C]aminopyrine breath test ([¹³C]ABT) measures the global activity of cytochrome P450 in vivo and is a sensitive indicator of liver metabolic dysfunction. The present study aims to determine whether gender and cigarette smoking influence the results of [¹³C]ABT as well as to confirm the effect of oral contraceptive steroids (OCS) intake on this metabolic test. Hundred and ten healthy subjects, including men and women, smoker and non-smoker, women taking OCS or not, were phenotyped for CYP1A2 using the [¹³C]caffeine breath test and underwent a [¹³C]ABT. Both tests showed large inter-individual variations in accordance with that of CYP450 liver content. [¹³C]ABT was sensitive enough to point out a significant induction or inhibition related to cigarette smoking habits or OCS. The combined effect of smoking and OCS resulted in an overall unchanged metabolic activity. Consequently, the impact of the studied conditions on the [¹³C]ABT parameters must be considered by clinicians or clinical investigators.     

The C1 IIg-A1 IIu Emission Spectrum of 12C13C

A few bands of the C¹II_g -A¹II_u system of ¹²C¹³C molecule have been photographed and five of them have been rotationally analyzed. Molecular constants for v = 0, 1 and 2 in the C¹ II_g and in A¹II_u states have been obtained using a nonlinear least-squares procedure in which all analyzed bands were fitted simultaneosly.     

Liver function assessment with three 13C breath tests by two-point measurements

In this study, we performed three breath tests – l-[1-¹³C ]phenylalanine breath test (PBT), l-[1-¹³C ] methionine breath test, and [¹³C]methacetin breath test (MethaBT) – in patients with chronic liver disease to determine the optimal timing of expired air collection for diagnosing chronic liver disease and evaluating the grade of fibrosis. The subjects were 61 adults with normal livers, 98 chronic hepatitis patients, and 91 liver cirrhosis patients. We investigated the relationships of breath test results with routine biochemical tests and the Child–Pugh score, as well as the diagnostic capacities of the breath tests for liver dysfunction/cirrhosis and grade of liver fibrosis. For the diagnosis of liver cirrhosis and correlations with liver fibrosis, the accuracy of the PBT at 30 min (PBT30) was similar to that of the MethaBT at 15 min (Metha15). For liver function assessment by two-point measurement with ¹³C breath tests, we recommend the PBT30 and the Metha15.     

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C]methacetin- and [methyl-13C]methionine-breath tests

The aim of this study was to investigate the hepatic microsomal and mitochondrial functions by using the ¹³CO₂-breath test in healthy subjects either before or after the consumption of red wine. Fourteen adults received [¹³C]methacetin and [methyl-¹³C]methionine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol/kg/day together with dinner over a 10-day period. Thereafter, ¹³C-tracer administration was repeated under identical conditions. The ¹³CO₂-enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage ¹³C-dose recovery (CPDR) after administration of [¹³C]methacetin and [methyl-¹³C]methionine either without or with red wine consumption amounted to 38.2±6.3 vs. 36.3±6.7% (p=0.363) and 9.5±3.3 vs. 8.8±2.5% (p=0.47), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the mitochondrial functions of the human liver in healthy subjects.     

Muon/Muonium in an Isotopically Pure 13C Diamond

A preliminary study of the diamagnetic (μ_d) and the paramagnetic (Mu _T ) states in a synthetic ¹³C diamond has been performed using the Transverse Field Muon Spin Rotation method. This system could be used to verify the quantum diffusion behaviour observed before, however, with a more reliable extraction of the hopping rate. The results were obtained in an applied magnetic field of 7.5 mT and at sample temperatures of 10 K, 100 K and 200 K. The prompt fraction, f, of the μ_d state remains constant at 22(5)% in the range 10–200 K; that of the Mu _T state increases from 53(10)% at 10 K to 78(10)% at 200 K. The fractions of the two states add to 100% at 200 K, suggesting non-population of the bond-centred state, Mu_BC, which is often observed in other diamond samples. The μ_d state has a spin relaxation rate of 0.20(5) μs⁻¹, in contrast to the zero value obtained in type II diamond samples. This indicates appreciable interaction of the μ_d state with the ¹³C atoms. The Mu _T state has a large spin relaxation rate ranging from 3.0(5) μs⁻¹ at 10 K to 7.0(5) μs⁻¹ at 200 K, consistent with values obtained in diamond samples with defects. This work is part of ongoing studies of muon/muonium-defect interactions in diamonds. This revised version was published online in September 2006 with corrections to the Cover Date.     

13C NMR Study of the Natural Glycosides Vicine and Convicine

¹³C NMR parameters have been obtained for vicine and convicine in DMSO, D₂O/DMSO and D₂O. Complete assignment of the spectra has been achieved. Interpretation of spin-lattice relaxation rates and heteronu-clear NOES has yielded evidence of intramolecular structuring in the case of vicine and not in that of ronvirine and also of a complex network of solute-solvent interactions.     

Structural and 14N EFG Information on Solid Imidazole by 13C CP/MAS NMR Data

Residual dipolar coupling between carbons and ¹⁴N nuclei in the ¹³C CPMAS NMR spectrum of solid imidazole is studied. Calculations of expected splittings with a previously reported equation leads to the complete assignment of the solid state carbon chemical shifts. Additionally, information is provided on the location of ¹⁴N electric field gradient axes at the N-H site.