Detection of lactate with a hadamard slice selected,selective multiple quantum coherence,chemical shift imaging sequence (HDMD‐SelMQC‐CSI) on a clinical MRI scanner: Application to tumors and muscle ischemia

Lactate is an important metabolite in normal and malignant tissues detectable by NMR spectroscopy; however, it has been difficult to clinically detect the lactate methyl resonance because it is obscured by lipid resonances. The selective homonuclear multiple quantum coherence transfer technique offers a method for distinguishing lipid and lactate resonances. We implemented a three‐dimensional selective homonuclear multiple quantum coherence transfer version with Hadamard slice selection and two‐dimensional phase encoding (Hadamard encoded–selective homonuclear multiple quantum coherence transfer–chemical shift imaging) on a conventional clinical MR scanner. Hadamard slice selection is explained and demonstrated in vivo. This is followed by 1‐cm³ resolution lactate imaging with detection to 5‐mM concentration in 20 min on a 3‐T clinical scanner. An analysis of QSel gradient duration and amplitude effects on lactate and lipid signal is presented. To demonstrate clinical feasibility, a 5‐min lactate scan of a patient with a non‐Hodgkin's lymphoma in the superficial thigh is reported. The elevated lactate signal coincides with the T₂‐weighted image of this tumor. As a test of selective homonuclear multiple quantum coherence transfer sensitivity, a thigh tourniquet was applied to a normal volunteer and an increase in lactate was detected immediately after tourniquet flow constriction. In conclusion, the Hadamard encoded–selective homonuclear multiple quantum coherence transfer–chemical shift imaging sequence is demonstrated on a phantom and in two lipid‐rich, clinically relevant, in vivo conditions. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Localized detection of glioma glycolysis using edited 1H MRS

In vivo ¹H MRS can be used to detect and quantify the lactate resonance at 1.3 ppm provided that overlapping lipid resonances are eliminated. A homonuclear spectral editing method was developed to acquire uncontaminated ¹H spectra of lactate with adiabatic pulses. An advantage of the adiabatic pulse sequence is the ability to induce uniform flip angles and to maximize sensitivity in applications employing surface coil transmitters which produce highly inhomogeneous B₁. Glycolytic activity in an intracerebral C6 glioma in rats was monitored by using adiabatic editing sequences to observe [3-¹³C]lactate produced from infused [1-¹³C]glucose. Acute hyperglycemia (serum glucose >22 mM, n = 10) had no significant effect (P = 0.08) on the total ([¹²C]+ [¹³C]) tumor lactate signal intensity.     

Phosphorus J-coupling constants of ATP in human brain

Proton decoupled ³¹P NMR spectroscopy of the occipital brain of healthy volunteers was performed with a 1.5 T whole-body imager. By use of two-dimensional chemical-shift imaging in combination with slice-selective excitation well resolved localized spectra (38 ml) were obtained within 34 min from which the homonuclear ³¹P-³¹P J-coupling constants of ATP could be determined: J_αβ = 16.1 Hz ± 0.2 Hz and J_αβ = 16.3 Hz ± 0.1 Hz (mean ± SEM, n = 14). Both, the J-coupling constants and the chemical-shift difference between α- and β-ATP (δ_αβ = 8.61 ppm ± 0.01 ppm) were used to calculate the concentration of intracellular free magnesium. The concentrations are 0.39 mM ± 0.09 mM by using the average of both coupling constants of each spectrum, which is in fair agreement with 0.32 mM ± 0.01 mM obtained from the chemical shift of α and β phosphate resonances, which is the more accurate result.     

13C isotopomer analyses in intact tissue using {13C}homonuclear decoupling

Entry of ¹³C-enriched acetyl-CoA into the citric acid cycle results in scrambling of ¹³C into the various carbon positions of all intermediate pools. The eventual result is that the ¹³C resonances of all detectable intermediates or molecules exchanging with those intermediates appear as multiplets due to nearest neighbor spin-spin couplings. We have previously shown that an isotopomer analysis of the glutamate ¹³C multiplets provides a history of ¹³C flow through the cycle pools and that relative substrate utilization and relative anaplerotic flux can be quantitated (C.R. Malloy, A.D. Sherry, and F.M.H. Jeffrey, Am. J. Physiol. 259, H987–H995 (1990)). A major limitation of the method for in vivo applications is spectral resolution of multiline resonances required for a complete isotopomer analysis. We now show that (¹³C)homonuclear decoupling of the glutamate C3 resonance collapses nine-line C4 and C2 resonances into three-line multiplets. We demonstrate that these three line ¹³C multiplets are well resolved in isolated, perfused rat hearts and present steady-state equations that allow an isotopomer analysis from data obtained in intact tissue. This advancement offers for the first time the possibility of extending ¹³C isotopomer methods to complex metabolic conditions in vivo.     

Comparison of methods for the determination of absolute metabolite concentrations in human muscles by 31P MRS

In order to determine metabolite concentrations in human skeletal muscles by in vivo ³¹P MRS, different quantification methods were analyzed with regard to the accuracy and reproducibility of results and the simplicity of handling. Each quantification method comprised a calibration strategy and a localization technique. Extensive in vivo and in vitro tests showed that homonuclear phantom-based calibration strategies yielded significantly more accurate (lower systematic errors) and more reproducible (lower statistical errors) concentration estimates than heteronuclear strategies using internal water as a concentration standard. Additionally, the former strategies are easier to handle than the latter. Localization with the volume-selective sequence lSlS yielded slightly more reproducible results than localization by surface coil. We conclude that phosphorus metabolite concentrations are determined most accurately with phantom-based calibration strategies in combination with lSlS localization (measurement errors ≈ 5–7%).     

In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (¹H) to a J-coupled phosphorus (³¹P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (～1.2) is lower than the theoretical maximum of γ¹H/γ³¹P≈ 2.4 resulting from ¹H-¹H homonuclear J couplings of similar magnitude competing with the ¹H →³¹P transfer. Nevertheless, compared with direct ³¹P Ernst-angle excitation, signal gains of up to × 1.8 were obtained mainly as a result of T¹ differences between ³¹P and the ¹H. Spectral interpretation is simplified by editing out all non-proton-coupled ³¹P signals. The duration, ～50 min, and power deposition, ～1 W · kg^?1, make the application suitable for human studies.     

Band-selective spin echoes for in vivo localized 1H NMR spectroscopy

This study describes a new single spin-echo spatial localization sequence, BASSALE or BAnd-Selective Spin echo Acquisition for Localized Editing, that overcomes a number of the limitations of the STEAM and PRESS volume selection pulse sequences. It achieves conformal volume localization in a single shot by spatially tailored suppression of all magnetization outside a 2D region of interest followed by selection of a single orthogonal slice. This separation of spatial localization from the echo formation process has permitted use of a spectrally selective cosine-modulated sinc refocusing pulse to acquire localized ¹H spectra with the water suppression efficiency of STEAM and the sensitivity of PRESS. Echoes formed by such spectrally selective pulses have been termed bandselective spin echoes. The BASSALE sequence attains shorter echo times than PRESS, inhibits scalar spin-spin interactions to permit localized editing and T₂ relaxometry of metabolites with J-coupled spins (e.g., lactate), is insensitive to homonuclear multiple-quantum and polarization transfer effects, and can be made sensitive or insensitive to spin displacement effects. Applications are shown both with phantoms and in situ in the rat brain.     

Sex differences in myocardial oxygen and glucose metabolism

Background  Both physiologic and pathophysiologic conditions affect the myocardium’s substrate use and, consequently, its structure, function, and adaptability. The effect of sex on myocardial oxygen, glucose, and fatty acid metabolism in humans is unknown. Methods and Results  We studied 25 young subjects (13 women and 12 men) using positron emission tomography, quantifying myocardial blood flow, myocardial oxygen consumption (MVO₂), and glucose and fatty acid extraction and metabolism. MVO₂ was higher in women than in men (5.74±1.08 μmol·g⁻¹·min⁻¹ vs 4.26±0.69 μmol·g⁻¹·min⁻¹,P<.005). Myocardial glucose extraction fraction and utilization were lower in women than in men (0.025±0.019 vs 0.062±0.028 [P<.001] and 133±96 nmol·g⁻¹·min⁻¹ vs 287±164 nmol·g⁻¹·min⁻¹ [P<.01], respectively). There were no sex differences in myocardial blood flow, fatty acid metabolism, or plasma glucose, fatty acid, or insulin levels. Female sex was an independent predictor of increased MVO₂ (P=.01) and decreased myocardial glucose extraction fraction and utilization (P<.005 andP<.05, respectively). Insulin sensitivity was an independent predictor of increased myocardial glucose extraction fraction and utilization (P<.01 andP=.01, respectively). Conclusions  Further studies are necessary to elucidate the mechanisms responsible for sex-associated differences in myocardial metabolism. However, the presence of such differences may provide a partial explanation for the observed sex-related differences in the prevalence and manifestation of a variety of cardiac disorders. This work was supported by grants HD145902 (Building Interdisciplinary Research in Women’s Health), RR00036 (General Clinical Research Center), DK56341 (Clinical Nutrition Research Unit), K23-HL077179, RO1-AG15466, PO1-HL13581, and HL73120 from the National Institutes of Health (Bethesda, Md) and grant 051893 (AHA02255732) from the Robert Wood Johnson Foundation (Princeton, NJ).     

Quantifying endogenous glucose production and contributing source fluxes from a single 2H NMR spectrum

Endogenous glucose production (EGP), gluconeogenic and glycogenolytic fluxes by analysis of a single ²H‐NMR spectrum is demonstrated with 6‐hr and 24‐hr fasted rats. Animals were administered [1‐²H, 1‐¹³C]glucose, a novel tracer of glucose turnover, and ²H₂O. Plasma glucose enrichment from both tracers was quantified by ²H‐NMR analysis of monoacetone glucose. The 6‐hr fasted group (n = 7) had EGP rates of 95.6 ± 13.3 μmol/kg/min, where 56.2 ± 7.9 μmol/kg/min were derived from PEP; 12.1 ± 2.1 μmol/kg/min from glycerol, and 32.1 ± 4.9 μmol/kg/min from glycogen. The 24‐hr fasted group (n = 7) had significantly lower EGP rates (52.8 ± 7.2 μmol/kg/min, P = 0.004 vs. 6 hr) mediated by a significantly reduced contribution from glycogen (4.7 ± 5.9 μmol/kg/min, P = 0.02 vs. 6 hr) while PEP and glycerol contributions were not significantly different (39.5 ± 3.9 and 8.5 ± 1.2 μmol/kg/min, respectively). These estimates agree with previous assays of EGP fluxes in fasted rats obtained by multinuclear NMR analyses of plasma glucose enrichment from ²H₂O and ¹³C‐glucose tracers. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Glucose metabolism in RIF-1 tumors after reduction in blood flow: An in Vivo 13C and 31P NMR study

Low pH appears to enhance the effectiveness of therapeutic hyperthermia. ¹³C and ³¹P NMR spectroscopy have been employed to examine the possibility that elevating glucose in a solid tumor while simultaneously reducing tumor blood flow would induce a more profound acidosis than either treatment alone. When blood flow in RIF-1 tumors was acutely reduced by administration of hydralazine and additional glucose was delivered locally by intratumoral injection, tumor acidosis (as determined by ³¹P NMR spectroscopy) during the period of reduced blood flow was not enhanced, relative to administration of hydralarine alone. Tumor NTP/P₁ ratios decreased significantly within 20 min of hydralazine administration, whether or not glucose was injected, although NTP/P₁ ratios were slightly higher in tumors that received extra glucose. Tumor lactate concentrations were not significantly different in glucose-supplemented tumors, despite glucose concentratlons that were 4 to 5 times higher. When the added glucose was labeled with ¹³C, no correlation was detected between the pH in an individual tumor and the intensity of the 3-[¹³C]-lactate resonance in the same tumor.     

On the use of two-dimensional-J NMR measurements for in Vivo proton MRS: Measurement of homonuclear decoupled spectra without the need for short echo times

The potential of two-dimensional (2D)-J NMR for in vivo proton MRS is examined. Single voxel measurements on the rat brain were performed at 4.7 T using point-resolved spectrocopy localization with a voxel size of 64 μl and total measuring times of 10-15 min. It is shown that a series of measurements with only 16 or fewer different echo times (TE) enables good signal localization in the f₁ axis corresponding to the coupling patterns. For data evaluation, the 2D-J NMR spectrum as well as cross-sections at given f₁ values and projections onto the f₂ axis are used. A comparison between cross-section spectra taken at different f₁ values may help to solve problems of peak assignment. The projection of the 2D magnitude spectrum onto the f₂ axis corresponds to a homonuclear decoupled 1D proton spectrum. Because the T₂ relaxation times of several coupled resonances (e.g., myo-inositol and glutamate) are rather long, only minor losses in the quality of the projection spectra occur if the measurements with short TE (≤ 50 ms) are not used for data processing. Thus, homonuclear decoupled proton spectra detecting uncoupled and several coupled resonances can be measured with high quality in vivo, even on MR systems that are not equipped with actively shielded gradients, prohibiting data acquisition with TEs of 50 ms or less.     

A new perfluorocarbon for use in fluorine-19 magnetic resonance imaging and spectroscopy

A new perfluorocarbon, PTBD (perfluoro-2,2, 2′, 2′-tetrameth-yl-4,4′-bis(1, 3-dioxolane)), is described for use in ¹⁹F MR imaging and spectroscopy. Two-thirds of the molecular fluorine in PTBD resonates at a single frequency and can be imaged without the use of frequency-selective spin-echo (SE) MRI pulse sequences to suppress chemical shift artifacts. The absence of strong homonuclear spin-spin coupling to the imagable -CF₃ groups in PTBD minimizes signal attenuation in ¹⁹F SE MRI due to J-modulation effects. For equimolar concentrations of perfluorocarbon, PTBD gives an approximately 17% increase in sensitivity, relative to literature results for perfluorinated amines, at short values of TE (～10 ms) in ¹⁹F SE MRI. These attributes allow ¹⁹F MRI of PTBD to be performed on standard clinical imaging instrumentation (without special hardware andJor software modification) and an in vivo example in a mouse is shown. This investigation involved characterizing the MR T₁ and T₂ relaxation times of PTBD as well as the MR spin-lattice relaxation rate, R₁ (1JT₁), of PTBD as a function of dissolved oxygen concentration. The T₁ and T₂ relaxation times and R₁ relaxation rates of perfluorooctyl bromide (PFOB) were also obtained, under similar experimental conditions, to compare and contrast PTBD with a representative perfluorocarbon that has been widely employed for ¹⁹F MRIJMRS applications.     

In vivo 23Na NMR studies of myotonic dystrophy

Myotonic dystrophy is an inherited multi-system disease. Its pathophysiology leading to muscle malfunction and damage is not well understood. ²³Na NMR spectroscopy was applied here for an in vivo comparative study of the calf muscles of 7 myotonic dystrophy patients at various stages of the disease and 11 healthy volunteers. Both the total sodium content, expressed as the ratio of the ²³Na and ¹H water signals, and the fast transverse relaxation time, T₂₁, determined from the triple quantum-filtered spectra, increased in correlation with the severity of the disease. The results demonstrate that ²³Na NMR enables the quantitation of myotonic dystrophy progression.     

In vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI): [3,4-13CH2]glutamate/glutamine tomography in rat brain

A method for in vivo carbon-edited detection with proton echo-planar spectroscopic imaging (ICED PEPSI) is described. This method is composed of an echo-planar based acquisition implemented with ¹³C-¹H J editing spectroscopy and is intended for high temporal and spatial resolution in vivo spectroscopic imaging of ¹³C turnover, from D-[1,6-¹³C]glucose to glutamate and glutamine, in the brain. At a static magnetic field strength of 7 T, both in vitro and in vivo chemical shift imaging data are presented with a spatial resolution of 8 μL (i.e., 1.25 × 1.25 × 5.00 mm³) and a maximum spectral bandwidth of 5.2 ppm in ¹H. Chemical shift imaging data acquired every 11 minutes allowed detection of regional [4-¹³CH₂]glutamate turnover in rat brain. The [4-¹³CH₂]glutamate turnover curves, which can be converted to tricarboxylic acid cycle fluxes, showed that the tricarboxylic acid cycle flux (V_TCA) in pure gray and white matter can range from 1.2 ± 0.2 to 0.5 ± 0.1 μmol/g/min, respectively, for morphine-anesthetized rats. The mean cortical V_TCA from 32 voxels of 1.0 ± 0.3 μmol/g/min (N = 3) is in excellent agreement with previous localized measurements that have demonstrated that V_TCA can range from 0.9–1.1 μmol/g/min under identical anesthetized conditions. Magn Reson Med 42:997–1003, 1999. © 1999 Wiley-Liss, Inc.     

A procedure for wall detection in [18F]FDG positron emission tomography heart studies

Quantitative positron emission tomography (PET) heart studies require the accurate localization of regions of interest (ROIs) on the myocardial wall (MW) and left ventricle (LV). The procedure is often inaccurate, especially when there is low tracer uptake. We implemented a data processing technique to improve the accuracy of the localization of ROIs on the MW and LV in fluorine-18 labelled deoxyglucose ([¹⁸F]FDG) PET heart studies. This technique combines transmission data, acquired before tracer administration and used for attenuation correction, and dynamic emission data (DY), acquired to obtain myocardial time-activity curves and used to calculate regional myocardial glucose utilization, to generate a new set of transmission images (TRDY) with enhanced contrast between MW and LV. These new transmission images identify the extravascular myocardial tissue and can be used for ROI placement. Validation of the method was performed in 25 patients, studied after an oral glucose load, by drawing irregular ROIs on three transaxial slices outlining the septum and anteriorapical and lateral wall on the last frame of the DY images (steady state) and then on the TRDY images. Two kinds of analysis were performed on a total of 225 myocardial segments: (1) mean counts per pixel in the DY images from ROIs independently drawn on DY and TRDY images were compared; (2) TRDY ROIs were copied onto DY images and repositioned in the event of mismatch between ROIs and myocardial tissue edge. Mean counts per pixel in the DY images from the original and the repositioned TRDY ROIs were compared. An excellent correlation was found in both cases (using TRDY and DY ROIs:y=0.908x+0.068,r=0.97; using TRDY ROIs alone:y=0.975x+0.006,r=0.99). This technique can be used for clinical applications in physiological and pathological conditions in which the myocardial [¹⁸F]FDG uptake is reduced or minimal, including diabetes and myocardial infarction.     

Aluminum-27 nuclear magnetic resonance spectroscopy and imaging of the human gastric lumen

Aluminum NMR is proposed as a new imaging and spectroscopy modality. Its potential is exemplified by in vivo studies of the human stomach. The dissolution kinetics of aluminum-containing drugs at physiological doses and their removal from the human stomach have been followed by ²⁷Al magnetic resonance spectroscopy (MRS). Aluminum concentrations as low as 0.5 mg Al³⁺ in the human stomach can be detected. The time course of gastric emptying has been visualized with ²⁷Al magnetic resonance imaging (MRI) under normal conditions and in the presence of an antimuscarinic agent, which reduces the gastric motor function. ²⁷Al MRI is the only direct method to visualize the gastric pH. ²⁷Al MRI opens new possibilities for medical and pharmaceutical science.     

Measurements of human cerebral GABA at 4.1 T using numerically optimized editing pulses

The goal of this work was to develop and evaluate a numerically optimized inversion pulse to be used with a homonuclear editing sequence to measure human cerebral GABA 117 vivo at 4.1 T in the occipital lobe. The optimized pulse was constructed using pallindromic symmetry with 30 pulses and 29 delays. The optimized pulse provided greater selectivity than the equivalent bandwidth matched DANTE pulse and sine shaped DANTE. The improved selectivity reduced the co-editing of the macromolecule resonance, permitting the GABA edited doublet to be resolved in vivo. Using cerebral creatine as a reference, 7.1 mM, the measured GABA level was 1.15 ± 0.13 mM in the occipital lobe.     

Two weeks of repetitive gut‐challenge reduce exercise‐associated gastrointestinal symptoms and malabsorption

Debilitating gastrointestinal symptoms is a common feature of endurance running and may be exacerbated by and/or limit the ability to tolerate carbohydrate intake during exercise. The study aimed to determine whether two weeks of repetitive gut‐challenge during running can reduce exercise‐associated gastrointestinal symptoms and carbohydrate malabsorption. Endurance runners (n =18) performed an initial gut‐challenge trial (GC 1) comprising 2‐hour running exercise at 60% VO _2max (steady state) while consuming a formulated gel‐disk containing 30 g carbohydrates (2:1 glucose‐fructose, 10% w/v ) every 20 minutes, followed by a 1‐hour running effort bout. Gastrointestinal symptoms, feeding tolerance, and breath hydrogen (H₂) were determined along the gut‐challenge trial. After GC 1, participants were randomly assigned to a blinded carbohydrate (CHO , 90 gCHO  hour⁻¹) or placebo (PLA , 0 gCHO  hour⁻¹) gut‐training group. This comprised of consuming the group‐specific feeding intervention during 1‐hour running exercise at 60% VO _2max equivalent, daily over a period of two weeks. Participants then repeated the gut‐challenge trial (GC 2). In GC 2, a reduced gut discomfort (P =.012), total (P =.009), upper‐ (P =.015), and lower‐gastrointestinal (P =.008) symptoms, and nausea (P =.05) were observed on CHO , but not PLA . Feeding tolerance did not differ between GC 1 and GC 2 on CHO and PLA . H₂ peak was attenuated in GC 2 (6±3 ppm) compared to GC 1 (13±6 ppm) on CHO (P =.004), but not on PLA (GC 1 11±7 ppm, and GC 2 10±10 ppm). The effort bout distance was greater in GC 2 (12.3±1.3 km) compared with GC 1 (11.7±1.5 km) on CHO (P =.035) only. Two weeks of repetitive gut‐challenge improve gastrointestinal symptoms and reduce carbohydrate malabsorption during endurance running, which may have performance implications.     

Evidence for 100% 13C NMR visibility of glucose in human skeletal muscle

The accuracy of the measurement of total muscle glucose by in vivo ¹³C NMR spectroscopy was tested in five normal volunteers during a euglycemic [1-¹³C]glucose infusion. The NMR visible concentration calibrated using an external reference was compared with that calculated from plasma glucose concentration, assuming that glucose remained extracellular. The NMR measurement always provided higher values than the calculation from plasma glucose: 0.51 ± 0.035 (mean ± SE) versus 0.38 ± 0.005 mmol/liter of muscle on average. This systematic difference was interpreted as reflecting the presence of muscle glucose-6-phospnate, co-resonating with free glucose. Thus, glucose appeared to be virtually 100% NMR visible in human skeletal muscle.     

Radioprotective efficacy of Ginkgo biloba and Angelica archangelica extract against technetium-99m-sestamibi induced oxidative stress and lens injury in rats

Purpose: Technetium-99m is a radioactive tracer that emits gamma rays. Its half-life time is 6?h. Similar to other ionizing radiations, the main mechanism of radiation-induced effects is initiated through the production of reactive oxygen species (ROS). This study was designed to determine the possible protective effects of Ginkgo biloba and Angelica archangelica against oxidative organ damage that was induced by ^99mTc-sestamibi.

Materials and methods: The experiments were performed on thirty-six Wistar-rats which were subdivided into control groups and groups exposed to ^99mTc-sestamibi. The irradiated groups were either untreated or pre-treated with G. biloba or A. archangelica. For all groups, the levels and/or activities of Catalase (CAT), Glutathione (GSH), Malondialdehyde (MDA) and Superoxide-dismutase (SOD) were measured in blood and lenses. The soluble/insoluble protein ratio was determined and lens-protein profiles were obtained via Sodium-Dodecyl-Sulfate Polyacrylamide Gel-Electrophoresis (SDS-PAGE).

Results: There were no significant difference between the pre-treated and irradiated G. biloba group and control group, while both groups were significantly different (p?A. archangelica did not confer any significant protection against ^99mTc-sestamibi induced toxicity.

Conclusions: This study demonstrated that G. biloba, through its free radical scavenging and antioxidant properties, successfully attenuated ^99mTc-sestamibi radiation-induced oxidative organ injury. The latter is a crucial factor of cataractogenesis in rats, suggesting that G. biloba may have a potential benefit in the protection against radiopharmaceuticals.