Determination of intracellular pH and compartmentation using diffusion-weighted NMR spectroscopy with pH-sensitive indicators.

The intracellular pH (pHi) of a series of cancer cell lines was determined using the pH-sensitive indicators imidazole (Im) or histidine (His) and diffusion-weighted (DW) proton NMR spectroscopy. The DW method allows the observation at high magnetic field gradient values of only the slow-moving (intracellular) components, thus ensuring complete separation between intra- and extracellular components. Using the chemical shift difference (deltadelta) between the imidazole ring C2-H and C4(5)-H peaks, we were able to measure the pHi independently of chemical shift standardization. With His, the cell lines gave pHi values of approximately 6.5-7.0, whereas with Im, a second, more acidic compartment (pHi = 5.5-5.8) was also observed. An inverse correlation was also found between pHi and the intracellular lactate concentration. This method may be applicable to in vivo pH determinations.     

Tumor 31P NMR pH measurements in vivo: A comparison of inorganic phosphate and intracellular 2-deoxyglucose-6-phosphate as pHnmr indicators in murine radiation-induced fibrosarcoma-1

Uncertainty regarding the intracellular/extracellular distribution of inorganic phosphate (P_i) in tumors has raised concerns that pH calculated from the tumor P_i chemical shift may not accurately represent the intracellular pH (pH_in). This issue was addressed in subcutaneously transplanted murine radiation induced fibrosarcoma-1 by directly comparing pH measured via P_i with pH measured via the in situ generated intracellular xenometabolite 2-deoxyglucose-6-phosphate (2DG6P). In 131 comparative measurements employing eight tumor-bearing mice under both control and hyperglycemic conditions (the latter to extend the range of tumor pH examined), the pH as derived from either 2DG6P or P_i showed only a small, but statistically significant, difference (0.07 ± 0.11 SD; P = 0.0001). Scatter in the comparative analysis over the pH range examined (ca. 5.5-7.5) was not uniform. Above pH 6.6, 2DG6P indicated a pH lower than that of P_i by 0.088 ± 0.105 SD (n = 107, P = 0.0001); below pH 6.6, 2DG6P indicated a pH essentially identical to and not statistically different from that of P_i (mean difference 0.003 ± 0.128 SD (n = 24, P = 0.92)). Evidence is presented in support of this differential arising from a systematic measurement error due to peak overlap between 2DG6P and endogenous phosphomonoester species. These results support the use of P_i as a tumor ³¹P NMR pH_in indicator, at least in RIF-1 tumors under control and hyperglycemic conditions.     

Erythropoietin does not reduce plasma lactate,H+, and K+ during intense exercise

It is investigated if recombinant human erythropoietin (rHuEPO) treatment for 15 weeks (n = 8) reduces extracellular accumulation of metabolic stress markers such as lactate, H⁺, and K⁺ during incremental exhaustive exercise. After rHuEPO treatment, normalization of blood volume and composition by hemodilution preceded an additional incremental test. Group averages were calculated for an exercise intensity ～80% of pre‐rHuEPO peak power output. After rHuEPO treatment, leg lactate release to the plasma compartment was similar to before (4.3 ± 1.6 vs 3.9 ± 2.5 mmol/min) and remained similar after hemodilution. Venous lactate concentration was higher (P < 0.05) after rHuEPO treatment (7.1 ± 1.6 vs 5.2 ± 2.1 mM). Leg H⁺ release to the plasma compartment after rHuEPO was similar to before (19.6 ± 5.4 vs 17.6 ± 6.0 mmol/min) and remained similar after hemodilution. Nevertheless, venous pH was lower (P < 0.05) after rHuEPO treatment (7.18 ± 0.04 vs 7.22 ± 0.05). Leg K⁺ release to the plasma compartment after rHuEPO treatment was similar to before (0.8 ± 0.5 vs 0.7 ± 0.7 mmol/min) and remained similar after hemodilution. Additionally, venous K⁺ concentrations were similar after vs before rHuEPO (5.3 ± 0.3 vs 5.1 ± 0.4 mM). In conclusion, rHuEPO does not reduce plasma accumulation of lactate, H⁺, and K⁺ at work rates corresponding to ～80% of peak power output.     

In vivo observation of intracellular oximetry in perfluorocarbon‐labeled glioma cells and chemotherapeutic response in the CNS using fluorine‐19 MRI

Preclinical development of therapeutic agents against cancer could greatly benefit from noninvasive markers of tumor killing. Potentially, the intracellular partial pressure of oxygen (pO₂) can be used as an early marker of antitumor efficacy. Here, the feasibility of measuring intracellular pO₂ of central nervous system glioma cells in vivo using ¹⁹F magnetic resonance techniques is examined. Rat 9L glioma cells were labeled with perfluoro‐15‐crown‐5‐ether ex vivo and then implanted into the rat striatum. ¹⁹F MRI was used to visualize tumor location in vivo. The mean ¹⁹F T₁ of the implanted cells was measured using localized, single‐voxel spectroscopy. The intracellular pO₂ in tumor cells was determined from an in vitro calibration curve. The basal pO₂ of 9L cells (day 3) was determined to be 45.3 ± 5 mmHg (n = 6). Rats were then treated with a 1× LD10 dose of bischloroethylnitrosourea intravenously and changes in intracellular pO₂ were monitored. The pO₂ increased significantly (P = 0.042, paired T‐test) to 141.8 ± 3 mmHg within 18 h after bischloroethylnitrosourea treatment (day 4) and remained elevated (165 ± 24 mmHg) for at least 72 h (day 6). Intracellular localization of the perfluoro‐15‐crown‐5‐ether emulsion in 9L cells before and after bischloroethylnitrosourea treatment was confirmed by histological examination and fluorescence microscopy. Overall, noninvasive ¹⁹F magnetic resonance techniques may provide a valuable preclinical tool for monitoring therapeutic response against central nervous system or other deep‐seated tumors. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Impact of salbutamol on muscle metabolism assessed by 31P NMR spectroscopy

The potential ergogenic effects of oral salbutamol intake were demonstrated for decades but the underlying mechanisms remain to elucidate. We hypothesized that improved exercise performance after acute oral salbutamol administration is associated with changes in muscle metabolism. Twelve healthy, nonasthmatic, moderately trained, male subjects were recruited to compare in a double‐blind crossover randomized study, an oral dose of salbutamol (4 mg) and a placebo. After treatment administration, subjects performed repetitive plantar flexions to exhaustion in a 3T magnet. Continuous ³¹P nuclear magnetic resonance spectroscopy assessment of the calf muscles was performed at rest, during exercise, and during recovery. No significant difference between treatments was detected in metabolite concentration at rest (P > 0.05). Creatine phosphate and inorganic phosphate changes during and immediately after exercise were similar between treatments (P > 0.05). Intramuscular pH (pHi) was significantly higher at rest, at submaximal exercise but not at exhaustion with salbutamol (pHi at 50% of exercise duration, 6.8 ± 0.1/6.9 ± 0.1 for placebo and salbutamol, respectively, P < 0.05). The maximal power (28 ± 7 W/23 ± 7 W; P = 0.001) and total work (1702 ± 442 J/1381 ± 432 J; P = 0.003) performed during plantar flexions were significantly increased with salbutamol. Salbutamol induced significant improvement in calf muscle endurance with similar metabolic responses during exercise, except slight differences in pHi. Other mechanisms than changes in muscle metabolism may be responsible for the ergogenic effect of salbutamol administration.     

Determination of the intracellular sodium concentration in perfused mouse liver by 31P and 23Na magnetic resonance spectroscopy

A combination of ³¹P and ²³Na NMR spectroscopy has been used to quantify the concentration of intracellular sodium, [Na]_IC in the isolated and perfused mouse liver. The ³¹P resonances of dimethyl methylphosphonate and LaDOTP^5?, markers of total tissue space and extracellular space, respectively, were used to determine the intracellular liver volume. For a mean wet weight of 1.7 ± 0.3 g, the intracellular liver volume as measured by ³¹P NMR averaged 1.2 ± 0.2 ml. The amount of intracellular sodium was measured from the baseline-resolved intracellular ²³Na resonance during perfusion of the shift reagent, TmDOTP^5?. These two measurements resulted in an NMR-determined value for [Na]_IC of 29.0 ± 5.2 mM. Separate measurement of total tissue Tm and Na by atomic absorption spectroscopy on the same samples provided an AAS-determined value for [Na]_Ic of 32.1 ± 7.4 mM. These results indicate that intracellular sodium in the isolated, perfused liver is 100% visible by ²³Na NMR spectroscopy.     

Simultaneous in vivo pH and temperature mapping using a PARACEST‐MRI contrast agent

Altered tissue temperature and/or pH is a common feature in pathological conditions, where metabolic demand exceeds oxygen supply such as in tumors and following stroke. Therefore, in vivo tissue temperature and pH may become valuable biomarkers for disease detection and the monitoring of disease progression or treatment response in conditions with altered metabolic demand. In this study, pH is measured using the amide protons of a thulium (Tm³⁺) complex with a DOTAM‐Glycine‐Lysine (ligand: Tm³⁺‐DOTAM‐Gly‐Lys). The pH was uniquely determined from the linewidth of the asymmetry curve of the chemical exchange saturation transfer spectrum, independent of contrast agent concentration, or temperature for a given saturation pulse. pH maps with an inter‐pixel standard deviation of less than 0.1 pH units were obtained in 10 mM Tm³⁺‐DOTAM‐Gly‐Lys solutions with pH ranging from 6.0 to 8.0 pH units at 37°C. Temperature maps were simultaneously obtained using the chemical shift of the chemical exchange saturation transfer peak. Temperature and pH maps are demonstrated in the mouse leg (N = 3), where the mean and standard deviation for pH was 7.2 ± 0.2 pH unit and temperature was 37.4 ± 0.5°C. Magn Reson Med, 70:1016–1025, 2013. © 2012 Wiley Periodicals, Inc.     

Dynamic Monitoring of Total-Body Absorption by 19F NMR Spectroscopy: One Hour Ventilation of HFA-134a in Male and Female Rats

Six male and six female Sprague-Dawley rats were ventilated head-only for 1 h on a 15% atmosphere of 1, 1, 1, 2-tetrafluoroethane (HFA-134a) in air in a magnetic resonance imaging spectrometer. Results from these dynamic ¹⁹F NMR studies suggest that a steady-state in vivo concentration of HFA-134a was approached at approximately 25 min into the exposure. Quantitative integration analysis using an external standard estimated this plateau to be 58.3 ± 11.9 mg of absorbed HFA-134a per rat. The HFA-134a ¹⁹F NMR signal disappeared rapidly following removal of the test atmosphere, with an elimination half-life of 4.6 ± 0.6 min in the male rats and 4.9 ± 1.5 min in the female rats. The data suggest that there was no statistical difference between the sexes in amount absorbed or in elimination half-lives.     

Proton transfer ratio,lactate, and intracellular pH in acute cerebral ischemia

The amide proton transfer ratio (APTR) from the asymmetry of the Z‐spectrum was determined in rat brain tissue during and after unilateral middle cerebral artery occlusion (MCAo). Cerebral lactate (Lac) as determined by ¹H NMR spectroscopy, water diffusion, and T_1ρ were quantified as well. Lac concentrations were used to estimate intracellular pH (pH_i) in the brain during the MCA occlusion. A decrease in APTR during occlusion indicated acidification from 7.1 to 6.79 ± 0.19 (a drop by 0.3 ± 0.2 pH units), whereas pH_i computed from Lac concentration was 6.3 ± 0.2 (a drop by 0.8 ± 0.2 pH units). Despite the disagreement between the two methods in terms of the size of the change in the absolute pH_i during ischemia, ΔAPTR and pH_i (and Lac concentration) displayed a strong correlation during the MCAo. Diffusion and T_1ρ indicated cytotoxic edema following MCA occlusion; however, APTR returned slowly toward the values determined in the contralateral hemisphere post‐ischemia. These data argue that the APTR during ischemia is affected not only by pH_i but by other physicochemical factors as well, and indicates different aspects of pathology in the post‐ischemic brain compared to those that influence water diffusion and T_1ρ. Magn Reson Med 57:647–653, 2007. © 2007 Wiley‐Liss, Inc.     

Localized 31P MR spectroscopy of the transplanted human kidney in situ shows altered metabolism in rejection and acute tubular necrosis

The purpose of this study was to investigate the function of transplant kidneys in situ, and to detect pathologic changes, using volume-selective phosphorous NMR spectroscopy (³¹P MRS). Localized ³¹P MR spectra were obtained from 37 patients using a whole-body MR scanner with a combination of surface coils, adiabatic excitation pulses, and a modified image-selected in vivo spectroscopy (ISIS) sequence. Seventeen patients with pathologic changes after renal transplant were compared with a control group of 20 patients with no evidence of transplant dysfunction. The transplant kidneys with rejection reaction showed higher ratios of inorganic phosphate (P_i) to adenosine triphosphate-α (ATP-α) than the normal control group (.4 ± .16 compared with .22 ± .11, P = .01) and reduced pH. The spectra of transplant kidneys with tubular necrosis had lower phosphomonoester (PME)/phosphodiester (PDE) ratios than the control group (.65 ± .35 compared with .96 ± .5, P = .04). The pathologies of rejection and tubular necrosis could be differentiated from each other by pH (6.93 ± .1 in rejection versus 7.14 ± .19 in tubular necrosis, P = .04). Preliminary results indicate that localized image-guided ³¹P MR spectroscopy of transplant kidneys in situ can detect rejection reactions and acute tubular necrosis noninvasively, providing an incentive for further research.     

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.     

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.     

Measurement of GABA following GABA-transaminase inhibition by gabaculine: A 1H and 31P NMR spectroscopic study of rat brain in vivo

A selective ¹H NMR spin-echo editing method was used to detect the CCH, of GABA in rat brain in vivo before and after intravenous administration of the highly selective GABA transaminase inhibitor, gabaculine (3-amino-2,3-dihydrobenzoic acid-HCl; 100 mg/kg, intravenously). The effects of the inhibitor on high energy phosphates and pH, were determined by ³¹P NMR. GABA levels increased approximately linearly (r = 0.81 to 0.94; P < 0.0005) from 1.9 ± 0.4 μmol/g (pre-gabaculine; mean ± SD) to between 6 and 8 μmollg after 4 hr at rates of accumulation of 1.1 to 2.9 μmol/hr/g. ¹H NMR spectroscopic measurements of cerebral GABA and its rate of turnover offers a new approach in the study of GABA-mediated processes in vivo.     

Increase of GPC Levels in Cultured Mammalian Cells during Acidosis. A 31P MR Spectroscopy Study Using a Continuous Bioreactor System

The purpose of this study was to study the metabolic events during a slow acidosis in three different cell lines by combining ³¹P magnetic resonance spectroscopy and hollow fiber bioreactor technology. The rate of change in intracellular pH, glycerophosphorylcholine (GPC), phophorylcholine (PCho), and nucleoside-triphosphate (NTP) levels were measured during 8 h of acidosis and 16 h of recovery in EPO, EAT, and RN1a cells, three cultured mammalians cell lines. Our results show a significant increase in GPC levels to 330 ± 21, 540 ± 25, and 220 ± 21% of their initial value correlated to a decrease of PCho levels to 57 ± 14, 58 ± 17 and 45 ± 15% of their initial value in EAT, RN1a, and EPO cells, respectively. These changes are discussed in terms of perturbation of energetic metabolism in cells undergoing a slow acidosis.     

Hepatic intracellular pH in vivo using F-quene 1 and 19F NMR spectroscopy

Intracellular pH (pHi) has been determined in vivo in livers from anaesthetized rats using both 31P NMR and 19F NMR spectroscopy. In the 31P NMR study pHi, determined from the chemical shift of endogenous Pi, was found to be 7.26 +/- 0.02. In the 19F NMR study on a separate group of animals pHi was determined from the chemical shift of F-Quene 1 infused via the portal vein and found to be 7.18 +/- 0.01. In approximately half of the 19F NMR studies no 19F signal could be detected in the liver probably because of the two probes could be caused by different intra- or intercellular distributions or by unknown effects of F-Quene 1 on metabolism.     

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.     

Simulated games activity vs continuous running exercise: A novel comparison of the glycemic and metabolic responses in T1DM patients

To compare the glycemic and metabolic responses to simulated intermittent games activity and continuous running exercise in type 1 diabetes. Nine patients (seven male, two female; 35 ± 4 years; HbA1c 8.1 ± 0.2%/65 ± 2 mmol/mol) treated on a basal‐bolus regimen completed two main trials, a continuous treadmill run (CON) or an intermittent running protocol (INT). Patients arrived to the laboratory fasted at ～ 08:00 h, replicating their usual pre‐exercise meal and administering a 50% reduced dose of rapid‐acting insulin before exercising. Blood glucose (BG), K⁺, Na⁺⁺, pH, triglycerides, serum cortisol and NEFA were measured at baseline and for 60 min post‐exercise. Interstitial glucose was measured for a further 23 h under free‐living conditions. Following exercise, BG declined under both conditions but was less under INT (INT ?1.1 ± 1.4 vs CON ?5.3 ± 0.4 mmol/L, P = 0.037), meaning more patients experienced hypoglycemia (BG ≤ 3.5 mmol/L; CON n = 3 vs INT n = 2) but less hyperglycemia (BG ≥ 10.9 mmol/L; CON n = 0 vs INT n = 6) under CON. Blood lactate was significantly greater, and pH lower, with a temporal delay in K⁺ under INT (P < 0.05). No conditional differences were observed in other measures during this time, or in interstitial glucose concentrations during the remaining 23 h after exercise. Simulated games activity carries a lower risk of early, but not late‐onset hypoglycemia than continuous running exercise in type 1 diabetes.     

Resting and end-diastolic [Ca2+]i measurements in the langendorff-perfused ferret heart loaded with a 19F NMR indicator

Intracellular free calcium concentration ([Ca²⁺]i) was measured in Langendorff-perfused ferret hearts (30°C, pH 7,4) by loading paced hearts with the ¹⁹F NMR calcium indicator, the 5,5′-difluoro derivative of 1,2-bis(o-aminophenoxy) ethane-N, N,N′,N′-tetraacetic acid (5FBAPTA), to an initial cytosolic concentration of approximately 120 uM. Increasing the pacing frequency raised the end-diastolic [Ca²⁺]i, from 299 ± 44 nM (mean ± SEM) at 0.2 Hz to 522 ± 54 nM at 1.0 Hz and 691 ± 166 nM at 2.0 Hz. Raising [Ca]^o from 1.8 to 7.0 mM at a pacing frequency of 1.0 Hz increased end-diastolic [Ca²⁺]i to 625 ± 39 nM. In unpaced hearts perfused with diltiazem (100 uM), [Ca²⁺]i fell rapidly to a steady-state value of <100 nM after 60 min. Raising [Ca]^o from 1.8 to 7.0 mM had no detectable effect on resting [Ca²⁺]i. The time course of the [Ca²⁺]i transient was measured in hearts paced at 1.1 Hz and perfused with 1.8 mM [Ca]^o. The peak [Ca²⁺]i was ～ 2 uM at approximately 150 msec after the pacing pulse, and peak developed LVP occurred at 550 msec compared with 280 msec in control hearts not loaded with 5FBAPTA. Comparisons with data obtained by other techniques, including fluorescent [Ca²⁺]i indicators, imply that although the end-diastolic [Ca²⁺]i values obtained with 5FBAPTA in beating hearts are elevated by the concentrations of intracellular 5FBAPTA required for signal detection, the changes in [Ca²⁺]i observed in response to experimental interventions are qualitatively consistent with previous data.     

Intracellular Volume Measurement and Detection of Edema: Multinuclear NMR Studies of Intact Rat Hearts during Normothermic Ischemia

The present study describes the cell volume dynamics in intact rat hearts, during ischemia and after reperfusion. Cell volumes were measured in isolated hearts by either ¹³C or ⁵⁹Co NMR of mannitol or cobalticyanide, respectively, as extracellular markers and ¹H NMR of water as the aqueous space marker. A constant volume chamber was built inside a 15-mm NMR tube; the contents of the chamber were measured with and without a heart. The intracellular volume of isolated rat hearts was estimated to be 2.45 ± 0.13 ml/g dry weight. In the perfused heart, adenosine triphosphate (ATP) and phosphocreatine (PCr) concentrations were calculated to be 12.2 ± 0.7 and 16.1 ± 1.0 mM, respectively. Consecutive volume measurements showed cell swelling of 16% during 30 min of ischemia, which was reduced at reperfusion to 7%. After 30 min of reperfusion, ATP and PCr concentrations were 4.5 ± 0.8 and 8.1 ± 0.9 mM. It is concluded that: (1) cell swelling is an ischemic event, which is partially reversed by reperfusion; and (2) continuous measurement of cell volumes provides intracellular molar concentrations of metabolites, which are the physiologically significant parameters.     

Metabolite kinetics in C6 rat glioma model using magnetic resonance spectroscopic imaging of hyperpolarized [1‐13C]pyruvate

In addition to an increased lactate‐to‐pyruvate ratio, altered metabolism of a malignant glioma can be further characterized by its kinetics. Spatially resolved dynamic data of pyruvate and lactate from C6‐implanted female Sprague–Dawley rat brain were acquired using a spiral chemical shift imaging sequence after a bolus injection of a hyperpolarized [1‐¹³C]pyruvate. Apparent rate constants for the conversion of pyruvate to lactate in three different regions (glioma, normal appearing brain, and vasculature) were estimated based on a two‐site exchange model. The apparent conversion rate constant was 0.018 ± 0.004 s^?1 (mean ± standard deviation, n = 6) for glioma, 0.009 ± 0.003 s^?1 for normal brain, and 0.005 ± 0.001 s^?1 for vasculature, whereas the lactate‐to‐pyruvate ratio, the metabolic marker used to date to identify tumor regions, was 0.36 ± 0.07 (mean ± SD), 0.24 ± 0.07, and 0.12 ± 0.02 for glioma, normal brain, and vasculature, respectively. The data suggest that the apparent conversion rate better differentiate glioma from normal brain (P = 0.001, n = 6) than the lactate‐to‐pyruvate ratio (P = 0.02). Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.