Double-tuned Surface Coil Research Articles

Correlation between skeletal muscle acetylcarnitine and phosphocreatine metabolism during submaximal exercise and recovery: interleaved 1H/31P MRS 7 T study

Acetylcarnitine is an essential metabolite for maintaining metabolic flexibility and glucose homeostasis. The in vivo behavior of muscle acetylcarnitine content during exercise has not been shown with magnetic resonance spectroscopy. Therefore, this study aimed to explore the behavior of skeletal muscle acetylcarnitine during rest, plantar flexion exercise, and recovery in the human gastrocnemius muscle under aerobic conditions. Ten lean volunteers and nine overweight volunteers participated in the study. A 7 T whole-body MR system with a double-tuned surface coil was used to acquire spectra from the gastrocnemius medialis. An MR-compatible ergometer was used for the plantar flexion exercise. Semi-LASER-localized 1H MR spectra and slab-localized 31P MR spectra were acquired simultaneously in one interleaved exercise/recovery session. The time-resolved interleaved 1H/31P MRS acquisition yielded excellent data quality. A between-group difference in acetylcarnitine metabolism over time was detected. Significantly slower τPCr recovery, τPCr on-kinetics, and lower Qmax in the overweight group, compared to the lean group was found. Linear relations between τPCr on-kinetics, τPCr recovery, VO2max and acetylcarnitine content were identified. In conclusion, we are the first to show in vivo changes of skeletal muscle acetylcarnitine during acute exercise and immediate exercise recovery with a submaximal aerobic workload using interleaved 1H/31P MRS at 7 T.

Muscle Glycogen Content during Endurance Training under Low Energy Availability

The present study investigated the effects of three consecutive days of endurance training under conditions of low energy availability (LEA) on the muscle glycogen content, muscle damage markers, endocrine regulation, and endurance capacity in male runners. Seven male long-distance runners (19.9 ± 1.1 yr, 175.6 ± 4.7 cm, 61.4 ± 5.3 kg, maximal oxygen uptake [V˙O2max]: 67.5 ± 4.3 mL·kg·min) completed two trials consisting of three consecutive days of endurance training under LEA (18.9 ± 1.9 kcal·kg FFM·d) or normal energy availability (NEA) (52.9 ± 5.0 kcal·kg FFM·d). The order of the two trials was randomized, with a 2-wk interval between trials. The endurance training consisted of 75 min of treadmill running at 70% of V˙O2max. Muscle glycogen content, respiratory gas variables, and blood and urine variables were measured in the morning for three consecutive days of training (days 1-3) and on the following morning after training (day 4). As an indication of endurance capacity, time to exhaustion at 19.0 ± 0.8 km·h to elicit 90% of V˙O2max was evaluated on day 4. During the training period, body weight, fat-free mass, and skeletal muscle volume were significantly reduced in LEA (P = 0.02 for body weight and skeletal muscle volume, P = 0.01 for fat-free mass). Additionally, muscle glycogen content was significantly reduced in LEA (~30%, P < 0.001), with significantly lower values than those in NEA (P < 0.001). Time to exhaustion was not significantly different between the two trials (~20 min, P = 0.39). Three consecutive days of endurance training under LEA decreased muscle glycogen content with lowered body weight. However, endurance capacity was not significantly impaired.

Quantitative Evaluation of the First Order Creatine-Kinase Reaction Rate Constant inin vivoShunted Ovine Heart Treated with Oxandrolone Using Magnetization Transfer31P Magnetic Resonance Spectroscopy (MT-31P-MRS) and1H/31P Double-Tuned Surface Coil: a Preliminary Study

Quantitative Evaluation of the First Order Creatine-Kinase Reaction Rate Constant in<i>in vivo</i>Shunted Ovine Heart Treated with Oxandrolone Using Magnetization Transfer³¹P Magnetic Resonance Spectroscopy (MT-³¹P-MRS) and¹H/³¹P Double-Tuned Surface Coil: a Preliminary Study

Energy Deregulation Precedes Alteration in Heart Energy Balance in Young Spontaneously Hypertensive Rats: A Non Invasive In Vivo31P-MR Spectroscopy Follow-Up Study.

IntroductionGradual alterations in cardiac energy balance, as assessed by the myocardial PCr/ATP-ratio, are frequently associated with the development of cardiac disease. Despite great interest for the follow-up of myocardial PCr and ATP content, cardiac MR-spectroscopy in rat models in vivo is challenged by sensitivity issues and cross-contamination from other organs.MethodsHere we combined MR-Imaging and MR-Spectroscopy (Bruker BioSpec 9.4T) to follow-up for the first time in vivo the cardiac energy balance in the SHR, a genetic rat model of cardiac hypertrophy known to develop early disturbances in cytosolic calcium dynamics.ResultsWe obtained consistent 31P-spectra with high signal/noise ratio from the left ventricle in vivo by using a double-tuned (31P/1H) surface coil. Reasonable acquisition time (<3.2min) allowed assessing the PCr/ATP-ratio comparatively in SHR and age-matched control rats (WKY): i) weekly from 12 to 21 weeks of age; ii) in response to a bolus injection of the ß-adrenoreceptor agonist isoproterenol at age 21 weeks.DiscussionAlong weeks, the cardiac PCr/ATP-ratio was highly reproducible, steady and similar (2.35±0.06) in SHR and WKY, in spite of detectable ventricular hypertrophy in SHR.At the age 21 weeks, PCr/ATP dropped more markedly (-17.1%±0.8% vs. -3,5%±1.4%, P<0.001) after isoproterenol injection in SHR and recovered slowly thereafter (time constant 21.2min vs. 6.6min, P<0.05) despite similar profiles of tachycardia among rats.ConclusionThe exacerbated PCr/ATP drop under ß-adrenergic stimulation indicates a defect in cardiac energy regulation possibly due to calcium-mediated abnormalities in the SHR heart. Of note, defects in energy regulation were present before detectable abnormalities in cardiac energy balance at rest.

Design and testing of a 1.5 Tesla double-tuned ( 1H/ 31P) RF surface coil with intrinsic geometric isolation

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton ( 1H) detection and localized spectra of phosphorous ( 31P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the 1H frequency and the internal coil tuned at the 31P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.

Pre-treatment energy status of primary rat tumours as the best predictor of response to 5-fluorouracil chemotherapy: a magnetic resonance spectroscopy study in vivo.

Fluorine-19 magnetic resonance spectroscopy (19F-M RS) studies of the pharmacokinetics of the anticancer drug 5-fluorouracil (FU) in patients at several clinical centres have shown that increased tumour retention of FU is associated with patient response. The mechanism of this increased tumour retention (FU trapping) is unknown. We used a pre-clinical model to investigate whether other MRS-measurable parameters would correlate with the response to FU treatment and, thus, help elucidate the mechanism(s) involved in FU trapping. MRS spectra were obtained using a double-tuned (31P/19F) surface coil from 29 N-methyl-N-nitrosourea-induced primary rat tumours. 31P-MRS spectra were acquired immediately prior to and at 2.5 h post-treatment with a bolus i.p. injection of FU (100 mg/ kg); 19F-MRS spectra were acquired during the intervening 2.5-h period for measurement of the tumour uptake and retention of FU and of its metabolism to the cytotoxic fluoronucleotides (FNuct). From these data, four parameters were measured: tumour pH and energy status (NTP/Pi) before treatment, total FU retention, and FU anabolism to FNuct (expressed as micromoles per gram per 2.5 h). In addition, tumour response was determined at 7 days post-treatment by measurement of the percentage of change in tumour weight and was classified according to standard oncological criteria as follows: progressive (P) for a > or =25% increase, remissive (R) for a > or =50% decrease or stable (S) for values lying between these two. Analysis of variance (ANOVA) for statistical assessment revealed that groups P, S and R were not distinguishable using the MRS parameters; although when S and R were combined as one group of non-progressive disease (NPD; n = 24), both the NTP/Pi ratio and the total FNuct formed were significantly greater (P = 0.04) than those observed in the P group (n = 5). Considering all 29 tumours, linear regression showed that there were positive significant correlations between the NTP/Pi ratio and (a) the percentage of response (P = 0.04), (b) the pre-treatment pH (P = 0.002) and (c) FU retention (P = 0.02), but not FNuct formation (P = 0.66). Unlike results reported in the clinic, the percentage of response and FU retention were neither significantly correlated (P = 0.22) nor associated when groups P and NPD were compared (P = 0.27, Fischer's exact test). FNuct, however, was significantly associated with response, as was the NTP/Pi ratio (P < or = 0.02). Combination of FNuct with the NTP/Pi ratio increased the significance of the association with response (P = 0.003, Fischer's exact test). Our results indicate that in this particular model the pre-treatment tumour NTP/Pi ratio was the best predictor of response to a bolus injection of FU, rather than FNuct formation or FU retention. An elevated NTP/Pi ratio could reflect a well-vascularised tumour with an improved capacity for energy-dependent FU uptake and metabolism to FNuct, suggesting that further investigation of this parameter could be an important line of research, which may aid the identification of tumours likely to be sensitive to FU chemotherapy in the clinic.

Surface coil cardiac tagging and 31P spectroscopic localization with B1-insensitive adiabatic pulses.

A technique is presented for MRI tagging in the presence of inhomogeneous B1 fields. A rectangular tagging grid is produced with B1-insensitive adiabatic pulses in a magnetization preparation period that precedes image acquisition. Phantom results demonstrate that the method is well-suited to surface coil experiments. The technique is applied to a canine model of myocardial ischemia to track the spatially dependent wall motion of the left ventricle during the cardiac cycle. Transmural 31P spectra are acquired from the same double-tuned surface coil, with tagging and spectroscopy performed for the first time, during normal, ischemic, and recovery conditions for the same animal.

Double resonant quadrature birdcage.

The combined acquisition of proton images and localized spectra is considered essential to the application of NMR techniques to human and animal research. The ideal imaging/spectroscopy coil for our purposes would be one that provides the highest possible signal-to-noise, high homogeneity, and operation on two or more frequencies without retuning requirements or cable changes. To address these needs we have developed a quadrature double-tuned birdcage. We have incorporated our earlier work on the transformer coupled double-tuned surface coil into the birdcage structure by placing two birdcages in a coaxial configuration. This structure resonates at 34.6 MHz (phosphorus resonance at 2.0 T) and 85.5 MHz (proton resonance at 2.0 T). The quadrature performance of this coil for phosphorus was excellent, with a signal-to-noise that was 133% of our linear reference. The proton performance was less efficient, with a signal to noise that was 67% of our linear reference, but still quite sufficient for imaging. A phosphorus spectra and proton image of a rat abdomen are shown.

Absolute quantitation of phosphorus metabolites in the cerebral cortex of the newborn human infant and in the forearm muscles of young adults using a double-tuned surface coil

The application of a double-tuned surface coil with strong coupling for both 31P and 1H to the in vivo measurement of metabolite concentrations by NMR spectroscopy is demonstrated. It is shown that sample loading, although important for a coil tuned to a single frequency, does not necessarily have a significant effect on absolute quantitation results if the coil is strongly coupled to the sample for both nuclei. For the coil used in the present study, the spectrometer calibration coefficient is almost independent of loading and the 1H and 31P flip angles at the coil center produced by fixed length pulses could be arranged to be nearly equal over a range of loading conditions. In seven normal infants, of gestational plus postnatal age 35 to 37 weeks, the cerebral cortex nucleotide triphosphate concentration was 3.7 ± 0.6 m M/liter wet (mean ± SD). Metabolite concentrations were low in the cerebral cortex of a severely birth asphyxiated infant. The adenosine triphosphate concentration in the resting, fresh forearm muscles of six young adults was 6.3 ± 0.8 m M/liter wet.

A comparison of double‐tuned surface coils

The combined acquisition of proton images and localized spectra is considered essential to the practical application of NMR techniques to human and animal research. Double-tuned surface coils which have been introduced to the literature are intended to address the problem; however, a careful evaluation of available designs is lacking. The "trap" method, the loop gap resonator design, and the transformer-coupled double-tuned design are evaluated here using bench tests of signal intensity and Q as well as signal-to-noise measurements on a 2-T imager/spectrometer. Comparisons are made relative to optimized single-tuned circuits of the same size for both protons at 85 MHz and phosphorus at 34 MHz. The results suggest that the "trap" design and the transformer coupled design are very efficient (98%) in the low-frequency mode (34 MHz) while the loop gap resonator is relatively inefficient (82%). In the high-frequency mode (85 MHz) the loop gap resonator is 75% efficient while the "trap" design and the transformer coupled coil are closer to 50% efficient.

Metabolic changes in rabbit spinal cord after trauma: magnetic resonance spectroscopy studies.

Combined phosphorus and proton magnetic resonance spectroscopy (MRS), using double-tuned surface coils, was used to monitor certain metabolic changes in the L-3 spinal segment of anesthetized rabbits prior to and following experimental spinal cord trauma. Following severe trauma, resulting in spastic paraplegia, there was a delayed and progressive accumulation of lactic acid, a decline in intracellular pH, and a loss of high-energy phosphates. Maximal alterations occurred between 2 and 3 hours after the trauma, with little further change by 4 hours. Histological examination 2 weeks after trauma showed tissue necrosis and cavitation. These findings support the concept of secondary tissue injury after spinal cord trauma and suggest that early changes in metabolism, as shown by MRS, may predict irreversible tissue damage.

INEPT-enhanced 13C spectroscopy using double-tuned surface coils

The problems of in vivo 13C spectroscopy are threefold, viz., the low sensitivity of the 13C nucleus, the low natural abundance of 13C (1. 1’S), and the low in vivo concentration of metabolites. Despite these difficulties 13C spectra of natural abundance glycogen have been obtained (I), but the experimental duration of such experiments is relatively long. This article describes an attempt to increase the sensitivity of 13C spectroscopy for in vivo applications by means of the INEPT polarization transfer technique (2). INEPT, nuclear Overhauser enhancement (NOE), and DEPT (3, 4) are established techniques for increasing the sensitivity of low-y nuclei, by a transfer of polarization from a J-coupled higher-y nucleus, normally ‘H. The in vivo application of these techniques for i3C spectroscopy is handicapped by the low intrinsic sensitivity of the experiment, which requires that signal reception be via a surface coil. However, if this is also used for transmission, then there is an extremely inhomogeneous Bi field. If signal transmission is by means of a larger coil, with a homogeneous field, then it may be necessary to decouple the coils. There is also a reduction in the effective bore size due to the presence of two coils. A number of schemes for 90” excitation, 180” refocusing, and inversion pulses have been suggested that are largely insensitive to the effects of BI inhomogeneity (5, 6). These in principle provide the requisite pulses for INEPT by surface coil excitation only. The full implementation of DEPT requires RF pulses having a range of flip angles, which is at present unrealistic for surface coil excitation, although DEPT enhancement of the signal from CH groups would be possible in these circumstances. INEPT has the advantage over NOE that the effective T1 is governed by the proton relaxation rate, not the longer ‘H-13C cross-relaxation rates, and the advantage over DEPT that CH, CH1, and CH3 groups are equally enhanced. However, the basic INEPT sequence gives spectra that are difficult to interpret, while refocused INEPT requires more RF pulses than DEPT. The basic INEPT pulse sequence is

31P and 1H NMR spectroscopy to study the effects of gallopamil on brain ischemia.

Studies were performed on 16 cats to evaluate the potential protective effects of Gallopamil on brain ischemia. Brain energy state was determined by 31P NMR and lactate concentration was determined by 1H NMR. Double-tuned surface coils (tuned to 35.8 and 88.4, respectively) were placed on the head after skin and muscle were removed from the calvarium. A 2.1-T, 25-cm-bore Oxford magnet interfaced to a Phosphoenergetics 250-80 spectrometer was used. The cats were bled to 50 mm Hg for 10 min with subsequent application of bilateral carotid occlusion for 10 min to produce ischemia. In all animals, brain energy state as measured by Pi/PCr and lactate concentrations were determined over 5-min intervals (before, during, and after the onset of ischemia). While Gallopamil did not prevent decreases in brain energy state or attenuate the rise in lactate concentration seen during ischemia, brain from animals treated with Gallopamil had a more rapid return of pHi to baseline during the recovery period. In Gallopamil-treated cats, higher levels of lactate were necessary to cause a similar decrease in pHi when compared to controls. The rate of lactate recovery to baseline levels was similar in both groups (control = -0.38 +/- 0.14 mM/min; Gallopamil = -0.44 +/- 0.32 mM/min). In conclusion, Gallopamil appears to lessen the acidosis caused by cerebral ischemia. In addition, we have demonstrated that multinuclear NMR spectroscopy is a powerful tool to study the effects of drugs on cerebral metabolism.

Effect of hypoglycemic encephalopathy upon amino acids, high-energy phosphates, and pHi in the rat brain in vivo: detection by sequential 1H and 31P NMR spectroscopy.

Metabolic alterations in amino acids, high-energy phosphates, and intracellular pH during and after insulin hypoglycemia in the rat brain was studied in vivo by 1H and 31P nuclear magnetic resonance (NMR) spectroscopy. Sequential accumulations of 1H and 31P spectra were obtained from a double-tuned surface coil positioned over the exposed skull of a rat while the electroencephalogram was recorded continuously. The transition to EEG silence was accompanied by rapid declines in phosphocreatine, nucleoside triphosphate, and an increase in inorganic orthophosphate in 31P spectra. In 1H spectra acquired during the same time interval, the resonances of glutamate and glutamine decreased in intensity while a progressive increase in aspartate was observed. Following glucose administration, glutamate and aspartate returned to control levels (recovery half-time, 8 min); recovery of glutamine was incomplete. An increase in lactate was detected in the 1H spectrum during recovery but it was not associated with any change in the intracellular pH as assessed in the corresponding 31P spectrum. Phosphocreatine returned to control levels following glucose administration, in contrast to nucleoside triphosphate and inorganic orthophosphate which recovered to only 80% and 200% of their control levels, respectively. These results show that the changes in cerebral amino acids and high-energy phosphates detected by alternating the collection of 1H and 31P spectra allow for a detailed assessment of the metabolic response of the hypoglycemic brain in vivo.

4443761 NMR spectroscopy

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton (1H) detection and localized spectra of phosphorous (31P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the 1H frequency and the internal coil tuned at the 31P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.

Use of double-tuned surface coils for the application of 13C NMR to brain metabolism

Use of double-tuned surface coils for the application of 13C NMR to brain metabolism