Diagnosing testicular function using 31P magnetic resonance spectroscopy: a current review

Patients with low sperm counts combined with normal concentrationsof gonadotrophins, and in whom physical examination and post-ejaculatoryurine analysis are normal, present a diagnostic dilemma. Thissituation can be caused by testicular failure or by ductal obstruction,which have very different clinical prognoses. Ductal obstructionmight be correctable by microsurgical vasovaso/vasoepididymostomy,whereas this approach is of no use in primary testicular failure.A possible diagnostic step for these patients is a testicularbiopsy to differentiate between hyposper-matogenesis and a normalgonad. However, to date testicular biopsy is seldom performedbecause of its invasive character. An alternative accurate,non-invasive method to assess testicular function could be veryhelpful in the evaluation of idiopathic azoosper-mia or idiopathicoligozoospermia. During the past decade, magnetic resonance(MR) spectroscopy has been developed from a scientific toolinto a non-invasive clinical diagnostic tool and has also beenused to study testicular function. Recent studies have shownthat ³¹P-MR spectroscopy, based upon differences in the ratioof peaks of phosphomonoester to P-adenos-inetriphosphate, isa non-invasive technique able to differentiate between groupsof patients with testicular failure and ductal obstruction,and it correlates reasonably well with the averaged mean Johnsenscore of testicular biopsy. The role for a non-invasive techniquein the diagnosis of male infertility, such as 31P-MR spectroscopy,can be manifold. It serves not only as an alternative for biopsybut can also be used to assess obstruction as the cause of infertilityin patients with subnormal sperm counts, and to predict thechances of pregnancy in patients planned for vaso-vasostomyto correct a prior vasectomy. However, the main limitation toMR spectroscopy becoming a universal clinical diagnostic techniqueis the limited availability of 1.5 Tesla MR scanners.     

In vivo 31P MRS detection of an alkaline inorganic phosphate pool with short T1 in human resting skeletal muscle

Non‐invasive determination of mitochondrial content is an important objective in clinical and sports medicine. ³¹P MRS approaches to obtain information on this parameter at low field strength typically require in‐magnet exercise. Direct observation of the intra‐mitochondrial inorganic phosphate (Pi) pool in resting muscle would constitute an alternative, simpler method. In this study, we exploited the higher spectral resolution and signal‐to‐noise at 7T to investigate the MR visibility of this metabolite pool. ³¹P in vivo MR spectra of the resting soleus (SOL) muscle were obtained with ¹H MR image‐guided surface coil localization (six volunteers) and of the SOL and tibialis anterior (TA) muscle using 2D CSI (five volunteers). A resonance at a frequency 0.38 ppm downfield from the cytosolic Pi resonance (Pi₁; pH 7.0 ± 0.04) was reproducibly detected in the SOL muscle in all subjects and conditionally attributed to the intra‐mitochondrial Pi pool (Pi₂; pH 7.3 ± 0.07). In the SOL muscle, the Pi₂/Pi₁ ratio was 1.6 times higher compared to the TA muscle in the same individual. Localized 3D CSI results showed that the Pi₂ peak was present in voxels well away from blood vessels. Determination of the T1 of the two Pi pools in a single individual using adiabatic excitation of the spectral region around 5 ppm yielded estimates of 4.3 ± 0.4 s vs 1.4 ± 0.5 s for Pi₁ and Pi₂, respectively. Together, these results suggest that the intra‐mitochondrial Pi pool in resting human skeletal muscle may be visible with ³¹P MRS at high field. Copyright © 2010 John Wiley & Sons, Ltd.     

Rat skeletal muscle metabolism in experimental heart failure: effects of physical training

Skeletal muscle metabolic abnormalities exist in chronic heart failure. The influence of physical training on muscle metabolism after myocardial infarction was studied in a rat model. ³¹P magnetic resonance spectroscopy and enzyme assays were performed in Wistar rats 12 weeks after coronary artery ligation. Infarcted rats were allocated randomly to either 6 weeks of training or non-training. Spectra were collected from the calf muscles during sciatic nerve stimulation at 2 Hz. Fibre typing and enzymatic assays were performed on the muscles of the contralateral non stimulated leg. Post-mortem rats were also divided into severe and moderate heart failure according to the lung weight per body weight. At 200 g twitch tension, phosphocreatine and pH were found to be significantly lower in the non-trained severe heart failure group compared with the other groups. Phosphocreatine recovery half-time was significantly longer in the non-trained group with severe heart failure and correlated with the citrate synthase activity in the muscle. The training did not induce a change in the enzyme activities in the infarcted animals with moderate heart failure but did correct the lower citrate synthase activity in the non-trained severe heart failure animals. This normalization of muscle metabolism was achieved by training without any change in calf muscle mass, making atrophy unlikely to be the sole cause of the metabolic changes in heart failure. Training in rats with severe heart failure can reverse the abnormalities of skeletal muscle metabolism, implicating decreased physical activity in the aetiology of these changes.     

31P magnetic resonance fingerprinting for rapid quantification of creatine kinase reaction rate in vivo

The purpose of this work was to develop a ³¹P spectroscopic magnetic resonance fingerprinting (MRF) method for fast quantification of the chemical exchange rate between phosphocreatine (PCr) and adenosine triphosphate (ATP) via creatine kinase (CK). A ³¹P MRF sequence (CK‐MRF) was developed to quantify the forward rate constant of ATP synthesis via CK ( ), the T ₁ relaxation time of PCr ( ), and the PCr‐to‐ATP concentration ratio ( . The CK‐MRF sequence used a balanced steady‐state free precession (bSSFP)‐type excitation with ramped flip angles and a unique saturation scheme sensitive to the exchange between PCr and γATP. Parameter estimation was accomplished by matching the acquired signals to a dictionary generated using the Bloch‐McConnell equation. Simulation studies were performed to examine the susceptibility of the CK‐MRF method to several potential error sources. The accuracy of nonlocalized CK‐MRF measurements before and after an ischemia–reperfusion (IR) protocol was compared with the magnetization transfer (MT‐MRS) method in rat hindlimb at 9.4 T (n  = 14). The reproducibility of CK‐MRF was also assessed by comparing CK‐MRF measurements with both MT‐MRS (n  = 17) and four angle saturation transfer (FAST) (n  = 7). Simulation results showed that CK‐MRF quantification of was robust, with less than 5% error in the presence of model inaccuracies including dictionary resolution, metabolite T ₂ values, inorganic phosphate metabolism, and B ₁ miscalibration. Estimation of by CK‐MRF (0.38 ± 0.02 s^?1 at baseline and 0.42 ± 0.03 s^?1 post‐IR) showed strong agreement with MT‐MRS (0.39 ± 0.03 s^?1 at baseline and 0.44 ± 0.04 s^?1 post‐IR). estimation was also similar between CK‐MRF and FAST (0.38 ± 0.02 s^?1 for CK‐MRF and 0.38 ± 0.11 s^?1 for FAST). The coefficient of variation from 20 s CK‐MRF quantification of was 42% of that by 150 s MT‐MRS acquisition and was 12% of that by 20 s FAST acquisition. This study demonstrates the potential of a ³¹P spectroscopic MRF framework for rapid, accurate and reproducible quantification of chemical exchange rate of CK in vivo .     

Phosphorus-31 magnetic resonance spectroscopy of forearm flexor muscles in student rowers using an exercise protocol adjusted for differences in cross-sectional muscle area

Summary To assess exercise energy metabolism of forearm flexor muscles in rowers, six male student rowers and six control subjects matched for age and sex were studied using phosphorus-31 magnetic resonance spectroscopy (³¹P-MRS). Firstly, to adjust for the effect of differences in cross-sectional muscle area, the maximal cross-sectional area (CSA_max) of the forearm flexor muscles was estimated in each individual using magnetic resonance imaging. Multistage exercise was then carried out with an initial energy production of 1 J · cm^–2 CSA_max for 1 min and an increment of 1 J · cm^–2 CSA_max every minute to the point of muscle exhaustion. A series of measurements of³¹P-MRS were performed every minute. The CSA_max was significantly greater in the student rowers than in the control subjects [19.8 (SD 2.2) vs 17.1 (SD 1.2) cm²,P<0.05]. The absolute maximal exercise intensity (J · min^–1) was greater in the rowers than in the control subjects. However, the maximal exercise intensity per unit of muscle cross sectional area (J · min^–1 · cm^–2) was not significantly different between the two groups. During mild to moderate exercise intensities, a decrease in phosphocreatine and an increase in inorganic phosphate before the onset of acidosis were significantly less in the rowers, indicating a requirement of less adenosine 5-diphosphate to drive adenosine 5-triphosphate production. The onset of acidosis was also significantly delayed in the rowers. No difference was observed in forearm blood flow between the two groups at the same exercise intensity (J · min^–1 · cm^–2). These results demonstrated that the findings of the maintenance of a higher level of phosphocreatine and a lower level of inorganic phosphate with less acidosis observed in the rowers were the results of the intrinsic characteristics of energy metabolism of their muscles and that these characteristics were independent of their greater cross-sectional muscle area.     

Muscle metabolism during exercise using phosphorus-31 nuclear magnetic resonance spectroscopy in adolescents

Very little has been reported on muscle energetics during exercise in adolescents. This is attributable to the difficulty of subjecting children to muscle biopsy. The purpose of this study was to investigate the characteristics of muscle metabolism during exercisein vivo in adolescents by comparing firstly, with adults and secondly, the differences resulting from physical activity using phosphorus-31 nuclear magnetic resonance (³¹PNMR) spectroscopy. The subjects were boys aged 12 to 15 years, comprising 21 trained boys and 23 control boys, and 6 adults controls. The ratio of phosphocreatine (PCr):(PCr + P_i), where P_i is inorganic phosphate intracellular pH at exhaustion and the time constant of PCr during recovery were measured in all the subjects using³¹PNMR. Both groups of children showed higher values of PCr:(PCr + P_i) and intracellular pH at exhaustion than did the adult control group (P < 0.01 orP < 0.05). However, no significant differences were found between the trained boys and the control boys with respect to PCr:(PCr + P_i) and intracellular pH at exhaustion. On the other hand, we found the same values for PCr time constant in all groups. This result suggested no differences of the muscle oxidative capacity between children and adults. We concluded that the adolescents, aged 12 to 15 years in both the trained and control groups, had less glycolytic ability during exercise than the adults.     

Absolute quantification of phosphorus metabolite concentrations in human muscle in vivo by 31P MRS: a quantitative review

31P MRS offers a unique view of muscle metabolism in vivo, but correct quantification is important. Inter-study correlation of estimates of [Pi] and [phosphocreatine (PCr)] in a number of published studies suggest that the main technical problem in calibrated 31P MRS studies is the measurement of PCr and Pi signal intensities, rather than absolute quantification of [ATP]. For comparison, we discuss the few published biopsy studies of calf muscle and a selection of the many studies of quadriceps muscle. The ATP concentration is close to the value that we obtained in calf muscle in our own study, presented here, on four healthy subjects, by localised 31P MRS using a surface coil incorporating an internal reference and calibrated using an external phantom. However, the freeze-clamp biopsy PCr concentration is approximately 20% lower than the value obtained by 31P MRS, consistent with PCr breakdown by creatine kinase during freezing. Finally, we illustrate some consequences of uncertainty in resting [PCr] for analysis of mitochondrial function from PCr kinetics using a published 31P MRS study of exercise and recovery: the lower the assumed resting [PCr], the lower the absolute rate of oxidative ATP synthesis estimated from the PCr resynthesis rate; in addition, the lower the assumed resting [PCr], or the higher the assumed [total creatine], the higher the apparent resting [ADP], and therefore the more sigmoid the relationship between the rate of oxidative ATP synthesis and [ADP]. Correct quantification of resting metabolite concentrations is crucially important for this sort of analysis. Our own results ([PCr] = 33 +/- 2 mM, [Pi] = 4.5 +/- 0.2 mM, and [ATP] = 8.2 +/- 0.4 mM; mean +/- SEM) are close to the overall mean values of the 10 published studies on calf muscle by 'calibrated' 31P MRS (as in the present work), and of [PCr] and [Pi] in a representative selection of 'uncalibrated' 31P MRS studies (i.e. from measured PCr/ATP and Pi/ATP ratios, assuming a literature value for [ATP]).     

Significance of bilayer-forming phospholipids for skeletal muscle insulin sensitivity and mitochondrial function

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE), which make up the bulk of mammalian cell membrane phospholipids, are recognized for their importance in metabolic health. Perturbations in the ratio of PC:PE can affect membrane integrity and function, which thus have serious health consequences. Imbalance in the hepatic PC and PE membrane content can be linked to metabolic disturbances such as ER stress, fatty liver and insulin resistance. Given that impaired insulin sensitivity underlies the pathology of many metabolic disorders and skeletal muscle is a significant regulator of energy metabolism, it is likely that aberrant phospholipid metabolism in skeletal muscle affects whole-body insulin sensitivity. Sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity and mitochondrial function respond to alterations in PC:PE ratio and are associated with glucose homeostasis. Moreover, PC and PE content within the mitochondrial membrane influence mitochondrial respiration and biogenesis and thus, metabolic function. As skeletal muscle phospholipids respond to stimuli such as diet and exercise, understanding the implications of imbalances in PC:PE ratio is of great importance in the face of the rising epidemic of obesity related diseases. This review will summarize the current state of knowledge signifying the links between skeletal muscle PC:PE ratio and insulin sensitivity with respects to PC and PE metabolism, SERCA activity, mitochondrial function and exercise.     

Assessment of muscular metabolism in peripheral arterial occlusive disease using31P nuclear magnetic resonance spectroscopy

Summary The behaviour of muscular metabolism was investigated in 10 patients with peripheral arterial occlusive disease stage II at rest and after maximum erometric calf exercise. The intracellular concentrations of phosphocreatine, inorganic phosphate and adenosine triphosphate as well as muscle pH were measured by means of³¹P magnetic resonance spectroscopy and compared with those from a control group. In addition, arteriovenous differences in concentrations of lactate, pyruvate, ammonia, hypoxanthine and alanine in the femoral blood were determined. The fall in intracellular phosphocreatine concentration during exercise was significantly greater in the calf muscles of patients with arterial occlusion than in controls and correlated linearly with the increase in femoral arteriovenous differences in lactate, ammonia and alanine. A significant fall in intracellular pH occurred during muscular activity only in the patient group, but not in the identically exercised control group. The fall in pH correlated closely with the rise in arteriovenous lactate difference in the femoral blood. The intramuscular ATP concentration remained constant throughout the exercise procedure. The behaviour of both the directly and indirectly measured metabolites permits the deduction of activation of the creatine kinase reaction, glycolysis, myokinase reaction and the purine nucleotide cycle during exercise-induced hypoxia in the presence of arterial occlusive disease. The anaerobic production of energy is sufficient to maintain the ATP concentration even during claudication pain. Magnetic resonance spectroscopy proved to be a useful tool for non-invasive assessment of the metabolic changes in peripheral arterial occlusive disease.Abbreviations ADP adenosine diphosphate - AMP adenosine monophosphate - ATP adenosine triphosphate - AVD arteriovenous difference - (P)AOD (peripheral) arterial occlusive disease - IMP inosine monophosphate - NAD⁺ nicotinamide adenine dinucleotide - PCr phosphocreatine - P₁ inorganic phosphate - ³¹P-MRS ³¹phosphorus magnetic resonance spectroscopy - NMR nuclear magnetic resonance - PNC purine nucleotide cycle     

Effects of exercise‐induced intracellular acidosis on the phosphocreatine recovery kinetics: a 31P MRS study in three muscle groups in humans

Little is known about the metabolic differences that exist among different muscle groups within the same subjects. Therefore, we used ³¹P‐magnetic resonance spectroscopy (³¹P‐MRS) to investigate muscle oxidative capacity and the potential effects of pH on PCr recovery kinetics between muscles of different phenotypes (quadriceps (Q), finger (FF) and plantar flexors (PF)) in the same cohort of 16 untrained adults. The estimated muscle oxidative capacity was lower in Q (29 ± 12 mM min^‐1, CV_{inter‐subject} = 42%) as compared with PF (46 ± 20 mM min^‐1, CV_{inter‐subject} = 44%) and tended to be higher in FF (43 ± 35 mM min^‐1, CV_{inter‐subject} = 80%). The coefficient of variation (CV) of oxidative capacity between muscles within the group was 59 ± 24%. PCr recovery time constant was correlated with end‐exercise pH in Q (p < 0.01), FF (p < 0.05) and PF (p <0.05) as well as proton efflux rate in FF (p < 0.01), PF (p < 0.01) and Q (p = 0.12). We also observed a steeper slope of the relationship between end‐exercise acidosis and PCr recovery kinetics in FF compared with either PF or Q muscles. Overall, this study supports the concept of skeletal muscle heterogeneity by revealing a comparable inter‐ and intra‐individual variability in oxidative capacity across three skeletal muscles in untrained individuals. These findings also indicate that the sensitivity of mitochondrial respiration to the inhibition associated with cytosolic acidosis is greater in the finger flexor muscles compared with locomotor muscles, which might be related to differences in permeability in the mitochondrial membrane and, to some extent, to proton efflux rates. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitative ATP synthesis in human liver measured by localized 31P spectroscopy using the magnetization transfer experiment

The liver plays a central role in intermediate metabolism. Accumulation of liver fat (steatosis) predisposes to various liver diseases. Steatosis and abnormal muscle energy metabolism are found in insulin-resistant and type-2 diabetic states. To examine hepatic energy metabolism, we measured hepatocellular lipid content, using proton MRS, and rates of hepatic ATP synthesis in vivo, using the 31P magnetization transfer experiment. A suitable localization scheme was developed and applied to the measurements of longitudinal relaxation times (T1) in six healthy volunteers and the ATP-synthesis experiment in nine healthy volunteers. Liver 31P spectra were modelled and quantified successfully using a time domain fit and the AMARES (advanced method for accurate, robust and efficient spectral fitting of MRS data with use of prior knowledge) algorithm describing the essential components of the dataset. The measured T1 relaxation times are comparable to values reported previously at lower field strengths. All nine subjects in whom saturation transfer was measured had low hepatocellular lipid content (1.5 +/- 0.2% MR signal; mean +/- SEM). The exchange rate constant (k) obtained was 0.30 +/- 0.02 s(-1), and the rate of ATP synthesis was 29.5 +/- 1.8 mM/min. The measured rate of ATP synthesis is about three times higher than in human skeletal muscle and human visual cortex, but only about half of that measured in perfused rat liver. In conclusion, 31P MRS at 3 T provides sufficient sensitivity to detect magnetization transfer effects and can therefore be used to assess ATP synthesis in human liver.     

The effect of iron deficiency on skeletal muscle metabolism of the rat

Using ³¹P magnetic resonance spectroscopy we compared skeletal muscle bioenergetics in Wistar rats made chronically anaemic by being fed a diet deficient in iron for 6 weeks with chronically iron deficient animals given a normal diet as well as 5 mg iron dextran at 2 or 7 days before experimentation. Spectra of the gastrocnemius muscle were taken at rest and during stimulation of the sciatic nerve at 2 Hz for 10 min. Relative concentrations of intracellular phosphate (Pi), phosphocreatine (PCr) and ATP were determined. Iron deficiency increased PCr breakdown and production of acid in stimulated skeletal muscle. Recovery of PCr and Pi concentrations after exercise was slow. These metabolic changes are consistent with either a reduction in supply of oxygen to the muscle cell or altered oxidative phosphorylation by the mitochondria. The latter may be mediated by defective function of iron-containing proteins crucial in oxidative phosphorylation and this is suggested both by the observation that treatment with iron, sufficient to correct the anaemia, does not completely reverse the metabolic changes and that there is a different time course for such metabolic improvements and the observed increase in haemoglobin concentration.     

Blood flow and muscle bio-energetics by31P-nuclear magnetic resonance after local cold acclimation

Summary To clarify the origin of local cold adaptation and to define precisely its influence on muscle bio-energetics during local exercise, five subjects were subjected to repeated 5°C cold water immersion of the right hand and forearm. The first aim of our investigation was therefore carried out by measuring local skin temperatures and peripheral blood flow during a cold hand test (5°C, 5 min) followed by a 10-min recovery period. The³¹P by nuclear magnetic resonance (³¹PNMR) muscle bio-energetic changes, indicating possible heat production changes, were measured during the recovery period. The second aim of our investigation was carried out by measuring³¹PNMR muscle bioenergetics during handgrip exercise (10% of the maximal voluntary contraction for 5 min followed by a 10-min recovery period) performed both at a comfortable ambient temperature (22°C; E) and after a cold hand test (EC), before and after local cold adaptation. Local cold adaptation, confirmed by warmer skin temperatures of the extremities (+30%,P<0.05), was related more to an increased peripheral blood flow, as shown by the smaller decrease in systolic peak [–245 (SEM 30) Hz vs –382 (SEM 95) Hz,P<0.05] than to a change in local heat production, because muscle bioenergetics did not vary. Acute local cold immersion decreased the inorganic phosphate: phosphocreatine (PC) ratio during EC compared to E [+0.006 (SEM 0.010) vs +0.078 (SEM 0.002) before acclimation and +0.029 (SEM 0.002) vs +0.090 (SEM 0.002) after acclimation respectively, P<0.05] without significant change in the PC:-adenosine triphosphate ratio and pH. Local adaptation did not modify these results statistically. The recovery of PC during E increased after acclimation [9.0 (SEM 0.2) min vs 3.0 (SEM 0.4) min,P<0.05]. These results suggested that local cold adaptation is related more to peripheral blood flow changes than to increased metabolic heat production in the muscle.     

31P nuclear magnetic resonance study on changes in phosphocreatine and the intracellular pH in rat skeletal muscle during exercise at various inspired oxygen contents

We measured ATP, phosphocreatine (PCr), inorganic phosphate (P_i), and the intracellular pH in rat hindlimb muscles during submaximal isometric exercise with various O₂ deliveries using³¹P nuclear magnetic resonance spectroscopy (³¹P NMR) to evaluate changes in energy metabolism in relation to O₂ availability. Delivery of O₂ to muscles was altered by controlling the fractional concentration of inspired oxygen (F _IO₂) at 0.50, 0.28, 0.21, 0.11 and 0.08 with monitoring partial pressure of oxygen and carbon dioxide, and bicarbonate at the femoral artery. The steady-state ratio of PCr : (PCr + P_i) during exercise decreased as a function ofF _IO₂ even at 0.21. Significant acidification of the intracellular pH during exercise occurred at 0.08F _IO₂. Change in the PCr : (PCr + P_i) ratio demonstrated that the oxidative capacity, i.e. the maximal rate of the oxidative phosphorylation reaction, in muscle was not limited by O₂ delivery at 0.50F _IO₂, but was significantly limited at 0.21F _IO₂ or below. Change in the intracellular pH at 0.08F _IO₂ could be interpreted as an increase in lactate, suggesting activation of glycolysis. Correlation between the PCr : (PCr + P_i) ratio and the intracellular pH revealed the existence of a critical PCr : (PCr + P_i) ratio and pH for glycolysis activation at around 0.4 and 6.7, respectively.     

Fatigue and recovery of phosphorus metabolites and pH during stimulation of rat skeletal muscle: an evoked electromyography and in vivo31P-nuclear magnetic resonance spectroscopy study

³¹P-nuclear magnetic resonance spectroscopy and evoked electromyography were applied to rat skeletal muscle to examine the mechanism of muscle fatigue and the recovery of muscle phosphorus metabolites and pH during fatigue. When the sciatic nerve was electrically stimulated at 1 Hz, the contraction force of the gastrocnemius muscle decreased gradually to 46% of the maximal force, accompanied by a decrease in phosphocreatine (PCr) and a corresponding increase in inorganic phosphate (P_i) and diprotonated inorganic phosphate (H₂PO₄ ^–). Neither the amplitudes of compound muscle action potentials (CMAP) nor muscle pH changed significantly. At 10-Hz stimulation, contraction force rapidly decreased to 26% of maximal force, accompanied by a decrease in PCr and increases in P_i and H₂PO₄ ^–. Muscle pH decreased for a few minutes, then gradually recovered during continued stimulation. The amplitude of the CMAP also decreased for a few minutes and then reached steady values. At 100-Hz stimulation, the contraction force decreased to 6% of the maximal force and there was a decrease in the amplitude of the CMAP. However, the changes in the phosphorus metabolites and pH were transient and recovered to the control value during the stimulation. These results indicated that fatigue at 1 and 100-Hz stimulation was mainly caused by the change in phosphorus metabolite concentrations and electrical failure, respectively, and that fatigue at 10-Hz stimulation might have been due to both of the these factors. These results also indicated that electrical failure might have been the cause of the recovery of the phosphorus metabolites and pH during 100-Hz stimulation and of pH during 10-Hz stimulation.     

Reproducibility of 31P cardiac magnetic resonance spectroscopy at 3 T

The purpose of this work was to take advantage of the new clinical field strength of 3 T to implement and optimize a chemical shift imaging (CSI) acquisition protocol to produce spectra of high quality with high specificity to the myocardium within a clinically feasible scan time. Further, an analysis method was implemented dependent purely on anatomical location of spectra, and as such free from any potential user bias caused by inference from spectral information. Twenty healthy male subjects were scanned on two separate occasions using the optimized CSI protocol at 3 T. Data were analyzed for intra‐ and inter‐subject variability, as well as intra‐ and inter‐observer variability. The average phosphocreatine (PCr)/adenosine triphosphate (ATP) value for scan 1 was 2.07 ± 0.38 and for scan 2 was 2.14 ± 0.46, showing no significant difference between scans. Intra‐subject variability was 0.43 ± 0.35 (percentage difference 20%) and the inter‐subject coefficient of variation was 18%. The intra‐observer variability, assessed as the absolute difference between analyses of the data by a single observer, was 0.14 ± 0.24 with no significant difference between analyses. The inter‐observer variability showed no significant differences between the PCr/ATP value measured by four different observers as demonstrated by an intra‐class correlation coefficient of 0.763. The increased signal available at 3 T has improved spatial resolution and thereby increased myocardial specificity without any significant decrease in reproducibility over previous studies at 1.5 T. We present an acquisition protocol that routinely provides high quality spectra and a robust analysis method that is free from potential user bias. Copyright © 2008 John Wiley & Sons, Ltd.     

Methodological standardization for a multi-institutional in vivo trial of localized 31P MR spectroscopy in human cancer research. In vitro and normal volunteer studies

A multi-institutional group has been created to demonstrate the utility of in vivo 31P magnetic resonance spectroscopy (31P-MRS) to study human cancers in vivo. This review is concerned with the novel problems concerning quality control in this large multinational trial of 31P MRS. Our results show that the careful and systematic performance of the quality control tests depicted here (standardized dual 1H/31P tuned radiofrequency probe, quality control procedures, routine use of 1H irradiation while acquiring 31P MR signals) has ensured comparable results between the different institutions. In studies made in vitro, the root-mean-square error was 3.6 %, and in muscle of healthy volunteers in vivo the coefficients of variance for the ratios phosphocreatine/nucleotide-triphosphates, phosphocreatine/noise and nucleotide-triphosphate/noise were 12.2, 7.0 and 10.8 %, respectively. The standardization of the acquisition protocol for in vivo-localized 31P MR spectroscopy across the different institutions has resulted in comparable in vivo data, decreasing the possible problems related to a research study carried out under a multi-institutional setting.