Quantitative evaluation of the lactate signal loss and its spatial dependence in press localized (1)H NMR spectroscopy.

Localized (1)H NMR spectroscopy using the 90 degrees -t(1)-180 degrees -t(1)+t(2)-180 degrees -t(2)-Acq. PRESS sequence can lead to a signal loss for the lactate doublet compared with signals from uncoupled nuclei which is dependent on the choice of t(1) and t(2). The most striking signal loss of up to 78% of the total signal occurs with the symmetrical PRESS sequence (t(1)=t(2)) at an echo time of 2/J (approximately 290 ms). Calculations have shown that this signal loss is related to the pulse angle distributions produced by the two refocusing pulses which leads to the creation of single quantum polarization transfer (PT) as well as to not directly observable states (NDOS) of the lactate AX(3) spin system: zero- and multiple-quantum coherences, and longitudinal spin orders. In addition, the chemical shift dependent voxel displacement (VOD) leads to further signal loss. By calculating the density operator for various of the echo times TE=n/J, n=1, 2, 3,..., we calculated quantitatively the contributions of these effects to the signal loss as well as their spatial distribution. A maximum signal loss of 75% can be expected from theory for the symmetrical PRESS sequence and TE=2/J for Hamming filtered sinc pulses, whereby 47% are due to the creation of NDOS and up to 28% arise from PT. Taking also the VOD effect into account (2 mT/m slice selection gradients, 20-mm slices) leads to 54% signal loss from NDOS and up to 24% from PT, leading to a maximum signal loss of 78%. Using RE-BURP pulses with their more rectangular pulse angle distributions reduces the maximum signal loss to 44%. Experiments at 1.5 T using a lactate solution demonstrated a maximum lactate signal loss for sinc pulses of 82% (52% NDOS, 30% PT) at TE=290 ms using the symmetrical PRESS sequence. The great signal loss and its spatial distribution is of importance for investigations using a symmetrical PRESS sequence at TE=2/J.

Unveiling extracellular inorganic phosphate signals from blood in human cardiac 31P NMR spectra.

31P NMR spectra of the human heart are usually contaminated by signals that originate from blood. The main blood signals are 2,3-diphosphoglycerate (2,3-DPG), which overlap and sometimes obscure the signal of myocardial inorganic phosphate used to calculate intracellular pH and to monitor metabolic changes in the heart. In this work we demonstrate, first, that even without proton decoupling the resolution of such spectra can be high enough to evaluate intracellular inorganic phosphate of myocardium in about 70% of the spectra and, second, that extracellular inorganic phosphate from blood contributes a signal in the chemical shift region of the 2-phosphate signal of 2,3-DPG.

Potential pitfall in the determination of free [Mg2+] by 31P NMR when using the beta/alpha-ATP peak height ratio method.

Recently, Clarke et al. (Clarke K, Kashiwaya Y, King MT, Gates D, Keon CA, Cross HR, Radda GK, Veech RL. The beta/alpha peak height ratio of ATP. A measure of free [Mg2+(free)] using 31P NMR, J. Biol. Chem. 1996;271:21142 21150.) reported a new method to noninvasively determine the concentration of intracellular free magnesium ([Mg2+(free)]) based on the measurement of the peak height ratio h(beta/alpha) of the beta- and alpha-ATP signals in 31P NMR spectra. h(beta/alpha) varies with [Mg2+(free)], however, the study presented here shows that h(beta/alpha) also strongly depends on the homogeneity of the static magnetic field. For this reason, we performed at a magnetic field strength of 1.5 T 31P NMR measurements of solutions that mimic intracellular medium. The magnetic field homogeneity was varied by changing the currents in the shim coils, and the effect on hbeta/alpha is demonstrated with and without proton decoupling. In both cases, h(beta/alpha) strongly depends on the magnetic field homogeneity and can therefore lead to a pitfall in the determination of [Mg2+(free)].

31P nuclear magnetic resonance spectroscopy: a noninvasive tool to monitor metabolic abnormalities in left ventricular hypertrophy in human.

31p nuclear magnetic resonance (NMR) spectroscopy represents a unique instrument to noninvasively monitor myocardial metabolism in humans. The technique has been used to study the metabolism in myocardial hypertrophy in humans with hypertension, aortic stenosis, aortic incompetence, mitral regurgitation, and hypertrophic cardiomyopathy, as well as after maintenance dialysis or long-term physical exercise in elite cyclists. A primary aim is the determination of the phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio, which reflects the energetic state of the myocardium. Recent investigations take advantage of proton decoupling in 31p NMR spectroscopy, which, besides the PCr/ATP ratio, also allows the determination of the inorganic phosphate/ PCr and the phosphomonoester/PCr ratios as additional indicators for alterations in myocardial metabolism. Abnormal myocardial metabolism was found in humans with aortic stenosis, mitral regurgitation, hypertrophic cardiomyopathy, and in patients who undergo maintenance dialysis. A trend toward a lower PCr/ATP ratio was reported in hypertension and aortic incompetence patients. Several studies have revealed a dependence of the metabolic abnormalities on the degree of heart failure, and one study claimed that a correlation with the extent of hypertrophy exists. No metabolic abnormalities were found in elite cyclists.

31P/1H WALTZ-4 broadband decoupling at 1.5 T: different versions of the composite pulse and consequences when using a surface coil.

Two derivatives of the wideband alternating-phase low-power technique for zero-residual splitting (WALTZ)-4 decoupling sequence for broadband decoupling named WALTZ-4a and WALTZ-4b were compared for their proton decoupling performance in 31P nuclear magnetic resonance (NMR) spectroscopy using a Siemens Magnetom SP 1.5 T whole-body imager. Version WALTZ-4a originally implemented by the manufacturer doubles and triples the transmitter amplitude of the 90 degrees pulse to achieve the 180 degrees and 270 degrees flip angle required for one composite pulse R in the WALTZ sequence. WALTZ-4b follows the sequence reported from Shaka et al. and leaves the transmitter amplitude constant but increases the durations of the 180 degrees and 270 degrees pulses. The decoupling performance of WALTZ-4b is superior because it requires less transmitter power and, therefore, it is advantageous in all in vivo studies where a low specific absorption rate is desired. When WALTZ-4 is used in combination with a surface coil for transmission the theoretically required flip angles cannot be achieved in the entire sensitive volume of the coil. The decoupling performance was therefore investigated at lower and higher flip angles. Again, WALTZ-4b is advantageous and provides, in certain ranges that are off-resonant from the decoupling frequency, a good decoupling quality even for flip angles that are only 60% of the theoretically required.

Detection of phosphomonoester signals in proton-decoupled 31P NMR spectra of the myocardium of patients with myocardial hypertrophy.

Proton-decoupled 31P NMR spectroscopy at 1.5 T of the anterior left ventricular myocardium was used to monitor myocardial phosphate metabolism in asymptomatic patients with hypertrophic cardiomyopathy (HCM, n = 14) and aortic stenosis (AS, n = 12). In addition to the well-known phosphorus signals a phosphomonoester (PME) signal was detected at about 6.9 ppm in 7 HCM and 2 AS patients. This signal was not observed in the spectra of normal controls (n = 11). We suggest that in spectra of patients with myocardial hypertrophy the presence of a PME signal reflects alterations in myocardial glucose metabolism.

Proton-decoupled myocardial 31P NMR spectroscopy reveals decreased PCr/Pi in patients with severe hypertrophic cardiomyopathy.

Disturbed myocardial energy metabolism may occur in patients with primary hypertrophic cardiomyopathy (HCM). A noninvasive way to gain insight into cardiac energy metabolism is provided by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. 31P NMR spectroscopy with proton decoupling was performed in 13 patients aged 13-36 years with HCM on a 1.5 T Magnetom with a double resonant surface coil. A 2D chemical shift imaging (CSI) sequence in combination with slice selective excitation was used to acquire spectra of the anteroseptal region of the left ventricle (volume element: 38 mL). The chemical shifts of the phosphorus metabolites, intracellular pHi, and coupling constants J(alphabeta) and J(gammabeta) were calculated. Peak areas of 2,3-diphosphoglycerate (DPG), Pi, and adenosine triphosphate (ATP) were determined and corrected for blood contamination, saturation, and differences in nuclear Overhauser enhancements (NOE). The maximum thickness of the interventricular septum (IVSmax) was determined from tomographic long-axis images and expressed as number of standard deviations above the mean of the normal population (Z score). The patients were then divided into 2 groups: 6 patients with moderate HCM (HCMm, Z score < or = 5) and 7 patients with severe HCM (HCMs, Z score > 5). No differences between both groups and a control group of healthy volunteers (n = 16) were found with respect to phosphocreatine (PCr)/gamma-ATP ratio, pHi, or the coupling constants. Only the PCr/Pi ratio differed significantly from the control group (HCM(all), alpha < 0.05, HCMs, alpha < 0.02, 2-sided U test). The decrease of the PCr/Pi ratio in patients with HCM is probably caused by ischemically decreased oxygen supply in the severely hypertrophied myocardium.

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(gammabeta) = 16.1 Hz +/- 0.2 Hz and J(alphabeta) = 16.3 Hz +/- 0.1 Hz (mean +/- SEM, n = 14). Both, the J-coupling constants and the chemical-shift difference between alpha- and beta-ATP (delta(alphabeta) = 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 alpha and beta phosphate resonances, which is the more accurate result.

31P NMR studies of human soleus and gastrocnemius show differences in the J gamma beta coupling constant of ATP and in intracellular free magnesium.

Localized proton decoupled 31P in vivo NMR spectroscopy of the human calf muscle was performed using a 1.5-T whole-body imager and the slice selective two-dimensional chemical-shift-imaging (2D-CSI) technique. The 31P-31P coupling constants and the chemical shifts of ATP were compared in gastrocnemius and soleus. Significant differences were found in the coupling constant J gamma beta: (18.1 +/- 0.7) Hz versus (17.1 +/- 0.6) Hz (means +/- SD, P < 10-5). Differences were also observed in the chemical shift separation delta alpha beta between the alpha- and beta-ATP signal: (8.498 +/- 0.023) ppm versus (8.522 +/- 0.222) ppm (p < 0.001) in gastrocnemius and soleus, respectively. A higher [MgATP]/[ATPfree] ratio and a significantly higher level of intracellular free magnesium of (0.52 +/- 0.06) mM in gastrocnemius versus (0.46 +/- 0.05) mM in soleus (p < 0.001) can be derived based on delta alpha beta and KDMgATP. Heterogeneity needs to be taken into account in clinical studies on magnesium by NMR methods in calf muscle. The coupling constant J gamma beta provides additional information, possibly on enzymatic processes, and correlates with [Mg2+free]. The detailed analysis of muscles with different fiber type characteristics lends support to the significance of this parameter in evaluating metabolism. The data reported can be used as prior knowledge for fits in which the coupling constants are set to a fixed value.

Change in chemical shift and splitting of 31P gamma-ATP signal in human skeletal muscle during exercise and recovery.

Proton decoupled 31P in vivo NMR spectroscopy of the human finger flexor muscles was performed during exercise and recovery using a 1.5 T whole-body imager. Predominantly the gamma-ATP signal shows a splitting caused by different signal contributions with chemical shifts that vary independently. Studies on the human gastrocnemius and biceps femoris muscle were undertaken to investigate the appearance of the splitting in these muscles as well. In all cases more than one signal contribution was found which might represent the different muscle fibre types and their recruitment pattern following exercise. An analysis of the chemical shifts (delta) of ATP results in changes of up to 0.4 ppm and 0.1 ppm for delta gamma- and delta beta-ATP, respectively. Based solely on the chemical shifts of the ATP 31P signals the tissue pH value following exercise was determined. The result was in good agreement with the value derived from delta Pi.

Phosphorus J coupling constants of ATP in human myocardium and calf muscle.

Proton-decoupled 31P NMR spectroscopy of the heart and calf muscle 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 (elements of 38 ml) were obtained within 20 to 35 min from which the homonuclear J coupling constants of ATP could be determined. In myocardium, J gamma beta = 16.03 +/- 0.17 Hz and J alpha beta = 15.82 +/- 0.23 Hz were obtained, while the values in calf muscle were J gamma beta = 17.16 +/- 0.12 Hz and J alpha beta = 16.04 +/- 0.09 Hz. The difference in J gamma beta was significant. According to the literature, a possible reason for greater ATP J coupling constants is a smaller fraction of ATP complexed to magnesium. However, the chemical-shift difference between alpha- and beta-ATP, which is also a measure for the fraction of ATP complexed to magnesium, showed only a small difference in ATP complexation: 88% in myocardium and 90% in calf muscle. This small difference cannot account for the observed difference in J gamma beta.

Characterization of bone marrow after transplantation by means of magnetic resonance.

Magnetic resonance (MR) has become a new tool for noninvasive characterization of bone marrow in patients with hematological disorders in the past few years. Experiences gained from 1H MR imaging and spectroscopic investigations in 48 healthy volunteers and more than 130 patients with hematological disorders are reported and interpreted. Twenty-four of the patients underwent bone marrow transplantation (BMT) before the MR examinations. The findings in these studies provided noninvasive characterization and monitoring of vertebral marrow after BMT. Specifically, MR techniques were found to be suitable for studies of different aspects in physiological and pathological alterations of bone marrow: The water content within the marrow can be analyzed by chemical-shift selective-imaging techniques with good spatial resolution. Spectroscopic methods also allow more sensitive quantification of the signal fractions, as well as separate evaluation of the relaxation times of water and lipids. Relaxometry might be useful to characterize the cellular and extracellular portions of water molecules. Furthermore, the distribution of the magnetic field within small-volume elements of vertebral marrow can be measured. The field distribution is influenced by the trabecular density and the composition of the marrow. High amounts of hemosiderin in the marrow result in clearly broadened field distributions, demonstrated by increasing line widths in MR proton spectra. Magnetic resonance techniques can be used to assess not only the cellularity of the bone marrow, but also metabolic alterations in this compartment which result from cytotoxic treatment or immunological processes.

Hematopoietic reconstitution after bone marrow transplantation: assessment with MR imaging and H-1 localized spectroscopy.

Magnetic resonance (MR) studies were performed in 14 patients as early as possible (21-110 days) after bone marrow transplantation (BMT). MR characteristics of lumbar vertebral bone marrow were studied with T1-weighted spin-echo imaging, water- and fat-selective imaging with a frequency-selective excitation technique, and point-resolved spatially localized proton spectroscopy. Signals from water and fat protons and their T1 and T2 values were analyzed. Water proton signal intensity correlated well with cellularity within bone marrow, as determined with parallel iliac crest biopsies. The fraction of signal from water in red bone marrow of patients with allogeneic transplants from siblings (four cases) was significantly higher than in four patients with autologous transplants. The latter showed very low cellularity in the period of about 4 weeks after BMT because of the cytotoxic pretreatment of the bone marrow. The MR results in six patients with allogeneic transplants from unrelated donors ranged widely, depending on the complications after BMT. Analysis of data obtained with the different techniques showed that water- and fat-selective MR imaging and spectroscopic methods are useful for noninvasive monitoring of hematopoietic reconstitution after BMT.

Spin-echo methods for the determination of 31P transverse relaxation times of the ATP NMR signals in vivo.

31P magnetic resonance spectroscopy (MRS) examinations of the calf muscles of healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the Hahn spin-echo and the frequency-selective spin-echo method. Additional measurements with the J-coupling refocused double echo are presented. The most reliable determination of T2 relaxation times is possible with the frequency-selective spin echo. The other methods yield substantially wrong results. Theoretical explanations are given how J-coupling and pulse-angle deviations affect the signals and therefore the T2 determinations. The calculations for a weakly coupled homonuclear AX spin system are shown because they demonstrate most of the relevant facts. In addition, some important results for a homonuclear AMX spin system, which the ATP is considered to be, are given.

31P transverse relaxation times of ATP in human brain in vivo.

31P MRS examinations of the brain of 10 healthy volunteers were performed to determine T2 of the coupled ATP signals by use of the localized 90 degrees-TE/2-2662-TE/2-acq frequency selective spin echo sequence for elimination of phase and intensity distortions. The T2 relaxation times obtained are much longer than usually assumed: gamma-ATP: 89 +/- 9 ms; alpha-ATP: 84 +/- 6 ms; beta-ATP: 62 +/- 3 ms.

[Special MR methods for primary bone tumors: II. Volume selective 1H-spectroscopy]. / Spezielle MR-Methoden bei primären Knochentumoren: II. Volumenselektive 1H-Spektroskopie.

The method of localised 1H MR spectroscopy was used in 19 examinations in 9 patients with primary bone tumours in order to obtain spectral signals and to determine whether these are specific for tumour classification. The spectra were obtained by a double spin echo method and the tumour tissue showed very high water content and only minor lipid and proton signals which showed J-coupling characteristics. The latter are not found in normal bone marrow and are probably due to products of tumour metabolism. The resolution of the spectra within a 13 mm or 20 mm tissue cube depends largely on the structural homogeneity of the tumour. The signal patterns in the spectra were not specific to histological tumour types.

[Special MR methods for primary bone tumors: I. Chemical shift selective imaging]. / Spezielle MR-Methoden bei primären Knochentumoren: I. Chemical-shift-selektive Bildgebung.

The value of selective imaging of fat and water compared with proton density, T1- and T2- weighted MR sequences was studied in the course of 32 examinations on 22 primary bone tumours in various parts of the body. Fat selective images showed practically signal free areas for osteogenic tumours which could be distinguished from surrounding fat containing soft tissues. Water selective images improved definition of the tumour margin from oedema in the bone marrow. Chemical shift artefacts are avoided by these methods and therefore fat and water selective images provide better spatial resolution for identical pixel sizes.

A pitfall associated with determination of transverse relaxation times of the 31P NMR signals of ATP using the Hahn spin-echo.

T2 measurements of 31P NMR signals of ATP using the Hahn 90 degrees-180 degrees spin-echo sequence imply difficulties whenever the 180 degrees pulse angle is not completely perfect. The reason for this finding is the crucial influence of the J-couplings of the ATP signals which result in intensity modulations and consequently in false T2 values even when the echo times are chosen to TE = n/J. Examinations on the calf muscles of healthy volunteers were performed to demonstrate this effect and its influence on in vivo T2 determinations. The T2 relaxation times evaluated with the Hahn spin-echo in combination with a Helmholtz coil are far shorter than the true T2 values.