Phase-modulated Rotating-frame Imaging Research Articles

Suppression of artifacts in the phase-modulated rotating-frame imaging experiment using the maximum-entropy method

Phase-modulated rotating-frame imaging, a technique used. for the detection of localized metabolites in vivo, is usually implemented in a less than ideal manner because of the practical constraints imposed by the human or animal sample. As a consequence, the spectra obtained by Fourier transformation contain artifacts which distort or obscure the genuine spectral features. An attractive alternative is to use the maximum-entropy method to process the data, incorporating the time-domain response of the nuclear spins predicted by the Bloch equations. Here we demonstrate this approach using simulated data, data from phantoms, and data from the human liver and chest wall. We show that artifacts in the Fourier-transform spectra arising from off resonance effects, imperfect pulse angles, and truncation can be effectively avoided by maximum-entropy processing.

Depth selective quantification of phosphorus metabolites in human calf muscle.

We have used phase modulated rotating frame imaging, a depth selective NMR technique, in conjunction with two methods of calibration, in order to determine the feasibility of quantifying phosphorus compounds in selected regions of a biological sample. In one method, we related peak areas obtained from a sample to the peak area of an external reference located within the receiver coil, previously calibrated against a standard. In the second method we measured peak areas from a standard separately and related them directly to the area of the sample peak. We examined the calf muscles of male volunteers, positioning the coil to obtain signal mainly from the gastrocnemius in the shallow slices and soleus in the deep slices. The concentrations of Pi, phosphocreatine and ATP (in mmol/kg tissue) were 3.0 +/- 0.5, 18 +/- 2 and 4.8 +/- 0.2 at 2 cm depth (mean +/- SD; n = 5). These results are similar to published biopsy data. A comparison with published values obtained from other NMR quantification methods suggests that, while it is possible to obtain consistent results within one laboratory, it is not currently possible to obtain similar results between laboratories. This is evident from the fact that different laboratories report different phosphocreatine/ATP ratios, indicating that the techniques are limited by variations in the processes of data collection and peak area measurement.

Spatially Localized Magnetic Resonance Spectroscopy of the Brains of Normal and Asphyxiated Newborns

Phase-modulated rotating frame imaging is a modification of magnetic resonance spectroscopy, which uses a linear radiofrequency field gradient to obtain spatially localized biochemical information. Phase-modulated rotating frame imaging was used to study regional cerebral energy metabolism in the brains of 9 normal newborns and 25 newborns after birth asphyxia. Relative concentrations of phosphorus-containing metabolites and intracellular pH were determined for brain tissue at three specified depths below the brain surface for all neonates. Wide variations in metabolite ratios were seen among normal neonates, and considerable metabolic heterogeneity was demonstrated in individual neonates by depth-resolved spectroscopy. Asphyxiated neonates with severe hypoxic-ischemic encephalopathy and a poor neurodevelopmental outcome showed the expected rise in inorganic orthophosphate and fall in phosphocreatine concentrations in both global and spatially localized spectra. Phase-modulated rotating frame imaging showed that metabolic derangement was less in superficial than in deeper brain tissue. The inorganic orthophosphate-adenosine triphosphate ratio from 1 to 2 cm below the brain surface was more accurate than any global metabolite ratio for the identification of neonates with a poor short-term outcome. These data are consistent with the known vulnerability of subcortical brain tissue to hypoxic-ischemic injury in the full-term neonate.

71 PHOSPHOMONOESTERS, PHOSPHODIESTERS AND PHOSPHOLIPID BILAYERS STUDIED BY MAGNETIC RESONANCE SPECTROSCOPY (MRS) OF INFANT BRAINS AND LIVERS

Phosphomonoesters (PME-mainly phosphoethanolamine), and phosphodiester + phospholipid bilayers (PDE + PB) can be quantified noninvasively using phosphorus MRS. Spectra from the livers of 7 normal infants (gest'n 27-40w, age 3-76d), and the brains of 12 other normal infants (gest'n 37-42w, age 1-14d) were obtained by MRS, using phase modulated rotating frame imaging (PMRFI) for spatial localisation. Global metabolite ratios relative to adenosine triphosphate (ATP) are shown with comparable data from adults. Liver and brain have more PME (p<0.001), and liver has less PDE + PB (p<0.02), in the infant than in the adult: Depth resolved PMRFI data show high PME/ATP at all depths in infant brain and liver. PDE+PB does not increase wich depth in the infant brain, unlike the fully myelinated adult brain. The sum of PDE(mainly phospholipid breakdown products)and PB is reduced compared to adults in localised spectra of white matter (p<0.01)

Rapid Communication: Response of the Human Brain to a Hypercapnic Acid Load in Vivo

1. The aim of this investigation was to measure the change in intracellular pH of human brain in vivo in response to hypercapnia. 2. Five healthy male subjects inspired air for 20 min and then 5% CO2/95% O2 for 30 min, of which the first 10 min was used to achieve a steady-state end-tidal CO2 measurement. 3. 31P nuclear magnetic resonance spectroscopy was used to measure intracellular pH while breathing air and during hypercapnia. Simultaneous localization between superficial and deep brain was achieved by using the phase-modulated rotating frame imaging technique. One subject volunteered to breath air for a further phase-modulated rotating frame imaging study while recovering from hypercapnia. 4. End-tidal CO2 increased when breathing 5% CO2/95% O2 (on air, 5.57 +/- 0.21%; on 5% CO2/95% O2, 6.41 +/- 0.16%; rise = +0.84 +/- 0.09%; means +/- SEM) causing a reduction in brain intracellular pH, which was more pronounced in deep brain (5 cm = mainly white matter, from 7.02 +/- 0.006 pH units to 6.96 +/- 0.001 pH units, mean +/- SEM) than in superficial brain (2 cm = mainly grey matter, from 7.02 +/- 0.006 pH units to 7.00 +/- 0.006 pH units, mean +/- SEM). 5. The white matter responded to hypercapnia with a greater fall in intracellular pH than the grey matter. This could either be due to differences in blood flow between grey and white matter in response to hypercapnia or to differences in intracellular pH regulation/buffering between these two tissues.

Spatially resolved changes in diabetic rat skeletal muscle metabolism in vivo studied by 31P-n.m.r. spectroscopy

Phase-modulated rotating-frame imaging (p.m.r.f.i.), a localization technique for 31P-n.m.r. spectroscopy, has been applied to obtain information on the heterogeneity of phosphorus-containing metabolites and pH in the skeletal muscle of control and streptozotocin-diabetic rats. Using this method, the metabolic changes in four spatially resolved longitudinal slices (where slice I is superficial and slice IV is deep muscle) through the ankle flexor muscles have been investigated at rest and during steady-state isometric twitch-contraction at 2 Hz. At rest, intracellular pH was lower, and phosphocreatine (PCr)/ATP was higher, throughout the muscle mass in diabetic compared with control animals. The change in PCr/ATP in diabetic muscle correlated with a decrease in the chemically determined ATP concentration. During the muscle stimulation period, the decrease in pH observed in diabetic muscle at rest was maintained, but not exacerbated, by the contractile stimulus. Stimulation of muscle contraction caused more marked changes in PCr/(PCr + Pi), PCr/ATP and Pi/ATP in the diabetic group. These changes were most evident in slice III, which contains the greatest proportion of fast glycolytic-oxidative (type IIa) fibres, in which statistically significant differences were observed for all metabolite ratios. The results presented suggest that some degree of heterogeneity occurs in diabetic skeletal muscle in vivo with respect to the extent of metabolic dysfunction caused by the diabetic insult and that regions of the muscle containing high proportions of type IIa fibres appear to be most severely affected.

Imaging of human brain creatine kinase activity in vivo.

Creatine kinase activity and high-energy phosphate concentration have been investigated using localized 31P spectroscopy in the human brain in vivo. The phase-modulated rotating frame imaging technique, incorporating magnetization transfer and inversion recovery, has been used to produce a 1-dimensional rate profile map of steady-state enzyme activity. Large differences in the flux from phosphocreatine (PCr) to ATP have been discovered between volumes of human brain consisting of predominantly gray (2.0 cm) and white (4.5 cm) matter. The concentration of PCr changes slightly (2.0 cm = 5.20 +/- 0.45 mmol.l-1, 4.5 cm = 4.63 +/- 0.31 mmol.l-1), while the ATP concentration remains within limits (3.30 +/- 0.4 mmol.l-1). No change in pHi was detected between the two regions in normal volunteers (n = 6). The forward rate constant of the PCr----ATP reaction in regions of predominantly gray matter (0.30 +/- 0.04 s-1) was twice that of white matter (0.16 +/- 0.02 s-1) in vivo.

PATTERNS OF ABNORMAL CEREBRAL ENERGY METABOLISM FOLLOWING BIRTH ASPHYXIA

Phase modulated rotating frame imaging (PMRFI) was used to study 23 asphyxiated neonates of gestation 34-42 (median 40) weeks by phosphorus magnetic resonance spectroscopy (MRS) at 1-16 (med. 4) days of age. Six infants with severe encephalopathy had global phosphocreatine/inorganic phosphate (PCr/Pi) ratios of 0.18-0.86 (med. 0.59) and global Pi/adenosine triphosphate (Pi/ATP) ratios of 0.5-1.59 (med. 0.64). PMRFI data showed a progressive rise in Pi/ATP in slices 1 and 2 cms below superficial brain tissue. Seventeen infants with mild or moderate asphyxia had median global PCr/Pi of 1.62 and Pi/ATP of 0.35, and PMRFI did not show any consistent pattern of changing energy metabolism with depth. However, many individual infants (e.g. Infant A, global Pi/ATP 0.27) had focal areas of impaired metabolism although ultrasound and conventional MRS were normal.

19 SPATIAL LOCALISATION OF MAGNETIC RESONANCE SPECTRA FROM NEONATAL BRAINS

Top of pageAbstract Studies of cerebral metabolism using phosphorus magnetic resonance spectroscopy (31P MRS) can be refined using phase modulated rotating frame imaging (PMRFI) for spatial localisation. Six full term infants were studied at 1-9 days of age, in a 1.9 tesla magnet, using a 6.5cm diameter radiofrequency receiver coil overlying the temporo-parietal skull. Conventional MRS was used to obtain metabolite ratios from a large volume of one hemisphere. Spectra were then obtained, using PMRFI, from 6.5cm diameter slices of cerebral tissue at increasing depths up to 3.5cm into the brain with 0.6cm depth resolution. Global phosphocreatine/inorganic phosphate (PCr/Pi) ratios from 4 mildly asphyxiated infants were between 1.54 and 4.35. Two babies with severe asphyxia had ratios of 0.55 and 0.86. The PMRF images from these two infants showed considerable heterogeneity, the PCr/Pi ratios from slices 2cm deep to the coil being 44% and 43% of the ratios from more superficial slices. The region of maximally impaired metabolism corresponds to the subcortical white matter known to be vulnerable to ischaemia.

The elimination of transmitter-receiver phase-twist artifacts in the phase-modulated rotating-frame imaging experiment

The elimination of transmitter-receiver phase-twist artifacts in the phase-modulated rotating-frame imaging experiment

Effect of pulse angle imperfection and resonance offset in the phase-modulated rotating-frame spectroscopic imaging experiment

Phase-modulated rotating-frame imaging, a technique which has been used for localized 31P spectroscopy in vivo, has been modeled using rotation matrices to predict the response of an isolated spin- 1 2 system to the two-pulse experiment under conditions of off resonance and nonideal phase-encoding pulse. Two experiments are carried out in order to remove the phase twist inherent in the phase-modulated experiment; the incremental pulse (θ) is applied with phase φ σ = 0 and φ σ = π with respect to the phase-encoding pulse (λ) phase of φ λ = π/2 The peak shape resulting from the 2D FT is described in terms of a combination of absorption- and dispersion-mode peaks in the chemical-shift and spatial dimensions. Using this model, it is possible to set out guidelines for the implementation of the phase-modulated rotating-frame imaging method. The effective sweep width in ( B 0) and ( B 1) over which the experiment can be usefully performed and the nature of the two-dimensional peak shape at a point can be readily derived from the model.

Spatial heterogeneity of metabolism in skeletal muscle in vivo studied by 31P-NMR spectroscopy.

Phase-modulated rotating-frame imaging, a localization technique for phosphorus nuclear magnetic resonance spectroscopy, has been applied to obtain information on heterogeneity of phosphorus-containing metabolites in skeletal muscle of the rat in vivo. The distal muscles of the rat hindlimb have been studied at rest and during steady-state isometric twitch contraction; the use of a transmitter surface coil and an electrically isolated, orthogonal receiver Helmholtz coil ensure accurate spatial assignment (1 mm resolution). At rest, intracellular pH was higher and PCr/(PCr + Pi) was lower in deeper muscles compared with superficial muscle of the distal hindlimb. Upon steady-state stimulation, the relatively more alkaline pH of deep muscle was maintained, whereas greater changes in PCr/(PCr + Pi) and Pi/ATP occurred in the superficial muscle layer. This method allows rapid (75 min for each spectral image) acquisition of quantitative information on metabolic heterogeneity in vivo.

Phase-modulated rotating-frame imaging of phosphorus metabolites in skeletal muscle in vivo

Conference Article| October 01 1987 Phase-modulated rotating-frame imaging of phosphorus metabolites in skeletal muscle in vivo MARTIN J. BLACKLEDGE; MARTIN J. BLACKLEDGE 1Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K. Search for other works by this author on: This Site PubMed Google Scholar R. A. JOHN CHALLISS; R. A. JOHN CHALLISS 1Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K. Search for other works by this author on: This Site PubMed Google Scholar GEORGE K. RADDA GEORGE K. RADDA 1Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1987) 15 (5): 869–870. https://doi.org/10.1042/bst0150869 Article history Received: April 01 1987 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation MARTIN J. BLACKLEDGE, R. A. JOHN CHALLISS, GEORGE K. RADDA; Phase-modulated rotating-frame imaging of phosphorus metabolites in skeletal muscle in vivo. Biochem Soc Trans 1 October 1987; 15 (5): 869–870. doi: https://doi.org/10.1042/bst0150869 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: n.m.r., nuclear magnetic resonance, PCr, phosphocrcatine, Pi, inorganic phosphate This content is only available as a PDF. © 1987 Biochemical Society1987 Article PDF first page preview Close Modal You do not currently have access to this content.

Quantitative studies of human cardiac metabolism by 31P rotating-frame NMR.

We have developed 31P NMR spectroscopic methods to determine quantitatively relative levels of phosphorous-containing metabolites in the human myocardium. We have used localization techniques based on the rotating-frame imaging experiment and carried out with a double-surface coil probe. Information is obtained from selected slices by rotating-frame depth selection and from a complete one-dimensional spectroscopic image using phase-modulated rotating-frame imaging. The methods collect biochemical information from metabolites in human heart, and we use the fact that the phosphocreatine/ATP molar ratio in skeletal muscle at rest is higher than that in working heart to demonstrate that localization has been achieved for each investigation. The phosphocreatine/ATP molar ratio in normal human heart has been measured as 1.55 +/- 0.20 (mean +/- SD) (3.5-sec interpulse delay) in six subjects using depth selection and as 1.53 +/- 0.25 (mean +/- SD) in four subjects using spectroscopic imaging. Measurement of this ratio is expected to give a useful and reproducible index of myocardial energetics in normal and pathological states.