Proton magnetic resonance spectroscopy of the brain in normal preterm and term infants, and early changes after perinatal hypoxia-ischemia

Proton magnetic resonance spectroscopy to study the metabolic changes in the brain of a patient with Leigh syndrome

Localized proton magnetic resonance spectroscopy (MRS) was performed to study the metabolic changes in the brain of a patient with Leigh syndrome, who had a T-->G point mutation at nt 8993 of mitochondrial DNA. In this patient, sodium dichloroacetate therapy normalized the lactate and pyruvate levels in both blood and cerebrospinal fluid (CSF). However, his psychomotor retardation did not improve and magnetic resonance imaging showed progressive cerebral atrophy. In the patient's spectra, elevation of brain lactate was observed throughout the brain with regional variations, predominantly in the basal ganglia and brainstem with an abnormal MRI appearance. Although the lactate/creatine ratio observed on proton-MRS was related to the CSF lactate level, the ratio did not completely parallel the CSF lactate level, i.e. brain lactate was detected even when the CSF lactate level had become normalized. Furthermore, proton-MRS revealed a decrease in the N-acetylaspartate/creatine ratio and an increase in the choline/creatine ratio, representing neuronal loss and breakdown of membrane phospholipids. The clinical and MRI findings were well related to the changes in spectroscopically determined brain metabolites. These results indicate that the brain metabolites observed on proton-MRS are useful indicators of a response to therapy and prognosis in Leigh syndrome.

Proton magnetic resonance spectroscopy of fetal lamb brain during hypoxia

Proton magnetic resonance spectroscopy of fetal lamb brain was performed simultaneously with repeated measurements of fetal arterial oxygen saturation during decrease of oxygen supply. Magnetic resonance spectra displayed the same metabolite peaks as detected in the human fetal brain. Cerebral lactate signals could be detected during fetal hypoxia.

Persistent increases in cerebral lactate concentration after birth asphyxia

In this prospective study proton magnetic resonance spectroscopy (1H MRS) was used to test the hypothesis that lactate can be detected later than 1 mo after birth in the brains of infants who display severe neurodevelopmental impairment 1 y after transient perinatal hypoxia-ischemia. Data were obtained from three groups of infants: 1) eight infants suffering birth asphyxia followed by perinatal encephalopathy and abnormal neurodevelopmental outcome at 1 y of age (defined as major neurologic impairment, Griffiths quotient <85%, and low optimality score); 2) 10 infants with signs of perinatal hypoxia-ischemia but normal neurodevelopmental outcome at 1 y; and 3) six control infants with uneventful perinatal courses and normal neurodevelopment at 1 y. Between one and four examinations (median 1) were performed at median (range) 11 (4-68) wk after birth, and the cerebral concentration ratio of lactate to creatine plus phosphocreatine (Cr) calculated from each spectrum. Lactate was detected later than the 1st mo after birth in seven of eight infants with abnormal neurodevelopmental outcome [maximum detected lactate/Cr was median (range) 0.44 (0.24-0.67)]. No lactate was detected later than the 1st mo after birth in infants with normal neurodevelopmental outcome, nor in five of six control subjects, although a small amount of lactate was detected in one control infant (lactate/Cr=0.04). These results suggest that the pathologic postasphyxial process, indicated by persistent cerebral lactate, may not be confined to the period immediately after injury.

Homonuclear J coupling effects in volume localized NMR spectroscopy: pitfalls and solutions

It has been observed that the signal amplitude of multiplet resonances such as the 1H doublet resonance of lactate varies with pulse sequence timing when echo-driven volume selective methods such as point resolved spectroscopy are used. Herein a standard vectorial description is presented for the mechanism of this artifact, which results from the chemical shift between homonuclear scalar-coupled (i.e., J coupled) nuclei. The chemical shift causes the extent of a signal phase modulation to vary for different spatial regions of the excited voxel. This variation results in spatial interference effects that can lead to marked loss of signal intensity as well as corruption of the size and shape of the voxel from which signal is obtained. The phenomenon is substantial at an imaging field of 1.5 T and becomes especially pronounced at higher field strengths. Several strategies to avoid the artifact are provided.

Prognostic value of 1H-MRS in perinatal CNS insults

The authors studied 37 term neonates (38-42 gestational weeks) at 1-11 days after central nervous system insult to determine whether proton magnetic resonance spectroscopy (1H-MRS) of the occipital gray/parietal white matter was useful in predicting outcomes. Etiologies included asphyxia, 18; sepsis/meningitis, 8; metabolic disorders, 5; stroke, 4; and trauma, 2. 1H-MRS data (1.5T; 8 cm3 vol, stimulated echo acquisition mode sequence, TE = 20 ms, TR = 3000 ms) were expressed as metabolite peak area ratios (NAA/Cr, NAA/Cho, Cho/Cr) and the presence or absence of lactate. Outcomes were assessed at 6 to 12 months post-insult using the Pediatric Cerebral Performance Scale and were dichotomized as follows: good/moderate outcome (good, mild or moderate disability) or poor outcome (severe disability, persistent vegetative state, death). Neonates with poor outcomes had significantly lower NAA/Cho and significantly higher Cho/Cr ratios in the occipital region, as compared with patients with good/moderate outcomes. No neonates with good/moderate outcomes had metabolite ratios that exceeded 2 standard deviations from the mean. In addition, the absence of lactate on 1H-MRS correlated with a good/moderate outcome. The study also showed that 1H-MRS metabolite ratio data, added to either the Sarnat or EEG scores, enhanced the correlation between these prognostic factors and outcomes. 1H-MRS provides additional objective data early after a wide variety of perinatal neurologic insults to enhance outcome prediction.

Keeping a cool head, post-hypoxic hypothermia--an old idea revisited

Hypoxia-ischaemia produces permanent brain damage by processes that continue for many hours after reoxygenation/reperfusion. This provides a window of opportunity for therapy aimed at preventing further loss of brain cells. Reducing brain temperature by 2-6 degrees C for 3-72 h after reoxygenation/reperfusion has been shown to reduce brain damage by 25-80% in controlled trials with six different neonatal animal models of hypoxia-ischaemia. No adverse effects from mild hypothermia have been documented. The mechanisms of protection are unknown but may include a reduction in extracellular excitotoxic amino acids, reduced nitric oxide synthesis and inhibition of apoptosis. Mild hypothermia is currently the most promising clinically feasible neural rescue therapy for full-term infants at risk of developing hypoxic-ischaemic encephalopathy, but clinical use must be restricted to approved trial protocols.

Mild hypothermia after severe transient hypoxia-ischemia reduces the delayed rise in cerebral lactate in the newborn piglet

This study tested the hypothesis that mild hypothermia after severe transient hypoxia-ischemia reduces the subsequent delayed rise in cerebral lactate peak-area ratios as determined by proton (1H) magnetic resonance spectroscopy (MRS) in the newborn piglet. Nine piglets aged < 24 h underwent temporary occlusion of the common carotid arteries and hypoxemia. Resuscitation was started when cerebral [phosphocreatine]/[inorganic phosphate] had fallen close to zero and [nucleotide triphosphate (NTP)]/[exchangeable phosphate pool (EPP)] was below about a third of baseline. On resuscitation rectal and tympanic temperatures were lowered to 35 degrees C for 12 h after which normothermia (38.5 degrees C) was resumed. 1H MRS data collected over 48 or 64 h after resuscitation were compared with concurrently established data from 12 piglets similarly subjected to transient cerebral hypoxia-ischemia, but maintained normothermic, and six sham-operated controls. The severity of the primary insult (judged from the time integral of depletion of [NTP]/[EPP]) was similar in the hypothermic and normothermic groups. The maximum lactate/N-acetylaspartate ratio observed between 24 and 48 h after resuscitation in the hypothermic group was 0.10 (0.05-0.97), median (interquartile range), which was significantly lower than that observed in the normothermic group, 1.28 (0.97-2.14), and not significantly different from that observed in the control group, 0.08 (0.06-0.11). Similar results were obtained for lactate/choline and lactate/total creatine. We conclude that mild hypothermia after a severe acute cerebral hypoxic-ischemic insult reduces the delayed elevation in lactate peak-area ratios, thus reflecting reduced lactate accumulation.

Proton magnetic resonance spectroscopy of the brain during acute hypoxia-ischemia and delayed cerebral energy failure in the newborn piglet

Studies of the brains of severely birth-asphyxiated infants using proton (1H) magnetic resonance spectroscopy (MRS) have shown changes indicating a rise in cerebral lactate (Lac) and a fall in N-acetylaspartate (Naa). The aim of this study was to test two hypotheses: 1) that these changes can be reproduced in the newborn piglet after transient reversed cerebral hypoxiaischemia, and their time course determined; and 2) that changes in Lac peak-area ratios are related to changes in phosphorylation potential as determined by phosphorus (31P) MRS. Eighteen piglets aged < 24 h were anesthetized and ventilated. Twelve underwent temporary occlusion of the carotid arteries and hypoxemia, and six served as sham-operated controls. 1H and 31P spectra were acquired alternately, both during the insult and for the next 48 h, using a 7-tesla spectrometer. During hypoxiaischemia, the median Lac/total creatine (Cr) peak-area ratio rose from a baseline of 0.14 (interquartile range 0.07-0.27), to a maximum of 4.34 (3.33-7.45). After resuscitation, Lac/Cr fell to 0.75 (0.45-1.64) by 2 h, and then increased again to 2.43 (1.13-3.08) by 48 h. At all stages after resuscitation Lac/Cr remained significantly above baseline and control values. Naa/Cr was significantly reduced below baseline and control values by 48 h after resuscitation. The increases in the Lac peak-area ratios were concomitant with the falls in the [phosphocreatine (PCr)*]/ [inorganic phosphate (Pi)] ratio, during both acute hypoxiaischemia and delayed energy failure. The maximum Lac/Naa during delayed energy failure correlated strongly with the minimum [nucleotide triphosphate (NTP)]/[exchangeable phosphate pool (EPP)] (r = -0.94, p < 0.0001). We conclude that both hypotheses have been confirmed.

Early cerebral proton MRS and neurodevelopmental outcome in infants with cystic leukomalacia

The present study tested the hypothesis that proton magnetic resonance spectroscopy (1H-MRS) predicted neurodevelopmental outcome in infants with cystic leukomalacia (CL). Nineteen infants with CL (grade 2, N = 7; grade 3, N = 7; grade 4, N = 5), graded according to the authors' classification, were examined at corrected ages of mean 1.5 +/- 2.1 SD weeks. 1H-MRS of the basal ganglia and the periventricular white matter was performed. Two infants died, 16 had an adverse neurodevelopmental outcome and one was normal at follow-up. N-acetylaspartate (NAA):choline (Cho) ratios were mean 1.12 +/- 0.19 (SD) (grade 2), mean 0.95 +/- 0.11 (SD) (grade 3), and mean 0.71 +/- 0.13 (SD) (grade 4). These differences are significant (P < 0.01, ANOVA). NAA:Cho ratios showed a positive correlation with developmental quotient (DQ) at the age of > or = 1 year (P < 0.05). In 13 infants lactate (Lac) was found. Lac:NAA ratios showed a negative correlation with NAA:Cho ratios, but not with DQ. We conclude that a low NAA:Cho ratio predicted a poor outcome, whereas some infants developed unfavourably despite a normal NAA:Cho ratio. We speculate that partial volume effects might explain this observation.

Magnesium sulfate after transient hypoxia-ischemia fails to prevent delayed cerebral energy failure in the newborn piglet

Severely birth-asphyxiated human infants develop delayed ("secondary") cerebral energy failure, which carries a poor prognosis, during the first few days of life. This study tested the hypothesis that i.v. magnesium sulfate (MgSO4) after severe transient cerebral hypoxia-ischemia decreases the severity of delayed energy failure in the newborn piglet. Twelve piglets underwent temporary occlusion of the common carotid arteries and hypoxemia. Resuscitation was started when cerebral [phosphocreatine (PCr)]/[inorganic phosphate (Pi)], as determined by phosphorus magnetic resonance spectroscopy, had fallen virtually to zero, and nucleotide triphosphate (NTP) had fallen below a third of baseline. The piglets were randomized to receive, blind, either: 1) three i.v. infusions of 12.5% MgSO4 heptahydrate solution: 400 mg.kg-1 MgSO4.7H2O starting 1 h after resuscitation, and 200 mg.kg-1 12 and 24 h later (n = 6); or 2) three infusions of placebo, 0.9% NaCl (n = 6). Phosphorus and proton spectroscopy were continued until 48 h after resuscitation, and values were compared between the two groups. Mean plasma magnesium levels, 1 h after each of the three doses of MgSO4, were 2.1, 2.0, and 1.9 mmol.L-1, respectively. The severity of the primary insult, determined by the time-integral of depletion of cerebral [NTP]/[exchangeable phosphate pool (EPP)], was similar in the MgSO4-treated and placebo groups. After resuscitation, there was no difference in the progression or severity of delayed energy failure between the two groups, as judged by cerebral [PCr]/[Pi], [NTP]/[EPP], or lactate/creatine and N-acetylaspartate/creatine peak-area ratios. We conclude that MgSO4 did not decrease the severity of delayed cerebral energy failure.

Lactate, N-acetylaspartate, choline and creatine concentrations, and spin-spin relaxation in thalamic and occipito-parietal regions of developing human brain

Previous studies of the brains of normal infants demonstrated lower lactate (Lac)/choline (Cho), Lac/creatine (Cr), and Lac/ N-acetylaspartate (Naa) peak-area ratios in the thalamic region (predominantly gray matter) compared with occipitoparietal (mainly unmyelinated white matter) values. In the present study, thalamic Cho, Cr, and Naa concentrations between 32-42 weeks' gestational plus postnatal age were greater than occipito-parietal: 4.6 +/- 0.8 (mean +/- SE), 10.5 +/- 2.0, and 9.0 +/- 0.7 versus 1.8 +/- 0.6, 5.8 +/- 1.5, and 3.4 +/- 1.1 mmol/kg wet weight, respectively: Lac concentrations were similar, 2.7 +/- 0.6 and 3.3 +/- 1.3 mmol/kg wet weight, respectively. In the thalamic region, Cho and Naa T2s increased, and Cho and Lac concentrations decreased, during development. Lower thalamic Lac peak-area ratios are principally due to higher thalamic concentrations of Cho, Cr, and Naa rather than less Lac. The high thalamic Cho concentration may relate to active myelination; the high thalamic Naa concentration may be due to advanced gray-matter development including active myelination. Lac concentration is higher in neonatal than in adult brain.

Metabolite concentrations and relaxation in perinatal cerebral hypoxic-ischemic injury

Regional cerebral metabolite concentrations, principally of choline-containing compounds (Cho), total creatine (Cr), N-acetylaspartate (Naa), and lactate (Lac), can be quantified by in vivo proton magnetic resonance spectroscopy. In order to estimate a metabolite concentration, it is often necessary to measure the transverse relaxation time (T2). Metabolite T2s depend on cytosolic viscosity: as [adenosine triphosphate] falls leading to Na+/K+ pump failure, cytosolic water increases and T2s lengthen. In central grey-matter in human infants, Naa may be almost exclusively neuronal: Naa T2 may index neuronal edema and energy generation. In this preliminary report, metabolite concentrations and T2s have been measured in central grey matter in human infants suspected of perinatal hypoxic-ischemic cerebral injury. In infants who developed serious cerebral injury or died, [Cho] and [Naa] were low (the latter suggesting neuronal loss), [Lac] and all metabolite T2s were increased: the Naa T2 increase possibly reflected neuronal edema following failure of energy generation in a fraction of remaining neurons.