Janet Sargentoni

Cerebral metabolism within 18 hours of birth asphyxia : A proton magnetic resonance spectroscopy study

Proton magnetic resonance spectroscopy (1H MRS) was performed within 18 h of birth (median 13, range 4-18 h) on 16 term infants with clinical features of birth asphyxia. Ten infants with no evidence of birth asphyxia were studied as controls at 5-18 (median 8) h after birth. To detect delayed impairments in cerebral energy metabolism, 15 infants suspected of asphyxia underwent 31P MRS at 33-106 (median 62) h of age. Choline, creatine, and N-acetylaspartate (NAA) were detected in spectra located to the basal ganglia in all infants. Lactate was detected in 15 of the 16 infants suspected of asphyxia, but in only 4 of the 10 controls (p < 0.05, χ2). Glutamine and glutamate (Glx) was detected in 11 infants suspected of asphyxia and in three controls, but this difference was not significant at the 5% level. The spectra revealed no other significant differences between asphyxiated infants and controls. In the asphyxiated infants, there was a negative correlation between the ratio of lactate to creatine in the first 18 h of life and phosphocreatine/inorganic phosphate(PCr/Pi) at 33-106 h (p < 0.001). Five severely asphyxiated infants had PCr/Pi < 0.75 (median 0.53, range 0.14-0.65), indicating a poor neurodevelopmental prognosis, and a further infant died before PCr/Pi could be measured. Ten infants had PCr/Pi > 0.75 (1.03, 0.76-1.49). Median lactate/creatine was 1.47(range 0.67-3.81) in the six severely affected subjects, 0.38 (0-1.51) in the latter group, and 0 (0-0.6) in controls (p < 0.0005, Kruskall-Wallis). These results suggest that, after birth asphyxia, cerebral energy metabolism is abnormal during the period when 31P MRS characteristically gives normal results. 1H MRS might be of value in predicting which infants are likely to suffer a decline in cerebral high energy phosphate concentrations and subsequent neurodevelopmental impairment.

Proton MR Spectroscopy of the Brain in AIDS Dementia Complex

Proton MR spectroscopy of the brain has been undertaken in 8 healthy volunteers and in 11 patients with human immunodeficiency virus infection and varying stages of AIDS dementia complex (ADC). Spectral appearances in patients with no ADC or early ADC were not significantly different from normal volunteers. Spectra from patients with moderate to severe ADC exhibited significant reductions in levels of N-acetyl aspartate (NAA) relative to creatine (Cr) and also showed elevations in choline containing compounds (relative to Cr). Because NAA is thought to be a metabolic marker for normally functioning neurons, these findings suggest the presence of neuronal injury or loss in moderate to severe ADC. The significance of these findings is discussed.

PROTON MR SPECTROSCOPY OF THE BRAIN IN INFANTS

Proton magnetic resonance spectroscopy (MRS) was used to study the brain of 2 normal and 15 abnormal infants aged from 33 weeks postmenstrual age (PMA) to 14 months postnatal age. Eleven of the infants were examined on at least two occasions. The principal clinical diagnoses in the abnormal infants were perinatal ischemic and hemorrhagic brain injury. All proton spectra demonstrated peaks that were assigned to N-acetylaspartate (NAA), choline containing compounds (Cho), and creatine plus phosphocreatine (Cr). The NAA/Cho and NAA/Cr ratios increased with age, while the Cho/Cr ratio decreased with age in the majority of infants. The NAA/Cho ratio was generally lower in abnormal infants, but the difference was not apparent before 40 weeks (PMA). This ratio was lowest in infants with the severest degree of neurological abnormality. Proton and phosphorus MRS was compared in seven infants. In those with severe brain lesions, early phosphorus spectra were abnormal. On follow-up the phosphorus spectra became normal, but the proton spectra showed persistently low NAA/Cho and NAA/Cr ratios. Proton MRS provides new information that may be complementary to phosphorus MRS in the diagnosis and monitoring of brain development in normal and neurologically damaged infants.

A 31P and 1H-NMR investigation in vitro of normal and abnormal human liver

Spectral changes in human hepatic tumours and possible systemic effects of tumour on host liver were assessed by 31P and 1H in vitro NMR spectroscopy. The 1H and 31P spectra from liver tumour biopsies showed significant elevation in phosphoethanolamine, phosphocholine, taurine, citrate, alanine, lactate and glycine, and significant reduction in GPE (glycerophosphoethanolamine), GPC (glycerophosphocholine), creatine and threonine compared to histologically normal tissue. 31P-NMR spectra obtained from histologically normal tissue within tumour-bearing livers showed significant elevation in phosphoethanolamine and phosphocholine compared to data from liver biopsies from nontumour-bearing patients (pancreatitis). These results suggest that alterations in membrane metabolism in host liver can be detected by 31P-NMR.

Magnetic resonance for the anaesthetist. Part I: Physical principles, applications, safety aspects.

Anaesthetists are being increasingly involved in magnetic resonance (MR) procedures, both in patient care and as a research tool. This paper outlines the physical basis of nuclear magnetic resonance and describes its application in magnetic resonance imaging and spectroscopy. Principles of magnet design and safety relevant to anaesthetic practice in a magnetic resonance environment are discussed and guidelines for anaesthetic practice suggested. Some recent clinical magnetic resonance studies of anaesthetic interest are reviewed.

PROTON SPECTROSCOPY OF THE NEONATAL BRAIN FOLLOWING HYPOXIC-ISCHAEMIC INJURY

Proton magnctic resonance spectroscopy was used to examine. within the first month of life, the brains of 11 infants born at term—10 with signs of hypoxic‐ischaernic encephalopathy (HIE) and one who was neurologically normal at birth. All the infants had peak resonances on their spectra which could be assigned to N‐acetylaspartase (NAA). choline‐containing compounds (Cho) and creatine plus phosphocreatine (Cr). When neurodevelopmental outcome at one year was correlated with initial spectroscopy findings, the NAA/Cho and NAA/Cr ratios reflected clinical outcome. This study suggests that proton spcctroxopy not only provides new information about biochemical changes occurring in the brains of infants with HIE, but also may help to predict outcomc within the first month of life.

Regional variations in cerebral proton spectroscopy in patients with chronic hepatic encephalopathy

Regional variations in proton magnetic resonance spectroscopy (MRS) were assessed in 26 patients and 14 healthy volunteers using a two dimensional chemical shift imaging technique. Patients were classified as being neuropsychiatrically unimpaired, or as having subclinical or overt chronic hepatic encephalopathy (CHE). Peak area ratios of choline (Cho), glutamine and glutamate (Glx) and N-acetylaspartate (NAA) relative to creatine (Cr) were measured. Significant reductions in mean Cho/Cr and elevations in mean Glx/Cr were observed in the patient population, which correlated with the severity of CHE. There were significant regional variations in these metabolite ratios with the mean Cho/Cr lowest in the occipital cortex and the mean Glx/Cr highest in the basal ganglia. NAA/Cr remained relatively constant in all areas of the brain analysed. The regional variation in the metabolite ratios suggests that spectral information from more than one voxel may be useful in the assessment of patients with CHE.

Relation between proton magnetic resonance spectroscopy within 18 hours of birth asphyxia and neurodevelopment at 1 year of age

The aim of the study was to test the hypotheses that elevated cerebral lactate, detected by proton spectroscopy performed within 18 hours of suspected birth asphyxia, is associated with adverse outcome, and that increased lactate can be used to predict adverse outcome. Thirty-one term infants suspected of having had birth asphyxia and seven control infants underwent proton magnetic resonance spectroscopy, using three-dimensional chemical shift imaging, within 18 hours of birth. Adverse outcome was defined as death or neurodevelopmental impairment at 1 year of age or more. Nine infants had an adverse outcome. The other 22 and all of the control infants remained normal. Median (range) lactate/creatine plus phosphocreatine (lactate/creatine) ratios in the abnormal, the normal, and the control group were 1.14 (0.17 to 3.81), 0.33 (0 to 1.51), and 0.05 (0 to 0.6) respectively (P=0.003). Lactate/creatine >1.0 predicted neurodevelopmental impairment at 1 year of age with sensitivity of 66% and specificity of 95%, positive and negative predictive values of 86% and 88%, and a likelihood ratio of 13.2. Elevated cerebral lactate/creatine within 18 hours of birth asphyxia predicts adverse outcome.

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.

Magnetic resonance for the anaesthetist. Part II: Anaesthesia and monitoring in MR units.

Anaesthetists are increasingly involved in patient care during magnetic resonance imaging and spectroscopy. This paper describes a system which has been developed for the management of critically ill patients and the conduct of anaesthesia in a magnetic resonance unit with a 1.6 tesla whole body magnet. Difficulties which arise from working in a confined space in a high magnetic field are highlighted. Different approaches to anaesthesia, sedation and the modification of equipment for use in this environment are reviewed. The problems associated with patient monitoring within a magnetic field are discussed and some solutions are suggested. A transport system for critically ill patients is described and a protocol for management is outlined.