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Biomedical subjects

O Henriksen

Publications and source records attributed to O Henriksen.

At least 73 records · Page 4Linked to original sources
PubMed1994

24-hour lithium concentration in human brain studied by Li-7 magnetic resonance spectroscopy.

Brain and serum lithium concentrations were measured every second hour during a 24-hr period following lithium intake, and again 48-hr later in two normal subjects in steady state lithium treatment receiving lithium carbonate (Priadel Synthelabo) once every evening. The brain-lithium concentration was measured by 7Li magnetic resonance spectroscopy (MRS). The brain lithium level was found to undulate in a peak-trough pattern that followed the serum lithium profile, although in an attenuated form. The brain/serum lithium concentration ratio varied considerably during the 48-hr period, ranging from 0.5 to 1.3, but the ratio was independent of the serum-lithium concentration. The median half-life for lithium was 28 hr in the brain, and 16 hr in serum. The brain lithium concentration in the morning was about 75% of the clinically relevant standard 12-hr serum lithium concentration. The finding that brain lithium undulates during the day means that MRS measurements of brain lithium can only be compared if carried out under standard conditions that include a fixed interval following lithium intake and an identical treatment regimen.

Adult↗
PubMed1994

[Frontal epileptic seizures].

Video-telemetry, with EEG recordings from intracranial electrodes, has been used for the past 15 years at the National Center for Epilepsy to identify candidates for epilepsy surgery. The recordings have been a useful tool for correlating neuroanatomy and ictal, epileptic symptoms. The authors describe the most characteristic clinical symptoms and electroencephalographic findings in seizures deriving from the frontal lobe. An attempt is made to subclassify seizures deriving from different parts of the frontal lobe. Frontal lobe seizures are illustrated by three case histories.

Adult↗
PubMed1994

[Vigabatrin--a new antiepileptic agent].

The new antiepileptic drug vigabatrin acts by preventing degradation of the inhibitory neurotransmitter GABA (gammaaminobutyric acid). This appears to decrease propagation of abnormal hypersynchronous discharges, thus reducing seizure activity. In an open study in 46 patients with intractable epilepsy, supplementary therapy with vigabatrin reduced seizure by at least 50% in 15 patients. Three patients became seizure-free. The best effect of vigabatrin is seen in patients with partial epilepsy. Tiredness and irritability were the most frequently reported side effects, but these were usually mild and transient.

Adolescent↗
PubMed1994

Hepatic metabolism during constant infusion of fructose; comparative studies with 31P-magnetic resonance spectroscopy in man and rats.

A protocol of constant infusion of fructose has been carried out both in human volunteers and in the perfused rat liver, aiming at a steady-state blood fructose concentration of 6-8 mM. Localized 31P-NMR spectroscopy and biochemical analyses were used to evaluate the metabolic changes. Comparison of the model experiment and the clinical study allowed an evaluation of this protocol as a clinically relevant assessment of the metabolic function of the liver. The time course of change, as well as the quasi steady-state levels reached during fructose infusion, for phosphomonoesters (PME), ATP and inorganic phosphate (Pi) provided the following results: During fructose infusion, ATP and Pi reached a steady-state level of 74.0 +/- 5.9 and 54.6 +/- 3.3% of control respectively, in the human volunteers. The corresponding data in the rat liver was 71.3 +/- 4.3 and 54.4 +/- 4.3%. Hepatic clearance of fructose was 0.53 and 0.52 ml.g liver-1.min-1 for volunteers and rats, respectively. The time course of intracellular metabolite recovery after fructose could be approximated by a first order kinetic. The rate constants for PME and ATP change were similar during fructose infusion and recovery, while after the discontinuation of fructose infusion, Pi increased with a rate constant significantly greater than during its fructose-induced depletion in human liver (P < 0.005). Thus, this relatively simple clinically applicable protocol seems to be verifiable in the well controlled perfused rat liver model, and it is argued that it may be useful in the clinical evaluation of the metabolic functional capacity of the human liver.

Adult↗
PubMed1994

Simultaneous 31P NMR spectroscopy and EMG in exercising and recovering human skeletal muscle: technical aspects.

The bioenergetics of human skeletal muscle can be studied by 31P NMR spectroscopy (31P-MRS) and by surface electromyography (SEMG). Simultaneous 31P-MRS and SEMG permit accurate and noninvasive studies of the correlation between metabolic and electrical changes in exercising and recovering human skeletal muscle, a relationship that is still poorly understood. This study describes the optimization of skeletal muscle 31P-MRS in a whole-body magnet, involving surface coil design, utilization of adiabatic radio frequency pulses and advanced time-domain fitting, to the technical design of SEMG. A nonmagnetic ergometer was used for ankle dorsiflexions that activated only the anterior tibial muscle as verified by post exercise imaging. The coil design and the adiabatic sech/tanh pulse improved sensitivity by 45% and 56% respectively, compared with standard techniques. Simultaneous electromyographic recordings did not deteriorate the NMR spectra. The VARPRO time domain fitting routine was very suitable for estimating 31P muscle spectra. With these methods it was possible to accurately estimate parameters describing metabolic and electrical changes during rest, exercise and the entire recovery period with a 20-s time resolution on a standard 1.5 T whole-body NMR scanner.

Ankle Joint↗
PubMed1994

Functional MRI of CO2 induced increase in cerebral perfusion.

The sensitivity of MR gradient echo imaging towards CO2 induced changes in cerebral blood flow was investigated in 10 normal subjects. The subjects were inhaling 5% and 7% CO2 and the experiments were carried out at 1.5 T (n = 6) and 2.0 T (n = 5), allowing a comparison of field strengths. Additional experiments were carried out using a higher spatial resolution. The largest signal increases were noted in areas corresponding to larger vessels, but significant changes were also conspicuous in deeper cortical and central grey matter. The changes appeared linearly related to the arterial CO2 tension, within the range of PaCO2 studied. In white matter, the changes were not statistically significant.

Administration, Inhalation↗
PubMed1994

Absolute quantitative proton NMR spectroscopy based on the amplitude of the local water suppression pulse. Quantification of brain water and metabolites.

Quantification in localized proton NMR spectroscopy has been achieved by various methods in recent years. A new method for absolute quantification is described in this paper. The method simultaneously rules out problems with B1 field inhomogeneity and coil loading, utilizing a relation between the locally optimized amplitude of a chemical shift selective water suppression pulse and the acquired signal. Validity and feasibility of quantification using the method of the water suppression pulse is demonstrated. Brain water and cerebral metabolites have been quantified in a study of 12 healthy volunteers. Localized proton NMR spectra were obtained from a region of primarily white matter in the occipital lobe. The observable water content in the NMR spectra was 0.685 +/- 0.025. The absolute metabolite concentrations were: [total choline] = 1.25 +/- 0.21 nM, [total creatine] = 6.71 +/- 0.59 nM and [NAA] = 9.15 +/- 0.74 nM. It is concluded that the quantification method is easily applied in vivo, and that the absolute concentrations obtained are similar to results in other studies except those relying on assumptions of the concentration of an internal reference. The advantage of the quantification method reported here is that it is independent of the assumptions needed for other methods.

Adult↗
PubMed1994

Cerebrospinal fluid flow and production in patients with normal pressure hydrocephalus studied by MRI.

An interleaved velocity-sensitised fast low-angle shot pulse sequence was used to study cerebrospinal fluid (CSF) flow in the cerebral aqueduct, and supratentorial CSF production in 9 patients with normal pressure hydrocephalus (NPH) and 9 healthy volunteers. The peak aqueduct CSF flow, both caudal and rostral, was significantly increased in patients with NPH. No significant difference in the supratentorial CSF production rate was found between patients (mean 0.60 +/- 0.59 ml/min) and healthy volunteers (mean 0.68 +/- 0.31 ml/min). Our method may be useful for investigation and monitoring of patients with NPH before and after ventriculoperitoneal shunt operations.

Adult↗
PubMed1994

Assessment of CSF dynamics and venous flow in the superior sagittal sinus by MRI in idiopathic intracranial hypertension: a preliminary study.

A velocity-sensitive magnetic resonance imaging (MRI) phase-mapping method was used for non-invasive study of cerebrospinal fluid (CSF) flow in the cerebral aqueduct, for indirect calculation of supratentorial CSF production, and for measurement of blood flow in the superior sagittal sinus (SSS). We examined 12 patients with idiopathic intracranial hypertension (IIH; pseudotumour cerebri), and 10 healthy volunteers. The peak caudal and rostral CSF flow in the aqueduct during the cardiac cycle did not differ significantly between the patients and the volunteers. A significant correlation was found between the CSF volume flow amplitude and the resistance to cerebrospinal fluid outflow in the patients (p < 0.05). The calculated mean supratentorial CSF production rate was 0.79 ml/min in the patients and 0.70 ml/min in the controls, but this difference was not statistically significant. However, the MRI measurements suggested CSF hypersecretion in three patients, whereas increased transependymal passage of CSF could have been the cause of negative calculated CSF production rates in two others. A tendency towards lower mean blood flow in the SSS (mean 345 ml/min) in the patients than in the controls (mean 457 ml/min) was found, and in two patients showed very low values. We showed that MRI phase-mapping may be used to study the relative importance of the pathophysiological factors thought to play a role in the development of IIH.

Adult↗
PubMed1994

Brain magnetic resonance imaging in children with optimally controlled hyperphenylalaninaemia.

This study was undertaken to investigate whether the white-matter changes on MRI and the EEG abnormalities detectable in treated adolescents and adults with hyperphenylalaninaemia (HPA) can be detected in younger children on an optimally controlled diet. The study included 17 children, 7-12 years of age, with HPA. The MRI of five healthy children were included in the blind evaluation of the MR images. According to mutation genotype and dietary tolerance of phenylalanine, 9 patients have severe HPA and 8 have moderate HPA, all requiring dietary treatment. Mild white-matter hyperintensity was detected in 1 of the 5 healthy children and in 10 of 17 patients. EEG was abnormal in 2 patients. This group of children was compared with a previously reported group of adolescents with HPA who had been treated according to the same dietary regimen. MRI changes and EEG abnormalities were significantly less frequent in the group of children than in the group of adolescents. It is suggested that the more frequent MRI changes and EEG abnormalities seen in adolescents are related to the fact that a relaxation of the dietary treatment after the age of 8 years is often accepted.

Adolescent↗
PubMed1994

MR-visible water content in human brain: a proton MRS study.

In vivo measurement of metabolite concentrations in the human brain by means of proton-MRS contributes significantly to the clinical evaluation of patients with diseases of the brain. The fully relaxed water signal has been proposed as an internal standard for calibration of the MRS measurements. The major drawbacks are the necessity to make the assumptions that the water concentrations in the brain and that all tissue water is MR-visible. A number of in vivo measurements were carried out to estimate the concentration of MR-visible water in the brain of healthy volunteers divided into four age groups: newborn (0-23 days), adolescents (10-15 yr), adults (22-28 yr), and elderly people (60-74 yr). The examinations were carried out using a Siemens Helicon SP 63/84 MR-scanner operating at 1.5 T. Except for the newborn, four regions were studied in each subject using stimulated echo (STEAM) sequences without water suppression. In vitro measurements on a standard phantom were used for calibration. The calculated water concentrations ranged between 35.8 and 39.6 (mean 36.9) mol.[kg wet weight]-1 in the three groups, whereas it was 51.5 mol.[kg wet weight]-1 in the newborn, p < .01. The observed water concentration of neither the four regions nor of the three oldest age groups were significantly different. Comparisons between the water concentrations measured and those expected based on estimation of the content of grey and white matter in the region of interest from T1-weighted images and biochemical data published, suggest that only a small fraction (< 5%) of the tissue water may be MR-invisible.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Pulse sequence design for MR velocity mapping of complex flow: notes on the necessity of low echo times.

Lowering of the echo time (TE) has been proposed as a way to reduce effects of phase dispersion in MR velocity mapping, because a low TE reduces sensitivity to higher-order motion terms while first-order velocity sensitivity is maintained. Methods of lowering TE involves the use of extreme gradient ramp times and gradient strengths as well as reduction of the duration of transmit/receive windows, the latter method causing decrements in image resolution. When reducing higher-order sensitivity, however, it is not the overall TE that is the critical parameter, but rather the time pattern of the gradients used in the experiment. Hence, changes in TE without subsequent variations in gradient pattern would, according to theory, not affect quantitative measurements of complex flow and vice versa. In this study, we experimentally demonstrate this relation and utilize the experience to create a sequence robust towards complex flow without sacrifices in image resolution. Our experimental observations show that variations in TE alone while maintaining the time course of the velocity-encoding gradient does not significantly affect measurements of through-plane average complex flow in the studied velocity range. A parameter that cannot be measured as accurately if TE is increased is the peak flow. A phase mapping sequence with prolonged TE from 3 ms to 5 ms but with short duration of the velocity-encoding (section-selective) gradient and improved in-plane resolution was demonstrated in vivo.

Aorta↗
PubMed1994

Quantification of liver fat using magnetic resonance spectroscopy.

Localized proton MR spectroscopy using stimulated echoes was used to quantify the liver fat concentration in patients with various degrees of fatty liver due to alcohol abuse. Ten patients underwent a liver biopsy followed by chemical triglyceride estimation of the fatty content. A statistically significant correlation was found between the fat concentration measured in the liver biopsies, and the concentration calculated from the spectroscopic experiments (r = 0.9, p < .001). Quantitative assessment of liver fat concentrations using localized spectroscopy is superior to methods based on differences in relaxation times, and can be used to estimate the fat concentration over the full range of fat content in contrast to the spectroscopic imaging methods. Localized spectroscopy may replace liver biopsy in the diagnosis of diffuse fatty infiltrations, and can be used for follow-up, due to its noninvasive nature.

Adult↗
PubMed1994

Short-term myeloid growth factor mediated expansion of bone marrow haemopoiesis studied by localized magnetic resonance proton spectroscopy.

Previously we have shown that short-term myeloid growth factor priming of haemopoiesis prior to bone marrow harvest increased the yield of myeloid progenitors in the graft. The present study is intended to investigate the expansion of haemopoiesis by volume selective proton magnetic resonance spectroscopy (MRS). Six patients were treated with daily subcutaneous injections of recombinant human granulocyte colony-stimulating factor (rhG-CSF, n = 2) or granulocyte-macrophage colony-stimulating factor (rhGM-CSF, n = 4) for 5d before marrow harvest. MRS investigations were performed prior to treatment (day 0), day 5 and day 12. Spectroscopic examinations were performed with the stimulated echo acquisition mode (STEAM) method on a 1.5 T clinical whole-body imaging unit. A cubic volume of interest (VOI) was selected in the bone marrow of the left iliac bone. The patients responded with a rise in blood absolute neutrophil count from median 3.3 x 10(9)/l (range 1.3-7.3 x 10(9)/l) before to 15.6 x 10(9)/l (range 6.8-22.0 x 10(9)/l) after treatment. Concomitantly an increase in bone marrow cellularity and myeloid:erythroid ratios documented the stimulation of myelopoiesis. During priming, the light-density cell proliferation rate in marrow samples increased from median 21.9 (range 4.5-31) x 10(3) cpm to 54.7 (range 13.9-94) x 10(3) cpm and the total number of myeloid progenitors enumerated as day 7/14 GM-CFUs per volume aspirated marrow increased from median 11/8 x 10(3) (range 4.0-87.5/2.2-103.0) to 64/76 x 10(3) (range 28.4-1180.6/23.2-2850.0). MRS detected a significant increase in bone marrow 'relative water content' day 12, 1 week after myeloid growth factor treatment was stopped, from median 30.5% (range 16-45) to 79% (range 56-93). In parallel, haemopoiesis was detected in new areas of femur. In conclusion, the non-invasive MRS method may be a useful and reliable in vivo examination for expansion of haemopoiesis and a correspondent reduction of fat tissue in bone marrow after priming with recombinant human haemopoietic growth factors.

Adult↗
PubMed1994

Cerebrospinal fluid production and dynamics in normal aging: a MRI phase-mapping study.

Magnetic resonance imaging (MRI) phase mapping was used for non-invasive evaluation of the to-and-fro motion of cerebrospinal fluid (CSF) in the cerebral aqueduct, and to measure the supratentorial CSF production in vivo, in 13 healthy volunteers to determine whether normal aging affects these parameters. Eight young healthy volunteers (mean age 29.8 years) and five elderly healthy volunteers (mean age 69.0 years) were examined, all were normal on conventional MRI. Slightly higher aqueductal CSF peak flow velocities and peak volume flow in both the caudal and rostral directions were found in the group of elderly healthy volunteers, however, this was not statistically significant. The calculated mean supratentorial CSF production rates in the two groups were almost identical, corresponding to approximately 900-1000 ml per 24 h, we suggest that supratentorial CSF production in healthy humans in fact occurs at this relatively high rate. Our study further suggests that the differences found in human CSF production rates are caused by interindividual factors other than age.

Adult↗
PubMed1994

The nocturnal increase in human cerebrospinal fluid production is inhibited by a beta 1-receptor antagonist.

A circadian variation in human cerebrospinal fluid (CSF) production has recently been demonstrated using magnetic resonance phase imaging. A nightly peak in CSF production was found at approximately 0200, when production is approximately twice the daytime values. In the present study, we have investigated the effect of a beta 1-receptor antagonist, atenolol, on the production of CSF, specifically the nocturnal production peak. CSF production was measured in fourteen healthy volunteers of both sexes in the time interval 1500-1800, with or without drug administration (100 mg orally) at 1800, and a second measurement was made in the time interval 2300-0200. In the absence of drug administration, all nine volunteers showed a significant increase in CSF production at night, from 0.34 +/- 0.06 ml/min in the time interval 1500-1800 to 0.61 +/- 0.05 (SE) ml/min (P < 0.005), confirming the presence of a circadian variation in these individuals. One week later, the experiment was repeated in five of these volunteers, plus an additional five volunteers, but with the administration of 100 mg atenolol orally immediately after the first measurement (at 1800). In five of the volunteers a decrease in CSF production was seen at midnight compared with daytime production values; in two volunteers CSF production remained unchanged, while three volunteers showed increased production. The average CSF production was 32% lower at night (0.27 +/- 0.10 ml/min) compared with the afternoon (0.40 +/- 0.07 ml/min), after administration of atenolol (P = 0.37).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1994

Long-term follow-up of cerebral infarction patients with proton magnetic resonance spectroscopy.

BACKGROUND AND PURPOSE: With proton magnetic resonance spectroscopy it is possible to measure the content of various brain metabolites in vivo, including N-acetylaspartate (which may be used as a neuronal marker), creatine, choline, and lactate. The content of these brain metabolites was measured serially from the acute stage to the chronic stage of infarction. Regional cerebral blood flow was also measured within the affected areas. These factors were compared with the clinical outcome. METHODS: Six patients with ischemic stroke were examined serially from the acute stage (< or = 2 days) to the chronic stage (> 6 months) with proton magnetic resonance spectroscopy. Cerebral blood flow was measured with single-photon emission-computed tomography with 99mTc-labeled d,l-hexamethylenepropyleneamine oxime as flow tracer. RESULTS: Lactate was found in all patients in the acute stage of stroke. Lactate was also found in the 3 largest lesions in the chronic stage; in 2 of these patients lactate was not found in the subacute stage. Reduced levels of N-acetylaspartate were found in 5 patients; in the sixth patient with a small lesion no reduction was found. In all lesions reduced blood flow was found in the acute and chronic stage, whereas hyperemia was found in 4 patients in the subacute stage. CONCLUSIONS: In this preliminary study no clear correlation was found between the level of N-acetylaspartate or lactate in the acute stage of stroke and the clinical outcome; however, there does appear to be some connection between the reduction of cerebral blood flow and the spectroscopic findings in the chronic stage and to some extent the clinical outcome. Studies of larger clinical groups will be necessary to further elucidate the prognostic potential of proton magnetic resonance spectroscopy in human stroke.

Adult↗