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Biomedical subjects

O Henriksen

Publications and source records attributed to O Henriksen.

At least 55 records · Page 3Linked to original sources
PubMed1995

Quality assessment in in vivo NMR spectroscopy: III. Clinical test objects: design, construction, and solutions.

Based on the requirements of test protocols developed to evaluate clinical MRS single slice and volume localisation sequences, two clinical test objects, STO1 and STO2 have been developed. The properties of a range of potential construction materials have been assessed, demonstrating that the water/Perspex interface produced minimum susceptibility effects. The design of the objects has been evaluated in trials on different magnetic resonance instruments, with size and loading being adjusted to allow use on currently available equipment. Appropriate test solutions for 31P and 1H measurements have been developed and their properties evaluated.

Magnetic Resonance Spectroscopy↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: IV. A multicentre trial of test objects and protocols for performance assessment in clinical NMR spectroscopy.

A multicentre trial of test objects and protocols for performance assessment in single volume and slice selective magnetic resonance spectroscopy (MRS) was conducted by the European Community Concerted Action on MRI and MRS. The trial assessed phosphorus and proton localisation techniques implemented on commercially available MR systems at ten sites in Europe. At each site, a number of parameters devised by the Concerted Action were measured using prototype test objects. Some of these parameters related to the quality of localisation and others to the overall performance of the spectrometer. Results were obtained for the ISIS, DRESS, STEAM, and PRESS sequences with a range of acquisition parameters, allowing evaluation of the assessment methodology and comparison of the efficacy of various implementations of these localisation techniques. The results of this trial have been important in the development of the Concerted Action's final recommendations for MRS performance assessment, and demonstrate that such assessment provides valuable information in the comparison of spectroscopy data from different sites and in the development of new localisation sequences, and provides a means of quality assurance in MRS.

Magnetic Resonance Spectroscopy↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: V. Multicentre evaluation of prototype test objects and protocols for performance assessment in small bore MRS equipment.

This paper reports the results of multicentre studies aimed at designing, constructing, and evaluating prototype test objects for performance assessment in small-bore MRS systems, by utilizing the test protocols already proposed by the EEC COMAC-BME Concerted Action for clinical MRS equipment. Three classes of test objects were considered: (1) a multicompartment test object for 31P MRS measurements performed with slice-selective sequences; (2) a two-compartment test object for volume-selection 1H MRS; and (3) two-compartment test objects for assessing the performance of experimental systems using ISIS as volume localization sequence in 31P MRS. The results suggested the interest of adopting some of these prototypes for improving the comparison of spectroscopy data obtained from different sites, for providing useful means of quality assurance in experimental MRS, and facilitating the validation of new localization sequences.

Magnetic Resonance Spectroscopy↗
PubMed1995

Reduced N-acetylaspartate content in the frontal part of the brain in patients with probable Alzheimer's disease.

The fully relaxed water signal was used as an internal standard in a STEAM experiment to calculate the concentrations of the metabolites: N-acetylaspartate (NAA), creatine + phosphocreatine [Cr + PCr], and choline-containing metabolites (Cho) in the frontal part of the brain in 12 patients with probable Alzheimer's disease. Eight age-matched healthy volunteers served as controls. Furthermore, T1 and T2 relaxation times of the metabolites and signal ratios: NAA/Cho, NAA/[Cr + PCr], and [Cr + PCr]/Cho at four different echo times (TE) and two different repetition times (TR) were calculated. The experiments were carried out using a Siemens Helicon SP 63/84 wholebody MR-scanner at 1.5 T. The concentration of NAA was significantly lower in the patients with probable Alzheimer's disease than in the healthy volunteers. No significant difference was found for any other metabolite concentration. For the signal ratios the only statistically significant difference was that the NAA/Cho ratio at TE = 92 ms and TR = 1.6 s was lower in the patients with probable Alzheimer's disease compared with the control group. A trend towards a longer T2 relaxation time for NAA in the patients with probable Alzheimer's disease than among the healthy volunteers was found, but no significant difference was found concerning the T1 and T2 relaxation times.

Aged↗
PubMed1995

Brain lactate in preterm and growth-retarded neonates.

Glucose is the predominant cerebral energy source under physiological conditions, although other substrates may support cerebral metabolism. The present study was undertaken to determine if lactate is present in the immature human brain, and if so, whether or not concentrations of lactate differ between small-for-gestational-age and appropriate-for-gestational-age infants. Thirty stable, healthy infants with normal brains were investigated. As the only nutrient, all received milk enterally prior to the investigation, which was carried out without sedation. Mean gestational age was 35 completed weeks (range 28-41 weeks) and mean birth weight was 2170 g (range 855-4100 g). Proton nuclear magnetic resonance spectra from the striatal region were obtained while the infants were sleeping quietly. Lactate was present in all 10 preterm small-for-gestational-age and 10 of 13 preterm appropriate-for-gestational-age infants, and the concentration was inversely related to postmenstrual age (p < 0.002). In addition, lactate increased with the degree of growth retardation (p < 0.01). At present the significance of lactate is unclear. Lactate may be produced locally or in peripheral tissues, and may support brain metabolism.

Brain↗
PubMed1995

Cerebral energy metabolism during hypoxaemia. A 31P and 1H magnetic resonance study.

By means of proton and phosphorous magnetic resonance spectroscopy at 1.5 Tesla the human cerebral metabolism was investigated during mild and moderate hypoxaemia. Seven volunteers participated and spectra were obtained while the subjects were breathing atmospheric air, 16, 12 and 10% oxygen in N2.PaO2, PCO2 and arterial oxygen saturation were determined during the spectroscopic measurements. Haemodynamic and respiratory mechanisms compensated the hypoxic condition and no lactate production was found. There was no change in N-acetyl-aspartate. No change in intracellular pH was found. A slight but non-significant decrease in PCr/P(i)-ratio was found, indicating a decrease in the phosphorylation potential of the brain in response to hypoxaemia. The brain sustains aerobic metabolism during mild to moderate hypoxaemia.

Adult↗
PubMed1995

Effect of microgravity on forearm subcutaneous vascular resistance in humans.

To test the hypothesis that the subcutaneous vascular constrictor response to an orthostatic stress in humans is augmented after exposure to microgravity, the following experiment was performed. Four male astronauts underwent a standardized stepwise lower body negative pressure (LBNP) profile 5 mo before and between 24 and 40 h after completion of the 10-day Spacelab D2 mission (STS-55). Forearm subcutaneous blood flow was continuously measured during LBNP by the 133Xe washout technique, and forearm subcutaneous vascular resistance (FSVR) was estimated by dividing mean arterial pressure by forearm subcutaneous blood flow. Relative to the pre-LBNP level, FSVR increased to 169 +/- 42 (P < 0.05), 176 +/- 12 (P < 0.05) and 158 +/- 27% during postflight LBNP of -11 (20 min), -23 (5 min), and -30 (7.5 min) mmHg, respectively. During the same LBNP levels of the same durations preflight, FSVR increased to 121 +/- 11 (not significant), 139 +/- 12 (P < 0.05), and 135 +/- 13% (P < 0.05), respectively. Thus, FSVR increased more promptly and, in three of the four subjects, was more pronounced during postflight than during preflight LBNP. In conclusion, the FSVR response was more prompt and tended to be accentuated after 1-2 days after exposure to 10 days of microgravity and could act as a defense mechanism to alleviate decreased orthostatic tolerance.

Adult↗
PubMed1995

Simultaneous 31P-NMR spectroscopy and EMG in exercising and recovering human skeletal muscle: a correlation study.

A large number of studies have shown amplitude and spectral changes of the electromyogram during exercise, leading to several theories of how these changes might be related to the underlying metabolic changes. The amplitude and spectral changes are generally interpreted as changes in motor unit recruitment and a reduction of the muscle fiber conduction velocity due to proton or lactate accumulation. This study focuses on the causality of spectral changes of the surface electromyogram and proton or lactate accumulation and how the changes in motor unit recruitment are related to the metabolic status of the muscle. Simultaneous 31P-nuclear magnetic resonance spectroscopy and surface electromyography were performed during sustained static exercise and recovery in healthy volunteers and a patient with McArdle's disease. A clear dissociation between the median power frequency of the surface electromyogram and pH was seen in the healthy volunteers during recovery and during exercise in the patient with McArdle's disease. The results indicate that proton or lactate accumulation is not primarily responsible for the spectral changes of the surface electromyogram as previously suggested. The motor unit recruitment (as judged by the root mean square of the surface electromyogram) increased hyperbolically during the submaximal static exercise, with decreasing phosphocreatine-to-P(i) ratio reaching maximum at 0.6 (exhaustion), and seems to constitute a consistent metabolic limit to the exercise. The increased myoelectrical activity seen after exercise is not caused by an incomplete recovery of phosphorous metabolism, pH, or lactate but could probably be an impairment of the excitation-contraction coupling.

Adult↗
PubMed1995

The accuracy of MRI-determined synovial membrane and joint effusion volumes in arthritis. A comparison of pre- and post-aspiration volumes.

Magnetic resonance imaging (MRI) of 18 knees of patients with arthritis was performed before and immediately after arthrocentesis. Pre- and post-aspiration volumes were calculated by adding the outlined areas of synovium/effusion from a continuous series of gadolinium-DTPA-enhanced 5 mm transversal T1-weighted MR-images. The difference between MRI-determined and syringe-determined volumes of aspirated joint fluid was 0-7 ml, median 2 ml, corresponding to 0-18%, median 7%, of the pre-aspiration effusion volume. Synovial membrane volumes, determined before and after arthrocentesis varied 0-10 ml, median 3 ml (0-17%, median 7%). No significant systematic misinterpretation of the borderline between joint fluid and synovium was found. We conclude that effusion volumes and in all probability also synovial membrane volumes, can be determined by MRI with a maximal analytical error of approximately 20%. The acceptable accuracy of the method encourages further studies of the value of effusion and synovial membrane volumes as markers of the activity and/or severity of joint inflammation.

Adult↗
PubMed1995

Scoring of synovial membrane hypertrophy and bone erosions by MR imaging in clinically active and inactive rheumatoid arthritis of the wrist.

MRI-scores of synovial membrane hypertrophy and bone erosions of the RA-wrist are introduced. Gadolinium-DTPA enhanced magnetic resonance imaging (MRI) and conventional radiography (CR) of the wrist were performed in 16 patients with rheumatoid arthritis (RA) and 3 healthy controls. A MRI-score of synovial membrane hypertrophy was obtained by summation of gradings of synovial hypertrophy in 6 regions of the wrist. The score was significantly higher in wrists with than in wrists without clinical signs of active arthritis. The score was 0 in all healthy controls. Each bone of the wrist was assessed by MRI and CR with respect to bone erosions. Bone erosions were detected by MRI in 14 wrists in contrast to only 6 wrists by CR. In all patients the erosions were more numerous on MRI. The introduced methods may be useful quantitative measures of synovitis and early joint destruction in RA.

Adult↗
PubMed1995

31P NMR spectroscopy and electromyography during exercise and recovery in patients with fibromyalgia.

OBJECTIVE: To investigate whether patients with fibromyalgia (FM) have normal motor unit recruitment in relation to muscle metabolism during exhausting exercise and recovery, and whether the reduced voluntary muscle force normally seen is related to a smaller muscle size. METHODS: Female patients with FM and sedentary controls were examined using simultaneous 31P nuclear magnetic resonance spectroscopy (NMR) and surface electromyography (SEMG) during exhaustive static exercise of the anterior tibial muscle and during recovery. The maximum voluntary contraction force was estimated, and the maximum cross sectional muscle area was evaluated using 1H NMR imaging. The sedentary controls were matched to patients for sex, age and, as far as possible, daily physical activity levels. RESULTS: Patients with FM had reduced maximum voluntary contraction force in relation to the sedentary controls, despite having similar muscle size. In general the myoelectrical-metabolic relation during exercise and recovery was normal in patients with FM. CONCLUSION: The less extreme changes in motor unit recruitment and metabolism during exhaustive exercise indicated a lower exercise tolerance that could be connected with the lower physical activity levels.

Adult↗
PubMed1995

Texture analysis in quantitative MR imaging. Tissue characterisation of normal brain and intracranial tumours at 1.5 T.

The diagnostic potential of texture analysis in quantitative tissue characterisation by MR imaging at 1.5 T was evaluated in the brain of 6 healthy volunteers and in 88 patients with intracranial tumours. Texture images were computed from calculated T1 and T2 parameter images by applying groups of common first-order and second-order grey level statistics. Tissue differentiation in the images was estimated by the presence or absence of significant differences between tissue types. A fine discrimination was obtained between white matter, cortical grey matter, and cerebrospinal fluid in the normal brain, and white matter was readily separated from the tumour lesions. Moreover, separation of solid tumour tissue and peritumoural oedema was suggested for some tumour types. Mutual comparison of all tumour types revealed extensive differences, and even specific tumour differentiation turned out to be successful in some cases of clinical importance. However, no discrimination between benign and malignant tumour growth was possible. Much texture information seems to be contained in MR images, which may prove useful for classification and image segmentation.

Algorithms↗
PubMed1995

Increased brain water self-diffusion in patients with idiopathic intracranial hypertension.

PURPOSE: To investigate changes in brain water diffusion in patients with idiopathic intracranial hypertension. METHODS: A motion-compensated MR pulse sequence was used to create diffusion maps of the apparent diffusion coefficient (ADC) in 12 patients fulfilling conventional diagnostic criteria for idiopathic intracranial hypertension and in 12 healthy volunteers. RESULTS: A significantly larger ADC was found within subcortical white matter in the patient group (mean, 1.16 x 10(-9) m2/s) than in the control group (mean, 0.75 x 10(-9) m2/s), whereas no significant differences were found within cortical gray matter, the basal nuclei, the internal capsule, or the corpus callosum. Four of 7 patients with increased ADC in subcortical white matter also had increased ADC within gray matter. CONCLUSION: Measurement of diffusion coefficients in vivo demonstrated increased local water mobility within subcortical white matter in 7 patients with idiopathic intracranial hypertension that otherwise appeared normal on conventional MR imaging. Further studies are necessary to assess the clinical significance of these observations.

Adolescent↗
PubMed1995

Ultrasonography in arthritis of the knee. A comparison with MR imaging.

Ultrasonography (US) of the knee in gonarthritis was evaluated with gadolinium-DTPA-enhanced MR imaging as a reference. The study included 13 patients with gonarthritis, 2 patients with osteoarthritis and 5 healthy controls. Compared to MR, US identified 100% (12/12) of joint effusions, 100% (5/5) of Baker's cysts, 57% (8/14) of the synovial membranes of the suprapatellar recess and 38% (3/8) of bone erosions. No MR or clinical findings characterized the patients with ultrasonographically identifiable synovial membranes. Quantitative MR- and US-estimates of effusion, synovial membrane and cartilage thicknesses were correlated. The Spearman correlation coefficients were 0.87, 0.86 and 0.82, respectively. US reliably demonstrated joint effusions and Baker's cysts but showed lack of sensitivity for demonstration of the synovial membrane and bone erosions. When the synovial membrane was identifiable, the measurements of synovial thickness by US appeared precise. Cartilage evaluation by US seemed dependable. The clinical value was limited, because the weight-bearing areas were inaccessible.

Arthritis, Rheumatoid↗
PubMed1995

Deuterium MR spectroscopy at 4.7 T. Quantification of tumour and subcutaneous tissue blood flow in animal models.

Deuterium MR spectroscopy was used for the determination of tissue blood flow (TBF). The tracer D2O was injected into the tissue of interest, and tracer washout was followed using a 4.7 T spectroscopy/imaging unit. Normal subcutaneous tissue in rats was studied, as well as tissue influenced by vasoactive agents (papaverine and adrenaline). The vasoactive agents introduced changes of 40% in TBF, compared with normal tissue. Normal tissue measurements were repeated using various D2O injection volumes (5-400 microliters). The injection volume 5 microliters gave TBF 11.7 +/- 2.0 ml/100 g.min (mean +/- 1 SD). This value was 40% higher than corresponding values observed at larger injection volumes (200-400 microliters). This injection volume effect is probably partly due to a capillary dilution caused by tracer administration, and partly related to the non-physiological deuterium signal decrease observed in dead rats. Blood flow measurements in human colon tumours implanted in nude mice showed a rather poor reproducibility, not improved by the use of a multiple site injection technique.

Adipose Tissue↗
PubMed1994

[Magnetic resonance spectroscopy in fibromyalgia. A study of phosphate-31 spectra from skeletal muscles during rest and after exercise].

31phosphorus nuclear magnetic resonance (31P NMR) spectroscopy of painful calf muscle was performed in 12 patients with fibromyalgia and 7 healthy subjects during rest, aerobic and anaerobic exercising conditions, and postexercise recovery. Ratios of inorganic phosphate and creatine phosphate (Pi/PCr) and pH were calculated from the collected 31P NMR spectra. Resting values of Pi/PCr were normal in the patients. Patients only tolerated 49% of the workload tolerated by the controls (P = 0.005). Patients and controls had similar rates of Pi/PCr and pH changes during work and recovery. The controls were able to change their Pi/PCr and pH more than the patients, due to the greater workload reached. However, statistical significance was only reached for the anaerobic static exercise (P = 0.003). It was concluded that fibromyalgia patients have a reduced voluntary capacity for work, but with a biochemical response to work and recovery similar to healthy subjects.

Adult↗
PubMed1994

[Magnetic resonance imaging of disseminated sclerosis].

Multiple sclerosis is a chronic demyelinating disease. Paraclinical examinations may contribute to the diagnosis of multiple sclerosis. Magnetic resonance imaging (MRI) has a very high sensitivity concerning multiple sclerosis, and has made it possible to visualize multiple sclerosis plaques in vivo, to follow each plaque over the course of time and in this way to obtain information about the pathogenesis. MRI has shown that the size of plaques may vary considerably, and that plaques are dynamic structures with the ability to change in size over few weeks. By using MRI and the contrast agent Gadolinium-DTPA, it is possible to distinguish a newly developed plaque from an older one. Therefore, MRI has become an important examination in therapeutic trials. Just now, MRI with Gadolinium-DTPA is being used to evaluate the efficacy of plasmapheresis and immunoglobulin treatment in a joint study between Rigshospitalet and Hvidovre Hospital.

Contrast Media↗