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Biomedical subjects

O Henriksen

Publications and source records attributed to O Henriksen.

At least 109 records · Page 6Linked to original sources
PubMed1993

Reproducibility of cardiac volume measurements including left ventricular mass determined by MRI.

Cardiac volumes including left ventricular mass were determined by magnetic resonance imaging (MRI) in 30 patients using a contiguous multislice technique. Eleven patients were studied on two different days. Intra- as well as interobserver and interstudy variation were evaluated. For volume measurements the standard deviation of differences (SDD) was rather constant, independent of the size of the measured volume indicating lower percentual variability in measuring large volumes. Lowest variability was noticed for left ventricular myocardial mass estimates between observers as well as between studies. In 13 patients left ventricular mass was estimated by this technique as well as by a method using only one long axis and four short axis slices and by two-dimensional echocardiography. Although highly correlated, limits of agreement between the methods were too wide to accept interchangeable clinical use of the methods.

Adult↗
PubMed1993

Increased water self-diffusion in chronic plaques and in apparently normal white matter in patients with multiple sclerosis.

A new method for measurement of water self-diffusion compensating for zeroth and first order movements was used to study the apparent diffusion coefficient (ADC) in 15 patients with chronic multiple sclerosis (MS) and in two patients with acute MS. Ten healthy volunteers served as controls. A significantly higher ADC was found within chronic plaques compared to the apparently normal white matter of the chronic patients. The ADC was higher in the acute plaques compared to the chronic plaques. The ADC in apparently normal white matter of the chronic patients were significantly higher than in white matter of healthy volunteers. We hypothesize that an increase of the ADC in plaques may be related to an increase in the extracellular space due to oedema and demyelination. The increased ADC in apparently normal white matter suggests that there may be a change in the composition of the white matter of chronic MS patients, perhaps related to oedema and expanded extracellular space.

Adult↗
PubMed1993

Normal left ventricular wall motion measured with two-dimensional myocardial tagging.

Using a myocardial tagging technique, normal left ventricular wall motion was studied in 3 true short axis views and a double oblique 4-chamber view in 14 and 11 volunteers, respectively. Three orthogonal directions of left ventricular motion were observed throughout the systole; a concentric contraction towards the center of the left ventricle, a motion of the base of the heart towards the apex, and a rotation of the left ventricle around its long axis. The direction of left ventricular rotation changed from early systole to late systole. The base and middle levels of the left ventricle rotated counterclockwise (CCW) at early systole and clockwise (CW) at late systole, whereas the apex of the heart rotated CW at early systole and CCW at late systole. The different directions of the rotation of base and apex resulted in a myocardial twisting that changed direction from early to late systole. We conclude that MR imaging with myocardial tagging is a method that can be used to study normal left ventricular wall motion, and that is promising for future use in patient groups.

Adult↗
PubMed1993

Functional MR imaging at 1.5 T. Initial results using photic and motoric stimulation.

A preliminary investigation of the effects of stimulation of the visual and the motor cortex was made on a conventional 1.5 T MR imaging scanner. Both types of activation gave a detectable change in the signal between rest and stimulation using a gradient echo sequence with an echo time of 60 ms. The observed effects were assumed to be caused by variation in the amount of paramagnetic deoxyhemoglobin between stimulation and rest due to local increase of capillary blood flow in the human brain during stimulation.

Brain↗
PubMed1992

[Magnetic resonance imaging (MRI) in central pontine myelinolysis].

Three cases of central pontine myelinolysis (CPM) including magnetic resonance (MRI), are presented and the literature describing the pathological physiological background for the appearance in MRI is reviewed. MRI is recommended as the method of choice in cases of suspected CPM.

Demyelinating Diseases↗
PubMed1992

[Monitoring of anesthesia during magnetic resonance imaging].

Clinical employment of magnetic resonance scanning presents great diagnostic possibilities, partly in the form of the quality of the imaging and also on account of the possibilities for carrying out spectroscopic measurements by mens of which in vivo non-invasive chemical analysis of drug concentrations in the tissues may be performed. In anticipation of the possibility of employing MR-scanning as an important diagnostic aid for assessing the causes of unconsciousness in patients in intensive care, attempts have been made to establish reliable and justifiable equipment for monitoring which can render possible investigation of unconscious or anaesthetized patients in scanners with magnetic fields of over 1.5 Tesla. The medical technical difficulties involved are mentioned and the solutions which are employed in the Danish scientific Centre for Magnetic Resonance in Hvidovre Hospital in Copenhagen are described. This monitoring includes continuous ECG recording, measurements of pulse and blood-pressure once per minute and continual monitoring of respiration including concentrations of carbon dioxide in the inspired and expired air and the concentration of oxygen in the inspired air. In addition, model solutions have be outlined for establishing mechanical ventilation with the servorespirator and the possibility of producing an employable pulse oxymeter is described. It is stated that, provided all of the elements in the above mentioned model solution for monitoring during anaesthesia in the MR laboratory have been carried out, it is considered justifiable to place all patients, including children, in the MR-scanner.

Anesthesia, General↗
PubMed1992

An occipito-temporal syndrome in adolescents with optimally controlled hyperphenylalaninaemia.

The study included 16 adolescents with optimally controlled hyperphenylalaninaemia (McKusick 26160), of whom six did not require treatment according to conventional criteria. All except the two patients with lowest median serum phenylalanine level throughout childhood (most values at 200-300 mumol/L) had white matter abnormalities detectable with magnetic resonance imaging. The lesions were particularly prominent in the watershed regions between the posterior and middle cerebral arteries. In most patients with moderate or severe hyperphenylalaninaemia frontal white matter lesions were present as well. Normal proton magnetic resonance spectra indicated that the lesions were stable. Occipital EEG abnormalities were frequent, and deficient performance on a pattern-recognition test was a characteristic neuropsychological finding. Serum phenylalanine levels at about 300 mumol/L or below throughout childhood and early adolescence may be required to avoid lesions. The present study demonstrates the limitations of even an optimally controlled dietary regimen in hyperphenylalaninaemia.

Adolescent↗
PubMed1992

Simultaneous electromyography and 31P nuclear magnetic resonance spectroscopy--with application to muscle fatigue.

The electromyogram (EMG) is often used to study human muscle fatigue, but the changes in the electromyographic signals during muscle contraction are not well understood in relation to muscle metabolism. The 31P NMR spectroscopy is a semi-quantitative non-invasive method for studying the metabolic changes in human muscle. The aim of this study was to develop a method by which EMG and NMR spectroscopy measurements could be performed simultaneously. All measurements were performed in a whole body 1.5 Tesla NMR scanner. A calf muscle ergometer, designed for use in a whole body NMR scanner, was used. The subject had the left foot strapped to the ergometer. The anterior tibial EMG was recorded by bipolar surface electrodes. A surface coil was strapped to the anterior tibial muscle next to the EMG electrodes. Simultaneous measurements of surface EMG and surface coil 31P NMR spectroscopy were performed in the scanner during an isometric submaximal voluntary contraction until exhaustion, in 6 normal volunteers. Concentrations of phosphocreatine (PCr), inorganic phosphate (P(i)) and pH were analysed together with root mean square (RMS) and median frequency of the EMG. The fatiguing contractions (endured 5-13 min) produced a rapid decline in PCr and pH accompanied by a rapid rise in P(i). The RMS was approximately constant until the normalized PCr concentration declined below 0.6-0.7 and the pH declined below 6.75-6.85; exceeding these metabolic limits was associated with a rapidly increasing RMS value (2-3 times the previous level by exhaustion). The median frequency declined linearly with time and was found to be highly linearly correlated with the pH value (r = 0.82).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

In vivo evaluation of the reproducibility of T1 and T2 measured in the brain of patients with multiple sclerosis.

The precision (reproducibility) of relaxation times derived from magnetic resonance images of patients with multiple sclerosis (MS) were investigated. Measurements of 10 MS patients were performed at 1.5 T on two occasions within 1 wk. T1 and T2 was measured using a partial saturation inversion recovery sequence (6 points) and a Carr-Purcell-Meiboom-Gill phase alternating-phase shift multiple spin-echo sequence with 32 echoes. Regions of interest (ROI) were placed both in apparently normal white matter and plaques. The precision (+/- 1.96 SD) and the confidence intervals for T1 and T2 for white matter and plaques were calculated. The precision of T1 for white matter and plaques was respectively +/- 94 msec and +/- 208 msec. The precision of T2 for white matter and plaques was respectively +/- 18 msec and +/- 26 msec. For all measurements the coefficient of variation was about 9%. Judging from our own study and others as well, a precision better than 10% for T1 and T2 would seem unrealistic at present.

Adult↗
PubMed1992

In vivo magnetic resonance diffusion measurement in the brain of patients with multiple sclerosis.

Measurement of water self-diffusion in the brain in 25 patients with multiple sclerosis was performed by magnetic resonance imaging. Quantitative diffusion measurements were obtained using single spin-echo pulse sequences with pulsed magnetic field gradients of different magnitude. Twenty-two of these patients also underwent measurement of the transverse relaxation time (T2). Only one plaque was evaluated in each patient. Based on prior knowledge, 12 plaques were classified as being 3 mo or less in age, and 7 plaques were classified as being more than 3 mo old. In all 25 plaques, water self-diffusion was found to be higher than in apparently normal white matter. Furthermore, water self-diffusion was found to be higher in acute plaques compared with chronic plaques. Finally, a slight tendency toward a relationship between the diffusion capability and T2 was found. We believe that an increased diffusion capability signifies an increase of the extracellular water space, which probably is related to the degree of demyelination. Thus, measurement of water self-diffusion in multiple sclerosis plaques may contribute to the study of pathogenesis of demyelination.

Adult↗
PubMed1992

Quantification of complex flow using MR phase imaging--a study of parameters influencing the phase/velocity relation.

In this study, we describe how motion-induced phase angle is affected by different flow models and imaging parameters when using the MR flow phase mapping technique. In a phantom with straight as well as constricted tubes, simulating healthy and stenotic vessels, nonpulsatile flow in the velocity range 0-1 m/sec was maintained. The phase/velocity relation was studied for various degrees of complex flow caused by the constriction, and regions with a breakdown in linearity were determined. Further studies in these regions were made regarding the influence of pulse sequence parameters on the phase/velocity relation. The results showed that in poststenotic areas characterized by so-called separated flow, the phase/velocity relation became nonlinear due to dephasing effects. In regions with fully developed turbulent flow in straight tubes, however, no breakdown in linearity was observed. Parameters seen to have a substantial influence on the phase/velocity relation were first- and second-order velocity encoding and voxel size. Finally, a pilot in vivo demonstration of complex flow was done using a sequence designed to be robust with respect to linearity of the phase/velocity relation. The results indicate that the MR phase mapping technique can be used to measure flow quantitatively in regions with complex flow. This opens possibilities for future clinical use of the technique in the study of areas of complex flow such as valvular heart disease.

Aortic Valve Stenosis↗
PubMed1992

Identification of patients with hereditary haemochromatosis by magnetic resonance imaging and spectroscopic relaxation time measurements.

A total of 4302 healthy blood donors were screened for elevated serum ferritin and transferrin saturation. Fifteen had increased serum ferritin at a follow-up examination. Five relatives of these donors also entered the study. Eleven patients had elevated liver iron concentrations, while five had normal liver iron concentrations. The R2 relaxation rate in the liver was first measured with a conventional multi-spin-echo imaging sequence, and then by a volume-selective spectroscopic multi-spin-echo sequence, in order to achieve a minimum echo time of 4 msec. No correlation was found between the relaxation rate R2 and the liver iron concentration, when R2 was calculated from the imaging data. Multi-exponential transverse relaxation could be resolved when the spectroscopic sequence was used. A strong correlation between the initial slope of the relaxation curve and the liver iron concentration was found (r = 0.90, p < 0.001). Signal intensity ratios between liver and muscle were calculated from the first three echoes in the multi-echo imaging sequence, and from a gradient echo sequence. A strong correlation between the logarithm of the signal intensity ratios and the liver iron concentration was found. Although both spectroscopic T2 relaxation time measurements and signal intensity ratios could be used to quantify liver iron concentration, the gradient echo imaging seemed to be the best choice. Gradient echo imaging could be performed during a single breath hold, so motion artifacts could be avoided. The accuracy of liver iron concentration estimates from signal intensity ratios in the gradient echo images was about 35%.

Biopsy↗
PubMed1992

In vivo relaxation of N-acetyl-aspartate, creatine plus phosphocreatine, and choline containing compounds during the course of brain infarction: a proton MRS study.

Localized water suppressed proton spectroscopy has opened up a new field of pathophysiological studies of severe brain ischemia. The signals obtained with the pulse sequences used so far are both T1 and T2 weighted. In order to evaluate the extent to which changes in metabolite signals during the course of infarction can be explained by changes in T1 and T2 relaxation times, eight patients with acute stroke were studied. STEAM sequences with varying echo delay times and repetition times were used to measure T1 and T2 of N-acetyl-aspartate (NAA), creatine plus phosphocreatine (Cr+PCr) and choline containing compounds (CHO) in a 27-ml voxel located in the affected area of the brain. Ten healthy volunteers served as controls. We found no difference in T1 or T2 of the metabolites between the patients and the normal controls. The T2 of CHO was longer than that of NAA and Cr+PCr. Our results indicate that spectra obtained in brain infarcts and normal tissue with the same acquisition parameters are directly comparable with respect to relative signal intensities as well as signals scaled with internal and external standards.

Adult↗
PubMed1992

Assessment of left ventricular volumes by magnetic resonance in comparison with radionuclide angiography, contrast angiography and echocardiography.

The present study shows that for assessment of LVEF, MRI and the standard methods seem to provide information of similar value. For absolute volume measurements, MRI and RNA are superior to single plane angiography and 2 DE using the modified Simpson-rule. The time consuming transversal MRI method does not seem to be superior to the oblique multislice method, when apical aneurysms can be ruled out. MRI thus seems to be an accurate method for determination of LV stroke volume as well as for determination of LVEF and hence for diastolic and systolic volumes. MRI, however, depends of a good image quality, which is crucial especially in dilated ventricles containing stagnant or slowly moving blood.

Adult↗
PubMed1992

Gd-DTPA-enhanced lesions in the brain of patients with acute optic neuritis.

The cerebral hemispheres of 19 patients with acute monosymptomatic optic neuritis (AMON) were investigated using magnetic resonance imaging (MRI) and Gadolinium-DTPA (Gd-DTPA). Using T1-weighted and T2-weighted imaging sequences it was disclosed that 14 of 19 patients had lesions and that enhancement was seen in seven patients. It is known that patients with AMON and silent lesions in the CNS have a highly increased risk of developing multiple sclerosis (MS) later on. If it is accepted that a silent lesion in patients with AMON does represent a multiple sclerosis (MS) plaque, and that an enhancing silent lesion represents an acute MS lesion, we may hypothesize that the disease process ultimately leading to MS starts long before the first symptom or sign ever appears. It would seem that at least half of the silent lesions in the cerebral hemispheres of patients with AMON had existed before the onset of the AMON, and that the disease actually started before the onset of the AMON.

Adult↗
PubMed1992

Circadian variation in human cerebrospinal fluid production measured by magnetic resonance imaging.

Recent advances in magnetic resonance imaging have made it possible to visualize and quantify flow of cerebrospinal fluid (CSF) in the brain. The net flow of CSF through the cerebral aqueduct was used to measure CSF production in six normal volunteers at different times during a 24-h period. CSF production varied greatly both intra- and interindividually. The average CSF production in each time interval showed a clear tendency to circadian variation, with a minimum production 30% of maximum values (12 +/- 7 ml/h) approximately 1800 h and a nightly peak production approximately 0200 h of 42 +/- 2 ml/h. The total CSF production during the whole 24-h period, calculated as an average of all measurements, was 650 ml for the whole group and 630 ml for repeated measurements in each time interval in one of the volunteers.

Adult↗
PubMed1992

Early time course of N-acetylaspartate, creatine and phosphocreatine, and compounds containing choline in the brain after acute stroke. A proton magnetic resonance spectroscopy study.

BACKGROUND AND PURPOSE: The early time course after acute stroke of cerebral N-acetylaspartate, creatine and phosphocreatine, and compounds containing choline was studied in vivo by means of localized water-suppressed proton magnetic resonance spectroscopy. METHODS: Eight patients with acute stroke were studied serially in the acute phase, 1 week after, and 2-4 weeks after the onset of clinical symptoms. Ten healthy volunteers served as controls. A stimulated echo (STEAM) sequence was used for measurement of the brain metabolites in a volume of interest located within the infarcted area as visualized by magnetic resonance imaging. For quantification, the unsaturated water signal was used as the internal standard. Regional cerebral blood flow in the infarcted area was measured relative to a symmetrically located unaffected area by means of single-photon emission computed tomographic scanning, using 99mTc-labeled d,l-hexamethylenepropyleneamine oxime as the flow tracer. RESULTS: Relative regional cerebral blood flow was considerably reduced in the infarcted area in the acute phase. After 1 week, hyperemia was seen in all but one patient. The N-acetylaspartate content was significantly reduced, with the loss appearing to occur between 6 and 24 hours after the stroke incident. The reduction in N-acetylaspartate content was greater in the central part than in the peripheral part of the infarcted area. Creatine and phosphocreatine were also reduced in the infarcted area, whereas no significant change was seen in the choline content. CONCLUSIONS: Assuming that N-acetylaspartate content reflects neuronal survival or loss, our results may suggest that treatment procedures with restoration of blood flow to severely ischemic areas should be initiated within the first 6 hours after stroke onset.

Acute Disease↗