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Biomedical subjects

O Henriksen

Publications and source records attributed to O Henriksen.

At least 91 records · Page 5Linked to original sources
PubMed1994

Synovial volume--a marker of disease severity in rheumatoid arthritis? Quantification by MRI.

Volumes of synovial membrane and joint effusion were determined by magnetic resonance imaging (MRI) in patients with inflammatory gonarthritis. 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. Ten knees with clinically active gonarthritis (CAG), 8 knees with clinically inactive gonarthritis (CIG) and 5 healthy controls (HC) were examined. The synovial volume of CAG-, CIG- and HC-knees were significantly different. The median volumes were 79 ml, 21 ml and 3 ml, respectively. Synovial and effusion volumes were highly correlated. A selected sagittal one-slice volume showed a high correlation to the total volumes. The reliable quantification of synovial and effusion volumes could be useful in the assessment of disease severity and as an outcome measure to treatment.

Arthritis, Rheumatoid↗
PubMed1994

Increased self-diffusion of brain water in hydrocephalus measured by MR imaging.

We used MR imaging to measure the apparent brain water self-diffusion in 5 patients with normal pressure hydrocephalus (NPH), in 2 patients with high pressure hydrocephalus (HPH), and in 8 age-matched controls. In all patients with NPH significant elevations of the apparent diffusion coefficients (ADC) of brain water were found within periventricular white matter, in the corpus callosum, in the internal capsule, within cortical gray matter, and in cerebrospinal fluid, whereas normal ADCs were found within the basal ganglia. In 2 patients with HPH elevated ADCs were found most prominently within white matter, and in one patient reexamined one year after surgery, ADCs were unchanged in nearly all brain regions. The increased ADC values in hydrocephalus patients may be caused by factors such as changes in myelin-associated bound water, increased Virchow-Robin spaces, and increased extracellular brain water fraction. For further studies of brain water diffusion in hydrocephalus patients, echo-planar imaging techniques with imaging times of a few seconds may be valuable.

Adult↗
PubMed1994

[Magnetic resonance imaging of the cardiovascular system].

Magnetic resonance (MR) is a noninvasive technique to obtain tomographic images in any desired plane of the body. MR offers possibilities not only for morphologic imaging, but also for various physiological measurements, e.g. investigation of blood flow and angiography. This paper summarizes the possibilities of the technique in evaluation of congenital and acquired cardiovascular diseases. The conclusion is that MR may become an important clinical tool for examination of the cardiovascular system providing high accuracy and quantitative measurements.

Angiography↗
PubMed1994

Age dependent white matter lesions and brain volume changes in healthy volunteers.

The brain of 142 healthy volunteers aged 21 to 80 years were investigated using MR imaging. The number and size of the white matter hyperintensity lesions (WMHL) in the cerebral hemispheres were determined. Furthermore, the volume of the cerebral hemispheres and of the lateral ventricles was measured. An almost linear increase in the number of volunteers with WMHL was seen with aging for males and females. With aging a significant decrease in the volume of the cerebral hemispheres was found for males, and a significant increase in the volume of the lateral ventricles was seen for both males and females. Our results suggest that with aging central atrophy increases more (relatively) than cortical atrophy. No correlation was found between the decreasing volume of the cerebral hemispheres and the increasing number and size of WMHL, nor between the increasing volume of the lateral ventricles and the increasing number and size of WMHL.

Adult↗
PubMed1994

Phosphorous and proton spectroscopy in relation to near incarceration and incarceration of the human brain.

We report 3 cases of 31P and 1H MR spectroscopy (MRS) performed at different stages on patients with clinical signs of near or fulminant incarceration of the brain. The measurements were made on a whole body, 1.5 T scanner. 1H-MRS was obtained with the STEAM sequence and 31P-spectra were obtained using the chemical shift imaging technique. Medical treatment including controlled ventilation and sedation of the patients was carried out during the examination. The first patient was evaluated on days 6 and 10 after evacuation of an acute subdural haematoma. An intracranial pressure of 35 mm Hg was registered during the first examination. The 2nd patient had suffered a spontaneous intracerebral haemorrhage and showed clinical signs of imminent incarceration during the examination. The 3rd patient showed clinical signs of incarceration just prior to the examination. In the 1st patient 1H-MRS showed a 3-fold increase in the concentration of choline-containing compounds and a small decrease in N-acetyl aspartate from the 1st to the 2nd examination, which we interpret as a loss of neurones. In case 2 only small changes in metabolism could be detected, indicating that, despite signs of imminent clinical incarceration, the energy supply to the brain was substantial. 1H-MRS of the 3rd patient showed massive lactate concentration, and 31P-MRS revealed the total absence of high-energy phosphorous compounds leaving only one single peak of inorganic phosphate, indicating irreversible brain death.

Adolescent↗
PubMed1994

MR spectroscopy in clinical research.

MR spectroscopy (MRS) offers unique possibilities for non-invasive evaluation of biochemistry in vivo. During recent years there has been a growing body of evidence from clinical research studies on human beings using 31P and 1H MRS. The results indicate that it is possible to evaluate phosphorous energy metabolism, loss of neurones, and lactate production in a large number of brain diseases. Furthermore, 31P and 1H MRS may be particularly clinically useful in evaluation of various disorders in skeletal muscle. In the heart 31P MRS seems at the moment the most suitable for evaluation of global affections of the myocardium. In the liver 31P MRS appears to be rather insensitive and non-specific, but absolute quantification of metabolite concentrations and using metabolic "stress models" may prove useful in the future. The clinical role of MRS in oncology is still unclear, but it may be useful for non-invasive follow-up of treatment. Taken together, the evidence obtained so far certainly shows some trends for clinical applications of MRS. Methods are now available for the clinical research necessary for establishing routine clinical MRS examinations.

Bone Marrow Diseases↗
PubMed1994

Dynamic gadolinium-enhanced MR imaging in active and inactive immunoinflammatory gonarthritis.

Dynamic T1-weighted FLASH MR imaging, obtained just after i.v. gadopentetate dimeglumine injection, and pre- and postcontrast T1-weighted spin-echo (T1-SE) MR imaging were performed to compare their information value with respect to inflammatory activity in immunoinflammatory gonarthritis. We examined 16 clinically active (CAG), 7 clinically inactive (CIG) and 4 healthy knees. The synovium of a preselected slice was outlined. Its area and relative signal intensity increase after gadopentetate dimeglumine on T1-SE and FLASH (at each time t) were calculated. The CAG knees showed a mean signal intensity increase on early dynamic FLASH images higher by far than the CIG knees, while no significant difference was found on spin-echo images obtained 5 to 15 min after contrast injection. The early signal enhancement probably reflects the perfusion and capillary permeability of the synovium. The area of synovium could differentiate between healthy and arthritic knees. Gadolinium-enhanced dynamic FLASH imaging may provide clinically useful information about the actual inflammatory activity of arthritic joints.

Adult↗
PubMed1993

[Magnetic resonance spectroscopy of acute cerebral infarctions].

Eight patients with brain infarction were examined serially in the acute phase and one week and two to four weeks after stroke with water-suppressed proton magnetic resonance spectroscopy. Ten healthy volunteers served as controls. The time courses of N-acetylaspartate (NAA), total creatine (Cr), choline containing compounds (Cho), lactate content, and regional cerebral blood flow (rCBF) measured by SPECT were studied. A high lactate level was found in the acute phase. The lactate content decreased to barely detectable levels during the following two to four weeks, while rCBF increased during this period. The content of NAA in infarcted tissue was significantly reduced (p < 0.01) compared to healthy controls, Cr was also reduced (p < 0.02), whereas Cho content did not change. The inverse relationship between lactate level and cerebral blood flow suggests that lactate plays no substantial role in the vasodilatation underlying the hyperaemia that follows reperfusion. The amount of lactate present in the acute phase reflects the severity of ischaemia in the affected region. The content of NAA may be used as a neuronal marker, and thus perhaps as a marker of the effect of future treatment procedures.

Acute Disease↗
PubMed1993

[CT and magnetic resonance imaging and spectroscopy for non-invasive study of regeneration of skeletal musculature after intensive therapy].

UNLABELLED: A 50 year old man was treated in the intensive care unit. Due to a prolonged catabolic state with a loss of 35 kg of body weight, he was practically paralyzed following 70 days of treatment. After 200 days of intensive physical training, he had recuperated remarkably. CT-scans before and after the physical training revealed 90-180% increase in the muscles examined. At the femoral level the muscle/fat ratio increased from 40% to 70%, indicating less atrophy. MR-imaging of the crural muscles showed a substantial increase in the muscle mass after training. MR-fat/water proton spectra showed a decrease in the relative fat content from 0.31 to 0.13 during training, objectively measuring the remission of the severe atrophy. CONCLUSION: CT- and MR-techniques can be used for objective, non-invasive, evaluations of muscle condition, and MR-proton spektroscopy can probably be used for following the remission of muscle atrophy during physical training.

Critical Care↗
PubMed1993

Quantification of aortic regurgitation by magnetic resonance velocity mapping.

The use of magnetic resonance (MR) velocity mapping in the quantification of aortic valvular blood flow was examined in 10 patients with angiographically verified aortic regurgitation. MR velocity mapping succeeded in identifying and quantifying the regurgitation in all patients, and the regurgitant volume determined with MR velocity mapping agreed well with the grade obtained by aortic root angiography (p < 0.02). The accuracy in quantification of the aortic valvular flow rate was demonstrated by a significant correlation between the stroke volume (ml) measured by MR velocity mapping and calculated from MR imaging of the left ventricular end-diastolic and end-systolic volumes in eight patients (Y = 0.89 x X + 11, r = 0.97, p < 0.001). This finding was confirmed by a good agreement between the net cardiac output (L/min) quantified with MR velocity mapping and simultaneous 125I-indicator dilution measurement in all subjects (Y = 0.89 x X + 0.08, r = 0.82, p < 0.01). In conclusion, MR velocity mapping may be used as a noninvasive tool in the quantification of aortic regurgitation.

Adult↗
PubMed1993

Valve area and cardiac output in aortic stenosis: quantification by magnetic resonance velocity mapping.

Valve area and cardiac output were determined with magnetic resonance (MR) velocity mapping in 12 patients with aortic stenosis. Heart catheterization, Doppler echocardiography, and indicator dilution were performed for comparison. Left ventricle could be catheterized in only nine patients; in these cases, MR measured a mean valve area of 1.2 cm2 compared with 0.9 cm2 derived from catheterization data, with a mean difference of 0.2 cm2 between the 2 methods. The limits of agreement were [0.0, +0.5] cm2, less in patients with an important degree of concomitant regurgitation. In the whole material, MR measured a mean area of 1.1 cm2 compared with 1.2 cm2 derived from Doppler echocardiography data, with a mean difference of 0.1 cm2 and [-0.5, +0.6] cm2 as limits of agreement. In 11 patients the cardiac output was quantified by MR to a mean of 4.9 L/min and by indicator dilution to 5.0 L/min, with a mean difference of 0.2 L/min, and [-0.6, +0.8] L/min as limits of agreement. In addition, MR offers the major advance of simultaneous quantification of regurgitant volume in cases of concomitant regurgitation. In conclusion, because the two important prognostic determinants in aortic stenosis--the valvular area and the cardiac output--may be quantified, MR has potential to become a clinical tool in assessment of severity in aortic stenosis.

Aged↗
PubMed1993

The concentration of N-acetyl aspartate, creatine + phosphocreatine, and choline in different parts of the brain in adulthood and senium.

The fully relaxed water signal was used as an internal standard in a STEAM experiment to calculate the concentrations of the metabolites: N-acetyl aspartate (NAA), creatine + phosphocreatine (Cr + PCr), and choline (Cho) containing compounds in four different parts of the brain in two age groups of healthy volunteers (20-30 yr, n = 8) and (60-80 yr, n = 8). Furthermore, T1 and T2 relaxation time of the metabolites and signal ratios: NAA/Cho, NAA/Cr + PCr, and Cho/Cr + PCr at TE = 272 msec were calculated. The experiments were carried out using a Siemens Helicon SP 63/84 wholebody MR-scanner at 1.5 T. In the younger age group, the concentration of NAA was significantly higher in the occipital part than in the other three parts of the brain. No significant regional variation was found for any other metabolite concentration. There was a significantly higher concentration of NAA in the occipital part of the brain in the younger age group compared to the older one. No significant regional or age dependent variation was found concerning the T1 and T2 relaxation times.

Adult↗
PubMed1993

In vivo measurements of proton relaxation times in human brain, liver, and skeletal muscle: a multicenter MRI study.

Quantitative magnetic resonance imaging may offer unique potential for tissue characterization in vivo. In this connection texture analysis of quantitative MR images may be of special importance. Because evaluation of texture analysis needs large data material, multicenter approaches become mandatory. Within the frame of BME Concerted Action on Tissue Characterization by MRI and MRS, a pilot multicenter study was launched in order to evaluate the technical problems including comparability of relaxation time measurements carried out in the individual sites. Human brain, skeletal muscle, and liver were used as models. A total of 218 healthy volunteers were studied. Fifteen MRI scanners with field strength ranging from 0.08 T to 1.5 T were induced. Measurement accuracy was tested on the Eurospin relaxation time test object (TO5) and the obtained calibration curve was used for correction of the in vivo data. The results established that, by following a standardized procedure, comparable quantitative measurements can be obtained in vivo from a number of MR sites. The overall variation coefficient in vivo was in the same order of magnitude as ex vivo relaxometry. Thus, it is possible to carry out international multicenter studies on quantitative imaging, provided that quality control with respect to measurement accuracy and calibration of the MR equipments are performed.

Adult↗
PubMed1993

In vivo field dependence of proton relaxation times in human brain, liver and skeletal muscle: a multicenter study.

T1 and T2 relaxation times are fundamental parameters for signal contrast behaviour in MRI. A number of ex vivo relaxometry studies have dealt with the magnetic field dispersion of T1. By means of multicenter study within the frame of the COMAC BME Concerted Action on Tissue Characterization by MRI and MRS, the in vivo field dispersion of T1 and T2 has been measured in order to evaluate whether ex vivo data are representative for the in vivo situation. Brain, skeletal muscle, and liver of healthy human volunteers were studied. Fifteen MR units with a field strength ranging from 0.08 T to 1.5 T took part in the trial, which comprised 218 volunteers. All the MR systems were tested for measurement accuracy using the Eurospin TO5 test object. The measured relaxation data were subsequently corrected according to the obtained calibration curves. The results showed a clear field dispersion of T1, whereas no significant variations were seen for T2. Our in vivo data were generally in reasonable agreement with proposed models based on ex vivo measurements.

Adult↗
PubMed1993

A software program for exchanging MR data.

In an MR multicenter project, data exchange is a problem because most MR scanners do not use the same data format or have data export facilities. In the COMAC-BME Concerted Action on Tissue Characterization by MRS and MRI, a subgroup of seven MR centers had a need for data exchange in the form of digital MR images of the human brain. Because there was no common data format, software package was developed for data exchange. This article describes the basic features of the developed software. The software package was written in the language of C and was successfully tested on an IBM-6150 UNIX workstation. The software is currently being tested on the following series of UNIX workstations: SUN SPARC, IBM RS6000, and HP 9000/700.

Animals↗
PubMed1993

In vivo quantification of brain metabolites by 1H-MRS using water as an internal standard.

The reliability of absolute quantification of average metabolite concentrations in the human brain in vivo by 1H-MRS using the fully relaxed water signal as an internal standard was tested in a number of in vitro as well as in vivo measurements. The experiments were carried out on a SIEMENS HELICON SP 63/84 wholebody MR-scanner operating at 1.5 T using a STEAM sequence. In vitro studies indicate a very high correlation between metabolite signals (area under peaks) and concentration, R = 0.99 as well as between metabolite signals and the volume of the selected voxel, R = 1.00. The error in quantification of N-acetyl aspartate (NAA) concentration was about 1-2 mM (6-12%). Also in vivo a good linearity between water signal and selected voxel size was seen. The same was true for the studied metabolites, N-acetyl aspartate (NAA), creatine/phosphocreatine (Cr/PCr), and choline (Cho). Calculated average concentrations of NAA, Cr/PCr, and Cho in the occipital lobe of the brain in five healthy volunteers were (mean +/- 1 SD) 11.6 +/- 1.3 mM, 7.6 +/- 1.4 mM, and 1.7 +/- 0.5 mM. The results indicate that the method presented offers reasonable estimation of metabolite concentrations in the brain in vivo and therefore is useful in clinical research.

Body Water↗
PubMed1993

Comparison between retrospective gating and ECG triggering in magnetic resonance velocity mapping.

ECG-triggered cinematographic studies of the cardiovascular system are hampered by several technical restrictions such as the inability to image end-diastole, ghosting, varying signal intensity, and phase contributions from eddy currents. Retrospective gating may solve these problems, but involves signal manipulation such as interpolating raw data from a time window. In this study, the performance of the two gating strategies was compared in quantitative MR velocity mapping on the abdominal aorta in eight healthy volunteers and on a pulsatile flow phantom. The results were compared to a one-dimensional velocity mapping technique and Doppler ultrasound. Finally, the consequence of decreasing the time window in the raw data interpolation used for retrospective gating was also examined. With retrospective gating, a low-pass filtering was seen, causing significantly prolonged duration and decreased amplitude of flow pulses. However, by reducing the time window retrospectively gated flow measurements were in good agreement with those that are ECG triggered. When fulfilling the demand of a narrow time window for interpolation, retrospective gating offers several advantages in MR velocity mapping.

Algorithms↗