Biomedical subjects

C Thomsen

Publications and source records attributed to C Thomsen.

At least 19 recordsLinked to original sources

PubMed1992

L-2-amino-4-phosphonobutyrate (L-AP4) is an agonist at the type IV metabotropic glutamate receptor which is negatively coupled to adenylate cyclase.

Glutamate and L-AP4 inhibited forskolin-stimulated cyclic AMP (cAMP) production in baby hamster kidney (BHK) cells transfected with the type IV metabotropic receptor (mGluR4). In situ hybridization revealed a high level of mRNA for the mGluR4 in the entorhinal cortex, but not in the dentate gyrus. These data demonstrate that mGluR4 receptors are negatively coupled to the cAMP cascade, and suggest that the mGluR4 receptor may be the previously described presynaptic L-AP4 receptor.

Adenylyl Cyclases↗

PubMed1992

Pulsatile brain movement and associated hydrodynamics studied by magnetic resonance phase imaging. The Monro-Kellie doctrine revisited.

Brain tissue movements were studied in axial, sagittal and coronal planes in 15 healthy volunteers, using a gated spin echo MRI sequence. All movements had characteristics different from those of perfusion and diffusion. The highest velocities occurred during systole in the basal ganglia (maximum 1.0 mm/s) and brain stem (maximum 1.5 mm/s). The movements were directed caudally, medially and posteriorly in the basal ganglia, and caudally-anteriorly in the pons. Caudad and anterior motion increased towards the foramen magnum and towards the midline. The resultant movement occurred in a funnel-shaped fashion as if the brain were pulled by the spinal cord. This may be explained by venting of brain and cerebrospinal fluid (CSF) through the tentorial notch and foramen magnum. The intracranial volume is assumed to be always constant by the Monro-Kellie doctrine. The intracranial dynamics can be viewed as an interplay between the spatial requirements of four main components: arterial blood, capillary blood (brain volume), venous blood and CSF. These components could be characterized, and the expansion of the arteries and the brain differentiated, by applying the Monro-Kellie doctrine to every moment of the cardiac cycle. The arterial expansion causes a re-moulding of the brain that enables its piston-like action. The arterial expansion creates the prerequisites for the expansion of the brain by venting CSF to the spinal canal. The expansion of the brain is, in turn, responsible for compression of the ventricular system and hence for the intraventricular flow of CSF.

Adult↗

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 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

The impact of abdominal computerized tomography on the pretreatment staging and prognosis of small cell lung cancer.

One hundred six patients with small cell lung cancer (SCLC) were prospectively evaluated with regard to the prognostic impact of abdominal CT-scan in the pretreatment staging when compared to ultrasonography of the abdomen. Staging based on abdominal ultrasonography (US) plus bilateral bone marrow examinations gave as a result that 47 patients had extensive disease (ED) (44%). Seventeen patients with proven ED at time of referral were not included in this study. Abdominal CT-scan was performed in 76 of the 106 patients. Thirty patients of these 76 patients (39%) were classified as having ED after staging including US, but abdominal metastases were disclosed in another ten patients at the subsequent CT-scan. Liver metastases seen in two patients at ultrasonography were overlooked on the CT-scans. Median survival of the 36 patients classified as having limited disease (LD) after both procedures was 458 days, which was significantly better compared to 330 days for the ten patients with stage migration from LD to ED based on CT-scan, (p less than 0.05) and compared to 242 days in the 30 patients with ED demonstrated by both US and CT-scans (p less than 0.05). The prognostic impact of the CT-scan was further investigated in a multivariate analysis (Cox). Stage disease, performance status, LDH and alkaline phosphatase were significant prognostic factors in a proportional hazards model based on the original 106 patients. Patients in the best prognostic group were characterized by LD, good performance status (0-1) and normal LDH and alkaline phosphatase serum values. This group consisted of 22 patients (21%).(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal Neoplasms↗

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

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

31P magnetic resonance spectroscopy of skeletal muscle in patients with fibromyalgia.

31Phosphorous nuclear magnetic resonance (31P NMR) spectroscopy of painful calf muscle was performed in 12 patients with fibromyalgia (FS) and 7 healthy subjects during rest, aerobic and anaerobic exercising conditions, and postexercise recovery. Ratios of inorganic phosphate and creatinine phosphate (Pi/PCr) and pH were calculated from the collected 31P NMR spectra. Resting values of Pi/PCr were normal in the patients. Patients delivered only 49% of the muscle power of 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 reached only for the anaerobic static exercise (p = 0.003). It was concluded that patients with FS have a reduced voluntary capacity for work, but normal biochemical response to work and recovery.

Adult↗

PubMed1992

MR imaging, flow and motion.

The present work is intended as a nonmathematical review of the role of flow and motion in nuclear magnetic resonance (MR) imaging. A historical review of MR flow measurement techniques is given, followed by a short overview of flow models in vitro and in vivo. The theory behind the influence of motion on the modulus and phase MR signal information is discussed and effects such as washin/washout, flow-induced signal void, phase offset, and phase dispersion are defined. A simple approach to the concept of MR angiography is given, and methods for quantitative flow measurements such as the phase mapping technique, are surveyed. Aspects of the measurement of diffusion and microcirculation are given, and finally, an overview of the role of MR flow imaging in present and future clinical application is given.

Blood Circulation↗

PubMed1992

The nuts and bolts of organizing and initiating a pediatric transport team. The Sutter Memorial experience.

Specialized interfacility transport teams are capable of delivering critical care medicine to the patient at the referring hospital and while en route to the tertiary care center. To do so effectively, however, requires adequate financial and human resources; management of equipment, supplies and personnel; ongoing education for transport team members; and an aggressive quality assurance program. Team members and team management should always be prepared for worst-case scenarios, and develop a method for problem resolution as troublesome issues arise. The ultimate goal of serving the needs of the critically ill child can be consistently met only if there is a high level of commitment of all involved--from the hospital administrator and medical director to the transport coordinator and team members.

California↗

PubMed1992

"Chess-board pattern" spatial modulation of magnetization. Assessment of myocardial function.

Heart motion is a complex combination of translation, rotation, and concentric contraction. Evaluation of these complex motions has been difficult using conventional slice-selective methods. Noninvasive tagging of the heart has been obtained by the use of slice-selective radiofrequency pulses. Through spatial modulation of the magnetization the entire image can be labeled in different patterns. Two new pulse sequences are presented, giving a chess-board like spatial modulation. These pulse sequences have several advantages compared with the previously published methods, as the modulation time is half that required to obtain a 2-dimensional grid, the area in the image with high signal intensity was significantly larger, and the radiofrequency power deposition was substantially decreased. By labeling the heart at diastole the chess-board pattern tagging of the heart wall could be followed through systole. Using this method the complex motions of the heart can be mapped.

Computer Simulation↗

PubMed1991

Ultrasound examination in jaundiced patients. Is computer-assisted preclassification helpful?

In this study we attempted to determine the diagnostic accuracy and reproducibility of ultrasonography (US) for jaundice and to see how US can best be combined with preliminary clinical-biochemical diagnoses to plan the invasive work-up. US proved reproducible in two diagnostic departments (127 agreements in 135 cases). But, since obstruction was underdiagnosed (15 double-false negatives), the predictive value of a negative result was only 0.83. By adding a term which represents the US conclusion, obstruction or not, to the Copenhagen pocket diagnostic chart score (based on the logistic model) we found that an obstructive conclusion increases the odds of obstruction by a factor of 25, and a non-obstructive conclusion decreases the odds by a factor of only 1.9. We conclude that the preliminary diagnosis is frequently sufficiently certain to be unalterable by US. This leaves only 40% of the jaundice cases in which US is necessary to plan invasive work-up. The US workload can even, it appears, be reduced to about 22% without appreciable penalty in terms of unrewarding invasive procedures. Using these strict indications, four US examinations seem to suffice to avoid one such error. Relying on either US or clinical-biochemical data alone is inferior to the combined strategy.

Algorithms↗

PubMed1991

Tissue characterization of intracranial tumors by MR imaging. In vivo evaluation of T1- and T2-relaxation behavior at 1.5 T.

The main purpose of this in vivo study was to provide a detailed description of the T1- and T2-relaxation processes in intracranial tumors at 1.5 T. A total of 100 patients were investigated. Optimal experimental conditions were carefully observed, including the use of long TR values. T1 determination was based on a partial saturation inversion recovery sequence covering 12 or 6 data points. T2 determination involved a multiple spin echo sequence with 32 echoes. Calculations included biexponential analysis of the 12-point T1 data and all T2 data obtained. The results were evaluated in accordance with histopathology. The T1- and the T2-relaxation times of the prevailing tumor types were significantly different (p less than 0.0005). However, biologic scatter and overlap between tumor types were considerable. In particular, no discrimination between benign and malignant tumor growth was possible. Biexponential evaluation did not increase the specificity, although a biexponential relaxation behavior was recognized in 37% of the T2 curves. The results indicate that tissue heterogeneity is responsible for most of the scatter in the relaxation times. It is concluded that tissue characterization by MR imaging, based solely on relaxation time measurements, seems to be of no value in the differentiation of intracranial tumors.

Adolescent↗

PubMed1991

Central nervous system involvement in human immunodeficiency virus disease. A prospective study including neurological examination, computerized tomography, and magnetic resonance imaging.

Sixty-seven patients with different stages of human immunodeficiency virus (HIV) infection (47 CDC group IV, 20 CDC groups II or III) were followed prospectively for a median of 18 months with neurological examination, magnetic resonance imaging (MRI), and computerized tomography (CT) to evaluate the incidence of the AIDS dementia complex (CDC definition) and other neurological complications. Ten patients developed CNS opportunistic infection or malignancy. Among the remaining 57 patients, 12 of 37 (32%) belonging to CDC group IV, and 1 of 20 (5%) belonging to CDC groups II/III developed the AIDS dementia complex (p = 0.03). MRI white matter lesions occurred in 32% of CDC group IV patients and 5% of CDC groups II/III patients (p = 0.03). The corresponding figures for brain atrophy at CT were 71% and 30% (p less than 0.01) and for neurologic signs 49% and 20% (p = 0.06). The development of the AIDS dementia complex was significantly associated with the occurrence of MRI white matter lesions and a CD4 cell count of less than 200 x 10(6)/l, whereas it was not statistical significantly associated with brain atrophy at baseline. It is concluded that the AIDS dementia complex is a common feature of late stage HIV infection. Brain atrophy occurs in a large percentage of HIV infected patients, but the clinical significance of this atrophy is not clear.

AIDS-Related Complex↗

PubMed1990

A simple calf muscle ergometer for use in a standard whole-body MR scanner.

A calf muscle ergometer, designed for use in a standard whole-body MR scanner, is described. The instrument allows isotonic or isometric calf muscle exercise over a continuous range of work loads from 0 to individual maximum work output. Work output may be recorded on a strip chart recorder. A sound encoding provides an effective guidance for the subject tested to accurately reproduce his performance in each contraction cycle at a given work load. The FID recording may be triggered from the ergometer at any point during the contraction cycle. Nonmetal materials are used for the instrument construction in order to eliminate potentially disturbing eddy currents. The force resistance of the ergometer is obtained by a combined hydraulic-pneumatic system, which is loaded by coupling to an outside source of compressed air equipped with a suitable pressure regulator. When varying the time of data sampling within a repeated 6-s contraction cycle it was found that the recorded Pi/PCr ratio remained essentially constant at low and moderate work loads. However, at work loads at or above 70% of individual Vmax a pronounced dependence of the time of sampling with the contraction cycle was observed.

Equipment Design↗

PubMed1990

Brain water accumulation in pseudotumour cerebri demonstrated by MR-imaging of brain water self-diffusion.

We studied brain water self diffusion in pseudotumour cerebri by MR-imaging using single spin echo pulse sequences with pulsed magnetic field gradients of different magnitude. The methods is based on the fact that the movement of water molecules is restricted in brain tissue and that accumulation of water in the brain tissue will enhance the self diffusion of water. In order to evaluate the brain water content in pseudotumour cerebri we compared the water self diffusion coefficient in various regions of the brain in pseudotumour patients with that of healthy controls. Ten patients with pseudotumour cerebri were studied. All had increased ICP and increased resistance to CSF outflow. All patients had normal conventional MR spin echo images without focal lesions and a normal sized ventricular system. All patients had abnormal diffusion images showing increased water diffusion. Some patients had in particular increased diffusion in the periventricular regions, others in the whole brain. The diffusion coefficients in all brain regions of interest were significantly higher in patients than in controls. The findings suggest that patients with pseudotumour cerebri have a convective transependymal flow of water causing an interstitial brain oedema and in addition an intracellular brain water accumulation.

Adult↗