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M Thelen

Publications and source records attributed to M Thelen.

At least 91 records · Page 5Linked to original sources
PubMed2001

[Dynamic imaging of the nasal cavity and the paranasal sinuses with polarized 3helium MRI].

PURPOSE: Reduced or blocked ventilation of the paranasal sinuses is probably the most important factor in the development of sinusitis. Recently, the use of optically polarized noble gas isotopes has attracted increasing interest for use in a variety of promising MR applications. The aim of this study was to test the feasibility of imaging and visualization ventilation of the nasal cavity and paranasal sinus in MR by inhalation of hyperpolarized (3)helium. The goal was to evaluate ventilation defects of the paranasal sinuses. VOLUNTEERS AND METHODS: Three volunteers were enrolled in the study. (3)Helium was polarized to 40 - 50 % by direct optical pumping. 300 ml of 100 % (3)helium were administered in the left nasal vestibule through a glass tube. With a closed contralateral nasal vestibule, the Valsalva maneuver was performed twice. Using a dedicated application unit, which is also used in MR imaging of the lung, an exact amount of (3)helium gas was administered at the beginning of inspiration. Measurements were carried out on a clinical 1.5 T scanner. Coronal images of the nasal cavity and paranasal sinuses were acquired using ultrafast gradient-echo pulse sequence (TR = 2 ms, TE = 0.7 ms, FA < 2 degrees, 75 x 128, FOV = 500) with an image aquisition time of 130 ms. RESULTS: The oral cavity and nasal cavities display a very high signal intensity after inhalation of polarized (3)helium gas. The signal intensity in the left maxillary sinus was higher compared to the right one. The mean signal intensity on the left side was 526 +/- 86 and on the right side 336 +/- 102. The left and right frontal sinus and ethmoid sinus only show signal of hyperpolarized (3)helium after two Valsalva maneuvers. Because of the low signal intensity of the frontal and ethmoid cells their visualization was incomplete. The signal to noise ratio was 14.1 for the left maxillary sinus, 8.9 for the right side, 6.3 for the left ethmoid sinus, 5.8 for the right side and 6.6 for the left frontal sinus and 7.8 for the right side. CONCLUSION: (3)Helium MR allows imaging of the nasal cavity and the paranasal sinuses. Perhaps this method could be a new tool to visualize the ventilation of the maxillary sinus without ionizing radiation. Interpretations about the ventilation of the frontal and ethmoid cells remain speculative.

Administration, Inhalation↗
PubMed2001

Temporal dynamics of lung aeration determined by dynamic CT in a porcine model of ARDS.

We used dynamic CT to identify two different time constants of lung aeration and their individual contribution to the total increase in cross-sectional lung area in healthy and experimentally damaged lungs. In five healthy pigs, inflation and deflation between 0 and 50 cm H2O was imposed during dynamic (250 ms/image) CT acquisition, and repeated after experimental lung injury by saline lavage. The fractional areas of density ranges, which represent aerated lung parenchyma, were determined planimetrically, and their time for expansion during the manoeuvre was fitted using a bi-exponential model. Thus, two compartments, their sizes, i.e. their relative contributions to lung area aerated by the manoeuvre, and their specific time constants (tau) were sought. Healthy lungs were characterized best by a one-compartmental behaviour with one tau only, both during inflation (median tau=0.5 s; range 0.4-0.6 s) and deflation (1.2 s; 1.1-1.3 s). In damaged lungs two compartments were found both during inspiration and expiration, with 86% (78-87%) of the recruitable lung area following a short tau of 0.5 s (0.5-0.6), and 14% (13-22%) following a longer tau of 9.1 s (8-16.8 s) during inflation. During expiration, damaged lungs had a short tau of 0.8 s (0.5-1.0 s) for 94% (84-100%) of deflated lung area, and a longer tau of 26.5 s (7.1-34.3 s) for 6% (0-16%). We conclude that dynamic CT indicates the relative size and temporal behaviour of functional compartments in normal and abnormal lungs. Our findings suggest that after lung damage, cyclic ventilation with inspiratory periods of <10 s duration will not achieve maximum recruitment for a chosen inspiratory pressure. In ARDS, the short expiratory tau predisposes to atelectasis formation if expiratory times are >1 s.

Animals↗
PubMed2001

Volumetry of ventilated airspaces by 3He MRI: preliminary results.

RATIONALE AND OBJECTIVES: To develop a validated post-processing routine for volumetry of the ventilated airspaces by 3He MRI. METHODS: 3Helium MRI and pulmonary function tests were performed in seven healthy volunteers. After segmentation of ventilated airspaces, their volumes were calculated. Functional residual capacity (FRC) was used as a reference. For comparison of absolute volumes, correction factors were evaluated. RESULTS: Mean lung volume (+/- standard deviation) calculated from 3He MRI was 4,082 +/- 908 mL and mean FRC was 3,696 +/- 1166 mL, with a mean difference of 386 mL (r = 0.88). After correction for the relative pulmonary air content (factor 0.82), posture (0.72), and the individual tidal volume, 3He MRI volume was 3,348 +/- 744 mL and mean FRC was 3,422 +/- 817 mL, with the mean difference down to -74 mL (r = 0.9). Comparison on an individual basis confirmed an improvement in the estimation of absolute lung volume. CONCLUSIONS: Volumetry of ventilated lung from 3He MRI shows high correlation and good agreement with the results of pulmonary function tests.

Adult↗
PubMed2001

In vitro investigation of prosthetic heart valves in magnetic resonance imaging: evaluation of potential hazards.

BACKGROUND AND AIM OF THE STUDY: Magnetic resonance (MR) imaging is used in an increasing number of patients, and not only after cardiac valve replacement. However, ferromagnetic biomedical implants are often considered a contraindication for MR imaging because of the potential hazards with respect to their movement, dislodgement, or heating effects during the procedure. The purpose of this study was to assess ferromagnetism, attraction forces, heating effects, and artifacts associated with prosthetic heart valve implants. METHODS: Seventeen common heart valve prostheses (12 mechanical, five biological) were examined in vitro using a high-field-strength 1.5 Tesla (T) MR system. Attractive forces, temperature changes and the amount of artifacts were assessed by applying turbo-spin and gradient-echo sequences. RESULTS: The maximal calculated corresponding ferromagnetic force was (0.22 x 10(-3) N) in the static magnetic field. The temperature changes ranged from 0 to 0.5 degrees C maximum. Artifacts produced by the presence of the heart valve prostheses were less evident using a spin-echo sequence than a gradient-echo sequence. CONCLUSION: MR imaging exerted no significant force on the examined heart valve prostheses, and did not result in significant biological relevant temperature increase. None of the associated artifacts is considered to pose a substantial risk on MR imaging. MR procedures performed with a 1.5 T MR system can be applied safely in patients with heart valve prostheses evaluated in this study.

Artifacts↗
PubMed2000

Evidence for a pool of coronin in mammalian cells that is sensitive to PI 3-kinase.

Coronin, a 57 kDa actin binding protein elutes with an apparent molecular mass of 400-600 kDa from gel filtration columns. This fraction is not unrelated to the reported 200 kDa complex where coronin is associated with phox proteins of the NADPH-oxidase. Phosphatidylinositol 3-kinase (PI 3-kinase) solubilizes coronin from the 400-600 kDa complex, thus constitutive active PI 3-kinase is sufficient to disrupt the complex, whereas wortmannin stabilizes it. Conversely, the phox protein associated pool of coronin is PI 3-kinase independent. During phagocytosis coronin is recruited together with PI 3-kinase to membranes of nascent and early phagosomes co-localizing with the actin cytoskeleton, confirming that coronin contributes to phagocytosis.

Actins↗
PubMed2000

Signal transduction by CXC chemokine receptor 4. Stromal cell-derived factor 1 stimulates prolonged protein kinase B and extracellular signal-regulated kinase 2 activation in T lymphocytes.

We report that stromal cell-derived factor (SDF)-1 has the remarkable capacity to induce sustained signaling through CXC chemokine receptor 4 (CXCR4). In contrast to other chemokines, such as monocyte chemotactic protein 1 (CC chemokine receptor 2 [CCR2]), macrophage inflammatory protein 1beta (CCR5), liver and activation-regulated chemokine (LARC [CCR6]), Epstein-Barr virus-induced molecule 1 ligand chemokine (ELC [CCR7]), and IP10 (CXCR3), SDF-1 stimulates the prolonged activation of protein kinase B and extracellular signal-regulated kinase (ERK)-2. Activation of protein kinase B is reversed by displacement of SDF-1 from CXCR4 or inhibition of phosphatidylinositol 3-kinase. Although increasing concentrations of SDF-1 enhance CXCR4 internalization, kinase activation is prolonged. In addition, restimulation yields >60% of initial protein kinase B activity, indicating that the remaining receptors are not desensitized. Furthermore, activation is prolonged by inhibiting SDF-1 degradation. The sustained activation of cell survival and mitogenic pathways may account for the unique role of SDF-1 and CXCR4 in embryogenesis and lymphopoiesis.

Androstadienes↗
PubMed2000

GAP43, MARCKS, and CAP23 modulate PI(4,5)P(2) at plasmalemmal rafts, and regulate cell cortex actin dynamics through a common mechanism.

The dynamic properties of the cell cortex and its actin cytoskeleton determine important aspects of cell behavior and are a major target of cell regulation. GAP43, myristoylated alanine-rich C kinase substrate (MARCKS), and CAP23 (GMC) are locally abundant, plasmalemma-associated PKC substrates that affect actin cytoskeleton. Their expression correlates with morphogenic processes and cell motility, but their role in cortex regulation has been difficult to define mechanistically. We now show that the three proteins accumulate at rafts, where they codistribute with PI(4,5)P(2), and promote its retention and clustering. Binding and modulation of PI(4, 5)P(2) depended on the basic effector domain (ED) of these proteins, and constructs lacking the ED functioned as dominant inhibitors of plasmalemmal PI(4,5)P(2) modulation. In the neuron-like cell line, PC12, NGF- and substrate-induced peripheral actin structures, and neurite outgrowth were greatly augmented by any of the three proteins, and suppressed by DeltaED mutants. Agents that globally mask PI(4,5)P(2) mimicked the effects of GMC on peripheral actin recruitment and cell spreading, but interfered with polarization and process formation. Dominant negative GAP43(DeltaED) also interfered with peripheral nerve regeneration, stimulus-induced nerve sprouting and control of anatomical plasticity at the neuromuscular junction of transgenic mice. These results suggest that GMC are functionally and mechanistically related PI(4,5)P(2) modulating proteins, upstream of actin and cell cortex dynamics regulation.

Actins↗
PubMed2000

(3)He MRI in healthy volunteers: preliminary correlation with smoking history and lung volumes.

MRI with hyperpolarized helium-3 ((3)He) provides high-resolution imaging of ventilated airspaces. The first aim of this (3)He-study was to compare observations of localized signal defects in healthy smokers and non-smokers. A second aim was to describe relationships between parameters of lung function, volume of inspired (3)He and signal-to-noise ratio. With Ethics Committee approval and informed consent, 12 healthy volunteers (seven smokers and five non-smokers) were studied. Imaging was performed in a 1.5 T scanner using a two-dimensional FLASH sequence at 30V transmitter amplitude (TR/TE/alpha = 11 ms/4.2 ms/<10 degrees ). Known amounts of (3)He were inhaled from a microprocessor-controlled delivery device and imaged during single breath-holds. Images were evaluated visually, and scored using a prospectively defined 'defect-index'. Signal-to-noise ratio of the images were correlated with localization, (3)He volumes and static lung volumes. Due to poor image quality studies of two smokers were not eligible for the evaluation. Smokers differed from non-smokers in total number and size of defects: the 'defect-index' of smokers ranged between 0.8 and 6.0 (median = 1.1), that of non-smokers between 0.1 and 0.8 (median = 0.4). Intraindividually, an anteroposterior gradient of signal-to-noise ratio was apparent. Signal-to-noise ratio correlated with the estimated amount of hyperpolarization administered (r = 0. 77), but not with static lung volumes. We conclude that (3)He MRI is a sensitive measure to detect regional abnormalities in the distribution of ventilation in clinically healthy persons with normal pulmonary function tests.

Adult↗
PubMed2000

Flip angle considerations in (3)helium-MRI.

3Helium-MRI ((3)He-MRI) can be used for analysis of lung function, e. g. dynamic imaging of ventilation and gas diffusion within the lung, assessment of intrapulmonary oxygen concentrations and their time course. During imaging, the irreversible signal loss due to depolarizing radio frequency excitations can be described using the flip angle (FA) alpha. This parameter has to be quantified in order to account for it during quantitative assessment of the (3)helium signal intensity and its temporal development. This technical report reviews two different methods to determine alpha. Limitations and possible error sources of each method are discussed.

Computer Simulation↗
PubMed2000

[Flow quantification in coronary and bypass vessels with MR phase contrast technique].

PURPOSE: To evaluate accuracy of velocity encoded cine MR imaging for determination of blood flow in coronary arteries and coronary bypass grafts. MATERIALS AND METHODS: 12 patients with 22 coronary bypass grafts underwent intraoperative flow quantification using the transit time ultrasound method. These values were compared to postoperative MR phase shift measurements. Flow measurements were performed preoperatively in 28 coronary arteries of 20 patients. For flow measurement, we used a velocity-encoded k-space segmented gradient echo sequence with a temporal resolution of 110 or 125 ms, respectively. 6-8 pase shift images could be acquired during one cardiac cycle. RESULTS: There was a significant correlation between intraoperative and flow measurements using velocity-encoded MR imaging (r = 0.74, p < 0.0001, t-test). Flow volumes determined by MR imaging were systematically larger than those determined by the transit time ultrasound method. Mean flow in coronary arteries was reduced in severely stenosed vessels (> 70%) compared to normal vessels. Intra- and interobserver variability were 10.5 and 15% (coronary bypass grafts), and 12.3 and 15.8% (coronary arteries), respectively. CONCLUSIONS: Velocity-encoded MR imaging enables determination of flow in coronary artery bypass grafts and coronary arteries. Future developments should aim at the improvement of spatial and temporal resolution of the method.

Adult↗
PubMed2000

[Pulmonary tuberculosis--the current radiological diagnosis of an old disease].

INCIDENCE: Decreasing numbers of tuberculosis cases in the western countries have led to diminished attention towards this disease. But worldwide, tuberculosis still is the leading cause of mortality due to any one single infectious agent. In the industrialized countries, immigration, growth of low-income groups and increasing numbers of immunocompromised patients, mainly due to the HIV epidemic, supply a reservoir for tuberculosis. DIAGNOSIS: Because of the option of a specific therapy, early diagnosis of tuberculosis is crucial for the course of the disease. In cases of multidrug resistant strains, further spread has to be prevented. Radiology with chest films and computed tomography has a central role in diagnosing tuberculosis. FINDINGS: However, as the disease produces a broad spectrum of radiographic findings, there are often difficulties in determining the underlying diagnosis. Additionally, there have been reports of atypical presentations of tuberculosis in immunocompromised as well as immunocompetent patients. This article reviews the current state of radiological diagnosis of pulmonary tuberculosis.

AIDS-Related Opportunistic Infections↗
PubMed2000

[Radiodiagnosis of the lung].

Radiological cross-sectional imaging modalities, particularly computed tomography (CT) have become the mainstays for diagnosing lung disease in recent years. These enable morphological visualization of pathological processes with the greatest possible spatial resolution. Modern technical developments and complementary strategies have led to new applications and new functional assessments which need to be reviewed together with state-of-the-art techniques in nuclear imaging. The diagnosis of pulmonary embolism using spiral CT angiography and magnetic resonance (MR) angiography certainly belongs in this category. CT has become the an alternative modality of first choice, and it is also challenging pulmonary angiography as the gold standard. Direct visualization of patent pulmonary arteries and thromboembolic material is complemented by that of effects on the pulmonary parenchyma and right heart function; it also provides perfusion studies and MR-based flow measurement to assess hemodynamic compromise. Ventilation studies have long been a domain of nuclear imaging, and new techniques for the direct visualization of ventilation are emerging from recent developments in the field of MR imaging, for example, using hyperpolarized inert gases. New functional parameters of ventilation can be derived from these studies. For the diagnosis of metabolically active disease, such as tumor and pneumonia, CT offers very high sensitivity, for example, in screening for intrapulmonary nodules using low-dose CT and in the early detection of pulmonary infiltrates in high-risk patients. Especially for characterizing pulmonary nodules there is a need to combine nuclear medicine techniques, such as in positron-emission tomography.

Angiography↗
PubMed2000

Focal airtrapping at expiratory high-resolution CT: comparison with pulmonary function tests.

This study was undertaken to determine prevalence, extent, and severity of focal airtrapping at expiratory high-resolution CT, and to compare focal airtrapping with age, gender, pulmonary function tests, and blood gas analysis. Two-hundred seventeen patients with and without pulmonary disease underwent paired inspiratory/expiratory high-resolution CT. Six scan pairs with corresponding scan levels were visually assessed for focal--not diffuse--airtrapping using a four-point scale. Pulmonary function tests and blood gas analysis were available for correlation in all patients (mean interval 5 days). Focal airtrapping with lower lung predominance was observed in 80% of patients. Twenty-six of 26 patients with restrictive lung function impairment exhibited focal airtrapping (mean score 2.4), whereas only 72 of 98 (74%) patients with obstruction did (mean score 1.5; p < 0.05). Fifty-eight of 70 (83%) patients with normal lung function (mean score 1.8) and 19 of 23 (83%) patients with mixed impairment (mean score 1.8) had focal airtrapping. Focal airtrapping showed negative correlations with static lung volumes (-0.27 to -0.37; p < 0.001) in all patients and moderate positive correlations with dynamic parameters (0.3-0.4; p < 0.001) in patients with obstruction. No significant correlations were found with age, gender, and blood gas analysis. Visual assessment of focal--not diffuse--airtrapping at expiratory high-resolution CT does not correlate with physiological evidence of obstruction as derived from pulmonary function tests since the perception of focal airtrapping requires an adequate expiratory increase in lung density.

Adolescent↗
PubMed2000

MR arthrography of the shoulder: comparison of low-field (0.2 T) vs high-field (1.5 T) imaging.

The objective of this study was to compare the image quality, sensitivity, specificity, and diagnostic accuracy of an open low-field MR system (0.2 T) with a standard high-field MR system (1.5 T) after arthrography of the shoulder. Thirty-eight patients either with suspected chronic instability (n = 12) or rotator cuff abnormalities (n = 26) were examined. Intra-articular injection of diluted Gd-DTPA was followed in randomized order either first by imaging on an open 0.2-T system or on a 1.5-T system. The image material was evaluated independently by two radiologists in a blinded fashion with respect to overall image quality and the detection of rotator cuff as well as capsular and labral abnormalities. Surgical correlation was available in 27 (71%) of 38 patients. For both systems, sensitivity and specificity for rotator cuff tears were 100% each, and for labrum pathologies, these values were 100 and 93%, respectively. The agreement for detection of labral pathologies between low-field and high-field examinations was good (kappa = 0.69, kappa = 0.61). For the detection of full-thickness tears of the rotator cuff, the agreement between the low-field and high-field MR examinations was very good and significant (kappa = 0.94, kappa = 1, p < 0.001). Overall image quality was rated good in 17 (45%) and fair in 21 (55%) of 38 cases on the 0.2-T MR system, and good in 32 (84%) and fair in 6 (16%) of 38 cases on the 1.5-T system. Motion artifacts were considered low in 24 (63%) and moderate in 14 (37%) of 38 cases for the 0.2-T system and low in 34 (89%) and moderate in 4 (11%) for 1.5-T system. Based on our results, low-field MR compares favorably to high-field MR in the detection of major abnormalities of the glenohumeral joint, at least when MR arthrography is used. Disadvantages are the duration of the examination and thus the risk of reduced image quality caused by motion artifacts.

Adult↗
PubMed2000

[Noninvasive evaluation of coronary bypass grafts by magnetic resonance imaging. Comparison of the Haste and Fisp-3-D sequences with the conventional coronary angiography].

The aim of the study was to evaluate the patency of coronary artery bypass grafts (CABG) with the 2D and 3D magnetic resonance (MR) imaging techniques. 29 patients with 74 bypass grafts and a total of 91 distal anastomoses were studied on a 1.5 Tesla scanner using a phased array body coil. A 2D T-2 weighted breathhold turbo spin echo sequence (Haste) and a 3D breath hold contrast enhanced MR angiography sequence (Fisp-3-D) were performed. With the Haste and Fisp-3-D sequences 55 of the 58 patent and 15 of the 16 occluded grafts were recognized; the sensitivity and specificity were 95% and 94%, respectively. With the Haste sequence 74% (47/63) and with the Fisp-3-D sequence 64% (40/63) of the distal anastomoses were seen in good image quality. Only 3 of 8 significant grafts stenoses were detected. The patency of CABGs can be evaluated non-invasively with the Haste and the Fisp-3-D angiography sequences. Better results can be expected with the development of a blood-pool contrast medium and the combination of MR flow measurements with imaging techniques.

Aged↗
PubMed2000

[Segmental anatomy of the liver in computed tomography: do we localize the lesion accurately?].

PURPOSE: To evaluate if Couinaud's model using the planes of the major veins is an adequate tool for the presurgical localization of focal liver lesions. METHODS: Biphasic helical CT scans were performed on patients evaluated for liver resection using an increased IV bolus of contrast medium (180 ml lopamidol) and 2 mm image reconstruction increments. During the first evaluation, all liver lesions were localized in the conventional way using the planes of the 3 major hepatic veins and the portal trunks as segmental boundaries. In a second review, all lesions were attributed to the nearest peripheral portal branches. The path and the segmental attribution of the portal branches were analysed. Evaluations were performed using an interactive cine mode as well as three-dimensional reconstructions. RESULTS: 20 of 126 (16%) liver lesions had a different segmental location if the individual anatomy of the peripheral portal branch was used instead of the conventional technique. These different locations were due to the path of the portal trunks or the path of the peripheral portal branches crossing the planes of the major hepatic veins. CONCLUSION: The segmental anatomy of the liver using the planes of hepatic veins and portal trunks according to Couinaud is not an accurate tool for the presurgical localization of liver lesions in many cases.

Carcinoma, Hepatocellular↗