Biomedical subjects
Publications and source records attributed to B Eberle.
By studying the conical emission of a blue femtosecond laser filament in air, it is shown that self-improvement of the beams' spatial mode quality occurs for a self-guided laser pulse.
PURPOSE: Visual assessment of the ventilation using HRCT and (3)He-MRI in patients after single lung transplantation (SLTX). Analysis of specific ventilation defects found with (3)He-MRI and morphological changes found with HRCT. MATERIALS AND METHODS: We evaluated 8male patients (54 +/- 6 years) suffering from emphysema and six patients (3males and 3 females, 58 +/- 9.5 years) suffering from idiopathic pulmonary fibrosis (IPF) after SLTX. The morphological changes at HRCT were classified and localized. In (3)He-MRI (2D FLASH), 10 to 14 slices (slice thickness 10 mm, gap 5 mm) were acquired in coronal orientation to cover the whole lung. Ventilation defects were localized and characterized. The visually estimated ventilation was recorded on a 5-point scoring system. A double threshold technique was applied to volumetric quantification in (3)He-MRI to serve as internal reference. RESULTS: We found no correlation between morphological changes in HRCT and ventilation defects in (3)He-MRI. The visual assessment of ventilation in (3)He-MRI was sufficient in patients with emphysema, but this was not confirmed in patients with IPF. The visual assessment in HRCT did not correlate with the volumetric evaluation in both conditions. CONCLUSION: The various ventilation defects were not linked to specific morphological changes. For the visually assessed ventilation in patients with emphysema, (3)He-MRI is superior to HRCT.
BACKGROUND: This study observed adverse events of rescue treatment with high-frequency oscillatory ventilation (HFOV) in head-injured patients with acute respiratory distress syndrome (ARDS). METHODS: Data of five male patients with ARDS and traumatic brain injury, median age 28 years, who failed to respond to conventional pressure-controlled ventilation (PCV) were analyzed retrospectively during HFOV. Adjusted mean airway pressure at initiation of HFOV was set to 5 cm H2O above the last measured mean airway pressure during PCV. Frequency of pulmonary air leak, mucus obstruction, tracheal injury, and need of HFOV termination due to increased intracranial pressure, decreased cerebral perfusion pressure, or deterioration in P(a)CO2 were analyzed. RESULTS: During HFOV we found no complications. We recorded 390 datasets of intracranial pressure, cerebral perfusion pressure and P(a)CO2 simultaneously. Intracranial pressure increased (>25 mmHg) in 11 of 390 datasets, cerebral perfusion pressure was reduced (<70 mmHg) in 66 of 390 datasets, and P(a)CO2 variations (<4.7 kPa; >6.0 kPa) were observed in eight of 390 datasets after initiation of HFOV. All these alterations were responsive to treatment. P(a)O2/F(I)O2-ratio improved in four patients during HFOV. CONCLUSION: High-frequency oscillatory ventilation appears to be a promising alternative rescue treatment in head-injured patients with ARDS if continuous monitoring of intracranial pressure, cerebral perfusion pressure and P(a)CO2 are provided, in particular during initiation of HFOV.
A decade after the onset of a discussion whether ventilation could be omitted from bystander basic life support (BLS) algorithms, the state of the evidence is reevaluated. Initial animal studies and a prospective randomized patient trial had suggested that omission of ventilation during the first minutes of lay cardiopulmonary resuscitation (CPR) did not impair patient outcomes. More recent studies demonstrate, however, that this may hold true only in very specific scenarios, and that the chest compression-only technique was never superior to standard BLS. Instead of calling basics of BLS training and practice into question, more and better training of lay persons and professionals appears mandatory, and targeted use of dispatcher-guided telephone CPR should be evaluated and, if it improves outcome, it should be encouraged. Future studies should focus much less on the omission but on the optimization of ventilation under the specific conditions of CPR.
BACKGROUND AND OBJECTIVE: This prospective observational study analyses cardiovascular changes in adult patients with acute respiratory distress syndrome (ARDS) during transition from pressure-controlled ventilation to high-frequency oscillatory ventilation (HFOV), using transoesophageal echocardiography (TOE) and invasive haemodynamic monitoring. METHODS: Nine patients (median age 65 years; range 42-70) with ARDS were studied. HFOV was started and maintained with an adjusted mean airway pressure of 5 cmH2O above the last measured mean airway pressure during pressure-controlled ventilation. Haemodynamic and TOE measurements were performed in end-expiration during baseline pressure-controlled ventilation, and again 5 and 30 min after the start of during uninterrupted HFOV. RESULTS: Right atrial pressure increased immediately (P = 0.004). After 30 min, pulmonary arterial occlusion pressure increased (P = 0.008), cardiac index decreased (P = 0.01), stroke volume index decreased (P = 0.02) and both left ventricular end-diastolic and end-systolic area indices decreased (P = 0.02). Fractional area change, left ventricular end-systolic wall stress, heart rate, mean arterial pressure and mean pulmonary artery pressure remained unchanged. CONCLUSIONS: Transition to HFOV at a mean airway pressure of 5 cmH2O above that during pressure-controlled ventilation induced significant, but clinically minor, haemodynamic effects, which are most probably due to airway pressure-related preload reduction.
PURPOSE: Dynamic CT (dCT) allows visualization and quantification of ventilated lung and atelectases with high temporal resolution during continuous ventilation. This study compares a quantitative image analysis in a subcarinal single slice dCT series versus a whole lung spiral-CT, in order to analyze, whether the distribution of atelectasis of a single dCT series is representative for the whole lung. MATERIALS AND METHODS: dCT in sliding windows technique (slice thickness 1 mm, temporal increment 100 ms) was performed in 8 healthy pigs 3 cm caudal to the carina during continuous mechanical ventilation. Subsequently, a spiral-CT of the whole lung (slice thickness 2 mm; pitch 1.5; increment 2 mm) was acquired during inspiratory breath hold (airway pressure 20 mbar). Lung segmentation and planimetry of predefined density ranges were achieved using a dedicated software tool in both data-sets. Thus, the fractions of the following functional lung compartments were averaged over time: hyperinflated lung (- 1024 to - 910 HE), normal ventilated lung -900 to -300 HE) and atelectasis (-300 to +200 HE). RESULTS: Quantitative analysis of dCT-series during continuous respiration correlated with the density analysis in spiral-CT as follows: hyperinflated lung r = 0.56; normal ventilated lung r = 0.83 and atelectases r = 0.84. Analysis of spiral-CT showed the following distribution of functional lung compartments: hyperinflated lung 3.1% normal ventilated lung 77.9% and atelectasis 19.0%. In dCT, hyperinflated lung represented 6.4%, normal ventilated lung 65.2% and atelectasis 28.4% of total the lung area. CONCLUSION: The results of our study demonstrate that dCT allows monitoring of atelectasis formation in response to different ventilatory strategies. However, a deviation between dCT and spiral-CT has to be taken into account. In subcarinal dCT series, hyperinflated lung areas and atelectases were overestimated due to a craniocaudal gradient of atelectases, whereas normal ventilated lung was underestimated.
PURPOSE: To develop a software tool for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) as well as its time course during apnea. MATERIAL AND METHODS: T (1)-relaxation times of hyperpolarized (3)He are reduced by paramagnetic oxygen rendering (3)He-MRI sensitive to oxygen and thus allowing the assessment of the local oxygen partial pressure in the pulmonary airspaces. Oxygen-related relaxation and loss of polarization by RF-excitation can be discriminated by acquiring two image series with varying interscan delay and/or flip angles. Software was developed to calculate the p(A)O(2) and the decay rate in user-defined regions of interest (ROIs) automatically. Moreover, parameter maps can be calculated. In addition to the analysis of 2-dimensional data sets, the software allows the evaluation of 3-dimensional measurements for the first time. Artifacts due to lung motion were reduced by implementing a motion correction algorithm. RESULTS: The software was successfully applied to data sets from healthy volunteers and from patients with various lung diseases. The parameter maps demonstrated a more homogeneous distribution of p(A)O(2) for the volunteers than for the patients. A regional increase in p(A)O(2) was found in a few patients. CONCLUSION: The described software allows the absolute quantification of p(A)O(2) as well as its variation over time. In the future, therefore, the software may gain importance for detecting mismatches between ventilation and perfusion, e. g., in patients with pulmonary embolism or chronic obstructive lung diseases.
PURPOSE: 3He-MRI of the lung has been shown to be a sensitive method for functional imaging of the lung. A previous study compared 3He-MRI (coronal planes) with CT (transverse planes) by looking for ventilation defects and their pathomorphologic correlation. Anatomic structures, such as lobar fissures and hilar vessels, were used for orientation, but the reliable assignment of ventilation defects to lung segments is problematic. The present work compares multiplanar reformations of 3He-MRI and HR-CT, which were generated from planes determined by the respective method, and investigates their suitability as a solution of this problem. MATERIALS AND METHODS: A total of 16 data sets taken from 15 patients with unilateral lung transplantation and one patient with lung emphysema were retrospectively evaluated. Transverse planes of 3He-MRI and coronal planes of HR-CT were reformatted on an external workstation and images evaluated by two readers in consensus. The evaluation searched for ventilation defects on 3He-MRI and their corresponding defects on HR-CT. The defects were related to anatomic structures, with hilar vessels and tracheobronchial tree selected for 3He-MRI reformations and lobar fissures for HR-CT reformations. RESULTS: All cases were successfully reformatted and all ventilation defects were correctly assigned to anatomic structures. On HR-CT reformations, the lobar fissures were partially visible in 12 of 16 cases and completely visible in the remaining 4 cases. Since reformation compromises the spatial resolution, the reformatted images should be evaluated together with the source images. CONCLUSION: Looking at HR-CT and 3He-MRI images and their reformations enables the detection of ventilation defects and their assignment to lung segments, facilitating the correlation of ventilation defects with a pathomorphologic pattern on HR-CT.
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BACKGROUND: Fast dynamic computed tomography (dCT) has been used to assess regional dynamics of lung inflation and deflation processes. The aim of this study was to relate ventilation-induced changes in lung density distribution, as measured over several respiratory cycles by dCT, to oxygenation and shunt fraction in a lavage acute respiratory distress syndrome model. METHODS: Six anaesthetized pigs underwent pressure-constant ventilation (FIO2=1.0, inspiratory:expiratory ratio=1:1) before and after induction of lung damage by saline lavage. Mean airway pressure (Paw) was varied (8, 13, 18, 23, 28, 33, and 38 cm H2O) in random order. At each Paw level, dCT acquisitions were performed over several respiratory cycles (Somatom Plus4, Siemens; supradiaphragmatic transverse slice; thickness=1 mm; temporal resolution=100 ms). During scanning at each Paw, arterial and mixed venous blood were obtained for blood gas analysis and shunt calculation. In each CT image, fractional areas (FA) of defined density ranges representing ventilated lung and atelectasis were determined by planimetry using dedicated software. The FA data of individual 100 ms scans were averaged over several respiratory cycles, and expressed as mean FA in percentage of total lung area at each Paw. For atelectatic lung parenchyma a quantitative relationship of the respective mean FA to shunt fraction was studied using regression analysis. RESULTS: Under steady-state conditions, mean FA of atelectasis correlated linearly with the calculated shunt fraction (healthy lungs, r=+0.76; lavaged lungs, r=+0.89). There is a non-linear relationship between mean FA of ventilated lung parenchyma and mean FA of atelectasis with PaO2. CONCLUSIONS: We conclude that dCT allows assessment of the effects of ventilator adjustments and resultant Paw; changes upon lung aeration and oxygenation rapidly, and with good spatial and temporal resolution. This may benefit patients with acute lung injury, whose ventilatory pattern may be optimized as early as during their first diagnostic workup.
MRI of the lungs using hyperpolarized helium-3 ((3)He) allows the determination of intrapulmonary oxygen partial pressures (p(O2)). The need to separate competing processes of signal loss has hitherto required two different imaging series during two different breathing maneuvers. In this work, a new imaging strategy to measure p(O2) by a single series of consecutive scans is presented. The feasibility of the method is demonstrated in three healthy human volunteers. Maps and histograms of intrapulmonary p(O2) are calculated. Changes in the oxygen concentration of the inhaled gas mixture are well reproduced in the histograms. Monte Carlo (MC) simulations of the temporal evolution of (3)He hyperpolarization within the lungs were performed to evaluate the accuracy of this measurement technique, and its limitations.
BACKGROUND: To use 3Helium (3He)-MRI in patients with unilateral lung grafts to assess the contributions of graft and native lung to total ventilated lung volume, and second to compare conventional measurements of intrapulmonary gas volume (spirometry, body plethysmography) with image-based volumetry of ventilated lung parenchyma visualized by hyperpolarized 3He-MRI. METHODS: With Ethics Committee approval, five patients with single lung transplantation (SLTX) for idiopathic pulmonary fibrosis (IPF) underwent both conventional pulmonary function testing (PFT) and 3He-MRI of the lung. Intrapulmonary gas volume (GV) during the inspiratory breathhold for 3He-MRI was calculated from measured functional residual capacity (corrected for supine position) and inspired tidal volume. Image-based global and regional lung volumetries (LV) were performed in three-dimensionally reconstructed 3He-MR images (corrected for the fraction of tissue and blood). RESULTS: Transplanted lungs were characterized by a homogeneous distribution of signal intensity, whereas the native lungs of the patients suffering from IPF displayed an inhomogeneous signal distribution pattern with numerous round or wedge-shaped ventilation defects. Total ventilated lung volume determined by 3He-MRI correlated well with PFT-based measurements, but with a systematic overestimation of the 3He-based lung volumetry of approximately 20%. Functioning lung grafts contributed 66+/-6% and their corresponding native IPF lungs 34+/-6% to total ventilated volume (P<0.05; mean+/-SD). CONCLUSION: 3Helium-MRI of the lung offers a novel approach to regional determination of ventilated lung volume, including its blood and tissue compartments. The advantage of this technique over computed tomography or ventilation scintigraphy is the lack of radiation exposure, and hence its repeatability. Follow up of SLTX patients with this new technique may allow the monitoring of functional and structural developments of grafted lungs with better sensitivity and specificity than PFT.
In magnetic resonance imaging (MRI), nuclear spins are the source of the image signal. In the lung, low-proton spin density in alveolar gas and abundant gas-tissue interfaces substantially impair conventional native 1H-MRI. Spin polarisation can be increased in two non-radioactive noble gas isotopes, 3He and 129Xe, by exposure to polarised laser light. When inhaled, such "magnetized" gases provide high-intensity MR images of the pulmonary airspaces. Thus, hyperpolarised gas (HPG) MRI opens up new routes to a) morphologic imaging of airways and alveolar spaces, and b) analysis of the intrapulmonary distribution of inhaled aliquots of these tracer gases; c) diffusion-sensitive MRI-techniques allow mapping of the "apparent diffusion coefficient" (ADC) of 3He within lung airspaces, where ADC is physically related to local bronchoalveolar dimensions; d) also, 3He magnetisation decays in an oxygen-containing atmosphere at a rate proportional to ambient PO2. This property allows image-based determination of regional broncho-alveolar PO2 and its decrease during a breathhold. Currently, these modalities of functional lung imaging are being assessed by several European and American research groups in animal models, human volunteers and patients. First results show good imaging quality with excellent spatial and unprecedented temporal resolution, and attest to the reproducibility, feasibility and safety of the technique. Regionally impaired ventilation of both structural and functional origin is detected with high sensitivity, e.g. in smokers, asthmatics, patients with COPD or after lung transplantation. Studies into regional ADC and PO2 measurement demonstrate good agreement with reference methods and physiological predictions. The present limitations of HPG-MRI include the HPG production rate and the US and EU health authorities' still pending final approval for clinical use.
A new method for dynamic imaging of pulmonary wash-in and wash-out kinetics of inhaled sulfur hexafluoride (SF(6)) gas was developed. Measurements at the fluorine-19 Larmor frequency were performed in pigs using a gradient echo pulse sequence with 0.5 ms echo time and a measurement time of 9.1 s per image. Dynamic MRI was performed during wash-in and wash-out of SF(6) gas in mechanically ventilated porcine lungs. A postprocessing strategy was developed for quantitative determination of wash-out time constants in the presence of noise. Mean wash-out constants were 4.78 +/- 0.48 breaths vs. 4.33 +/- 0.76 breaths for left and right lung when ventilation was performed with low tidal volume, and 1.73 +/- 0.16 breaths vs. 1.85 +/- 0.11 breaths with high tidal volume ventilation. In conclusion, breath-hold MRI of SF(6) gas is feasible in large animals. Moreover, regional wash-in and wash-out kinetics of SF(6) can be determined noninvasively with this new method. Potential human applications are discussed. Magn Reson Med 45:605-613, 2001.
PURPOSE: Aim of the study was to investigate alveolar inspiration and expiration using multiscan CT. Results of a visual assessment using a scoring system were compared with density ranges known to represent alveolar ventilation best. METHOD: Pigs were examined before and after lavage-induced ARDS. All animals were examined using dynamic multiscan CT. The visual assessment was done by a scoring system proposed by Gattinoni. The results were compared with planimetric determination of defined density ranges. RESULTS: In the healthy lung, the visual analysis showed higher scores at lower airway pressures with a marked gradient, whereas at higher pressures neither opacities nor gradients were observed. In ARDS-lungs, the scores were double as high as in healthy lungs at low pressures. At the same time the differences between inspiration and expiration were minor. There was good correlation between lung density measurements and lung opacities under different airway pressures. In healthy lungs, the greatest area increase is found between -910 and -700 HU. The biggest area growth in the ARDS-model is observed between -910 and -300 HU. CONCLUSION: Dynamic multiscan CT allows for determining different ventilation-relevant lung compartments and lung density ranges.
PURPOSE: Density measurements in dynamic CT image series of the lungs allow one to quantify ventilated, hyperinflated, and atelectatic pulmonary compartments with high temporal resolution. Fast automatic segmentation of lung parenchyma and a subsequent evaluation of it's respective density values are a prerequisite for any clinical application of this technique. MATERIAL AND METHODS: For automatic lung segmentation in thoracic CT scans, an algorithm was developed which uses (a) different density masks, and (b) anatomic knowledge to differentiate heart, diaphragm and chest wall from ventilated and atelectatic lung parenchyma. With Animal Care Committee approval, the automated technique was tested in 8 anaesthetized ventilated pigs undergoing dynamic CT before and after induction of lavage-ARDS. Images were acquired in one supradiaphragmatic, cross-sectional slice (temporal resolution of 100 ms; slice thickness of 1 mm, high resolution reconstruction algorithm). In 120 CT images the total pixel number and the calculated MLD from the automatically segmentated lung were compared to the values obtained from an interactive lung segmentation. RESULTS: The software tool was able to read all image series (DICOM standard). Automatic and interactive segmentation were in high agreement (R(2) = 0.99 for the total number of pixels and the MLD). Originally, the most frequent error was misclassification of atelectasis as extrapulmonary solid tissue. CONCLUSION: An automatic software tool is presented for lung segmentation in healthy lungs and in ARDS. Aerated lung and atelectasis were identified with high accuracy. This post-processing tool allows for a quantitative, CT based assessment of ventilation and recruitment processes in the lung. Thus, it may help to optimize ventilation patterns in patients with ARDS.
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.
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.