Ultrasonography of the Lung

Publisher Copyright: © Georg Thieme Verlag KG, Stuttgart New York.Background High diagnostic accuracy, increasing clinical experience and technical improvements are good reasons to consider lung ultrasound (US) for the assessment of pleural and pulmonary diseases. In the emergency room and in intensive care, it is well acknowledged, but application in other settings is rare. The aim of this review is to update potential users in general radiology about the diagnostic scope of lung US and to encourage more frequent use of this generally underestimated lung imaging modality. Method Literature review was done independently by the two authors in MEDLINE (via PubMed) covering a time span from 2002 until 2017 using free text and Medical Subject Headings/MeSH. Article selection for the bibliography was based on consensus according to relevance and evidence. Results and Conclusion The technical prerequisites include a standard ultrasound unit with a suitable transducer. Pleural effusion and pneumothorax, atelectasis, interstitial edema, pneumonia, exacerbated chronic obstructive pulmonary disease/asthma and pulmonary embolism can be distinguished by particular ultrasound signs, artifacts and their combinations. A highly standardized selection of access points and terminology for the description of imaging findings contributes to high diagnostic accuracy even in challenging patients and settings. Besides the assessment of acute respiratory failure in the emergency room, lung US may be used for monitoring interstitial fluid accumulation in volume therapy and for the diagnosis of pneumonia or the assessment of pleural effusion and pleurisy in a routine outpatient setting. Last but not least, the increasing concerns about medical radiation exposure warrant a more extensive use of this sometimes underestimated modality as a cost-, time- and radiation-saving alternative or valuable adjunct to the standard imaging modalities. Key Points: Lung US is a safe, quick and readily available method with options for dynamic imaging of respiratory function. Proper selection of technical parameters customized to the clinical question and standardized terminology for the precise description and interpretation of the imaging signs regarding patient history determine its diagnostic accuracy. In dyspnea lung US differentiates pneumothorax, lung edema, pneumonia, pulmonary embolism, atelectasis and pleural effusion. In intensive care, lung US allows monitoring of lung ventilation and fluid administration. It saves radiation exposure in serial follow-up, in pregnancy and pediatric radiology. Citation Format Radzina M, Biederer J, Ultrasonography of the Lung. Fortschr Röntgenstr 2019; 191: 909 - 923.publishersversionPeer reviewe

Morpho-Functional 1H-MRI of the Lung in COPD: Short-Term Test-Retest Reliability

Purpose Non-invasive end-points for interventional trials and tailored treatment regimes in chronic obstructive pulmonary disease (COPD) for monitoring regionally different manifestations of lung disease instead of global assessment of lung function with spirometry would be valuable. Proton nuclear magnetic resonance imaging (1H-MRI) allows for a radiation-free assessment of regional structure and function. The aim of this study was to evaluate the short-term reproducibility of a comprehensive morpho-functional lungMRI protocol in COPD. Materials and Methods 20 prospectively enrolled COPD patients (GOLD I-IV) underwent 1H-MRI of the lung at 1.5T on two consecutive days, including sequences for morphology, 4D contrast-enhanced perfusion, and respiratory mechanics. Image quality and COPD-related morphological and functional changes were evaluated in consensus by three chest radiologists using a dedicated MRI-based visual scoring system. Test-retest reliability was calculated per each individual lung lobe for the extent of large airway (bronchiectasis, wall thickening, mucus plugging) and small airway abnormalities (tree in bud, peripheral bronchiectasis, mucus plugging),consolidations, nodules, parenchymal defects and perfusion defects. The presence of tracheal narrowing, dystelectasis, pleural effusion, pulmonary trunk ectasia, right ventricular enlargement and, finally, motion patterns of diaphragma and chest wall were addressed. Results Median global scores [10(Q1:8.00;Q3:16.00) vs. 11(Q1:6.00;Q3:15.00)] as well as category subscores were similar between both timepoints, and kappa statistics indicated "almost perfect" global agreement (kappa = 0.86, 95% CI = 0.81-0.91). Most subscores showed at least "substantial" agreement of MRI1 and MRI2 (kappa = 0.64-1.00),whereas the agreement for the diagnosis of dystelectasis/effusion (kappa = 0.42, 95% CI = 0.00-0.93) was "moderate" and of tracheal abnormalities (kappa = 0.21, 95% CI = 0.00-0.75) "fair". Most MRI acquisitions showed at least diagnostic quality at MRI1 (276 of 278) and MRI2 (259 of 264). Conclusion Morpho-functional 1H-MRI can be obtained with reproducible image quality and high short-term test-retest reliability for COPD-related morphological and functional changes of the lung. This underlines its potential value for the monitoring of regional lung characteristics in COPD trials

cOOpD: Reformulating COPD classification on chest CT scans as anomaly detection using contrastive representations

Classification of heterogeneous diseases is challenging due to their complexity, variability of symptoms and imaging findings. Chronic Obstructive Pulmonary Disease (COPD) is a prime example, being underdiagnosed despite being the third leading cause of death. Its sparse, diffuse and heterogeneous appearance on computed tomography challenges supervised binary classification. We reformulate COPD binary classification as an anomaly detection task, proposing cOOpD: heterogeneous pathological regions are detected as Out-of-Distribution (OOD) from normal homogeneous lung regions. To this end, we learn representations of unlabeled lung regions employing a self-supervised contrastive pretext model, potentially capturing specific characteristics of diseased and healthy unlabeled regions. A generative model then learns the distribution of healthy representations and identifies abnormalities (stemming from COPD) as deviations. Patient-level scores are obtained by aggregating region OOD scores. We show that cOOpD achieves the best performance on two public datasets, with an increase of 8.2% and 7.7% in terms of AUROC compared to the previous supervised state-of-the-art. Additionally, cOOpD yields well-interpretable spatial anomaly maps and patient-level scores which we show to be of additional value in identifying individuals in the early stage of progression. Experiments in artificially designed real-world prevalence settings further support that anomaly detection is a powerful way of tackling COPD classification

Functional Lung MRI in Chronic Obstructive Pulmonary Disease: Comparison of T1 Mapping, Oxygen-Enhanced T1 Mapping and Dynamic Contrast Enhanced Perfusion

Purpose Monitoring of regional lung function in interventional COPD trials requires alternative end-points beyond global parameters such as FEV1. T1 relaxation times of the lung might allow to draw conclusions on tissue composition, blood volume and oxygen fraction. The aim of this study was to evaluate the potential value of lung Magnetic resonance imaging (MRI) with native and oxygen-enhanced T1 mapping for the assessment of COPD patients in comparison with contrast enhanced perfusion MRI. Materials and Methods 20 COPD patients (GOLD I-IV) underwent a coronal 2-dimensional inversion recovery snapshot flash sequence (8 slices/lung) at room air and during inhalation of pure oxygen, as well as dynamic contrast-enhanced first-pass perfusion imaging. Regional distribution of T1 at room air (T1), oxygen-induced T1 shortening (Delta T1) and peak enhancement were rated by 2 chest radiologists in consensus using a semi-quantitative 3-point scale in a zone-based approach. Results Abnormal T1 and Delta T1 were highly prevalent in the patient cohort. T1 and Delta T1 correlated positively with perfusion abnormalities (r = 0.81 and r = 0.80;p&0.001), and with each other (r = 0.80;p< 0.001). In GOLD stages I and II Delta T1 was normal in 16/29 lung zones with mildly abnormal perfusion (15/16 with abnormal T1). The extent of T1 (r = 0.45;p< 0.05), T1 (r = 0.52;p< 0.05) and perfusion abnormalities (r = 0.52;p< 0.05) showed a moderate correlation with GOLD stage. Conclusion Native and oxygen-enhanced T1 mapping correlated with lung perfusion deficits and severity of COPD. Under the assumption that T1 at room air correlates with the regional pulmonary blood pool and that oxygen-enhanced T1 reflects lung ventilation, both techniques in combination are principally suitable to characterize ventilation-perfusion imbalance. This appears valuable for the assessment of regional lung characteristics in COPD trials without administration of i. v. contrast

High resolution propagation-based lung imaging at clinically relevant X-ray dose levels

Absorption-based clinical computed tomography (CT) is the current imaging method of choice in the diagnosis of lung diseases. Many pulmonary diseases are affecting microscopic structures of the lung, such as terminal bronchi, alveolar spaces, sublobular blood vessels or the pulmonary interstitial tissue. As spatial resolution in CT is limited by the clinically acceptable applied X-ray dose, a comprehensive diagnosis of conditions such as interstitial lung disease, idiopathic pulmonary fibrosis or the characterization of small pulmonary nodules is limited and may require additional validation by invasive lung biopsies. Propagation-based imaging (PBI) is a phase sensitive X-ray imaging technique capable of reaching high spatial resolutions at relatively low applied radiation dose levels. In this publication, we present technical refinements of PBI for the characterization of different artificial lung pathologies, mimicking clinically relevant patterns in ventilated fresh porcine lungs in a human-scale chest phantom. The combination of a very large propagation distance of 10.7 m and a photon counting detector with [Formula: see text] pixel size enabled high resolution PBI CT with significantly improved dose efficiency, measured by thermoluminescence detectors. Image quality was directly compared with state-of-the-art clinical CT. PBI with increased propagation distance was found to provide improved image quality at the same or even lower X-ray dose levels than clinical CT. By combining PBI with iodine k-edge subtraction imaging we further demonstrate that, the high quality of the calculated iodine concentration maps might be a potential tool for the analysis of lung perfusion in great detail. Our results indicate PBI to be of great value for accurate diagnosis of lung disease in patients as it allows to depict pathological lesions non-invasively at high resolution in 3D. This will especially benefit patients at high risk of complications from invasive lung biopsies such as in the setting of suspected idiopathic pulmonary fibrosis (IPF)

Design and application of an MR reference phantom for multicentre lung imaging trials

Introduction As there is an increasing number of multicentre lung imaging studies with MRI in patients, dedicated reference phantoms are required to allow for the assessment and comparison of image quality in multi-vendor and multi-centre environments. However, appropriate phantoms for this purpose are so far not available commercially. It was therefore the purpose of this project to design and apply a cost-effective and simple to use reference phantom which addresses the specific requirements for imaging the lungs with MRI. Methods The phantom was designed to simulate 4 compartments (lung, blood, muscle and fat) which reflect the specific conditions in proton-MRI of the chest. Multiple phantom instances were produced and measured at 15 sites using a contemporary proton-MRI protocol designed for an in vivo COPD study at intervals over the course of the study. Measures of signal- and contrast-to-noise ratio, as well as structure and edge depiction were extracted from conventionally acquired images using software written for this purpose. Results For the signal to noise ratio, low intra-scanner variability was found with 4.5% in the lung compartment, 4.0% for blood, 3.3% for muscle and 3.7% for fat. The inter-scanner variability was substantially higher, with 41%, 32%, 27% and 32% for the same order of compartments. In addition, measures of structure and edge depiction were found to both vary significantly among several scanner types and among scanners of the same model which were equipped with different gradient systems. Conclusion The described reference phantom reproducibly quantified image quality aspects and detected substantial inter-scanner variability in a typical pulmonary multicentre proton MRI study, while variability was greater in lung tissue compared to other tissue types. Accordingly, appropriate reference phantoms can help to detect bias in multicentre in vivo study results and could also be used to harmonize equipment or data

Towards quantitative perfusion MRI of the lung in COPD: The problem of short-term repeatability

Purpose 4D perfusion magnetic resonance imaging (MRI) with intravenous injection of contrast agent allows for a radiation-free assessment of regional lung function. It is therefore a valuable method to monitor response to treatment in patients with chronic obstructive pulmonary disease (COPD). This study was designed to evaluate its potential for monitoring short-term response to hyperoxia in COPD patients. Materials and methods 19 prospectively enrolled COPD patients (median age 66y) underwent paired dynamic contrast-enhanced 4D perfusion MRI within 35min, first breathing 100% oxygen (injection 1, O-2) and then room air (injection 2, RA), which was repeated on two consecutive days (day 1 and 2). Post-processing software was employed to calculate mean transit time (MTT), pulmonary blood volume (PBV) and pulmonary blood flow (PBF), based on the indicator dilution theory, for the automatically segmented whole lung and 12 regions of equal volume. Results Comparing O-2 with RA conditions, PBF and PBV were found to be significantly lower at O-2, consistently on both days (p<10-8). Comparing day 2 to day 1, MTT was shorter by 0.59 +/- 0.63 s (p<10-8), PBF was higher by 22 +/- 80 ml/min/100ml (p<3.10-4), and PBV tended to be lower by 0.2 +/- 7.2 ml/100ml (p = 0.159) at both, RA and O-2, conditions. Conclusion The second injection (RA) yielded higher PBF and PBV, which apparently contradicts the established hypothesis that hyperoxia increases lung perfusion. Quantification of 4D perfusion MRI by current software approaches may thus be limited by residual circulating contrast agent in the short-term and even the next day

Reproducibility and comparison of oxygen-enhanced T-1 quantification in COPD and asthma patients

T1 maps have been shown to yield useful diagnostic information on lung function in patients with chronic obstructive pulmonary disease (COPD) and asthma, both for native T1 and Delta T1, the relative reduction while breathing pure oxygen. As parameter quantification is particularly interesting for longitudinal studies, the purpose of this work was both to examine the reproducibility of lung T1 mapping and to compare T1 found in COPD and asthma patients using IRSnapShotFLASH embedded in a full MRI protocol. 12 asthma and 12 COPD patients (site 1) and further 15 COPD patients (site 2) were examined on two consecutive days. In each patient, T1 maps were acquired in 8 single breath-hold slices, breathing first room air, then pure oxygen. Maps were partitioned into 12 regions each to calculate average values. In asthma patients, the average T-1,T-RA = 1206ms (room air) was reduced to T-1,T-O2 = 1141ms under oxygen conditions (Delta T1 = 5.3%, p < 5.10(-4)), while in COPD patients both native T-1,T-RA = 1125ms was significantly shorter (p < 10(-3)) and the relative reduction to T-1,T-O2 = 1081ms on average Delta T1 = 4.2%(p < 10(-5)). On the second day, with T-1,T-RA = 1186ms in asthma and T-1,T-RA = 1097ms in COPD, observed values were slightly shorter on average in all patient groups. Delta T1 reduction was the least repeatable parameter and varied from day to day by up to 23% in individual asthma and 30% in COPD patients. While for both patient groups T1 was below the values reported for healthy subjects, the T1 and Delta T1 found in asthmatics lies between that of the COPD group and reported values for healthy subjects, suggesting a higher blood volume fraction and better ventilation. However, it could be demonstrated that lung T1 quantification is subject to notable inter-examination variability, which here can be attributed both to remaining contrast agent from the previous day and the increased dependency of lung T1 on perfusion and thus current lung state