Increased Lung Density Research Articles

Retrospective cohort study identifying pulmonary complications in a cohort of patients with systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with multi organ involvement. One of the most common manifestations is pulmonary disease with a reported prevalence between 5%-90%. Given this wide range of prevalence, there is a need to more closely define types of pulmonary disease in SLE and associated risk factors. We sought to characterize the presentation of pulmonary manifestations in an established SLE cohort using electronic health record data. All patients were >18 years of age and had confirmed SLE by a rheumatologist using SLICC or 2019 ACR/EULAR classification criteria. 220 patients with imaging were included in this study; average age was 42.5 years, 86.7% identified as female, 60.5% identified as white, 37.3% as Black, and 1.82% as Asian. Generalized estimating equations were utilized to analyze the data, accounting for its repeated measured nature. We found an association between smoking (present/prior smoker) and radiologist reported disease on computerized tomography (CT) scan, as well as an association between smoking (present/prior smoker), older age, and male sex with having pulmonary disease identified on chest X-ray. The most common findings on CT and X-ray were increased lung density (24%, 12%) and atelectasis (18%, 10%). The most common disease found on CT was pleural effusion (24%) and mediastinal/axillary lymphadenopathy (16%). While our study is limited by the retrospective nature, our results show that certain factors, namely smoking, older age, or male sex should prompt clinicians to have a higher suspicion for lung disease in SLE patients.

Future directions of lung-protective ventilation strategies in acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is characterized by the heterogeneous distribution of lung aeration along a gravitational direction due to increased lung density. Therefore, the lung available for ventilation is usually limited to ventral, nondependent lung regions and has been called the "baby" lung. In ARDS, ventilator-induced lung injury is known to occur in nondependent "baby" lungs, as ventilation is shifted to ventral, nondependent lung regions, increasing stress and strain. To protect this nondependent "baby" lung, the clinician targets and limits global parameters such as tidal volume and plateau pressure. In addition, positive end-expiratory pressure (PEEP) is used to prevent dorsal, dependent atelectasis and, if successful, increases the size of the baby lung and lessens its susceptibility to injury from inspiratory stretch. Although many clinical trials have been performed in patients with ARDS over the last two decades, there are few successfully showing benefits on mortality (ie, prone positioning and neuromuscular blocking agents). These disappointing results contrast with other medical disciplines, especially in oncology, where the heterogeneity of diseases is recognized widely and precision medicine has been promoted. Thus, lung-protective ventilation strategies need to take an innovative approach that accounts for the heterogeneity of injured lungs. This article summarizes ventilator-induced lung injury and ARDS and discusses how to implement precision medicine in the field of ARDS. Potentially useful methods to individualize PEEP with esophageal balloon manometry, lung recruitability, and electrical impedance tomography were discussed.

The HLA-DRB1*07 Allele Is Associated with Interstitial Lung Abnormalities (ILA) and Subpleural Location in a Mexican Mestizo Population.

Interstitial lung abnormalities (ILA) are defined as the presence of different patterns of increased lung density, including ground glass attenuation and reticular opacities on chest high-resolution computed tomography (HRCT). In this study, we included 90 subjects with ILA and 189 healthy controls (HC) from our Aging Lung Program. We found that subjects with ILA are older, have a significant smoking history, and have worse pulmonary function than HC (p < 0.05). When we evaluated the allele frequencies of the human leukocyte antigen (HLA) system, we found that HLA-DRB1*07 was associated with a higher risk for ILA (p < 0.05, OR = 1.95, 95% CI = 1.06-3.57). When we compared subjects with subpleural ILA vs. HC, the association with HLA-DRB1*07 became stronger than the whole ILA group (p < 0.05, OR = 2.29, 95% CI = 1.24-4.25). Furthermore, subjects with subpleural ILA and central ILA display differences in allele frequencies with HLA-DRB1*14 (3.33% vs. 13.33%, p < 0.05) and *15 (3.33% vs. 20%, p < 0.05). Our findings indicate that the HLA-DRB1*07 allele contributes to the risk of ILA, especially those of subpleural locations.

Chronic lung allograft dysfunction subtype analysis by computed tomography volumetry.

Chronic lung allograft dysfunction (CLAD) limits long-term survival after lung transplantation. Of the two subtypes, restrictive allograft syndrome (RAS) is characterized by a larger lung volume decrease and worse prognosis than bronchiolitis obliterans syndrome (BOS). We used computed tomography (CT) volumetry to classify CLAD subtypes and determined their clinical impact. Adult primary lung transplants performed 2003-2015 (n=167) were retrospectively evaluated for CLAD and subclassified with CT volumetry. Lung volume decrease of<15% from baseline resulted in BOSCT-vol and ≥15% resulted in RASCT-vol diagnosis. Clinical impact of CLAD subtypes was defined, and the prognostic value of different lung function, radiological, and lung volume parameters present at the time of CLAD diagnosis were compared. CLAD affected 43% of patients and was classified with CT volumetry as BOSCT-vol in 89% and RASCT-vol in 11%. Median graft survival estimate in RASCT-vol was significantly decreased compared to BOSCT-vol (1.6vs. 9.7 years, P=.038). At CLAD onset, RASCT-vol diagnosis (P=.05), increased lung density (P=.007), and more severe FEV1 (P=.004) decline from baseline, increased graft loss risk in multivariate analysis. CT volumetry serves to identify lung transplant patients with a poor clinical outcome but should be validated in prospective trials.

Signs and lines in lung ultrasound.

Point-of-care ultrasound has become firmly established in acute and critical care settings, and is now increasingly being used as an important tool in the assessment of the lungs. In this article, we briefly describe the technique of lung ultrasound and the various lines and signs commonly encountered during sonography of the lung, namely the normally visualised A- and T-lines and the bat sign, sliding sign (power slide sign on colour Doppler), sea-shore sign, curtain sign, and the lung pulse. We have also described signs seen in various pathological conditions like B-lines seen in cases of increased lung density; the quad sign, sinusoid sign, thoracic spine sign, plankton sign and the jelly fish sign seen in pleural effusion; the stratosphere sign and the lung point sign seen in pneumothorax; the shred/fractal sign and tissue-like sign in consolidation, and the double lung point sign seen in transient tachypnoea of the newborn. With adequate and appropriate training, lung ultrasound can be effectively utilised as a point-of-care investigation.

A-lines and B-lines in patients with acute heart failure.

Lung ultrasound (LUS) relies on detecting artefacts, including A-lines and B-lines, when assessing dyspnoeic patients. A-lines are horizontal artefacts and characterize normal lung, whereas multiple vertical B-lines are associated with increased lung density. We sought to assess the prevalence of A-lines and B-lines in patients with acute heart failure (AHF) and examine their clinical correlates and their relationship with outcomes. In a prospective cohort study of adults with AHF, eight-zone LUS and echocardiography were performed early during the hospitalization and pre-discharge at an imaging depth of 18 cm. A- and B-lines were analysed separately off-line, blinded to clinical and outcome data. Of 164 patients [median age 71 years, 61% men, mean ejection fraction (EF) 40%], the sum of A-lines at baseline ranged from 0 to 19 and B-line number from 0 to 36. One hundred and fifty-six patients (95%) had co-existing A-lines and B-lines at baseline. Lower body mass index and lower chest wall thickness were associated with a higher number of A-lines (P trend < 0.001 for both). In contrast to B-lines, there was no significant change in the number of A-lines from baseline to discharge (median 6 vs. 5, P = 0.80). While B-lines were associated with 90-day HF readmission or death, A-lines were not [HR 1.67, 95% confidence interval (CI) 1.11-2.51 vs. HR 0.97, 95% CI 0.65-1.43]. A-lines and B-lines on LUS co-exist in the vast majority of hospitalized patients with AHF. In contrast to B-lines, A-lines were not associated with adverse outcomes.

A Closer Radiological Look at Chronic Rejection after Murine Orthotopic Lung Transplantation

<h3>Purpose</h3> Chronic lung allograft dysfunction (CLAD) is the main culprit for low survival after human lung transplantation (LTx). Within the clinical identification of CLAD, the immunological enigma of <i>chronic rejection</i> was lost. This is difficult to study in the complex patient setting; but an appropriate experimental model may help. Our goal was to further elaborate our mouse model of chronic rejection by implementing <i>in vivo</i> microCT (µCT). <h3>Methods</h3> Using the orthotopic single left LTx model with cuffing method, isografts (n=9; C57BL/6N to C57BL/6N) and allografts (n=8; Balb/c to C57BL/6N) were transplanted. Mice received daily immunosuppression with 10 mg/kg cyclosporine A and 1.6 mg/kg methylprednisolone for 10 weeks. <i>In vivo</i> respiratory-gated time resolved µCT (SkyScan 1278, Bruker) was performed at postoperative week 1, 5 and 10, lung density and volume (at in and expiration) were quantified. <h3>Results</h3> In 1 isografts technical failure was observed (on both CT and histology), the other 8 demonstrated normal lung structure at week 10. 5 isografts had normal lung density at week 1, 5 and 10 (1.03±0.02; 1.04±0.01; 1.01±0.02), compared to 3 isografts which had significant increased lung density at week 1 (1.22±0.01; p<0.0001) (Figure) that decreased to normal at week 5 and week 10 vs week 1 (0.99±0.04; p=0.001; 1.00±0.01; p<0.0001). Within allografts, 2 failures were observed. Lung density of 6 allografts at week 1 was comparable to isografts at week 1 (1.01±0.01; p=0.92) but increased at week 5 and week 10 vs week 1 (1.09±0.02; p=0.002; 1.08±0.03; p=0.005). In allografts, 4 had a mild pattern and 2 had a severe pattern with density difference at week 10 (1.05±0.04 versus 1.14±0.01; p=0.002) (Figure). Same patterns were observed for lung volume, tidal volume and airway volume. <h3>Conclusion</h3> Longitudinal µCT is useful to investigate lung volume, lung density, lung ventilation/tidal volume of the transplanted lung and can identify and monitor the evolution/severity of both chronic rejection and primary graft dysfunction (PGD).

The infusion effect in postmortem lung CT

Abstract The purpose of this study was to evaluate the influence of infusion on cadaver lung, and to evaluate the mechanism of increasing lung density in postmortem CT. From December 2017 to January 2018, 6 New Zealand White rabbits were examined by postmortem CT with saline injection (total 80 cml, and 160 ml) after humane killing. Postmortem CT finding on lung field, and hisopathological evaluation were compared. The average CT densities were antemortem (-524.8 ± 16.1 HU), 80 ml injection (-474.2 ± 25.9 HU) and 160 ml injection (-225.3 ± 23.1 HU), and there was no significant difference between antemortem and the 80 ml injection group, but the 160 ml injection group presented statistically increased lung density compared with antemortem and the 80 ml injection group. From segmented volume data analysis, after saline infusion, the aerated lung area and less edematous lung area decreased their volumes. In addition, highly edematous lung area, organ parenchymal area, and blood and/or calcification area increased. In contrast, the lung volume was not changed. In conclusion, depending on the infusion volume, the average lung density increases, the aerated lung volume decreases, and the edematous lung volume increases in postmortem CT.

Deep learning, reusable and problem-based architectures for detection of consolidation on chest X-ray images

Background and objectiveIn most patients presenting with respiratory symptoms, the findings of chest radiography play a key role in the diagnosis, management, and follow-up of the disease. Consolidation is a common term in radiology, which indicates focally increased lung density. When the alveolar structures become filled with pus, fluid, blood cells or protein subsequent to a pulmonary pathological process, it may result in different types of lung opacity in chest radiograph. This study aims at detecting consolidations in chest x-ray radiographs, with a certain precision, using artificial intelligence and especially Deep Convolutional Neural Networks to assist radiologist for better diagnosis. MethodsMedical image datasets usually are relatively small to be used for training a Deep Convolutional Neural Network (DCNN), so transfer learning technique with well-known DCNNs pre-trained with ImageNet dataset are used to improve the accuracy of the models. ImageNet feature space is different from medical images and in the other side, the well-known DCNNs are designed to achieve the best performance on ImageNet. Therefore, they cannot show their best performance on medical images. To overcome this problem, we designed a problem-based architecture which preserves the information of images for detecting consolidation in Pediatric Chest X-ray dataset. We proposed a three-step pre-processing approach to enhance generalization of the models. To demonstrate the correctness of numerical results, an occlusion test is applied to visualize outputs of the model and localize the detected appropriate area. A different dataset as an extra validation is used in order to investigate the generalization of the proposed model. ResultsThe best accuracy to detect consolidation is 94.67% obtained by our problem based architecture for the understudy dataset which outperforms the previous works and the other architectures. ConclusionsThe designed models can be employed as computer aided diagnosis tools in real practice. We critically discussed the datasets and the previous works based on them and show that without some considerations the results of them may be misleading. We believe, the output of AI should be only interpreted as focal consolidation. The clinical significance of the finding can not be interpreted without integration of clinical data.

Pre-existing interstitial lung abnormalities are risk factors for immune checkpoint inhibitor-induced interstitial lung disease in non-small cell lung cancer.

Approximately 5% of non-small cell lung cancer (NSCLC) patients develop immune checkpoint inhibitor (ICI)-induced interstitial lung disease (ICI-ILD), 10% of whom die. However, there are no established risk factors for its occurrence. Interstitial lung abnormalities (ILA) are areas of increased lung density on lung computed tomography (CT) in individuals with no known ILD. This study retrospectively investigated whether any patient characteristics, including ILA, were risk factors for ICI-ILD in patients with NSCLC. NSCLC patients who received anti-programmed death (PD)-1 antibody treatment at our hospital between September 2015 and December 2017 were enrolled. Information on patient characteristics before anti-PD-1 antibody administration, including chest CT findings and laboratory data, were obtained. Among 83 enrolled patients, the incidence of ICI-ILD was 16.9% (14/83). All ICI-ILD cases developed by the third line of treatment. The incidence of ICI-ILD was significantly higher in patients with pre-existing ILA than that in those without (p = 0.007). Furthermore, patients with ground glass attenuation (GGA) in ILA had a higher incidence of ICI-ILD than that in those without (p < 0.001). In univariate logistic analysis, ILA were significant risk factors for ICI-ILD (p = 0.005). Multivariate logistic analysis revealed that only GGA in ILA was a significant risk factor for ICI-ILD (p < 0.001). Pre-existing ILA are risk factors for ICI-ILD and GGA in ILA is an independent risk factor for ICI-ILD. Therefore, we should be more aware of the development of ICI-ILD in patients with ILA, especially those with GGA.

Profound Increase of Lung Airway Resistance in Heart Failure: a Potential Important Contributor for Dyspnea.

Dyspnea is a major symptom of heart failure (HF). Here, we have studied the lung remodeling and airway resistance in HF mice. We demonstrated that aortic banding-induced HF caused a dramatic decrease of lung compliance and an increase of lung airway resistance. The decrease of lung compliance was correlated with the increased lung weight in a linear fashion (γ2 = 0.824). An HF-induced increase of lung airway resistance and a decrease of lung compliance were almost identical in anesthetized mice and in the isolated lungs from these mice. HF caused profound lung fibrosis in mice with increased lung weight. Moreover, HF patients of NYHA class III-IV showed increased lung density as revealed by high-resolution CT scanning. These data indicate that lung compliance and lung airway resistance may be useful in determining lung remodeling after HF, and lung structure changes may contribute to dyspnea in HF.

Correction: Lung density change after SABR: A comparative study between tri-Co-60 magnetic resonance-guided system and linear accelerator.

[This corrects the article DOI: 10.1371/journal.pone.0195196.].

Lung density change after SABR: A comparative study between tri-Co-60 magnetic resonance-guided system and linear accelerator.

Radiation-induced lung damage is an important treatment-related toxicity after lung stereotactic ablative radiotherapy (SABR). After implementing a tri-60Co magnetic-resonance image guided system, ViewRayTM, we compared the associated early radiological lung density changes to those associated with a linear accelerator (LINAC). Eight patients treated with the tri-60Co system were matched 1:1 with patients treated with LINAC. Prescription doses were 52 Gy or 60 Gy in four fractions, and lung dose-volumetric parameters were calculated from each planning system. The first two follow-up computed tomography (CT) were co-registered with the planning CT through deformable registration software, and lung density was measured by isodose levels. Tumor size was matched between the two groups, but the planning target volume of LINAC was larger than that of the tri-60Co system (p = 0.036). With regard to clinically relevant dose-volumetric parameters in the lungs, the ipsilateral lung mean dose, V10Gy and V20Gy were significantly poorer in tri-60Co plans compared to LINAC plans (p = 0.012, 0.036, and 0.017, respectively). Increased lung density was not observed in the first follow-up scan compared to the planning scan. A significant change of lung density was shown in the second follow-up scan and there was no meaningful difference between the tri-60Co system and LINAC for all dose regions. In addition, no patient developed clinical radiation pneumonitis until the second follow-up scan. Therefore, there was no significant difference in the early radiological lung damage between the tri-60Co system and LINAC for lung SABR despite of the inferior plan quality of the tri-60Co system compared to that of LINAC. Further studies with a longer follow-up period are needed to confirm our findings.

Image-Guided Fluorescence Endomicroscopy: From Macro- to Micro-Imaging of Radiation-Induced Pulmonary Fibrosis

Radiation-induced pulmonary fibrosis (RIPF) is a debilitating side effect of radiation therapy (RT) of several cancers including lung and breast cancers. Current clinical methods to assess and monitor RIPF involve diagnostic computed tomography (CT) imaging, which is restricted to anatomical macroscopic changes. Confocal laser endomicroscopy (CLE) or fluorescence endomicroscopy (FE) in combination with a fibrosis-targeted fluorescent probe allows to visualize RIPF in real-time at the microscopic level. However, a major limitation of FE imaging is the lack of anatomical localization of the endomicroscope within the lung. In this work, we proposed and validated the use of x-ray fluoroscopy-guidance in a rat model of RIPF to pinpoint the location of the endomicroscope during FE imaging and map it back to its anatomical location in the corresponding CT image. For varying endomicroscope positions, we observed a positive correlation between CT and FE imaging as indicated by the significant association between increased lung density on CT and the presence of fluorescent fiber structures with FE in RT cases compared to Control. Combining multimodality imaging allows visualization and quantification of molecular processes at specific locations within the injured lung. The proposed image-guided FE method can be extended to other disease models and is amenable to clinical translation for assessing and monitoring fibrotic damage.

HIV Infection Is Independently Associated with Increased CT Scan Lung Density

Noninfectious pulmonary complications are common among HIV-infected individuals and may be detected early by quantitative computed tomography (CT) scanning. The association of HIV disease markers with CT lung density measurement remains poorly understood. One hundred twenty-five participants free of spirometry-defined lung disease were recruited from a longitudinal cohort study of HIV-infected and HIV-uninfected individuals to undergo standardized CT scan of the chest. Parenchymal density for the entire lung volume was calculated using computerized software. Qualitative assessment of CT scans was conducted by two radiologists masked to HIV status. Linear regression models were developed to determine the independent association of markers of HIV infection on inspiratory scan mean lung density (MLD). HIV-infected participants had a significantly higher MLD (denser lung) compared to HIV-uninfected participants (-815 Hounsfield unit [HU] vs -837 HU; P = 0.002). After adjusting for relevant covariates, HIV infection was independently associated with 19.9 HU higher MLD (95% CI 6.04 to 33.7 HU; P = 0.005). In qualitative assessment, only ground glass attenuation and cysts were noted more commonly among HIV-infected individuals compared to HIV-uninfected individuals (34% vs 17% [P = 0.045] and 27% vs 10% [P = 0.03], respectively). No qualitative radiographic abnormalities attenuated the association between HIV infection and increased MLD. HIV infection is independently associated with increased lung density. Although qualitative CT abnormalities were common in this cohort, only ground glass attenuation and cysts were noted more frequently in HIV-infected participants, suggesting that the increased lung density observed among HIV-infected individuals may be associated with subclinical inflammatory lung changes.

Reduced pulmonary blood flow in regions of injury 2 hours after acid aspiration in rats.

BackgroundAspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury).MethodsAnesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [68Ga]-radiolabeled microspheres using positron emission tomography.ResultsCT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016).ConclusionsThe PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation.Please see related article: http://dx.doi.org/10.1186/s12871-015-0014-z.

Computed tomographic features predictive of local recurrence in patients with early stage lung cancer treated with stereotactic body radiation therapy

IntroductionThe objective of this study is to identify computed tomography (CT) features of local recurrence (LR) after stereotactic body radiation therapy (SBRT) for lung cancer. MethodsTwo hundred eighteen patients underwent SBRT for lung cancer from January 1st, 2006 to March 1st, 2011. Signs of LR recorded: opacity with new bulging margin, opacification of air bronchograms, enlarging pleural effusion, new or enlarging mass, and increased lung density at the treatment site. ResultsA new bulging margin at the treatment site was the only feature significantly associated with LR (P<.005). ConclusionMost CT features classically associated with LR following conventional radiation therapy are unreliable for predicting LR following SBRT.

Pulmonary Hypertension Presenting With Apnea, Cyanosis, and Failure to Thrive in a Young Child

Pulmonary Hypertension Presenting With Apnea, Cyanosis, and Failure to Thrive in a Young Child

Ovine pulmonary adenocarcinoma as an animal model of progressive lung cancer and the impact of nutritional selenium supply

Jaagsiekte sheep retrovirus (JSRV) is known to induce ovine pulmonary adenocarcinoma (OPA). Several studies have suggested an influence of selenium (Se) status on cancer progression. Thus, combining OPA with a defined Se supply might serve as a suitable animal model to study the impact of Se on lung cancer progression. 16 naturally JSRV-infected sheep were divided into 2 treatment groups receiving (a) <0.05 and (b) 0.2 mg Se/kg dry matter in diet, respectively. Computed tomography (CT) was performed repeatedly and evaluated using a CT-OPA-score system. Liver biopsies were taken three-monthly, blood samples were collected biweekly to study treatment effects on Se concentrations and glutathione peroxidase (GPx) activity. Cell pellets from bronchoalveolar lavage fluid (BALF) were tested for JSRV by PCR to approve the infection. To date, four animals of the ongoing study have been euthanised. Autopsy and histopathology were performed and correlated to CT analysis. JSRV was detected in BALF cell pellets. Progression of lung tumours was monitored successfully by repeated CT examinations, enabling the detection of even small nodules or increased lung density. Histopathology revealed bronchioloalveolar adenocarcinoma in lung areas suspicious to be OPA from CT evaluation. Score-based analysis of CT images for quantifying tumour progression proved as a valuable tool. Se concentration and GPx activity increased in liver and serum of group b and verified the efficiency of different feeding regime. In conclusion, OPA along with CT, autopsy/histopathology, trace element and enzyme activity analysis provide a suitable large animal model to examine the impact of Se supply on lung tumourigenesis.

Lungs of patients with acute respiratory distress syndrome show diffuse inflammation in normally aerated regions: A [18F]-fluoro-2-deoxy-D-glucose PET/CT study

Neutrophilic inflammation plays a key role in the pathogenesis of acute respiratory distress syndrome (ARDS) and acute lung injury (ALI). Positron emission tomography (PET) with [F]-fluoro-2-deoxy-D-glucose (FDG) can be used to image cellular metabolism that, during lung inflammatory processes, likely reflects neutrophils activity. The aim of this study was to assess the magnitude and regional distribution of inflammatory metabolic activity in the lungs of patients with ALI/ARDS by PET with FDG. Prospective clinical investigation. Ten patients with ALI/ARDS; four spontaneously breathing and two mechanically ventilated subjects, without known lung disease, served as controls. In each individual we performed an FDG PET/computed tomography of the thorax. FDG cellular influx rate constant (Ki) was computed for the imaged lung field and for regions of interest, grouping voxels with similar density. In all patients with ALI/ARDS, Ki was higher than in controls, also after accounting for the increased lung density. Ki values differed greatly among patients, but in all patients Ki of the normally aerated regions was much higher (2- to 24-fold) than in controls. Whereas in some patients the highest Ki values corresponded to regions with the lowest aeration, in others these regions had lower Ki than normally and mildly hypoaerated regions. In patients with ALI/ARDS, undergoing mechanical ventilation since days, the metabolic activity of the lungs is markedly increased across the entire lung density spectrum. The intensity of this activation and its regional distribution, however, vary widely within and between patients.