Airway Cross-section Research Articles

A Precise Pulmonary Airway Tree Segmentation Method Using Quasi-Spherical Region Constraint and Tracheal Wall Gap Sealing.

Accurate segmentation of the pulmonary airway tree is crucial for diagnosing lung diseases. To tackle the issues of low segmentation accuracy and frequent leaks in existing methods, this paper proposes a precise segmentation method using quasi-spherical region-constrained wavefront propagation with tracheal wall gap sealing. Based on the characteristic that the surface formed by seed points approximates the airway cross-section, the width of the unsegmented airway is calculated, determining the initial quasi-spherical constraint region. Using the wavefront propagation method, seed points are continuously propagated and segmented along the tracheal wall within the quasi-spherical constraint region, thus overcoming the need to determine complex segmentation directions. To seal tracheal wall gaps, a morphological closing operation is utilized to extract the characteristics of small holes and locate low-brightness tracheal wall gaps. By filling the CT values at these gaps, the method seals the tracheal wall gaps. Extensive experiments on the EXACT09 dataset demonstrate that our algorithm ranks third in segmentation completeness. Moreover, its performance in preventing airway leaks is significantly better than the top-two algorithms, effectively preventing large-scale leak-induced spread.

A Deep Attention-based U-Net for Airways Segmentation in Computed Tomography Images.

Airway segmentation is a way to quantify the diagnosis of pulmonary diseases, including chronic obstructive problems and bronchiectasis. Manual analysis by radiologists is a challenging task due to the complex airway structure. Additionally, tree-like patterns, varied shapes, sizes, and intensity make the manual airway segmentation task more complex. Deeper airways are even more difficult to segment as their intensity starts matching the lung parenchyma as the diameter of the airway cross-section gets reduced. Many earlier works have proposed different deep learning networks for airway segmentation but were unable to achieve the desired performance; hence the task of airway segmentation still possesses challenges in this field. This work proposes a convolutional neural network based on deep U-Net architecture and employs an attention block technique for airway segmentation. The attention mechanism aids in the extraction of the complicated and multi-sized airways found in the lung region, hence increasing the efficiency of the U-Net architecture. The model has been validated using VESSEL12 and EXACT09 datasets, individually and combined, with and without trachea images. The best DSC scores on EXACT09 and VESSEL12 datasets are 95.21% and 95.80%, respectively. The performance on both datasets combined gave a DSC score of 94.1%, showing that the overall performance of the proposed methodology is quite satisfactory. The generalizability of the model is also confirmed using k-fold cross-validation. The comparison of the proposed model to existing research on airway segmentation found competitive results. The use of an attention unit in the proposed model highlights the relevant information and reduces the irrelevant features, which helps to improve the performance and saves time.

Quantifying airway remodelling for research or clinical purposes: How should we normalize for airway size?

Quantifying airway remodelling for research or clinical purposes: How should we normalize for airway size?

TRANSITION AND LAMINAR FLOWS IN A REALISTIC GEOMETRY OF HUMAN UPPER AIRWAY

In this study, a realistic respiratory airway model extending from oral to the end of the trachea including all the key details of the passage was produced. A series of CT scan images were used to generate the topological data of airway cross-sections that were used to generate the computational model, as well as the three-dimensional (3D) printed model of the passage for experimental study. The airflow velocity field and pressure drop in the airway for different breathing rates of 5, 7.5, 10, and 12.5[Formula: see text]L/min were investigated numerically (by laminar and transition models) and experimentally. The velocity distributions, pressure variation, and streamlines along the oral–trachea airway model were studied. The maximum pressure drop was shown to occur in the narrowest part of the larynx region. It was also concluded that the laryngeal jet could significantly influence the airway flow patterns in the trachea. A comparison between the numerical results and experimental data showed that the transition [Formula: see text]–kl–[Formula: see text] model can give better predictions of pressure losses, especially for flow rates higher than 10[Formula: see text]L/min. The simulation results for the velocity profiles in the trachea were also compared with the available particle image velocimetry (PIV) data and earlier simulations. Despite inter-personal variability and difference in the flow regime, the qualitative agreement was found.

Threshold of the upper airway cross-section for hypopnea onset during sleep and its identification under waking condition

BackgroundThere is currently no method that can predict whether or under what condition hypopnea, even obstructive sleep apnea (OSA), will occur during sleep for individuals based on credible parameters measured under waking condition. We propose a threshold concept based on the narrowest cross-sectional area of the upper airway (CSA-UA) and aim to prove our hypothesis on the threshold of the area for hypopnea onset (TAHO), which can be used as an indicator of hypopnea onset during sleep and measured while awake.MethodsWe performed magnetic resonance imaging for 20 OSA patients to observe CSA-UA changes during fluid accumulation in the neck caused by elevating their legs, and identified TAHO by capturing the sudden enlargement in CSA-UA. Correlation analyses between TAHO and the body mass index (BMI), and between the reduction in CSA-UA and the increase in the neck circumference (NC) with fluid accumulation were performed. Logistic regression analysis was performed for identifying OSA patients based on the behaviors of their CSA-UA changes during leg raising. Shape changes of airway cross-section were also investigated.ResultsFour CSA-UA change patterns after fluid redistribution were identified. Six patients had similar CSA-UA variation behaviors observed in healthy subjects. From the other three change patterns involving 14 patients, a threshold value of CSA-UA 0.63 ± 0.21 cm2 was identified for normal breathing. Data showed a positive correlation between TAHO and BMI (r = 0.681, p = 0.0007), and a negative correlation between the reduction in CSA-UA and the increase in NC (r = − 0.513, p = 0.051) with fluid accumulation. A sigmoid function for the probability of being a OSA patient p = 1/[1 + exp. (4.836 + 3.850 t-8.4 h)] was obtained to effectively separate OSA patients from normal subjects. The upper airway narrowing occurred in anteroposterior, lateral, or both directions, suggesting different tendencies of upper airway collapse in patients. Three types of shape changes in the cross-section of the upper airway, which had different effects on airway resistance, were measured.ConclusionsOur findings prove TAHO hypothesis. The threshold measured while awake for normal breathing can be used clinically as the indicator of hypopnea onset during sleep, and therefore to identify OSA patients under waking condition and design effective personalized treatments for OSA patients. Both shape and size changes in the cross-section of the upper airway affect airway resistance significantly. Shape change in the cross-section of the upper airway can provide key clinical information on the collapse patterns of the upper airway for individuals.

Directional preference of airway smooth muscle mass increase in human asthmatic airways.

Airway smooth muscle (ASM) orientation and morphology determine the ability of the muscle to constrict the airway. In asthma, ASM mass is increased, but it is unknown whether ASM orientation and morphology are altered as well or whether the remodeling at the source of the mass increase is ongoing. We dissected human airway trees from asthmatic and control lungs. Stained, intact airway sections were imaged in axial projection to show ASM bundle orientation, whereas cross-sectional histological slides were used to assess ASM area, bundle thickness, and ASM bundle-to-basement membrane distance. We also used these slides to assess cell size, proliferation, and apoptosis. We showed that ASM mass increase in cartilaginous airways is primarily the result of an increase of ASM bundle thickness (as measured radially in an airway cross section) and coincides with an increased distance of the ASM bundles to the airway perimeter. ASM orientation was unchanged in all airways. Apoptosis markers and cell size did not show differences between asthmatics and controls. Our findings show that ASM mass increase likely contributes to the airway-constricting capacity of the muscle. Both the increased bundle thickness and increased thickness of the airway wall inwards of the ASM bundles could further enhance this capacity. Turnover of ASM appears to be the same in airways and biopsies, but the lack of correlation between different markers of proliferation casts doubt on the specificity of markers generally used to assess proliferation.

Paediatric lung isolation

### Key points Lung isolation is required for a wide variety of pathology in paediatric patients. The varying size of the paediatric airway and size limitations of each lung isolation device poses a challenge to paediatric anaesthesiologists. The need for lung isolation includes: the prevention of contamination of one lung from the other due to haemorrhage or infection, the need to control the distribution of ventilation secondary to a bronchopulmonary fistula, a lung cyst or bullae, or severe hypoxaemia from unilateral lung disease. Extensive bronchopulmonary lavage may also necessitate lung isolation. Although lung isolation can assist in surgical exposure, in the paediatric population, surgical exposure for lung resections, mediastinal exposure, and thorascopy can often be accomplished by the CO2 pneumothorax and retraction of the operative lung without the need for lung isolation. This is most common in the young patient (<2 yr of age). Slinger1 teaches that there are the ‘ABCs’ of adult lung isolation: anatomy, bronchoscopy, and chest imaging. In paediatric lung isolation, there are still all the same ‘ABC’ considerations, with the addition of ‘D’—the varying diameter of the paediatric airway with age. ### Anatomy It has been long established that there are differences between the paediatric …

Effects of maxillary protraction therapy on the pharyngeal airway in patients with repaired unilateral cleft lip and palate: A 3-dimensional computed tomographic study.

The purposes of this study were to assess the effects of maxillary protraction therapy on the pharyngeal airways in patients with repaired unilateral cleft lip and palate (UCLP) 3 dimensionally. Eighteen patients with repaired UCLP and anterior crossbite (ages, 10.4±1.3years) were enrolled in the study group. Hyrax appliances and reverse headgears were used. Cone-beam computed tomography volume scans were taken before and immediately after treatment. Fourteen patients (ages, 9.6±1.7years) with UCLP who did not receive orthopedic treatment served as the control group. The volumes of the pharyngeal airways, cross-sectional areas, sagittal diameters, and transversal diameters of 3 levels of airway cross-section were measured. After protraction, the volumes of the pharyngeal airway increased significantly. Cross-sectional area, sagittal diameter, and transversal diameter of the upper and lower pharyngeal airways also had significant increases. These changes were significant when compared with the untreated subjects except for the transversal diameter of the lower pharyngeal airway. Dimensions of the middle pharyngeal airway remained unchanged. Maxillary protraction therapy significantly affects airway dimensions in patients with repaired UCLP 3 dimensionally.

Upper Airway Changes after Orthodontic Extraction Treatment in Adults: A Preliminary Study using Cone Beam Computed Tomography

ObjectiveWhether the orthodontic treatment with premolar extraction and maximum anchorage in adults will lead to a narrowed upper airway remains under debated. The study aims to investigate the airway changes after orthodontic extraction treatment in adult patients with Class II and hyperdivergent skeletal malocclusion.Materials and MethodsThis retrospective study enrolled 18 adults with Class II and hyperdivergent skeletal malocclusion (5 males and 13 females, 24.1 ± 3.8 years of age, BMI 20.33 ± 1.77 kg/m2). And 18 untreated controls were matched 1:1 with the treated patients for age, sex, BMI, and skeletal pattern. CBCT images before and after treatment were obtained. DOLPHIN 11.7 software was used to reconstruct and measure the airway size, hyoid position, and craniofacial structures. Changes in the airway and craniofacial parameters from pre to post treatment were assessed by Wilcoxon signed rank test. Mann-Whitney U test was used in comparisons of the airway parameters between the treated patients and the untreated controls. Significant level was set at 0.05.ResultsThe upper and lower incisors retracted 7.87 mm and 6.10 mm based on the measurement of U1-VRL and L1-VRL (P < 0.01), while the positions of the upper and lower molars (U6-VRL, and L6-VRL) remained stable. Volume, height, and cross-sectional area of the airway were not significantly changed after treatment, while the sagittal dimensions of SPP-SPPW, U-MPW, PAS, and V-LPW were significantly decreased (P < 0.05), and the morphology of the cross sections passing through SPP-SPPW, U-MPW, PAS, and V-LPW became anteroposteriorly compressed (P <0.001). No significant differences in the airway volume, height, and cross-sectional area were found between the treated patients and untreated controls.ConclusionsThe airway changes after orthodontic treatment with premolar extraction and maximum anchorage in adults are mainly morphological changes with anteroposterior dimension compressed in airway cross sections, rather than a decrease in size.

Simulation study about the accuracy of advanced airway geometry determination on MDCT using a computer-generated phantom

We developed a computer-generated phantom simulating cross sections of airways with different inner diameters (1.2 – 18.0 mm) and wall thicknesses (0.3 – 1.5 mm) for the examination of the accuracy of our input parameter-free integral-based method (IBMpf) for airway geometry determination.

On the Role of Mechanics in Chronic Lung Disease.

Progressive airflow obstruction is a classical hallmark of chronic lung disease, affecting more than one fourth of the adult population. As the disease progresses, the inner layer of the airway wall grows, folds inwards, and narrows the lumen. The critical failure conditions for airway folding have been studied intensely for idealized circular cross-sections. However, the role of airway branching during this process is unknown. Here, we show that the geometry of the bronchial tree plays a crucial role in chronic airway obstruction and that critical failure conditions vary significantly along a branching airway segment. We perform systematic parametric studies for varying airway cross-sections using a computational model for mucosal thickening based on the theory of finite growth. Our simulations indicate that smaller airways are at a higher risk of narrowing than larger airways and that regions away from a branch narrow more drastically than regions close to a branch. These results agree with clinical observations and could help explain the underlying mechanisms of progressive airway obstruction. Understanding growth-induced instabilities in constrained geometries has immediate biomedical applications beyond asthma and chronic bronchitis in the diagnostics and treatment of chronic gastritis, obstructive sleep apnea and breast cancer.

Differences in the pattern of bronchoconstriction induced by intravenous and inhaled methacholine in rabbit

We measured bronchoconstriction in central bronchi, and in small peripheral airways causing the emergence of ventilation defects (VD), through two delivery routes: intravenous (IV) and inhaled MCh, in 2 groups of rabbits (A: n=5; B: n=4), using synchrotron imaging of regional lung structure and ventilation. We assessed the effect an initial IV challenge on a subsequent inhaled challenge in group B. Inhaled MCh decreased central airway cross-sections (CA) by 13–22%, but increased VD area by 25–49%. IV MCh decreased CA by 44% but increased the area of ventilation defects (VD) by 13% only. An initial IV MCh challenge reduced regional ventilation heterogeneity following a subsequent inhaled MCh challenge, suggesting the role of agonist–receptor interaction in the response pattern. Heterogeneous agonist distribution due to uneven aerosol deposition could explain the different patterns of response between IV and inhaled routes. This mechanism could participate in the emergence of ventilation heterogeneities during bronchial challenge, or exposure to allergen in asthmatic patients.

Airway Dimensions in Asthma and COPD in High Resolution Computed Tomography: Can We See the Difference?

Airway remodeling in asthma and COPD results in bronchial wall thickening. The thickness of the bronchial wall can be measured in high-resolution computed tomography. The objectives of the study were to assess the bronchial lumen and wall dimensions in asthma and COPD patients, in relation to disease severity, and to compare the airway dimensions in patients with asthma and COPD. Ten asthma subjects and 12 COPD subjects with stable, mild to moderate disease were investigated. All subjects underwent chest high-resolution computed tomography (window level - 450 Hounsfield units, window width 1,500 Hounsfield units). Cross-sections of bronchi (external diameter 1.0-5.0 mm) were identified on enlarged images. The following variables were measured: external and internal diameter, wall area, lumen area, total airway area, the percentage of airway wall area, wall thickness, and the ratio of wall thickness to external diameter. Separate sub-analyses were performed for airways with external diameter ≤ 2.0 mm and external diameter > 2.0 mm. We measured 261 and 348 cross-sections of small airways in subjects with asthma and COPD, respectively. There was a significant difference in wall thickness and wall area, which were both greater in asthmatics than in COPD patients. In bronchi with external diameter > 2.0 mm, all measured parameters were significantly higher in asthma than COPD. In individual asthmatics the airway wall thickness was similar in all the assessed bronchi, while in COPD it was related to the external airway diameter. Our results indicate that bronchial walls are thicker in asthmatics than in patients with COPD. It seems that airway wall thickness and the lumen diameter in patients with asthma are related to disease severity. There is no such a relationship in COPD patients. High-resolution computed tomography may be a useful tool in the assessment of airway structure in obstructive lung disease.

Measurements of normal nasal airway assessed by 3-dimensional computed tomography in Chinese children and adolescents

ObjectiveTo establish normative data of nasal airway dimensions in Chinese children and adolescents by age and sex. MethodsCT images of 281 Chinese children and adolescents (140 girls and 141 boys) aged from 6 to 18 years (yr) were selected among the patients who visited in Shanghai Ninth People's Hospital from September 2009 to August 2010. Subjects were divided into four age groups as group 1 (6–9yr), group 2 (10–12yr), group 3 (13–15yr), and group 4 (16–18yr). Child was defined as 6–12yr, and adolescent as 13–18yr. Nasal parameters were as follow: nasal volume (NV), length of nasal airway (NL), minimal cross-section area (CSA 1) and its location (D 1), inferior turbinate head's location (D 2) and its airway cross-section area (CSA 2), and cross-sectional area of choanal (CSA 3). ResultsThere was no significant sex dimorphism in nasal parameters in children (group 1 and group 2). In adolescents, male's nasal dimension were larger than female's. CSA 1, D 1, CSA 2, CSA 3, NL and NV correlated with age in male and female respectively. ConclusionsVolume, length and cross-section area of nasal airway were correlated with age in Chinese children and adolescents aged from 6 to 18yr. In children, nasal conformations of male and female are similar. In adolescents, sex dimorphisms in nasal parameters were significant.

Anästhesiologische Besonderheiten bei der laryngotrachealen Chirurgie

During surgical procedures of the upper respiratory tract anesthesiologists and surgeons are in a kind of competition situation because of the close spatial relationship between the airway of the patient and the surgical area. Especially in laryngeal surgery the use of high-frequency jet ventilation (HFJV) offers an alternative to the endotracheal tube. During HFJV the ventilation gas is intermittently administered by an injector with a high frequency into the airway which is open to the outside. Exhalation occurs passively in the area nearby the wall of the airway cross-section. According to the availability of the technique and the indications jet ventilation can be implemented in an infraglottic, supraglottic, transtracheal or transluminal manner. To exert influence on gas exchange of the patient the respiratory rate, driving pressure, oxygen concentration and inspiration time can be changed according to the needs. Severe tracheal stenosis, risk of excessive bleeding during the procedure, patients at risk for aspiration and exacerbation of lung diseases are depicted as contraindications for HFJV. Complications under HFJV are rare despite the limited conditions for monitoring gas exchange and mechanics of ventilation in contrast to conventional ventilation. A particular challenge for the anesthesiologist is the use of HFJV during laryngeal laser surgery.

Design, Development, and Analysis of a Surrogate for Pulmonary Injury Prediction

Current anthropomorphic test devices (ATDs) measure chest acceleration and deflection to assess risk of injury to the thorax. This study presents a lung surrogate prototype designed to expand the injury assessment capabilities of ATDs to include a risk measure for pulmonary contusion (PC). The surrogate augments these existing measures by providing pressure data specific to the lung and its lobes. The prototype was created from a rendering of a 50th percentile male lung inflated to normal inspiration, obtained from clinical CT data. Surrogate size, lobe volume, and airway cross sections were selected to match the morphology of the lung. Elastomeric urethane was molded via rapid prototyping to create a functional prototype. Pressure sensors in each of the five terminal airways independently monitored pressure traces in the lobes during impacts to the surrogate. Software was created to analyze the surrogate impact pressure data, determine the lobe with the greatest pressure rise for a particular impact, and estimate the initial speed of surface deformation. Calibration testing indicates an approximately linear relationship between peak lobe pressure and surface impact speed. No type I or II errors were demonstrated during lobe detection testing. During repeatability testing, the standard deviation was between 2 and 4% of the mean peak pressure. Ongoing research will focus on correlating surrogate data, pressure pulses, or surface deformation, to risk functions for PC.

Bubble transitions in strongly collapsed elastic tubes

The selection of long air bubbles propagating steadily in a strongly collapsed fluid-filled elastic tube is investigated experimentally in a benchtop model of airway reopening. Localized regions of strong collapse are likely in the lung, because collapsing fluid-elastic instabilities promote extensive deformation of the airway cross-section beyond the point of opposite wall contact. We find that radical changes in the reopening mechanics occur at this point. We build on the recent identification by Heap &amp; Juel (Phys. Fluids, vol. 20, 2008, article no. 081702) of three different steadily propagating bubbles (asymmetric, double-tipped and pointed) that are selected successively for increasing values of the capillary number (Ca, ratio of viscous to surface tension forces) in tubes initially collapsed beyond the point of opposite wall contact. The asymmetric bubble is also observed in less collapsed tubes for small values of Ca, and we show that it bifurcates super-critically from the usual parabolic-tipped bubble as Ca increases. We also characterize the mechanisms underlying the discontinuous transitions between asymmetric and double-tipped bubbles, and double-tipped and pointed bubbles. In particular, we find that the tube must reopen to a critical height for double-tipped bubbles to be selected. The length of the precursor fingers in the double-tipped bubble decreases with Ca, and the bubble loses stability to pointed bubbles when this length is less than the height of the tube at the point where the fingers merge. By contrast with the asymmetric and double-tipped bubbles, the pointed bubble infiltrates the most collapsed part of the tube to yield the rapid reopening of the airway at low pressure, with the potential to reduce ventilation-induced lung damage.

CT comparison of primary snoring and obstructive sleep apnea syndrome: role of pharyngeal narrowing ratio and soft palate-tongue contact in awake patient

Soft palate-tongue contact and automatically calculated pharyngeal narrowing ratio (PNR), defined as a ratio between the airway cross-section at the hard palate level and the narrowest cross-section from the hard palate to the epiglottis, could assist in earlier identification of potential obstructive sleep apnea syndrome (OSA) patients even on awake individuals. Parameters were studied on carotid CTA images from 67 consecutively included awake Caucasians who were later classified by second independent physician into the primary snorers (SNORE, n = 34) or obstructive sleep apnea syndrome patient (OSA, n = 33) group according to the clinical examination, laboratory testing and a full-night video polysomnography (PSG) in the sleep laboratory. Imaging and clinical data were statistically compared between groups. The odd's ratio calculation showed a 2.95 (P = 0.0354) higher risk for OSA development in snoring person with a PNR greater than 8.6. The loose-contact subgroup among OSA patients showed significantly (P = 0.002) higher values of AHI in contrast to the in-contact subgroup.

Correlation between retroglossal airway size and body mass index in OSA and non-OSA patients using cone beam CT imaging

Most obstructive sleep apnea (OSA) patients are overweight, and OSA is substantially more common in obese individuals. In morbidly obese patients, at least 70% suffer from OSA. However, the exact mechanism by which obesity causes OSA is unclear. The aim of this study is to evaluate the retroglossal airway configuration quantitatively and to make clear the relationship between Body mass index (BMI) and airway configuration. This retrospective study included 15 OSA patients (male = 11; female = 4) and 14 normal controls (male = 8; female = 6). We studied the airway configuration on an axial slice at the level of the anterior-inferior corner of the second cervical vertebra. Maximum anterior-posterior diameter (AP) and lateral width (LW) of the airway were measured, and the square area (SA) was calculated. The airway cross-section area (AWA) was also measured, and then the AWA/SA ratio was calculated. AP, LW, and AWA were not statistically significantly different between controls and OSA patients. On the other hand, the AWA/SA ratio in OSA patients was 8.8% statistically significantly smaller than in controls after adjusting for sex, age, and BMI. In this sample, there was a negative correlation between age and the AWA/SA ratio but only in the OSA group. The AWA/SA ratio was significantly negatively correlated with OSA status (R = -0.5; p = 0.008) after adjusting for BMI and age. In this present study, we could evaluate the retroglossal airway configuration quantitatively. The AWA/SA ratio was correlated with OSA status after adjusting for BMI and age.

Upper airway segmentation and dimensions estimation from cone-beam CT image datasets

Objective To segment and measure the upper airway using cone-beam computed tomography (CBCT). This information may be useful as an imaging biomarker in the diagnostic assessment of patients with obstructive sleep apnea and in the planning of any necessary therapy. Methods With Institutional Review Board Approval, anonymous CBCT datasets from subjects who had been imaged for a variety of conditions unrelated to the airway were evaluated. DICOM images were available. A segmentation algorithm was developed to separate the bounded upper airway and measurements were performed manually to determine the smallest cross-sectional area and the anteriorposterior distance of the retropalatal space (RP-SCA and RP-AP, respectively) and retroglossal space (RG-SCA and RG-AP, respectively). A segmentation algorithm was developed to separate the bounded upper airway and it was applied to determine RP-AP, RG-AP, the smallest transaxial-sectional area (TSCA) and largest sagittal view airway area (LCSA). A second algorithm was created to evaluate the airway volume within this bounded upper airway. Results Measurements of the airway segmented automatically by the developed algorithm agreed with those obtained using manual segmentation. The corresponding volumes showed only very small differences considered clinically insignificant. Conclusion Automatic segmentation of the airway imaged using CBCT is feasible and this method can be used to evaluate airway cross-section and volume comparable to measurements extracted using manual segmentation.