Stereology as the 3D tool to quantitate lung architecture

Comparative Histological Analysis of the Parotid and Submandibular Glands in Ovine and Caprine Species Using Histochemical, Immunohistochemical, and Stereological Methods

This work was designed to compare the histochemical, immunohistochemical, and stereological features of the parotid and mandibular glands of sheep and goat as representative for ovine and caprine species. The parotid gland was serous in both species, while the mandibular gland was a mixed one. Mucous acini were Periodic Acid-Schiff positive and Aldehyde Fuchsin (AF) negative. Serous acini were AF positive. The parotid gland of goat was significantly larger than that of sheep; however, the mandibular gland of sheep was significantly larger than that of goat. The volume of isolated serous acini in the mandibular gland of goat was significantly higher than that of sheep. The total length of ductal system was nonsignificant in both species, but the total volume of parotid glands' ducts was significantly higher than those of mandibular glands. The parotid glands were negative for Mucin-1; however, the mandibular glands were moderately positive. Cytokeratin 7 exhibited a pronounced expression within the ductal systems of both glands. S100 proteins were expressed intensely by serous acini of glands in sheep; however, its expression was confined to the intercalated ducts and myoepithelial cells in goat. The obtained results suggest that the feeding modalities may lead to significant variations in histological and histophysiological characteristics.

Morphological and molecular aspects of lung development

Healthy breathing relies on normal morphological and functional development of the lung. This includes different prenatal and postnatal developmental stages. Depending on species and postnatal behavior as nest escapers or nest squatters, the duration of individual developmental phases and the state of differentiation of the lungs at birth differ. However, the sequence and morphology of the lung developmental stages are similar in all mammals, so knowledge gained from animal models about development-specific genetic control and regulatory mechanisms can be translated in principle to the human lung. Functional lung development comprises the maturation of the surfactant system, which is closely linked to the morphological development of the pulmonary acini. Although a number of reviews are found in the literature, a presentation that integrates the morphological and molecular regulatory mechanisms is missing. Therefore, the aim of this article was to provide an up-to-date comprehensive review of the main morphological steps and regulatory mechanisms of lung development, including clinical aspects related to developmental disorders.

Automated Euler number of the alveolar capillary network based on deep learning segmentation with verification by stereological methods

Diseases like bronchopulmonary dysplasia (BPD) affect the development of the pulmonary vasculature, including the alveolar capillary network (ACN). Since pulmonary development is highly dependent on angiogenesis and microvascular maturation, ACN investigations are essential. Therefore, efficient methods are needed for quantitative comparative studies. Here, the suitability of deep learning (DL) for processing serial block-face scanning electron microscopic (SBF-SEM) data by generating ACN segmentations, 3D reconstructions and performing automated quantitative analyses based on them, was tested. Since previous studies revealed inefficient ACN segmentation as the limiting factor in the overall workflow, a 2D DL-based approach was used with existing data, aiming at the reduction of necessary manual interaction. Automated quantitative analyses based on completed segmentations were performed subsequently. The results were compared to stereological estimations, assessing segmentation quality and result reliability. It was shown that the DL-based approach was suitable for generating segmentations on SBF-SEM data. This approach generated more complete initial ACN segmentations than an established method, despite the limited amount of available training data and the use of a 2D rather than a 3D approach. The quality of the completed ACN segmentations was assessed as sufficient. Furthermore, quantitative analyses delivered reliable results about the ACN architecture, automatically obtained contrary to manual stereological approaches. This study demonstrated that ACN segmentation is still the part of the overall workflow that requires improvement regarding the reduction of manual interaction to benefit from available automated software tools. Nevertheless, the results indicated that it could be advantageous taking further efforts to implement a 3D DL-based segmentation approach. As the amount of analysed data was limited, this study was not conducted to obtain representative data about BPD-induced ACN alterations, but to highlight next steps towards a fully automated segmentation and evaluation workflow, enabling larger sample sizes and representative studies.

Distribution and volume of mitochondria in alveolar epithelial type 1 cells in infant and adult human lungs

Alveolar epithelial type I (AE1) cells with their wide spatial expansion form approximately 95% of the outer surface area of the air-blood barrier inside the lung. Serial block-face scanning electron microscopy (SBF-SEM) investigations led to the hypothesis that AE1 cell mitochondria are preferentially distributed as aggregates in those parts of AE1 cells that are located above connective tissue pillars between capillaries, thus not increasing the thickness of the diffusion distance for oxygen and carbon dioxide. Furthermore, it was hypothesised that postnatal development requires adapting the amount and distribution of mitochondria in AE1 cells. Human lung samples from three infant (26 and 30 days, 6 months) and three adult (20, 39 and 40 years) samples were investigated by light microscopy, transmission electron microscopy and stereology. The volume fraction of mitochondria was similar in infant and adult lungs with a mean value of 6.3%. The ratio between mitochondrial profiles on top of capillaries or above connective tissue pillars was approximately 3:1 in infants and adults. However, regarding the volume of both cytoplasmic compartments, infants showed a higher number of mitochondrial profiles on top of capillaries while adults showed a higher number above connective tissue pillars. Samples of three additional adult lungs were analysed by confocal laser scanning microscopy. Again, mitochondria were not preferentially found as aggregates above connective tissue pillars. In conclusion, AE1 cell mitochondria were not preferentially found as aggregates, showed the same volume density in infants and adults but differed in distribution between the age groups.

Three-dimensional morphometry of kidney in New Zealand rabbit using unbiased design-based stereology

The rabbit is widely used as a laboratory animal in experimental models of kidney diseases. This species is also important from a veterinary perspective as a companion animal. Stereology has been accepted as an accurate approach to kidney morphometry. The objective of the present project was to provide normal quantitative stereological parameters for adult rabbit kidneys. The left kidneys of five adult male New Zealand rabbits were used. Isotropic sections were obtained using the orientation method. Total kidney volume was calculated by the Cavalieri principle. The volume fraction of the renal structures was estimated using the point counting system. The lengths of the proximal convoluted tubule (PCT) and distal convoluted tubule (DCT) were calculated using counting frames. The total glomerular number was accounted for using the physical/fractionator technique. The mean glomerular volume was obtained by dividing the total volume of glomeruli by their total number. The total volume of rabbit kidneys calculated was 10.39 ± 1.98 cm3. The fractional volume of the kidney cortex and medulla accounted for 57.79 ± 0.65% and 42.2 ± 0.65%, respectively. The total glomerular volume was 2.18 ± 0.32% of the whole kidney. The total number of glomeruli in the rabbit kidney was estimated as 204.68 ± 12 × 103. The mean glomerular volume measured 1.07 ± 0.12 × 106 μm3. The total length of PCT and DCT was 2.96 ± 0.29 km and 1.38 ± 0.24 km, respectively. These findings can be used as a reference in experimental nephrology research and may help to expand the knowledge of nephrology in mammals by comparing with available data on humans and other species. RESEARCH HIGHLIGHTS: Three-dimensional morphometry of adult rabbit kidney structures was analyzed using quantitative stereology. Total volume of kidney, fractional volume of cortex and medulla, length of renal tubules and number of nephrons were estimated. These three-dimensional morphometrical data can be used as a reference in experimental nephrology research and may help to expand the knowledge of nephrology in mammals.

Three-dimensional morphometry of the testis in dog using design-unbiased stereology

Testis is considered the main organ of the male reproductive system. Dogs are used as a suitable experimental model of testicular diseases in humans. From the veterinary aspect, several disorders have been reported to affect the testis in dogs. Thus, the objective of the present study was to investigate the morphometrical features of the dog testis using design-based stereology. The testes of six male dogs were used. Isotropic, uniform random sections were obtained and processed for light microscopy. Testicular total volume and the fractional volume of the seminiferous tubules, interstitial tissue and germinal epithelium were measured using the Cavalieri's estimator and the point counting system. Germinal epithelial surface area was estimated using test lines, and total length of seminiferous tubules was analysed using the counting frames. The total volume of testis was calculated 13.64 ± 1.94 cm3 . The relative volume fractions of the seminiferous tubules, interstitial tissue and germinal layer expressed as a percentage of total testicular volume were found to be 75.87 ± 6.11%, 23.68 ± 5.15% and 64.15 ± 4.82%, respectively. The surface area of the germinal layer was 915.25 ± 150.48 cm2 . The thickness of germinal layer was estimated to be 96.18 ± 10.72 μm. The total length of seminiferous tubules measured 290.8 ± 35.86 m. No statistical difference in investigated parameters was found between the left and right testes (p > 0.05). Our data might contribute to the male reproductive knowledge, help develop experimental studies in this field and possibly lead to advancement in the diagnosis and treatment of testicular diseases in the dog.

Analysis of pulmonary artery variation based on 3D reconstruction of CT angiography

Objective: The aim of this study is to acquire pulmonary CT (Computed tomography) angiographic data for the purpose of creating a three-dimensional reconstruction. Additionally, we aim to analyze the features and deviations of the branches in both pulmonary lobes. This information is intended to serve as a more comprehensive and detailed reference for medical professionals when conducting preoperative evaluations and devising surgical plans. Method: Between August 2019 and December 2021, 420 patients were selected from the thoracic surgery department at the First Hospital of Jilin University, and underwent pulmonary 64 channel contrast enhanced CT examinations (Philips ICT 256). The images were acquired at a 1.5 mm slice thickness, and the DCM files that complied with DICOM (Digital Imaging and Communications in Medicine) standards were analysed for 3D (three dimensional) reconstruction using Mimics 22.0 software. The reconstructed pulmonary artery models were assessed by attending chest surgeons and radiologists with over 10 years of clinical experience. The two-dimensional image planes, as well as the coronary and sagittal planes, were utilized to evaluate the arteries. The study analyzed the characteristics and variations of the branches and courses of pulmonary arteries in each lobe of the lungs, with the exception of the subsegmental arterial system. Two chest surgeons and two radiologists with professional titles-all of whom had over a decade of clinical experience-jointly evaluated the 3D models of the pulmonary artery and similarly assessed the characteristics and variations of the branches and courses in each lobe of the lungs. Results: Significant variations were observed in the left superior pulmonary artery across the 420 subjects studied. In the left upper lobe, the blood supply of 4 arteries accounted for 50.5% (n = 212), while the blood supply of 2 arteries in the left lower lobe was the most common, accounting for 79.5% (n = 334). The greatest variation in the right pulmonary artery was observed in the branch supply of the right upper lobe mediastinal artery. In the majority of cases (77.9%), there were two arteries present, which was the most common configuration observed accounting for 64% (n = 269). In the right inferior lobe of the lung, there were typically 2-4 arteries, with 2 arteries being the most common configuration (observed in 79% of cases, n = 332). Conclusion: The three-dimensional reconstruction of pulmonary artery CT angiography enables clear observation of the branches and distribution of the pulmonary artery while also highlighting any variations. This technique holds significant clinical value for preoperative assessments regarding lesions and blood vessels.

Acinar micromechanics in health and lung injury: what we have learned from quantitative morphology

Within the pulmonary acini ventilation and blood perfusion are brought together on a huge surface area separated by a very thin blood-gas barrier of tissue components to allow efficient gas exchange. During ventilation pulmonary acini are cyclically subjected to deformations which become manifest in changes of the dimensions of both alveolar and ductal airspaces as well as the interalveolar septa, composed of a dense capillary network and the delicate tissue layer forming the blood-gas barrier. These ventilation-related changes are referred to as micromechanics. In lung diseases, abnormalities in acinar micromechanics can be linked with injurious stresses and strains acting on the blood-gas barrier. The mechanisms by which interalveolar septa and the blood-gas barrier adapt to an increase in alveolar volume have been suggested to include unfolding, stretching, or changes in shape other than stretching and unfolding. Folding results in the formation of pleats in which alveolar epithelium is not exposed to air and parts of the blood-gas barrier are folded on each other. The opening of a collapsed alveolus (recruitment) can be considered as an extreme variant of septal wall unfolding. Alveolar recruitment can be detected with imaging techniques which achieve light microscopic resolution. Unfolding of pleats and stretching of the blood-gas barrier, however, require electron microscopic resolution to identify the basement membrane. While stretching results in an increase of the area of the basement membrane, unfolding of pleats and shape changes do not. Real time visualization of these processes, however, is currently not possible. In this review we provide an overview of septal wall micromechanics with focus on unfolding/folding as well as stretching. At the same time we provide a state-of-the-art design-based stereology methodology to quantify microarchitecture of alveoli and interalveolar septa based on different imaging techniques and design-based stereology.

A short primer on lung stereology

The intention of this short primer is to raise your appetite for proper quantitative assessment of lung micro-structure. The method of choice for obtaining such data is stereology. Rooted in stochastic geometry, stereology provides simple and efficient tools to obtain quantitative three-dimensional information based on measurements on nearly two-dimensional microscopic sections. In this primer, the basic concepts of stereology and its application to the lung are introduced step by step along the workflow of a stereological study. The integration of stereology in your laboratory work will help to improve its quality. In a broader context, stereology may also be seen as a contribution to good scientific practice.

Using virtual microscopy for the development of sampling strategies in quantitative histology and design-based stereology

Only a fraction of specimens under study are usually selected for quantification in histology. Multilevel sampling or tissue probes, slides and fields of view (FOVs) in the regions of interest (ROIs) are required. In general, all parts of the organs under study should be given the same probability to be taken into account; that is, the sampling should be unbiased on all levels. The objective of our study was to provide an overview of the use of virtual microscopy in the context of developing sampling strategies of FOVs for stereological quantification. We elaborated this idea on 18 examples from multiple fields of histology, including quantification of extracellular matrix and muscle tissue, quantification of organ and tumour microvessels and tumour-infiltrating lymphocytes, assessing osseointegration of bone implants, healing of intestine anastomoses and osteochondral defects, counting brain neurons, counting nuclei in vitro cell cultures and others. We provided practical implications for the most common situations, such as exhaustive sampling of ROIs, sampling ROIs of different sizes, sampling the same ROIs for multiple histological methods, sampling more ROIs with variable intensities or using various objectives, multistage sampling and virtual sampling. Recommendations were provided for pilot studies on systematic uniform random sampling of FOVs as a part of optimizing the efficiency of histological quantification to prevent over- or undersampling. We critically discussed the pros and cons of using virtual sections for sampling FOVs from whole scanned sections. Our review demonstrated that whole slide scans of histological sections facilitate the design of sampling strategies for quantitative histology.

Small Airway Reduction and Fibrosis is an Early Pathologic Feature of Idiopathic Pulmonary Fibrosis

RATIONALE

To improve disease outcomes in idiopathic pulmonary fibrosis (IPF) it is essential to understand its early pathophysiology so that it can be targeted therapeutically.

OBJECTIVES

Perform three-dimensional (3D) assessment of the IPF lung micro-structure using stereology and multi-resolution computed tomography (CT) imaging.

METHODS

Explanted lungs from IPF patients (n=8) and donor controls (n=8) were inflated with air and frozen. CT scans were used to assess large airways. Unbiased, systematic uniform random (SUR) samples (n=8/lung) were scanned with microCT for stereological assessment of small airways (number, airway wall and lumen area) and parenchymal fibrosis (volume fraction of tissue, alveolar surface area, and septal wall thickness).

RESULTS

The total number of airways on clinical CT was greater in IPF lungs than control lungs (p<0.01), due to an increase in the wall (p<0.05) and lumen area (p<0.05) resulting in more visible airways with a lumen larger than 2 mm. In IPF tissue samples without microscopic fibrosis, assessed by the volume fraction of tissue using microCT, there was a reduction in the number of the terminal (p<0.01) and transitional (p<0.001) bronchioles, and an increase in terminal bronchiole wall area (p<0.001) compared to control lungs. In IPF tissue samples with microscopic parenchymal fibrosis, terminal bronchioles had increased airway wall thickness (p<0.05), and dilated airway lumens (p<0.001) leading to honeycomb cyst formations.

CONCLUSION

This study has important implications for the current thinking on how the lung tissue is remodeled in IPF, and highlights small airways as a potential target to modify IPF outcomes.

Stereology and three-dimensional reconstructions to analyze the pulmonary vasculature

The pulmonary vasculature consists of a large arterial and venous tree with a vast alveolar capillary network (ACN) in between. Both conducting blood vessels and the gas-exchanging capillaries are part of important human lung diseases, including bronchopulmonary dysplasia, pulmonary hypertension and chronic obstructive pulmonary disease. Morphological tools to investigate the different parts of the pulmonary vasculature quantitatively and in three dimensions are crucial for a better understanding of the contribution of the blood vessels to the pathophysiology and effects of lung diseases. In recent years, new stereological methods and imaging techniques have expanded the analytical tool box and therefore the conclusive power of morphological analyses of the pulmonary vasculature. Three of these developments are presented and discussed in this review article, namely (1) stereological quantification of the number of capillary loops, (2) serial block-face scanning electron microscopy of the ACN and (3) labeling of branching generations in light microscopic sections based on arterial tree segmentations of micro-computed tomography data sets of whole lungs. The implementation of these approaches in research work requires expertise in lung preparation, multimodal imaging at different scales, an advanced IT infrastructure and expertise in image analysis. However, they are expected to provide important data that cannot be obtained by previously existing methodology.

Nanoparticle delivery system, highly active antiretroviral therapy, and testicular morphology: The role of stereology

The conjugation of nanoparticles (NPs) with antiretroviral drugs is a drug delivery approach with great potential for managing HIV infections. Despite their promise, recent studies have highlighted the toxic effects of nanoparticles on testicular tissue and their impact on sperm morphology. This review explores the role of stereological techniques in assessing the testicular morphology in highly active antiretroviral therapy (HAART) when a nanoparticle drug delivery system is used. Also, NPs penetration and pharmacokinetics concerning the testicular tissue and blood-testis barrier form the vital part of this review. More so, various classes of NPs employed in biomedical and clinical research to deliver antiretroviral drugs were thoroughly discussed. In addition, considerations for minimizing nanoparticle-drugs toxicity, ensuring enhanced permeability of nanoparticles, maximizing drug efficacy, ensuring adequate bioavailability, and formulation of HAART-NPs fabrication are well discussed.