Three-dimensional visual truth of the normal airway tree for use as a quantitative comparison to micro-CT reconstructions

Abstract

Mouse models are important for pulmonary research to gain insight into structure and function in normal and diseased states, thereby extending knowledge of human disease conditions. The flexibility of human disease induction into mice, due to their similar genome, along with their short gestation cycle makes mouse models highly suitable as investigative tools. Advancements in non-invasive imaging technology, with the development of microcomputed tomography (µ-CT), have aided representation of disease states in these small pulmonary system models. The generation of µ-CT 3D airway reconstructions has to date provided a means to examine structural changes associated with disease. The degree of accuracy of µ-CT is uncertain. Consequently, the reliability of quantitative measurements is questionable. We have developed a method of sectioning and imaging the whole mouse lung using the Large Image Microscope Array (LIMA) as the gold standard for comparison. Fixed normal mouse lungs were embedded in agarose and 250µm sections of tissue were removed while the remaining tissue block was imaged with a stereomicroscope. A complete dataset of the mouse lung was acquired in this fashion. Following planar image registration, the airways were manually segmented using an in-house built software program PASS. Amira was then used render the 3D isosurface from the segmentations. The resulting 3D model of the normal mouse airway tree developed from pathology images was then quantitatively assessed and used as the standard to compare the accuracy of structural measurements obtained from µ-CT.

Comparison of Manual and Automated Measurements of Tracheobronchial Airway Geometry in Three Balb/c Mice

“…Previous studies with mice have reported measurements by generation, noted the monopodial structure as opposed to the symmetric dichotomous structure of human lungs, and considered implications to dosimetry and particle deposition (Oldham and Phalen, ; Oldham and Robinson, ; Madl et al, ; Moss and Oldham, ; Winkler‐Heil and Hofmann, ). Studies have also discussed the use of micro‐CT imaging in analyzing mouse airway structure (Thiesse et al, ; Thiesse et al, ). Other methods, such as photographic processing (Onuma et al, ) and MRI (Einstein et al, ; Oakes et al, ), have also been used on lung tissue and lung casts to extract geometry.…”

Large Image Microscope Array for the Compilation of Multimodality Whole Organ Image Databases

“…The LIMA system has also been used to acquire the first 3D pathology representations of the entire mouse at 250‐μm slice increments (Fig. 9; Thiesse et al, 2005, 2007). The 3D reconstruction of the LIMA stacks in Figure 9 have jarred edges between slices, which is due to the nonisotropic nature of the voxels, that is, higher resolution in the x ‐ and y ‐axes as compared with the z ‐axis.…”

“…The agarose is made from standard biological grade agarose, mixed with distilled water, and heated in a microwave on high for 20 sec. The agarose is allowed to cool down to 10 degrees above the gelling temperature and then poured into a custom container that houses the mouse lung in the correct orientation with respect to the ex vivo micro‐CT scan (Thiesse et al, 2005). The container is then placed in a refrigerator where the agarose is allowed to gel and cool for a further 6 hr.…”

3D Airway Reconstruction Using Visible Human Data Set and Human Casts with Comparison to Morphometric Data

“…Using a two step process that included staining the lung tissue with a radiopaque solution and imaging with a microfocal X‐ray CT, rat airways as small as 150 μm were resolved and an airway model through generations 8–16 was constructed (Sera et al,2003). One study compared 3D reconstruction methods on the first three generations of a fixed excised mouse lung, using μ‐CT and fixed slices, and reported a 3% difference at the trachea and 15% difference at the third generation (Thiesse et al,2005). A model of a pulmonary artery and vein were reconstructed using the cryosection color images from the National Institute of Health (NIH) Visible Human male data set.…”