Tag Archives: microtomography

Brian Metscher

Following bachelor’s work in applied physics at Caltech and a first career as a research engineer at NASA/JPL, Brian Metscher completed his PhD in the then-new interdiscipline of evo-devo at the University of California, Irvine. He did postdoctoral research on the development and evolution of appendages and teeth at The Natural History Museum (London) and Penn State University, and then served five years as an Assistant Professor in southern Indiana. During the summers he carried out research at Yale University and came to the University of Vienna in 2006, to set up the imaging lab in the Department of Theoretical Biology, where he is now Senior Scientist. He helped to establish X-ray microtomography as an essential method for imaging ex vivo biological samples, especially embryos and invertebrates. His lab is developing new and refined sample preparation and imaging methods, with applications including molecular imaging and imaging of specific cells types. He coordinates a MicroCT Methods Forum. Here a brief interview …

What are the basic principles of these methods mixing histology and digital anatomy?

MicroCT provides 3D images of intact samples at resolutions that overlap with what is achieved by light microscopy of sectioned material. Contrast-enhanced X-ray images give only histomorphological information, so microCT images are a powerful complement to traditional histology, which takes advantage of a vast array of stains with different tissue specificities. MicroCT gives a 3D overview and context for more detailed section-based images from histology (and also electron microscope).

So, you stain specimens before microtomographic scan … what about these staining techniques?

The familiar X-ray images of bones or teeth inside the body are possible because the dense calcium-rich materials absorb a lot more X-ray energy than the soft tissues around them – skin, muscle, and internal organs, which are made up mostly of proteins and water. To make soft tissues clearly visible in X-ray images, it helps to add a contrast agent: this can be a suspension of an iodine- or barium-containing liquid injected or swallowed, as is common in clinical radiology examinations. In the case of non-living samples (ex vivo imaging, most of what I do), the sample can be stained with a substance that actually binds to the tissues and has a higher X-ray absorption. The contrast stains used most often are inorganic iodine, phosphotungstic acid, and (less frequently) osmium tetroxide. None of these is specific to any one tissue type, but they do allow the different tissues and structures to be distinguished clearly in the X-ray images.

What kind of expertise, career, and tools are necessary to work in this field?

As with any kind of biological imaging, it is necessary to have a good understanding both of the biological systems under study and of how the imaging systems actually work. So a strong background in microscopy, histology, and image acquisition and analysis is important. And one must always complement one’s own expertise with good working collaborations with partners in other fields.

What is, at present, the most intriguing current challenge?

We would really like to make microCT imaging more tissue- and molecule-specific. Thus I have collaborative projects to test new staining methods and calibrate their functions in microCT images with histological baselines. And my lab is working on refining the antibody imaging method we published a few years ago to make this a more robust and routine method for 3D imaging of gene expression and other molecular patterns in developmental, comparative, and medical-related research.

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Cranial thickness

estimation-of-skull-table-thicknessThe cranial vault is composed by three bone layers (inner table, diploe, outer table), and its principal function is to safeguard the brain from impacts. Bone thickness is a crucial parameter to understand the biomechanical factors contributing to skull deformations and fractures after head injury. It is therefore  important to establish an accurate measurement system to quantify its variation. Lillie et al., 2015 analyzed microCT scans of two cadavers to evaluate the accuracy of the estimated cortical thickness from clinical CT data. Microscans were acquired at 25-microns, while CT scans had a resolution of 0.48-0.62 mm. The skull average thickness in both cases was below 4 mm. Cortical thickness measurements obtained from CT scans are more accurate compared with traditional physical methods, although results are comparable with those available in literature. The average cortical thickness discrepancy between microCT scans (higher resolution) and CT scans (lower resolution) is 0.078+ 0.58 mm. Such methodological validation is necessary when dealing with age-related changes in distribution of the skull cortical thickness, and to identify species-specific or population differences.

Gizéh Rangel de Lázaro