Microtomography, often referred to as micro-CT or μCT, is a non-destructive imaging technique that generates three-dimensional (3D) images of objects. It operates on a significantly smaller scale and with much higher resolution compared to hospital CT scans, allowing for detailed examination of internal structures. This technology provides a way to “see inside” materials, revealing intricate details that would otherwise require destructive methods to observe. The pixel sizes of the cross-sections generated by microtomography are typically in the micrometer range, hence the “micro” prefix.
How Microtomography Works
Microtomography relies on the interaction of X-rays with a sample to create detailed internal images. An X-ray source emits a beam that penetrates the object. As the X-rays pass through, different materials within the sample absorb or attenuate the radiation to varying degrees based on their density and composition.
A detector positioned on the opposite side of the sample captures the attenuated X-rays, forming a two-dimensional (2D) “shadow image” or projection. To build a 3D model, the sample is precisely rotated on a stage, and numerous 2D projection images are acquired from different angles, typically over a 180° or 360° rotation.
These hundreds or thousands of 2D images are then sent to a computer, which uses computational algorithms, such as filtered back-projection, to reconstruct a 3D dataset. This process produces a representation of the X-ray density and brightness of each volumetric pixel, or voxel. The core components of a micro-CT system include an X-ray tube as the source, a sample manipulator (rotation stage), and a 2D X-ray detector.
Seeing Inside: What Microtomography Reveals
Microtomography provides high-resolution 3D insights into the internal structures of objects without altering them. This non-destructive analysis allows researchers to visualize intricate details, preserving the integrity of the sample for future studies. The technique excels at differentiating between materials of varying densities or compositions within a sample, as denser materials absorb more X-rays and appear brighter in the resulting images.
It can achieve pixel sizes as small as 100 nanometers, providing a level of detail comparable to light microscopy, but for the entire volume of an intact sample. From the reconstructed 3D dataset, researchers can create virtual slices through the object in any plane. These virtual slices and full 3D renderings make internal features apparent, enabling thorough examination and quantitative analysis of the microstructure.
Microtomography in Action: Diverse Applications
Microtomography’s ability to provide 3D insights has led to its widespread adoption across various scientific and industrial fields. Its versatility allows for detailed investigations into the internal architecture of diverse materials and organisms.
Materials Science
In materials science, microtomography is used to study the internal structure of engineering materials. It can identify and characterize defects such as cracks, pores, and voids in composites, metals, and other manufactured parts. For example, it helps visualize the distribution of fibers in composite materials or analyze delamination and internal cracking in products like candy bars. This detailed 3D information about defects and microstructure aids in understanding material behavior, predicting failure, and improving manufacturing processes.
Paleontology and Archaeology
Microtomography is a tool in paleontology and archaeology for examining delicate and irreplaceable specimens. It allows researchers to virtually “extract” and study fossils embedded within rock matrices, or analyze the internal structures of ancient artifacts. This technique reveals intricate details of fossilized bones, teeth, and even prehistoric insects preserved in amber, which would be impossible to observe using traditional destructive methods. For instance, it has been used to study the internal anatomy of small vertebrate fossils or to virtually reconstruct endocranial casts of extinct animals to infer locomotor strategies.
Biology and Medicine
In biology and medicine, microtomography provides a non-invasive way to visualize the internal structures of small organisms, tissues, and engineered constructs. It offers high-resolution 3D imaging of biological samples, useful for studying bone structure and density, and for visualizing vascular networks within tissues. While dense structures like bones are easily imaged, soft tissues often require contrast agents to enhance X-ray absorption and improve image clarity. This method is applied in developmental biology to examine embryos, in pathology to analyze diseased tissues, and in tissue engineering to assess the microstructure of scaffolds designed for tissue regeneration and drug delivery systems.
Food Science
Microtomography applies to food science to analyze the microstructure of food products. It can visualize internal features such as the distribution of air bubbles, fat, and ice crystals in frozen desserts like ice cream and sorbet. The technique helps researchers understand how processing and storage conditions affect food texture and quality by quantifying parameters like porosity and ingredient distribution. It can also be used for quality control, identifying foreign materials or assessing coating coverage on products like chicken patties.
Geology
Geologists utilize microtomography to investigate rock samples and porous media, relevant for the oil and gas industry. The technique allows for the characterization of porosity, including the total porosity, types of pores, and their size distribution within rocks. It provides 3D insights into complex pore systems, helping to understand fluid flow and transport within geological formations. Microtomography can also reveal mineralogical differences and the presence of fractures within rock samples, which is useful for reservoir characterization and geological carbon sequestration studies.