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Micro-CT scan of a piranha fish

What is Micro-CT? An Introduction

  • 23 February, 2018
  • Ann Bagnell
  • Micro-CT


ABOVE: Micro-CT scanned image of the piranha Catoprion mento. The blue dyed segments inside the skeleton are fish scales eaten by the piranha (also shown enlarged next to the fish). Credit: University of Washington.

What is micro-CT scanning?

Micro-CT is a 3D imaging technique utilizing X-rays to see inside an object, slice by slice.  Micro-CT, also called microtomography or micro computed tomography, is similar to hospital CT or “CAT” scan imaging but on a small scale with greatly increased resolution. Samples can be imaged with pixel sizes as small as 100 nanometers and objects can be scanned as large as 200 millimeters in diameter.

Micro-CT scanners capture a series of 2D planar X-ray images and reconstruct the data into 2D cross-sectional slices. These slices can be further processed into 3D models and even printed as 3D physical objects for analysis. With 2D X-ray systems you can see through an object, but with the power of 3D micro- CT systems you can see inside the object and reveal its internal features. It provides volumetric information about the microstructure, nondestructively.

How does a micro-CT scanner work?

X-rays are generated in an X-ray source, transmitted through the sample, and recorded by the X-ray detector as a 2D projection image. The sample is then rotated a fraction of a degree on the rotational stage, and another X-ray projection image is taken. This step is repeated through a 180-degree turn (or sometimes 360 degrees, depending on sample type). The series of X-ray projection images is then computed into cross-sectional images through the computational process called “reconstruction”. These slices can be analyzed, further processed into 3D models, made into movies, printed into 3D physical objects, and more.

How does micro-CT work?

READ MORE about how a micro-CT scanner works.

What does nondestructive testing mean?

Nondestructive testing (NDT) means that the sample or specimen being scanned isn’t altered or destroyed during testing or in the preparation for testing.  This allows the sample to be preserved for historical record, tested again at a later date, used in another test, or put into final production.  Some other techniques require staining, cutting, or coating of samples, which can affect sample’s structure, its ongoing usefulness, or its use in later studies. There are several techniques which allow samples to be imaged in their native states, including light microscopy, laser scanning, visible and other spectrum photography, and more. Micro-CT is one such technique where most of the samples studied are scanned in an unaltered state.

What are the advantages of micro-CT scanning?

Micro-CT provides high resolution 3D imaging information that can’t be obtained by any other non-destructive technology. It can be used to study the interior structure of both material and biological samples without having to cut the samples, preserving the samples or specimens for future studies. The quantitative information obtained from micro-CT scanning can only be obtained from 3D images, and 3D digital models created from micro-CT virtual slices allow scientists to measure any parameters for comparison in before-and-after studies.

These unique features of micro-CT scanning allow scientists to look at the morphology of a sample and study features such as: porosity, structure / bone thickness, volume fraction, defect analysis, density, particle size, voids, fiber orientation, etc.  Researchers use micro-CT to study bone, teeth, tissue / organs, composite materials, medical devices, batteries, and more.

READ MORE about different types of micro-CT scanners.

What is the difference between medical CT and micro-CT scans?

Micro-CT scanning is X-ray imaging in 3D, using the same method as medical CT (or “CAT”) scans, but micro-CT is on a much smaller scale with greatly increased resolution. Medical CT scanning was introduced as a tool for medical imaging in the 1970s;  CT (or computed tomography) scans are limited to a resolution of 1 millimeter, which provides sufficient detail for clinical use. For materials science and small animal imaging, much higher resolution was needed, and micro-CT scanning was introduced in the 1980s. Micro-CT scanners can work at the level of one micron, which is a thousandth of a millimeter, and smaller.

What is the difference between in vivo and ex vivo micro-CT scanning?

Simply put, in vivo (Latin for within life) is the scanning of live specimens and ex vivo (Latin for out of living) typically refers to things that used to be alive or samples excised from something that had been alive.  For micro-CT, in vivo typically refers to systems that scan mice and rats and in some cases rabbits, while ex vivo systems typically handle the remainder of the applications.

With in vivo micro-CT instruments, since the animal remains alive, longitudinal studies can be performed to measure the affects of drug, diet, hormonal, and other treatments on tumors; bone growth and quality; body mass; and other applications on the same subject.  This can reduce the number of animals needed for a study.

Ex vivo micro-CT instruments typically handle the remaining applications, which include end point studies of specific regions of an animal that get excised (lungs, bone, tumors, implants, grafts, etc.), biomaterial studies, implants in large animals, materials studies, compression studies, and more. Ex vivo micro-CT instruments allow for higher spatial resolution, longer scan times (since dose to the sample isn’t of concern), better signal to noise ratios, and therefore better images.  Ex vivo systems have typically been used for most applications outside of a living animal.

READ MORE about the differences between in vivo and ex vivo micro-CT scanning.

What is nanotomography or nano-CT scanning?

Nanotomography (nano-CT) is similar to micro-CT and medical CT scanning but at resolutions in nanometers instead of microns or mm.  Nano-CT uses a nano-focus X-ray source to capture 2D images during a 180 or 360 degree rotation of a sample.  Advanced software is then used to turn those images into 2D cross-sections or slices through the sample.  These cross-sections give a researcher the chance to look inside the sample without having to cut it open.  The smaller the focal spot of the source, the higher the resolution which can be achieved on the sample scan.  Nano-CT is critical for looking at fine details which would be destroyed when the sample would be cut open.

READ MORE about multiscale X-ray nano-CT non-destructive, high resolution microtomography.

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