The Engineer

CT system shows bone structure at high resolution

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A computer-tomography system that can produce images of bone structure at nanometre resolutions has been developed by a team of researchers from the Technische Universitaet Muenchen, the Paul Scherrer Institute and the ETH-Zurich.

Franz Pfeiffer, a professor of Biomedical Physics at the Technische Universitaet Muenchen (TUM), led the research team that developed new nano-CT imaging system, which can produce images showing bone structure and changes in bone density at high resolutions and in 3D.

Pfeiffer’s team built on existing X-ray computed tomography (CT) systems that X-ray the body while a detector records how much radiation is being absorbed from different angles. A number of such pictures are then used to generate digital 3D images of the body’s interior using image processing.

The method measures not only the overall beam intensity absorbed by the object under examination at each angle, but also those parts of the X-ray beam that are diffracted from it. The diffraction patterns are then processed using an algorithm developed by the team.

TUM researcher Martin Dierolf said: ’We developed an image-reconstruction algorithm that generates a high-resolution, three-dimensional image of the sample using over 100,000 diffraction patterns. This algorithm takes into account not only classical X-ray absorption, but also the significantly more sensitive phase shift of the X-rays.’

To highlight the capabilities of the system, the researchers examined the bone of a laboratory mouse. The so-called phase-contrast CT pictures show even smallest variations in the specimen’s bone density with extremely high precision; cross-sections of cavities where bone cells reside and their roughly 100-nanometre-fine interconnection network are clearly visible.

’Although the new nano-CT procedure does not achieve the spatial resolution currently available in electron microscopy, it can − because of the high penetration of X-rays − generate three-dimensional tomography images of bone samples,’ said Roger Wepf, director of the Electron Microscopy Center of the ETH Zurich (EMEZ).

The researchers believe that the system could assist with the study of osteoporosis, a medical condition in which bones become brittle and fragile from a loss of density.