An X-ray beam tracking approach to retrieve directional information in biological specimens

The analysis of the directionality of fibres forming the white matter is a fundamental task in the investigation of the nervous system (NS), in terms of understanding its development and ageing as well as many neurological conditions.

The imaging of white matter directionality is usually accomplished by means of diffusion tensor magnetic resonance imaging (DTI), which exploits the anisotropic diffusion of water molecules in the NS parenchyma.

While DTI meets all the requirements for clinical imaging, it suffers from low resolution, which makes it difficult for pre-clinical small animal imaging where high resolution is required.

In addition, it cannot be used for the imaging of materials where no water is present, requiring an alternative technique.

In both cases, this can be represented by X-rays, which provide high resolution as well as the capability to extract directional information.

However conventional, attenuation-based imaging is not directional, and the multi-modal capability offered by the new phase contrast techniques must be used.

In addition to attenuation, these techniques also provide refraction and ultra-small angle scattering, which are directional signals and can be exploited to retrieve fibre orientation on a multi-scale level, above and below the system’s resolution.

In particular, the retrieval of directional information from dark-field has been demonstrated by means of grating interferometry, which requires the use of two or three optical elements depending on the source size.

The main goal of the project is to introduce a beam tracking (BT) multi-modal technique as an alternative for directional imaging.

BT is based on the use of a single mask regardless of the source size, therefore providing the same capabilities as grating interferometry but a significantly simpler and more versatile setup.

Directional BT will be used to extract the direction of fibres in sections of murine NS using both synchrotron facilities and laboratory sources.