Speaker
Description
Mogno is a microCT beamline at the Brazilian Synchrotron Light Source designed for full-field imaging with hard X-rays (67.5 keV) in a cone-beam geometry, enabling the investigation of samples with dimensions of up to several centimetres. The beamline is equipped with a large-area CdTe Pimega detector, composed of a 6 × 6 array of Medipix3RX ASICs, providing a total sensitive area of 85 × 85 mm$^2$. With a physical pixel size of 55 × 55 $\mu$m$^2$ and an image size of 1536 × 1536 pixels, the detector offers high dynamic range (up to 24 bits) and high frame rates (up to 2 kHz). These characteristics make Mogno particularly suitable for fast acquisitions and time-resolved microCT experiments, taking advantage of the high brilliance of a fourth-generation synchrotron source. A major challenge associated with the Pimega detector is the presence of inactive regions between ASICs, resulting in missing data in the projections. These gaps measure between 48 and 51 pixels in the vertical direction and 3 or 4 pixels in the horizontal direction. Two main strategies have been developed to recover complete projection data. The first approach consists of acquiring a second projection after diagonally shifting the detector so that the inactive regions of the first acquisition are covered. The final projection is obtained by combining the original and shifted images, filling most part of the gaps. This method was successfully applied to reservoir rock plugs provided by Petrobras, allowing the visualization of fine features such as grains and pores with sizes of a few tens of micrometres. However, this approach is not compatible with time-resolved microCT, as it requires two projections per angular position, effectively decreasing the temporal resolution. To address this limitation, a second approach was implemented by physically rotating the detector by 90°, placing the larger gaps along the horizontal direction. In this configuration, missing data in a given projection can be complemented by the corresponding projection acquired after a 180° rotation of the sample. The final projection is obtained by stitching each image with its complementary one at +180°, preserving the original temporal resolution since no additional acquisitions are required. Nevertheless, some degradation in spatial resolution is observed due to the cone-beam geometry, which causes features to be projected onto different detector positions at 0° and 180°. Solving the problem of missing data is essential for ongoing developments aimed at pushing the temporal resolution of microCT down to the exposure time of individual projections, using a parametrization of the continuous-time evolution of each voxel rather than discrete time-lapse reconstructions. As a proof of concept, the injection of KI-doped water through a vertical column of glass beads was monitored, enabling the tracking of fluid motion during continuous acquisition and demonstrating the potential of this approach for truly time-resolved microCT studies.
| Country | Brazil |
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