firefly [ezrt] – Intelligent algorithms to improve CT image quality and measurement times

The Fraunhofer EZRT, a division of Fraunhofer IIS, is developing innovative software modules for industrial applications with computed tomography (CT). While standard processes repeatedly reach their limits, these intelligent algorithms help system manufacturers and users to significantly improve the results of three-dimensional imaging and enable the high-precision dimensional measurement for many applications for the first time. The firefly library offers software modules for reconstruction and data improvement for licensing. Beside standard algorithms, like firefly [circle] for classical CT on circular trajectories, we provide several modules for special purposes.

The firefly [helix] module provide the reconstruction of X-ray data recorded with a helical trajectory. This innovative reconstruction process allows reconstruction true to absorbtion density in all layers of the scanned volume. This completely eliminates Feldkamp artifacts that occur in conventional, axial CT. Thanks to increased image quality, the results of 3-D image analysis, e.g. the detection of defects, also improve significantly. Probing errors with regard to dimensions and shape are minimized in dimensional measurement, too.

With the firefly [flexpress] reconstruction module, the measuring time for component testing can be significantly reduced. Depending on the test specimen property, time savings of 50 percent and more are possible. The process requires considerably fewer projections than conventional processes to calculate with comparably good reconstruction quality. If standard scanning geometries, e.g., circles, cannot be used with the component to be tested, another unique selling point of this process comes to the fore: it can deal with any type of recording trajectory.

Scattered radiation has a negative effect on the achievable image quality. With just one additional calibration measurement, the firefly [descatter] module corrects image distortions caused by the scattered radiation associated with the test specimen and the scattered radiation inside the detector in the recorded X-ray projections. This is also possible with test specimens that are not homogenous, i.e., that consist of various different materials. Based on the calibration measurements with specified X-ray parameters, entire measurement series of identical and similar test objects can be corrected without having to consider the orientation of the components in the beam path.

This module contains the patented process (EP1415179) of iterative artifact reduction for correcting X-ray images of components consisting of homogeneous materials by using a correction characteristic curve. The process is able to correct image distortions and artifacts caused by any type of physical effects, particularly beam-hardening. It increases image quality and, along with it, improves the achievable accuracy of measurement. The required correction characteristic curve is determined from the scan of the test specimen itself with using image processing methods. This makes it quite easy to generate the correction characteristic curve without much effort: no step wedges or other reference is required. Previous knowledge of the spectrum of the applied X-ray radiation or the material properties of the test specimen is also not necessary.

The firefly [multimat] module optimizes inspections of components consisting of a variety of materials. Connectors for electronics made of an insulating plastic housing and metallic electrical contacts provide a classic example. In general, especially when dealing with materials that have very different absorption properties, this type of material mix results in significant artifacts in X-rays near the areas that are strongly absorptive. The firefly [multimat] module can compensate for this by using two scans of the same object generated with differing energies of X-ray radiation. This significantly reduces artifacts and generates sharper divisions between the various materials, and thus considerably increases image quality.