ASTRA: All Scale Tomographic Reconstruction Antwerp
There are many situations where one wants to know what a certain object looks like from the inside, without actually being able to see the interior directly. For medical doctors, seeing a three-dimensional view of the organs of a patient before performing surgery can be crucial to the success of the operation. In the semiconductor industry, images of the interior of manufactured chips can be used to detect defects in an early stage. Visualizing the interior of nanoparticles can provide valuable research insights to Materials Scientists, Microbiologists are interested in the internal structure of human cells.
In many cases, it is possible to acquire projection images of the object of interest. Consider, for example, a medical X-ray photo. The X-ray contains some information about the internal organs of the patient, yet from a single X-ray it is impossible to determine their exact position. If one organ lies behind another organ in the direction the X-ray is taken, it is not possible to determine from the X-ray which of the organs was actually in front. Projection images can be acquired using many different techniques. In the nanosciences, for example, such images can be made using an electron microscope instead of an X-ray device. Although a single projection image can provide valuable information about the interior structure of the object, its full three-dimensional structure cannot be determined from it.
Fortunately, it is often possible to compute a complete three-dimensional image of the object, from a series of projection images. A projection images always corresponds to a certain viewing direction (the direction of the camera). If many projections are recorded from different viewing angles, rotating around the object, each projection image will contain some new information about the internal structure of the object. The procedure of combining the information from all these two-dimensional projection images into a single three-dimensional reconstruction is known as tomography.
The most common practical example of tomography can be found in the medical CT-scanner. A CT-scanner consists of an assembly of one or more X-ray sources and one or more cameras, which rotate around the patient to acquire a series of projection images. The resulting three-dimensional reconstructions of a patient's body can be highly accurate.
Less known is the fact that tomography has many important applications outside the field of medical imaging as well. In fact, tomography can be used, and is being used, at all imaginable scales. It reaches from the reconstruction of individual atom positions in nanocrystals at sub-Angstrom resolution, to the determination of galaxy locations in astronomy. The entire spectrum of scales between these two extremes is covered fairly well by a range of other applications.
Most research groups that deal with tomographic image reconstruction focus on a specific application domain, such as Medical Imaging or Materials Science. Yet, reconstruction problems at different scales share many common features and can often be solved using similar methods.
ASTRA is a research group that is part of the VisionLab at the University of Antwerp. It targets the entire range of tomographic reconstruction problems, at all scales. By focusing on the underlying general mathematical problems, instead of a specific application field, we develop reconstruction methods that can be shared between the various application fields. ASTRA is funded by the flemish government and by IBBT.