Biomedical subjects

Claas Bontus

Publications and source records attributed to Claas Bontus.

5 recordsLinked to original sources

PubMed2006

Circular CT in combination with a helical segment.

The combination of circular CT with a helical trajectory segment results in a mathematically complete data set. We present a reconstruction algorithm which is mathematically exact and of the filtered back-projection type. The algorithm ensures that only Radon planes which are not covered along the circle are taken into account, when data from the helical segment are back-projected. Therefore, the helical segment contributes only to low-frequency parts of trans-axial slices. Data along the helix can be obtained with a very low acquisition dose.

Algorithms↗

PubMed2006

The radon-split method for helical cone-beam CT and its application to nongated reconstruction.

The mathematical analysis of exact filtered back-projection algorithms is strictly related to Radon inversion. We show how filter-lines can be defined for the helical trajectory, which serve for the extraction of contributions of particular kinds of Radon-planes. Due to the Fourier-slice theorem, Radon-planes with few intersections with the helix are associated with low-frequency contributions to transversal slices. This insight leads to different applications of the new method. The application presented here enables the incorporation of an arbitrary amount of redundant data in an approximate way. This means that the back-projection is not restricted to an n-Pi interval. A detailed mathematical analysis, in which we demonstrate how the defined filter-lines work, concludes this paper.

Algorithms↗

PubMed2006

CEnPiT: helical cardiac CT reconstruction.

Computer tomography (CT) scanners with an increasing number of detector rows offer the potential of shorter scanning times. Nevertheless, the reconstruction problem becomes more challenging, since cone beam artifacts are likely to enter. Here, we consider helical cardiac CT. We analyze how a relationship can be established between exact reconstruction algorithms and the demand to perform a cardiac gating. Utilizing the redundancies requires the consideration of all kinds of Radon planes. For the reconstruction algorithm proposed here, we separate the data into two parts. The first part contains contributions of Radon planes, which are measured with a large number of redundancies. The second part contains the remaining contributions. As it turns out, the second part contributes rather to the low-frequency contents of trans-axial slices. Therefore, we propose to perform a gated back-projection only for the first part, while the second part is back-projected in an ungated way. Data from the complete source trajectory are employed in the reconstruction process in contrary to conventional helical cardiac reconstruction methods. Moreover, all different types of Radon planes are taken into account in the reconstruction, though an ECG-dependent cardiac gating is applied. The reconstruction results, which we present for clinical and simulated data, demonstrate the high potential of CEnPiT for helical cardiac CT with large cone angle systems.

Algorithms↗

PubMed2005

EnPiT: filtered back-projection algorithm for helical CT using an n-Pi acquisition.

In this paper, we formulate a reconstruction algorithm for an n-Pi acquisition, where n can be any positive odd integer. The algorithm is a generalization of the method presented in (Bontus et al. 2003). It is based on the results obtained by Katsevich (2004). For the algorithm, different sets of filter-lines have to be defined. We describe the variation of these lines along the detector in some detail, before we discuss, how the method gives all Radon-plane contributions the correct weighting. The different sets of filter-lines are all contained within the n-Pi window, such that a practical realization is possible. Reconstruction results, which we present in the final section, show convincing image quality.

Algorithms↗

PubMed2003

A quasiexact reconstruction algorithm for helical CT using a 3-Pi acquisition.

Recently, an exact reconstruction method for helical CT was published by A. Katsevich. The algorithm is of the filtered backprojection type and is, therefore, computationally efficient. Moreover, during backprojection, only data are used which correspond to an illumination interval of 180 degrees as seen from the object-point. We propose a new reconstruction method, which is applicable to data obtained with a 3-Pi acquisition [IEEE Trans. Med. Imaging 19, 848-863 (2000)]. The method uses the same filter types as the Katsevich algorithm, but the directions and the number of the filter lines are chosen differently. For the derivation of the new algorithm, we analyze the relationship of the Katsevich method and radon inversion. A certain radon plane can intersect with the backprojection interval related to a 3-Pi acquisition either once, three, or five times. In analogy to the definition of quasiexactness introduced by Kudo et al. for a 1-Pi acquisition, we use the term quasiexactness for algorithms on a 3-Pi acquisition, if radon planes with one or three intersections within the backprojection interval are treated correctly. Using the results on the relationship with radon inversion, we can prove that our algorithm is quasiexact in this sense. We use simulation results in order to demonstrate that the algorithm yields excellent image quality.

Algorithms↗