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Katsuyuki Taguchi

Publications and source records attributed to Katsuyuki Taguchi.

3 recordsLinked to original sources
PubMed2003

Temporal resolution and the evaluation of candidate algorithms for four-dimensional CT.

The four-dimensional computed tomography ("4D-CT") with area detector has been developed for dynamic volumetric imaging with large longitudinal coverage. In this paper one of the key technologies for 4D-CT development is discussed: Image reconstruction algorithm with high temporal resolution. All of the cone-beam algorithms investigated previously assume that the object is stationary. In this paper a new class of cone-beam problem is addressed: a dynamic volumetric (4-D) imaging. A continuously rotating circular (stationary couch) scanning is employed, and then, a generalized version of the well-known Feldkamp algorithm with the following three steps is performed: (1) applying a weighting function (along the time axis) to projection data, (2) filtering the weighted data along the detector row direction, (3) cone-beam backprojecting of the filtered data along the corresponding x-ray path. The weighting function controls the time center, the temporal resolution, and the image quality. Four weighting functions developed for fan-beam reconstruction were applied to the first step: (a) a constant weight fixed at 0.5 (FS-FDK), (b) feathering both edges of the (time) window (OS-FDK), (c) Parker's weight for a half-scan (HF-FDK), and (d) an extended Parker's weight, which allows us to use a larger range of projection data up to one rotation (NHS-FDK). We evaluated them in terms of temporal resolution, image noise, and image quality. Also, the cause of the artifact has been investigated. The temporal resolution of NHF-FDK equals that of HS-FDK, which is half of the one rotation period. For the moving object, NHS-FDK offers the best image quality. The images with FS-FDK are degraded by streak artifacts; HS-FDK provides poor image quality with good temporal resolution; and images by OS-FDK are blurred due to insufficient temporal resolution. The cause of the artifact was found as an inconsistency of projection data due to object motion (in FS-FDK) and lost 3-D-Radon data caused by applying Parker's weight (in HS-FDK). A hand toy was employed for the preliminary evaluation of dynamic volumetric imaging with the real 256-slice scanner. In an overall evaluation, NHS-FDK provides the stable and the sufficient image quality both with moving and stationary objects.

Artifacts↗
PubMed2003

Feldkamp-based cone-beam reconstruction for gantry-tilted helical multislice CT.

Depending on the clinical application, it is frequently necessary to tilt the gantry of an x-ray CT system with respect to the patient and couch. For single-slice fan-beam systems, tilting the gantry introduces no errors or artifacts. Most current systems, however, are helical multislice systems with up to 16 slices. The multislice helical reconstruction algorithms used to create CT images must be modified to account for tilting of the gantry. If they are not, the quality of reconstructed images will be poor with the presence of significant artifacts, such as smearing and double-imaging of anatomical structures. Current CT systems employ three primary types of reconstruction algorithms: helical fan-beam approximation, advanced single-slice rebinning, and Feldkamp-based algorithms. This paper presents a generalized helical cone-beam Feldkamp-based algorithm that is valid for both tilted and nontilted orientations of the gantry. Unlike some of the other algorithms, generalization of the Feldkamp algorithm to include gantry tilt is simple and straightforward with no significant increase in computational complexity. The effect of gantry tilt for helical Feldkamp reconstruction is to introduce a lateral shift in the isocenter of the reconstructed slice of interest, which is a function of the tilt, couch speed, and view angle. The lateral shift is easily calculated and incorporated into the helical Feldkamp backprojection algorithm. A tilt-generalized helical Feldkamp algorithm has been developed and incorporated into Aquilion 16-slice CT (Toshiba, Japan) scanners. This paper describes modifications necessary for the tilt generalization and its verification.

Algorithms↗