Novel geometrical designs of computed tomography (CT) scanners in combination with novel image reconstruction
algorithms promise to reduce ionizing radiation exposure to the patient in CT scans. While the sampling
density of the Field Of View (FOV) is retained, the image quality can even be increased in contrast to conventional
CT scanners. In this study, we present first images obtained with a novel CT scanner that we developed
in our working group. In this open CT system with irradiation within a fan beam, parallel Radon data are
directly obtained for image reconstruction using the OPED (Orthogonal Polynomial Expansion on the Disk)
algorithm. This algorithm uses Radon data directly, i.e., without any further data processing such as rebinning
and interpolation. We experimentally test theoretical predictions for this system by quantifying image quality
parameters in comparison with corresponding parameters that are derived from the images of a conventional
scanner of the 3rd generation. The modulation transfer function (MTF) and noise power spectrum (NPS) are
determined using a test phantom. The novel CT system quantitatively shows the same noise property as the
conventional scanner. The resolution that is reached in the center of a reconstructed image is nearly identical for
both scanner types. But we found that the resolution that is achieved in the novel CT system does not depend on the image position while the MTF of the conventional scanner decreases for radially outer regions of the image.
KEYWORDS: Scanners, Reconstruction algorithms, Modulation transfer functions, Sensors, Monte Carlo methods, Data acquisition, X-rays, Algorithm development, Photons, Image restoration
A new type of X-ray CT scanning geometry is proposed. The geometry of the scanner includes a half ring
detector array and resembles the geometry of a scanner of the fourth generation. Unlike the latter, the proposed
system collects parallel projections allowing efficient collimation of the incident beam for the purpose of scatter
reduction. The geometry of the data collected with the proposed scanner is ideal for algorithms developed for
image reconstruction from parallel projections with a non-uniform sampling such as the Orthogonal Polynomial
Expansion on Disk (OPED) algorithm. This scanner can be efficiently used in applications where high precision
measurements at micrometer scales are required, e.g. in the exact quantification of the morphology of small
animals.
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