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Proceedings Paper

Analysis of in-plane signal-to-noise ratio in computed tomography
Author(s): Takanori Hara; Katsuhiro Ichikawa; Shigeru Sanada; Yoshihiro Ida
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Paper Abstract

The purposes of this study are to analyze signal-to-noise ratio (SNR) changes for in-plane (axial plane) position and in-plane direction in X-ray computed tomography (CT) system and to verify those visual effects by using simulated small low-contrast disc objects. Three-models of multi detector-row CT were employed. Modulation transfer function (MTF) was obtained using a thin metal wire. Noise power spectrum (NPSs) was obtained using a cylindrical water phantom. The measurement positions were set to center and off-centered positions of 64mm, 128mm and 192mm. One-dimensional MTFs and NPSs for the x- and y-direction were calculated by means of a numerical slit scanning method. SNRs were then calculated from MTFs and NPSs. The simulated low-contrast disc objects with diameter of 2 to 10mm and contrast to background of 3.0%, 4.5% and 6.0% were superimposed on the water phantom images. Respective simulated objects in the images are then visually evaluated in degree of their recognition, and then the validity of the resultant SNRs are examined. Resultant in-plane SNRs differed between the center and peripheries and indicated a trend that the SNR values increase in accordance with distance from the center. The increasing degree differed between x- and y-direction, and also changed by the CT systems. These results suggested that the peripheries region has higher low-contrast detectability than the center. The properties derived in this study indicated that the depiction abilities at various in-plane positions are not uniform in clinical CT images, and detectability of the low contrast lesion may be influenced.

Paper Details

Date Published: 19 March 2008
PDF: 9 pages
Proc. SPIE 6913, Medical Imaging 2008: Physics of Medical Imaging, 691353 (19 March 2008); doi: 10.1117/12.768968
Show Author Affiliations
Takanori Hara, Nakatsugawa Municipal General Hospital (Japan)
Kanazawa Univ. (Japan)
Katsuhiro Ichikawa, Kanazawa Univ. (Japan)
Shigeru Sanada, Kanazawa Univ. (Japan)
Yoshihiro Ida, Fujita Health Univ. Hospital (Japan)

Published in SPIE Proceedings Vol. 6913:
Medical Imaging 2008: Physics of Medical Imaging
Jiang Hsieh; Ehsan Samei, Editor(s)

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