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Spatially varying longitudinal aliasing and resolution in spiral computed tomography
1Department of Electrical Engineering, Information Systems Laboratory, Stanford University, California 94305, USA. shin@s-word.stanford.edu
Medical Physics
|January 5, 2000
Summary
Longitudinal resolution in spiral computed tomography (CT) varies spatially due to aliasing. A new parameter, contrast-to-aliased-noise ratio (CNaR), characterizes this resolution degradation, which worsens with distance from the isocenter.
Area of Science:
- Medical Imaging
- Radiology
- Computed Tomography
Background:
- Spiral CT offers true 3D imaging, advancing over conventional CT.
- Longitudinal resolution in spiral CT is crucial but often overlooked.
- The spatially varying nature of this resolution has not been fully addressed.
Purpose of the Study:
- To investigate how longitudinal aliasing affects spiral CT longitudinal resolution.
- To introduce a new image quality parameter, the contrast-to-aliased-noise ratio (CNaR).
- To characterize the spatially varying longitudinal resolution in spiral CT.
Main Methods:
- Simulations and phantom scans using a longitudinal resolution phantom.
- Analysis of aliasing as signal-dependent, additive noise.
- Definition and application of the contrast-to-aliased-noise ratio (CNaR).
Main Results:
- Off-isocenter longitudinal resolution significantly differs from isocenter resolution.
- CNaR decreases with increasing distance from the isocenter.
- CNaR is dependent on pitch and helical interpolation algorithm; resolution worsens as CNaR decreases.
Conclusions:
- Longitudinal resolution in spiral CT is not uniform; it varies spatially.
- CNaR effectively characterizes this spatially varying longitudinal resolution.
- CNaR provides a quantifiable measure of image quality degradation due to aliasing.
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