New efficient Fourier-reconstruction method for approximate image reconstruction in spiral cone-beam CT at small cone angles

Stefan Schaller; Thomas Flohr; Peter Steffen

doi:10.1117/12.273987

2 May 1997 New efficient Fourier-reconstruction method for approximate image reconstruction in spiral cone-beam CT at small cone angles

Stefan Schaller, Thomas Flohr, Peter Steffen

Author Affiliations +

Proceedings Volume 3032, Medical Imaging 1997: Physics of Medical Imaging; (1997) https://doi.org/10.1117/12.273987
Event: Medical Imaging 1997, 1997, Newport Beach, CA, United States

Abstract

We present an approximate algorithm for image reconstruction in spiral cone-beam CT at small cone-angles. The first step of the algorithm is a rebinning from fanbeam to parallel beam projections, that is performed independently for each detector row. The result of this rebinning procedure is a set of parallel views, where all rays are tilted against the z-axis by their cone angle and the rays within each view have different z-positions. After that, as with most of the approximate algorithms, the basic idea is to let each oblique ray contribute to the image with a weight that depends on its distance to the image plane. Because the distance of a ray to the image plane changes along the ray, so does its weight. This is the one important difference compared to standard 2D reconstruction procedures. However, for small cone angles, the variation of the weight along a ray is rather smooth, so that we can synthesize it as a Fourier series using only few Fourier coefficients. In standard 2D image reconstruction, we can build the 2D Fourier spectrum of the image on a polar grid from the Fourier transforms of the views, where each view contributes to a radial line only, because the weights are constant along the rays. In our algorithm, the weights change along the rays. This variation is modeled as a Fourier series with 2N_(mu ) + 1 coefficients. Hence, the views contribute not only to one but to 2N_(mu ) + 1 lines in the 2D Fourier space of the image. For a given pitch, the Fourier coefficients that take into account the variations of the weights are precalculated before the reconstruction and stored in a table. From the generated 2D image spectrum, we calculate the final image using a gridding technique to convert the sampling grid to cartesian and finally doing a 2D IFFT. We have evaluated our method using simulated test data for various test cases assuming sampling conditions and image quality requirements typical to medical CT. These experiments have shown that the method is applicable for detector arrays with up to at least 32 rows.

Citation Download Citation

Stefan Schaller, Thomas Flohr, and Peter Steffen "New efficient Fourier-reconstruction method for approximate image reconstruction in spiral cone-beam CT at small cone angles", Proc. SPIE 3032, Medical Imaging 1997: Physics of Medical Imaging, (2 May 1997); https://doi.org/10.1117/12.273987

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available