Device for determining a radiation attenuation distribution in a

Details Device for determining a radiation attenuation distribution in a Device for determining a radiation attenuation distribution in a

1980-07-08

1983-02-15

Smith, Alfred E.

Boots, shoes, and leggings

378901, A61B 600

Patent

active

043744192

ABSTRACT:
For the backprojection of the convoluted measurement signals in a cartesian coordinate system in a computer tomography device, it is necessary to recalculate the weighting factors for each position of the source in order to determine the contribution of a convoluted measurement signal to the attenuation value associated with a given element of the output image matrix. This is a time consuming and hence expensive form of reconstruction, and can be avoided by storing all the weighting factors required; this, however, implies a very large memory, and is also expensive.
The invention relates to the use of a matrix of elements organised in polar coordinates, which is stored in the memory, the origin central coordinate of said matrix coinciding with the center of rotation of the X-ray source about the object section. The weighting factors are also stored in a polar organized memory. The angular component of the address of the weighting factors is incremented with a rotational increment in the corresponding position of the X-ray source, so that for each group of measurement values, the same weighting factors can be used. The invention enables all the weighting factors to be stored in a memory of limited capacity, the more so because all weighting factors are mirror-symmetrical with respect to a central axis connecting the X-ray source to the center of rotation, so that the angular coordinates of the memory need only extend from 0 to .pi. instead of from 0 to 2.pi..

REFERENCES:
patent: 4135247 (1979-01-01), Gordon et al.
Alvarez, R. E., Extraction of Energy Dependent Information, (Doctoral Dissertation) Jul. 1976, pp. 100-102.

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