Patent EP0242909A1 successfully refreshed from Google Patents.
EP0242909A1
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EP
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Computer tomography apparatus including a combined recursive and convolution filter
Assignee: Koninklijke Philips NV
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Filing: 1987-04-07
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Granted: —
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Expires: 2007-04-07
Abstract
Abstract In a computer tomography apparatus in accordance with the invention of advantages of the convolution calculation are combined with the advantages of recursive filtering. The processing unit for the measurement data includes a convolution filter which has only 64 convolution factors and which performs the central part of a convolution calculation (the number of measurement data amounts to, for example 512 or 1024) and a parallel-operating recursive filter which approximates the rests of the convolution calculation situated outside the central part by recursive filtering of the measurement data. Using five different multiplication factors and a corresponding number of attenuation factors, ample accuracy is achieved. By variation of only the 64 convolution factors, a large number of different filters can be realized, without it being necessary to change the factors for recursive filtering.
Inventors
- 👤 Steven Lobregt
- 👤 Johannes Catharina Antonius Op De Beek
- 👤 Roelof Werkman
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 23:35
CPC Classifications
G; G06; G06T; G06T12/00; G06T12/10; Y; Y10; Y10S; Y10S378/00; Y10S378/901
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
139 words
A computer tomography apparatus for determining a radiation attenuation distribution in a slice of a body, including a radiation source and radiation source displacement means for irradiating a region of the body from a plurality of source positions, which apparatus also includes detection means for detecting the attenuated radiation having passed through the body in order to form groups of measurement data, a filter device for determining groups of back-projecticndata from the groups of measurement data, a back projection unit for determining the attenuation distribution from the groups of back-projection data, and storage means for the storage of at least the attenuation distribution determined characterized in that the arithmetic means include at least a convolution unit and at least one recursive filter unit whose outputs are connected to an adder unit whose output is connected to the back-projection unit.
Claim 2
Dependent Claim
139 words
A computer tomography apparatus for determining a radiation attenuation distribution in a slice of a body, including a radiation source and radiation source displacement means for irradiating a region of the body from a plurality of source positions, which apparatus also includes detection means for detecting the attenuated radiation having passed through the body in order to form groups of measurement data, a filter device for determining groups of back-projecticndata from the groups of measurement data, a back projection unit for determining the attenuation distribution from the groups of back-projection data, and storage means for the storage of at least the attenuation distribution determined characterized in that the arithmetic means include at least a convolution unit and at least one recursive filter unit whose outputs are connected to an adder unit whose output is connected to the back-projection unit.
Claim 3
Dependent Claim
47 words
A computer tomography apparatus as claimed in Claim 1, characterized in that the convolution unit includes a convolution factor memory for the storage of at least one progression of convolution factors, the number of factors of a progression being more than thirty and less than one hundred.
Claim 4
Dependent Claim
29 words
A computer tomography apparatus as claimed in Claim 2, characterized in that the convolution factor memory comprises several sections, one progression of convolution factors being stored in each section.
Claim 5
Dependent Claim
20 words
A computer tomography apparatus as claimed in Claim 2 or 3, characterized in that a progression comprises 64 convolution factors.
Claim 6
Dependent Claim
59 words
A computer tomography apparatus as claimed in Claim 1, 2,3 or 4, characterized in that the convolution unit includes a multiplier which includes two inputs for receiving convolution factors and measurement data to be multiplied thereby and an adder having an input which is connected to the output of the multiplier, its output being connected to a second input.
Claim 7
Dependent Claim
91 words
A computer tomography apparatus as claimed in Claim 5, characterized in that the convolution unit includes a further adder and a register, the output of the adder being connected to an input of the multiplier, a first input of the further adder being connected to the output of the register, the register storing a first measurement data and the further adder receiving a second measurement data on its second input in order to add the first and the second measurement data which is to be multiplied by the same convolution factor.
Claim 8
Dependent Claim
25 words
A computer tomography apparatus as claimed in any one of the preceding Claims, characterized in that at least two convolution units are connected in parallel.
Claim 9
Dependent Claim
116 words
A computer tomography apparatus as claimed in any one of the Claims 1 to 7, characterized in that the recursive filter unit includes a first multiplier, a second multiplier and an adder, the first multiplier including a first and a second input for receiving a multiplication factor and measurement data, respectively, and an output which is connected to a first input of the adder whose output constitutes the output of a recursive filter formed by the two multipliers and the adder and which is connected to a first input of the second multiplier, whose output is connected to a second input of the adder, the second multiplier including a second input for receiving an attenuation factor.
Claim 10
Dependent Claim
58 words
A computer tomography apparatus as claimed in Claim 8, characterized in that the first input of the first multiplier as well as the second input of the second multiplier is connected to an output of a memory which includes ten memory locations for the storage of a number of multiplication factors and a corresponding number of attenuation factors.
Claim 11
Dependent Claim
55 words
A computer tomography apparatus as claimed in Claim 9, characterized in that the output of the adder is connected to a further adder whose output is connected to an input of a buffer memory whose output is connected to an input of the adder unit as well as to an input of the further adder.
References Cited (Backward Citations)
US3924129A
Cited
US4212062A
Cited
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