Claims
- 1. A computerized tomographic apparatus comprising:
- scanning means for moving an object in a direction, for producing and rotating radiation rays within a plane intersecting the direction of movement to perform a helical scan on said object, and for receiving a plurality of sets of projection data points, each set of projection data points corresponding to a 360.degree. portion of a helix in the object;
- first interpolation means, coupled to the scanning means, for calculating a set of output data points corresponding to a desired slice of the object, an output data point of the desired slice being calculated by determining a first projection data point from a first adjacent 360.degree. portion of the helix and a second projection data point from a second adjacent 360.degree. portion of the helix located on both sides of the desired slice, both projection data points having the same desired projection angle as that of the output data point, and by interpolating the distances between each of the first and second projection data points and a plane containing the desired slice to determine the output data point; and
- second interpolation means for calculating one of the projection data points if either set of projection data points corresponding to the first or second 360.degree. portions of the helix does not include a projection data point having the desired projection angle by interpolating a third projection data point and a fourth projection data point, the third and fourth projection data points being located on the 360.degree. portion of the helix which does not include a projection data point having the desired projection angle, and the third and fourth projection data point having projection angles adjacent to the desired projection angle.
- 2. An apparatus according to claim 1, wherein said first interpolation means calculates the desired output data point P.sub.C (.phi., .theta.) of the desired slice having a projection angle .phi. by processing two projection data points P.sub.A (.phi., .theta.) and P.sub.B (.phi., .theta.) of the first and second adjacent 360.degree. portions of a helix, both projection data points having the projection angle .phi. as follows:
- P.sub.C (.phi., .theta.)=.alpha..multidot.P.sub.A (.phi., .theta.)+1-.alpha.).multidot.P.sub.B (.phi., .theta.)
- where .alpha. is an interpolation ratio and is expressed as follows:
- .alpha.=(X.sub.C -X.sub.B)/(X.sub.A -X.sub.B)
- where X.sub.A -X.sub.B and X.sub.C -X.sub.B are respectively the distance between the first and second 360.degree. portions of the helix and the distance between the desired slice and the 360.degree. portion of the helix which corresponds to projection data point P.sub.B (.phi., .theta.).
- 3. An apparatus according to claim 1, wherein said first interpolation means comprises:
- means for calculating a second projection data point P'.sub.B (.phi., .theta.) of a first 360.degree. portion of the helix having a projection angle .phi. from counter beams; and
- means for calculating the output data point P.sub.C (.phi., .theta.) of the desired slice having the projection angle .phi. by interpolating the first projection data point P.sub.A (.phi., .theta.) of a second 360.degree. portion of the helix having the projection angle .phi. and the projection data P'.sub.B (.phi., .theta.) of the first slice as follows:
- P.sub.C (.phi., .theta.)=.alpha.'.multidot.P.sub.A (.phi., .theta.)+(1-.alpha.').multidot.P'.sub.B (.phi., .theta.)
- where .alpha.' is an interpolation ration and is expressed as follows: .alpha.'=(X.sub.C[-X'.sub.B)/(X.sub.A -X'.sub.B)
- where X.sub.A -X'.sub.B and X.sub.C -X'.sub.B are respectively the distance between the first and second 360.degree. portions of the helix and the distance between the desired slice and the first 360.degree. portion of the helix.
- 4. An apparatus according to claim 1, further comprising:
- image reconstruction means for processing an output of said first and said second interpolation means; and
- means for displaying an output of said image reconstruction means.
- 5. A method for providing a slice image of an object, comprising the steps of:
- moving said object in a direction while rotating radiation rays within a plane intersecting the direction of movement to perform a helical scan on said object, thereby providing a plurality of sets of projection data points, each set of projection data points corresponding to a 360.degree. portion of a helix in the object;
- designating a desired slice of said object;
- interpolating to calculate a desired output data point in the desired slice having a given projection angle by processing a first projection data point located in a first 360.degree. portion of the helix and a second projection data point located in a second 360.degree. portion of the helix located on both sides of the desired slice and by processing a distance between the first and second 360.degree. portions of the helix and the desired slice;
- calculating one of the projection data points if either set of projection data points corresponding to the first or second 360.degree. portions of the helix does not include a projection data point having the desired projection angle by interpolating a third projection data point and a fourth projection data point, the third and fourth projection data points being located on the 360.degree. portion of the helix which does not include a projection data point having the desired projection angle, and the third and fourth projection data point having projection angles adjacent to the desired projection angle; and
- reconstructing an image based on the desired projection data obtained by said interpolation.
- 6. A computerized tomographic apparatus comprising:
- means for helically scanning an object and providing a plurality of sets of projection data points along a helical line;
- means for interpolating a first and a second projection data point to generate an output data point having a given projection angle;
- means for sampling the first projection data point having the given projection angle from a first 360.degree. portion of the helical line and the second projection data point having the given projection angle from a second 360.degree. portion of the helical line, the first and second 360.degree. portions being adjacent to and located on both sides of a desired slice of the object;
- means for calculating the first projection data point if the first 360.degree. portion does not include a projection data point having the given projection angle by interpolating a third projection data point and a fourth projection data point, the third and fourth projection data points being located on the first 360.degree. portion of the helix; and
- means for reconstructing an image of the desired slice based on a plurality of the output data points of the desired slice obtained from said interpolating means.
- 7. An apparatus according to claim 6, wherein said sampling means and interpolating means interpolate the projection data through a linear interpolation system.
- 8. An apparatus according to claim 6, wherein said sampling means and interpolating means interpolate the projection data through a nonlinear interpolation system.
- 9. An apparatus according to claim 6, wherein said sampling means and interpolating means interpolate the projection data through a spline interpolation system.
- 10. An apparatus according to claim 6, wherein said third and fourth projection data points have projection angles closer to the given projection angle than any other projection data points on the first 360.degree. portion.
Priority Claims (1)
Number |
Date |
Country |
Kind |
1-31016 |
Feb 1989 |
JPX |
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Parent Case Info
This application is a continuation of application Ser. No. 07/478,316, filed Feb. 12, 1990 now abandoned.
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4630202 |
Mori |
Dec 1986 |
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4789929 |
Nishimura et al. |
Dec 1988 |
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Continuations (1)
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Number |
Date |
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Parent |
478316 |
Feb 1990 |
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