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Hybrid Fiducial System for Tuned-Aperture Computed Tomography

Hybrid Fiducial System for Tuned-Aperture Computed Tomography. R.L. Webber, S.B. Robinson, and F.H. Fahey Wake Forest University. Supported in part by NIH RO1 DE12227, DAMD 17-98-1-8349, and Instrumentarium Imaging. Objectives:. Simplify extraction of essential fiducial information

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Hybrid Fiducial System for Tuned-Aperture Computed Tomography

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  1. Hybrid Fiducial System for Tuned-Aperture Computed Tomography R.L. Webber, S.B. Robinson, and F.H. Fahey Wake Forest University Supported in part by NIH RO1 DE12227, DAMD 17-98-1-8349, and Instrumentarium Imaging

  2. Objectives: • Simplify extraction of essential fiducial information • Eliminate obscuration of desired information by superposition of fiducial shadows • Facilitate quantitative 3D radiography with conventional (2D) imaging systems

  3. Methods: • Use digital camera to isolate radiolucent fiducials from underlying tissues as seen from a variety of projection angles • Geometrically couple resulting photographic image with respective simultaneously exposed x-ray projection images • Use photographic data to infer the associated x-ray projection geometry required for 3D reconstruction • Compute 3D radiograph using TACT algorithm

  4. Projection Schematic:

  5. Mathematical Justification: • P(P1,P2,…,Pn) are x-ray source positions • P*(P*1,P*2,…,P*n) are corresponding camera positions • x is point in object projected by x-ray beam • x* is point in object seen by ‘coupled’ camera • Theorem: Whenever an image of a point xi is created using pi,then thebackprojection using p*i yields an unambiguous point x*, i.e. the homologous projection lines intersect at x*. • This geometry can be realized with reasonable ‘coupling’ constraints

  6. Methods (cont’d): Expose isolated tooth from 12 arbitrary angles

  7. Methods (cont’d): Photograph coupled fiducials from 12 homologous angles

  8. Results: Reconstruct arbitrary slices from optically registered x-ray projections

  9. Results (cont’d): Reconstruct arbitrary 3D projections from same data

  10. Conclusions: • Hybrid photographic/radiographic system can produce accurately registered 3D reconstructions using TACT algorithms • Potential obscuration of information caused by overlying fiducial shadows can be eliminated completely from TACT 3D reconstructions • Hybrid method facilitates automated 3D analysis by simplifying isolation of essential fiducial registration data from radiographic information

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