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Three‐dimensional computed tomographic reconstruction using a C‐arm mounted XRII: Correction of image intensifier distortion
Author(s) -
Fahrig R.,
Moreau M.,
Holdsworth D. W.
Publication year - 1997
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.598013
Subject(s) - distortion (music) , projection (relational algebra) , image intensifier , iterative reconstruction , pixel , mathematics , rotation (mathematics) , reduction (mathematics) , optics , artificial intelligence , computer vision , physics , algorithm , geometry , computer science , amplifier , optoelectronics , cmos
X‐ray image intensifiers (XRIIs) have many applications in diagnostic imaging including acquisition of near‐real‐time projection images of the intracranial and coronary vasculature. Recently, there has been some interest in using this projection data to generate three‐dimensional (3‐D) computed tomographic (CT) reconstructions. The XRII and x‐ray tube are rotated around the object, acquiring sufficient data for the simultaneous reconstruction of many transverse slices. Three‐dimensional reconstructions are compromised, however, if the projection data is geometrically distorted in any way. Previous studies have shown the distortion in XRIIs to be substantial and to be highly angular dependent. In this paper, we present a global correction technique which provides a table of correction coefficients for an image acquired at any arbitrary angle about the patient. The coefficients are generated using a linear least‐squares fit between the detected and known locations of a grid of small steel beads which is attached to the XRII (27 cm nominal diameter). We have performed corrections on 100 images obtained during rotation of the gantry through 200° and find that a fifth‐order polynomial provides optimum image distortion reduction (mean residual distortion of 0.07 pixels), however, fourth‐order polynomials provide sufficient distortion reduction for our application (mean residual displacement of 0.1 pixels). Using sixth‐order polynomials does not provide a statistically significant reduction in image distortion. The spatial distribution of residual distortion did not demonstrate any particular pattern over the face of the XRII. Image angle and coefficient angle must be known to within ± 2 ° in order to keep the mean residual distortion below ∼ 0.5 pixels.