Affiliations: Department of Radiology, University of Rochester
Medical Center, Rochester, NY 14642, USA
Note: [] Department of Radiology, University of Rochester Medical Center,
Rochester, NY 14642, USA. Tel.: +1 716 275 1350; Fax: +1 716 273 1033
Abstract: {\it Rational and objectives.} The recent development of image
intensifier-based volume tomographic digital angiography has attracted interest
in the development of an effective correction protocol for image distortion
introduced by an image intensifier (II)-based image chain. This paper presents
an effective II distortion-correction method for II-based volume tomographic
digital angiography (VTDA). {\it Methods.} In this calibration protocol, two types of
predominant distortion: Global variable magnetic field (GVMF) distortion and
pincushion distortion were corrected separately using global mapping functions.
GVMF distortion-correction parameters were determined by measuring the
translational and rotational parameters from the projection images of a
specially designed phantom acquired at different gantry angular positions. A
new pincushion distortion-correction algorithm was then developed which remapps
projection data acquired with the curved detector onto an imaginary flat
detector. The corrected projection data were used for direct 3D reconstruction
with a cone-beam reconstruction algorithm for a flat detector. The method was
validated through 3D reconstructions of a vascular phantom, a specially
designed resolution phantom and animal studies using the newly built II-based
volume tomographic digital angiography imaging system. {\it Results.} Artifacts caused by II distortion in reconstructed
images can be completely removed using the II distortion-correction technique.
With the distortion-correction, the geometric reconstruction accuracy is
significantly improved and the maximum error in vessel diameter is reduced from
2.0 mm without distortion-correction, to 0.3 mm. Moreover, after the
distortion-correction, the spatial resolution of the system becomes uniform.
The results of 3D reconstruction from phantom and animal studies indicate that
the accuracy of the distortion-correction technique is acceptable for volume
tomographic digital angiography reconstruction. {\it Conclusion.} The distortion-correction technique is efficient
and provides acceptable accuracy for volume tomographic digital angiography
imaging.
