title: Progressive attenuation fields: fast 2D-3D image registration without precomputation.
abstract: Computation of digitally reconstructed radiograph (DRR) images is the rate-limiting step in most current intensity-based algorithms for the registration of three-dimensional (3D) images to two-dimensional (2D) projection images. This paper introduces and evaluates the progressive attenuation field (PAF), which is a new method to speed up DRR computation. A PAF is closely related to an attenuation field (AF). A major difference is that a PAF is constructed on the fly as the registration proceeds; it does not require any precomputation time, nor does it make any prior assumptions of the patient pose or limit the permissible range of patient motion. A PAF effectively acts as a cache memory for projection values once they are computed, rather than as a lookup table for precomputed projections like standard AFs. We use a cylindrical attenuation field parametrization, which is better suited for many medical applications of 2D-3D registration than the usual two-plane parametrization. The computed attenuation values are stored in a hash table for time-efficient storage and access. Using clinical gold-standard spine image data sets from five patients, we demonstrate consistent speedups of intensity-based 2D-3D image registration using PAF DRRs by a factor of 10 over conventional ray casting DRRs with no decrease of registration accuracy or robustness.
authors.affiliation: Neuroscience Program, SRI International, Menlo Park, California 94025-3493, USA. torsten@synapse.sri.com
authors.forename: Torsten
authors.initials: T
authors.lastname: Rohlfing
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Russakoff
authors.forename: Joachim
authors.initials: J
authors.lastname: Denzler
authors.forename: Kensaku
authors.initials: K
authors.lastname: Mori
authors.forename: Calvin R
authors.initials: CR
authors.lastname: Maurer
mesh_terms: D000465:Algorithms; D006801:Humans; D021621:Imaging, Three-Dimensional; D011857:Radiographic Image Interpretation, Computer-Assisted; D013131:Spine / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed