title: Fast generation of digitally reconstructed radiographs using attenuation fields with application to 2D-3D image registration.
abstract: Generation of digitally reconstructed radiographs (DRRs) is computationally expensive and is typically the rate-limiting step in the execution time of intensity-based two-dimensional to three-dimensional (2D-3D) registration algorithms. We address this computational issue by extending the technique of light field rendering from the computer graphics community. The extension of light fields, which we call attenuation fields (AFs), allows most of the DRR computation to be performed in a preprocessing step; after this precomputation step, DRRs can be generated substantially faster than with conventional ray casting. We derive expressions for the physical sizes of the two planes of an AF necessary to generate DRRs for a given X-ray camera geometry and all possible object motion within a specified range. Because an AF is a ray-based data structure, it is substantially more memory efficient than a huge table of precomputed DRRs because it eliminates the redundancy of replicated rays. Nonetheless, an AF can require substantial memory, which we address by compressing it using vector quantization. We compare DRRs generated using AFs (AF-DRRs) to those generated using ray casting (RC-DRRs) for a typical C-arm geometry and computed tomography images of several anatomic regions. They are quantitatively very similar: the median peak signal-to-noise ratio of AF-DRRs versus RC-DRRs is greater than 43 dB in all cases. We perform intensity-based 2D-3D registration using AF-DRRs and RC-DRRs and evaluate registration accuracy using gold-standard clinical spine image data from four patients. The registration accuracy and robustness of the two methods is virtually identical whereas the execution speed using AF-DRRs is an order of magnitude faster.
authors.affiliation: Department of Computer Science, Stanford University, Stanford, CA 94305 USA. daniel.russakoff@cs.stanford.edu
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Russakoff
authors.forename: Torsten
authors.initials: T
authors.lastname: Rohlfing
authors.forename: Kensaku
authors.initials: K
authors.lastname: Mori
authors.forename: Daniel
authors.initials: D
authors.lastname: Rueckert
authors.forename: Anthony
authors.initials: A
authors.lastname: Ho
authors.forename: John R
authors.initials: JR
authors.lastname: Adler
authors.forename: Calvin R
authors.initials: CR
authors.lastname: Maurer
mesh_terms: D000465:Algorithms; D003199:Computer Systems; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013131:Spine / Q000000981:diagnostic imaging* / Q000601:surgery; D013382:Subtraction Technique; D025321:Surgery, Computer-Assisted / Q000379:methods*