PET-CT image registration in the chest using free-form deformations

IEEE Trans Med Imaging. 2003 Jan;22(1):120-8. doi: 10.1109/TMI.2003.809072.


We have implemented and validated an algorithm for three-dimensional positron emission tomography transmission-to-computed tomography registration in the chest, using mutual information as a similarity criterion. Inherent differences in the two imaging protocols produce significant nonrigid motion between the two acquisitions. A rigid body deformation combined with localized cubic B-splines is used to capture this motion. The deformation is defined on a regular grid and is parameterized by potentially several thousand coefficients. Together with a spline-based continuous representation of images and Parzen histogram estimates, our deformation model allows closed-form expressions for the criterion and its gradient. A limited-memory quasi-Newton optimization algorithm is used in a hierarchical multiresolution framework to automatically align the images. To characterize the performance of the method, 27 scans from patients involved in routine lung cancer staging were used in a validation study. The registrations were assessed visually by two expert observers in specific anatomic locations using a split window validation technique. The visually reported errors are in the 0- to 6-mm range and the average computation time is 100 min on a moderate-performance workstation.

Publication types

  • Evaluation Study
  • Research Support, U.S. Gov't, P.H.S.
  • Validation Study

MeSH terms

  • Algorithms*
  • Artifacts
  • Carcinoma, Non-Small-Cell Lung / diagnostic imaging
  • Fluorodeoxyglucose F18
  • Humans
  • Lung Neoplasms / diagnostic imaging
  • Motion
  • Radiography, Thoracic / methods*
  • Radiopharmaceuticals
  • Subtraction Technique*
  • Thorax / diagnostic imaging*
  • Tomography, Emission-Computed / methods*


  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18