Automatic coregistration of whole-body positron emission tomography images using piece-wise rigid body transformations

The coregistration of whole body PET images runs into certain problems. On the one hand if one uses non-rigid transformatin the validity of the data might be compromised. On the other hand if one uses only rigid body transformations, it is hardly possible to take all details of the images into account. We developed a method that circumvents this problem by using piecewise rigid body transformation.

This method evaluates the alignment of the images by the correlation of intensities and the mutual information of the data. The best transformation parameters are searched for by a modified conjugate gradient method.

The complete functionality is implemented in form of a libarary, which might be linked to an application. A command line and graphical user interface is provided. This program allows to define several areas in the images on which a separate coregistration is performed. All areas can be viewed in the same transformed image. The regions in between are interpolated by a Fermi box for each area in order to keep as much of the original information as possible.

The user interaction is reduced to a minimum, besides the coregistration areas only some information about the image content used for optimization and acceleration might be provided. However, the method will lead to improved alignment even without this additional information.

We will present the method as well as result for the different fields of application, e.g. follow up studies or dynamical studies.