Hextuple registration of interim and follow-up PET-CT images for the accurate tracking of patient recovery after therapy.

An extended registration framework is presented to accurately register follow-up PET-CT study triples. Since there are six images to register, sophisticated feature extraction and similarity measurement methods are proposed. An irregular sampling method is introduced to decrease the processing speed of the hextuple registration. The similarity measurement is based on a normalized hybrid extended SSD (Sum of Squared Differences) and and extended NMI (Normalized mutual Information). The method has been tested on a huge amount of simulated data to avoid observer specific results. Based on the validation, our method outperforms prior solutions in both speed and accuracy, hence it should be the subject of further investigations.