Longitudinal registration of liver PET scans using four phase CT

We have developed an image registration approach for longitudinal liver PET studies using the anatomical information in two sets of associated four phase CT images. We first used the level set method to segment the whole liver in the venous phase CT image. We then applied a non-rigid mutual information based method to register the two venous phase liver images. In our data acquisition protocol, the four phase CT and PET/CT images of the patient are acquired in the same scanning session so can be co-registered using rigid registration. We finally combined the non-rigid registration of 2 set of four phase CT images at different time points with the 2 rigid registrations between corresponding PET/CT and four phase CT image. The result was a single non-rigid transformation between longitudinal pairs of PET images. The method is for use in tracking disease progression and treatment in colon cancer patients with metastatic liver disease. We illustrate the method using a clinical dataset.