Fusion of CT and PET data: method and clinical relevance for planning laser-induced thermotherapy of liver metastases.

Aim: Catheter-placement in liver metastases is difficult when the lesions a re not visible on plain images. We evaluated the use of image fusion using CT and PET data, providing information on anatomy and liver lesions, respec tively. Methods: Plain CT of the liver and whole body FDG-PET were performe d in 28 patients with colorectal carcinoma in preparation for laser-induced thermotherapy. Fusions of image data and 2D-visualisation were performed a nd evaluated with regard to quality of the registration, number of detected lesions and influence of the procedure on laser-induced thermotherapy. Ima ge fusion was performed using an algorithm which was developed by our group . Results: 84 focal liver lesions were visible on CT, 107 on PET images. Th is means that CT guided catheter placement would have to be performed "blin dly" in 23 lesions. In 6 patients previously unknown extra-hepatic tumor de posits were seen on PET images (local recurrence, 2 extrahepatic metastases , 2 second primaries). Conclusion: Hot spots from metastases, which are dif ficult to locate on PFT images alone, may be identified on images generated by fusion of CT and PET data. These images facilitate an interventional ap proach to liver lesions which are not visible on plain CT. As PET allows fo r whole body screening, it helps identifying patients who would not profit from laser-induced thermotherapy.