Application of nonrigid registration in ablation of liver cancer

Ablation is a kind of successful treatment for cancer. The technique inserts a special needle into a tumor and produces heat from Radiofrequency at the needle tip to ablate the tumor. Open configure MR system can take MR images almost real time and now is applied in liver cancer treatments. During a surgery, surgeons select images in which liver tumors are seen clearly, and use them to guide the surgery. However, in some cases with severe chirrhosis, the tumors can't be visualized in the MR images. In such cases, the combination of preoperative CT images will be greatly helpful, if CT images can be registered to the position of MR images accurately. It is a difficult work since the shape of the liver in the MR image is different from that of CT images due to the influent of the surgery. In this paper, we use Bspline based FFD nonrigid image registration to attack the problem. The method includes four steps. Firstly the MRI inhomogeneity is corrected. Secondly, parametric active contour with the gradient vector flow is used to extract the liver as region of interest (ROI) because the method is robust and can obtain satisfied results. Thirdly, affine registration is use to match CT and MR images roughly. Finally, Bspline based FFD nonrigid registration is applied to obtain accuracy registration. Experiments show the proposed method is robust and accuracy.