Ablation Monitoring with Elastography: 2D In-vivo and 3D Ex-vivo Studies Hassan Rivaz ⋆ , Ioana Fleming, Lia Assumpcao, Gabor Fichtinger, Ulrike Hamper, Michael Choti, Gregory Hager, and Emad Boctor ERC for Computer Integrated Surgery, Johns Hopkins University. Dept. of Surgical Oncology, Johns Hopkins Medicine. School of Computing, Queens University {rivaz,inicola1}@jhu.edu, eboctor1@jhmi.edu Abstract. The clinical feasibility of 2D elastography methods is hin- dered by the requirement that the operator avoid out-of-plane motion of the ultrasound image during palpation, and also by the lack of volumet- ric elastography measurements. In this paper, we develop and evaluate a 3D elastography method operating on volumetric data acquired from a 3D probe. Our method is based on minimizing a cost function using dynamic programming (DP). The cost function incorporates similarity of echo amplitudes and displacement continuity. We present, to the best of our knowledge, the first in-vivo patient studies of monitoring liver ablation with freehand DP elastography. The thermal lesion was not dis- cernable in the B-mode image but it was clearly visible in the strain image as well as in validation CT. We also present 3D strain images from thermal lesions in ex-vivo ablation. Good agreement was observed between strain images, CT and gross pathology. 1 Introduction Hepatocellular carcinoma (HCC) is one of the most common tumors, caus- ing 662,000 deaths worldwide annually. Minimally invasive RF ablation [1] has gained much interest recently since only 10% to 20% of patients with HCC are amenable to traditional therapy of surgical resection of the tumor. In RF ab- lation, an electrode is placed into the tumor to cauterize it [1]. Monitoring the ablation process in order to document adequacy of margins during treatment is a significant importance. Ultrasonography is the most common modality for both target imaging and for ablation monitoring. However, ultrasonographic ap- pearance of ablated tumors only reveals hyperechoic areas due to microbubbles and outgasing and cannot adequately visualize the margin of tissue coagulation. Accordingly, ultrasound elastography (Ophir et al, 1991) has emerged as a useful augmentation to conventional ultrasound imaging. Elastography has been used for monitoring RF ablation [2], [3] by observing that ablated region is harder than surrounding tissue. In the most common variation of elastography, ultrasound images are captured while the tissue is being compressed, and images ⋆ Supported by the Link Foundation Fellowship. D. Metaxas et al. (Eds.): MICCAI 2008, Part II, LNCS 5242, pp. 458–466, 2008. c  Springer-Verlag Berlin Heidelberg 2008