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Real-time monitoring of radiofrequency ablation is important to ensure adequate treatment coverage of tumors as well as protection of healthy tissues. The high stiffness contrast between ablated and non-treated tissues has led to the use of ultrasound elastography for coagulation zone visualization but its use has been limited to shallow depths. A shear wave decorrelation mapping approach was developed for ablation boundary detection at clinically relevant depths. The shear wave elastography technique was evaluated using ex vivo bovine liver samples as well as whole livers from fresh cadavers and anesthetized live pigs. Overall the shear wave technique appears feasible for defining and monitoring the progression of thermal lesion boundary.

The increase of tissue temperature in monopolar electrome electrosurgery will damage the tissue inevitably. A water-cooling electrome is proposed to minimize tissue thermal damage. The coolant pours to the surgical tissue interface from the water-cooling electrome tip and takes away extra tissue heat. Consequently, the tissue damage decreases. A water-cooling electrome prototype is designed and comparative experiments with ordinary electrome are conducted. The experimental results show that the water-cooling electrome reduces the tissue damage at least 100 um compared with the ordinary electrome at the same output power. When the electrome power reaches 60 W, the average thermal lesion width of water-cooling electrome compared with that of ordinary electrome decreases 23.2%. The experiment results show that the water-cooling electrome is feasible.

Volumetric HIFU ablation has been implemented in clinical practice to create large thermal lesion while reducing treatment durations. However, it still takes several hours to cover the whole target using volumetric ablation. Multiple focus intensity patterns have been proved beneficial to create larger lesions. The feasibility of dual-focus scanning in volumetric ablation has been evaluated. Simulations of dual-focus scanning and single-focus scanning were performed with the treatment cells of 4, 8, 12 and 16 mm in diameter. Comparison of both scanning approaches indicates that the dual-focus scanning saves treatment time by 20% and needs lower peak acoustic pressure, therefore the potential cavitation could be avoided. Although the maximum near-field temperatures are slightly higher than single-focus scanning, they are acceptable in HIFU treatment.

Thermal dose indicates the level of thermal lesion. During a thermal therapy, desired thermal dose distribution along a tissue can be obtained by proper manipulation of heat source. In this study, the inverse heat transfer problem is applied to estimate the external heat source in a living tissue for a desired thermal dose. The inverse method is the conjugate gradient method with the adjoint problem. The inverse method is function estimation type, since there is not any information exists about the distribution form of the external heat source. The results show that the heat source is estimated precisely for the test cases discussed in this paper.

In this paper we present results showing that Graphic Processing Units (GPUs) can be used to accelerate the simulation of the thermal field dose during Radio Frequency Ablation (RFA). Specifically we show that this simulation can be conducted in real-time, allowing the development of intraopera- tive guidance platforms that track and display the thermal lesion as it forms during the intervention. Real time simulation has not been reported before, and has been a critical factor preventing development of intraoperative guidance tools. I. INTRODUCTION

In this paper, the numerical and experimental evaluation of the dimension of the tissue's ablated area in microwave ablation procedures is discussed. The dependence of the temperature on time, both during and after the end of the ablation procedure, is studied both experimentally and numerically. Results show that the thermal lesion continues to grow after the end of the ablation procedure.

Here, we report that a new design of High Intensity Focused Ultrasound transducer can significantly enlarge the coagulated volume over short periods of time. Our long-term objective is to develop a device that can be used during a surgery, for eventual clinical use in conjunction with hepatic resection. Eight ultrasound emitters, divided into 256 elements, were created by sectioning a single toroid piezocomposite transducer. The focal zone was conical in shape and located 70 mm from the transducer; enabling the treatment of deep-seated tumors. A single thermal lesion was created when the eight emitters performed alternative and consecutive 5s ultrasound exposures. This paper presents in vivo evidence that the coagulated volume obtained from a 40 s total exposure in the liver was 7.0 plusmn 2.5 cm3 (1.5 - 20.0 cm3) with an average diameter of 19.5 plusmn 3.8 mm (10.0 - 29.0 mm). All lesions were visible with high contrast on sonograms. The correlation between the diameter of lesions observed on sonograms and during gross examination was 92%. This method also allowed the user to easily enlarge the coagulated volume by juxtaposing single lesions.

Solid tumors are being treated using radiofrequency (RF) thermal ablation under interventional MRI image guidance. We are investigating the ability of MR to accurately predict the region of cell death by comparing MR thermal lesion images to tissue damage as seen histologically. We developed a methodology using a three-dimensional computer registration. An open MR imaging system was used to guide an RF ablation electrode into rabbit thigh muscles, and acquire in vivo postablation MR volumes. After MR and histology images were registered with an accuracy of 1.32/spl plusmn/0.39 mm (mean/spl plusmn/SD), we compared a boundary of necrosis identified in histology with the outer boundary of the hyperintense rim in MR images. For 14 T2-weighted MR images, the absolute distance between boundaries was 0.96/spl plusmn/0.34 mm. Similar correlations were obtained from experiments with rabbits sacrificed four days postablation. This is good evidence that during ablation treatments, MR images can accurately identify the necrotic region.

Thermal ablation has been investigated as a treatment for a variety of cancers. Heat treatments have not gained large-scale clinical acceptance due to inconsistencies in controlling heat deposition in vivo and the lack of precise temperature measurement. Interstitial ultrasound provide a good method of controlling the radial depth of a thermal lesion and the applicator designs evaluated in this study allow for dynamic angular control of the shape of the lesion. A trisectored internally water-cooled applicator (TriAD) and a rotating catheter water-cooled applicator (RIUS) angularly controlled thermal dose to a target area. Both devices were small in diameter (1.8 mm-2.4 mm), making them clinically feasible for minimally invasive treatment in device size-sensitive tissues. A biothermal model accounting for changes in acoustic attenuation and perfusion as a function of thermal dose was used to evaluate and predict applicator performance. The MR susceptibility artifact of the applicators was examined with MR temperature imaging (MRTI) sequences at 1.5 T and 0.5 T. Ex vivo experiments in turkey and beef muscle with realtime MRTI correlated well with results from the biothermal model. These results display the feasibility of thermally treating tumors with controllable interstitial ultrasound applicators under real-time MRTI and bracket the applicators' predicted performance in vivo.

High-Intensity Focused Ultrasound (HIFU) has become a viable alternative for treatment of primary and metastatic liver tumors. We evaluated the effects of presence of a large blood vessel and its distance to the tumor on lesion size during HIFU heating. A finite element method (FEM) was used to obtain the temperature distribution for a transfer equation based on large blood vessels convection effect. In 3-D FEM simulation, a 4-mm diameter, 10-mm height cylindrical tumor tissue was heated by different heating schemes with a large blood vessel (10-mm diameter) located at different positions nearby. The distance between the vessel and the tumor tissue varied from 1 mm to 3 mm. For HIFU therapy, the large blood vessel of different locations do not have significant effect on temperature distribution and thermal dose profile, when the heating duration is short (~2s) or the distance of the large blood vessel from the tumor is larger than 2 mm. The domain of thermal lesion can effectively cover the desired therapeutic region with short ultrasound exposure duration (~2s).

Interventional ARM-guided radiofrequency (RF) thermal ablation has been applied clinically for minimally invasive treatment of cancer. A principal advantage of MR is that it can reveal the treated region, hereafter called a thermal lesion. To study this, the authors have developed a method to allow accurate correlation of MR images and tissue response. The method includes new tissue-handling techniques and 3D image registration to geometrically align MR images of thermal lesions with optical images of gross pathology and histology tissue response. Using this new method one will be able to achieve accurate correlation of MR images with tissue response in various organs from animal models.