Images showing the needle holder with the RFA device (top) on one side and, on the other, the IREDs (bottom) that provide position data to the Optotrak tracking system. Fiducial markers were used to coregister the CT model of the device.
Rendering of segmented CT image of RFA device attached to the needle holder showing the deployed tines. The floating objects are the Acustar markers, while the H-shaped object near the top of the image is the frame that houses the IREDs.
(left) 3D rendering of barium tracks imaged in CT. An Acustar marker is shown on the left. (right) Schematic showing between needle tip location predicted by Optotrak measurements and the needle track segmented in the CT image.
(top left) Photograph of the phantom housing along with the needle holder and the RFA device in a setup representative of the ablation experiments. (top right) A close-up of the phantom housing showing the needle holes, the slice guides used to aid in cutting the phantom, and the location of the grounding pad. (bottom left) Schematic showing inner dimensions of the phantom housing and its local coordinate systems. The phantom material is filled from the bottom up to an approximate height of . (bottom right) Top-down view of the phantom housing. The dark circles represent the needle holes. The dark lines show the location of the slice planes. From top to bottom, these planes are , 0, , and .
(left) The surface model of a commercially used ablation device along with its local coordinate system. (middle) A close-up of the tine arrangement from the bottom. The thermocouple readings from the RITA probe correspond to the modeled temperatures at the tips of the outer tines located on the cardinal axes as well as at the tip of the central tine. (right) A cut view of the surface mesh of the phantom geometry with a needle penetrating the phantom surface and placed in the approximate location measured in experimental Case 2.
Histogram of the distance between needle tip location predicted by Optotrak and as observed in CT imaging.
Temperature traces from (left) Case 1 and (right) Case 2. The marked points are the recorded temperatures provided by the RFA system. The solid lines represent the model predictions.
Ablation outcome for the slice at .
Ablations at slice for (left pair) Case 1 and (right pair) Case 2. In each pair, the left image depicts the camera view and the right image the back view. The light mask represents the segmented pixels corresponding to the ablated albumin. The surfaces provide a 3D context of the overall ablation shapes. The intersection of the surface with the plane is given by the black outline.
The diagram shows, in the coordinate system of the phantom, the largest spheres that fit the ablated pixels with the corresponding FEM prediction overlaid. (left) Case 1. (right) Case 2.
Receiver operator characteristics of sensitivity, , and positive predictive value, , values using sphere and FEM ablation models for each of the two ablation results. The curve was generated for the FEM model by varying the contour threshold, whereas for the sphere model, the sphere radius was varied.
List of material properties used in RFA simulation. Values represent the initial properties used in the simulations. As simulations proceed, the temperature-dependent properties change.
Table of parameters characterizing model accuracy. The bottom row lists the maximum displacement of a tine in the repositioning process.
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