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Microwave Ablation with a Single Small-Gauge Triaxial Antenna: In Vivo Porcine Liver Model¹

¹ From the Departments of Radiology (C.L.B., L.A.S., T.M.F., F.T.L.), Biomedical Engineering (P.F.L.), and Electrical and Computer Engineering (D.W.v.d.W.), University of Wisconsin–Madison, 600 Highland Ave, Madison, WI 53792. Received August 22, 2005; revision requested October 24; revision received January 31, 2006; accepted March 3; final version accepted May 1. Supported by National Institutes of Health grant R21 RR018303-01. Address correspondence to C.L.B. (e-mail: clbrace{at}wisc.edu).

View larger version (18K): [in this window] [in a new window] [Download PPT slide]   Figure 1: Graph of theoretic thermal profile based on Equation (1), with sources producing a temperature of either 100°C or 150°C at x = 0. When zone of ablation was defined at 60°C, 100°C source produced a 2.0-cm ablation diameter, whereas the 150°C source produced a 3.2-cm diameter. Thus, the larger thermal gradient created with 150°C source results in larger ablation zone.

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Triaxial antenna. Reflection coefficient of the antenna in liver was minimized, for an active length of 12.3 mm and an insertion depth of 3.5 mm (12).

View larger version (120K): [in this window] [in a new window] [Download PPT slide]   Figure 3: Diagram of perfusion scoring of typical ablation zone. For each vessel, the distance from ablation track to vessel center (R) and vessel diameter (d) were recorded and input into Equation (2). Dotted lines indicate other vessels scored for this ablation zone. Total perfusion score for each ablation was the sum of scores for all vessels.

View larger version (10K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Graph of mean minimum (min) and maximum (max) ablation zone diameter versus application time. Logarithmic dependence on application time similar to results of previous numeric and ex vivo studies was seen (11). Relatively small increases in ablation diameter were seen after 5 minutes. Anomalous points at 10 minutes are thought to be caused by an abnormally high perfusion rate and overused antennas.

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Left: Representative slice at 2 minutes. Right: Representative slice at 12 minutes. Average ablation zone diameter was significantly larger at 12 minutes than at 2 minutes. Note highly circular shape of each ablation zone and lack of deflection caused by local blood flow. Input power was 68 W in both cases.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 6: Ablation zone of 3.6 x 3.2 cm created with triaxial antenna. In this case, a vessel approximately 5 x 9 mm was able to be coagulated (arrow).