DOI: 10.1148/radiol.2301021512
Radiofrequency Ablation: Modeling the Enhanced Temperature Response to Adjuvant NaCl Pretreatment1
S. Melvyn Lobo, MD,
Karim S. Afzal, BS,
Muneeb Ahmed, MD,
Jonathan B. Kruskal, MD, PhD,
Robert E. Lenkinski, PhD and
S. Nahum Goldberg, MD
1 From the Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Ave, Boston, MA 02215. Supported by grants from the National Cancer Institute, National Institutes of Health, Bethesda, Md (RO1-CA87992–01A1), and Radionics/Tyco Healthcare, Burlington, Mass. Received November 19, 2002; revision requested February 6, 2003; revision received March 5; accepted May 27. Address correspondence to S.N.G. (e-mail: sgoldber@caregroup.harvard.edu).
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Figure 1. Experimental apparatus. An internally cooled RF electrode (solid arrow) has been inserted into an NaCl gel-filled well within an agar phantom (short open arrow), which is placed in a saline bath at a fixed distance from the grounding pad (G). A thermocouple probe (arrowheads) has been inserted to measure temperature 20 mm from the electrode. An acrylic guide (long open arrow) ensures proper positioning of the thermocouple. The RF generator and a temperature measurement device can be seen in the background.
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Figure 2. Effect of NaCl concentration. Drawing demonstrates shifting maximum temperatures with a fixed NaCl volume (Vol) as the NaCl concentration is varied. Three volumes are depicted.
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Figure 3. Effect of NaCl volume. Drawing demonstrates shifting maximum temperatures with a fixed NaCl concentration (Conc) as the NaCl volume is varied. Three NaCl concentrations are depicted. A similar phenomenon was observed with fixed NaCl volumes and varying NaCl concentrations (Fig 2).
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Figure 4a. Temperature response surface for NaCl pretreatment. (a, b) Two drawings graphically represent the three-dimensional relationship of temperature at 2 cm from the RF electrode with NaCl concentration and NaCl volume in two different projections. Note the steep upslope to the temperature maximum, which is the region that fits a modified gamma-variate function that corresponds to the generator energy-dependent region. Beyond the maximum temperature, in the generator current-limited region, temperature decreases exponentially.
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Figure 4b. Temperature response surface for NaCl pretreatment. (a, b) Two drawings graphically represent the three-dimensional relationship of temperature at 2 cm from the RF electrode with NaCl concentration and NaCl volume in two different projections. Note the steep upslope to the temperature maximum, which is the region that fits a modified gamma-variate function that corresponds to the generator energy-dependent region. Beyond the maximum temperature, in the generator current-limited region, temperature decreases exponentially.
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Figure 5. Illustration of temperature response surface of NaCl pretreatment in an animal model. Three-dimensional modeling of a previously described (22) in vivo porcine liver involving the use of various volumes and concentrations of NaCl pretreatment for RF ablation is shown. Mathematically derived equations that produce the surface response depicted by Figure 4 produced an r2 value of 0.86 for these data.
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Copyright © 2004 by the Radiological Society of North America.
