Factors That Affect Radiofrequency Heat Lesion Size

ObjectiveThis study aims to compare radiofrequency (RF) heat lesion size across electrodes and generator settings available for interventional pain management. MethodsMonopolar lesions are generated ex vivo in animal tissue using sharp cannulae with tip diameters 23, 22, 20, 18, 16 gauge; tip lengths 5, 6, 10, 15mm; set temperatures 60, 70, 80, 90 degrees C; set times 1, 1.5, 2, 3, 5, 10minutes. Lesions are generated using the RRE electrode, cooled RF, and parallel-tip bipolar RF for comparison. Lesion sizes are assessed by automated photographic temperature inference from over 400 lesions, using multiple lesions per configuration. ResultsMonopolar lesion width and length increase with each factor (P<0.001). Increasing cannula diameter from 22 to 16 gauge increases average lesion width 58-65% (3-4mm) at 80 degrees C and 2minutes. Increasing temperature from 60 degrees C to 90 degrees C increases lesion width 108-152% at 2minutes. Although dimensions grow most rapidly over the first minute, average lesion width is 11-20% larger at 2minutes, and 23-32% larger at 3minutes, compared with 1minute. Lesion length extends distal and proximal to the tip, and exceeds tip length by 1-5mm at 80 degrees C and 2minutes. Conventional 16 gauge cannulae at 80-90 degrees C for 2-3minutes generate lesions of average width similar to that produced by the cooled RF configuration proposed for sacroiliac joint denervation. Bipolar RF between parallel cannulae produces a rounded brick-shaped lesion of comparable shape to three sequential monopolar lesions generated using the same cannulae and generator settings. ConclusionsTip gauge, tip length, temperature, and time substantially affect RF lesion size.