Tissue ablation: devices and procedures John G. Webster Ablation is a method of delivering physical, chemical, or energy treatment to tissue for the purpose of removing, altering, creating scar tissue or causing aposis (cell death). Cardiac accessory pathways permit ventricular excitation to escape to the atria and cause ventricular tachycardia. Catheters permit mapping the location of the accessory pathways. 2.6 mm diameter catheter electrodes pass 450 kHz power of about 20 W for about 20 s to heat the pathway above 50 C to kill the pathway tissue. To kill hepatic cancer, the radiologist inserts a probe percutaneously, expands an umbrella-like array and applies power for about 8 min. Alternatively in an open procedure the surgeon can heat using a variety of probes or freeze using cryo-ablation. To avoid exceeding 100 C, which causes charring, steam and popping, saline may circulate through the probe interior or perfuse into the tissue. Microwave ablation provides quicker heating to prevent hepatic vessels from carrying heat away during ablation. Finite element method electrical-thermal models help to develop new methods including bipolar, multiple, phased array, noncontact and needle electrodes. Applications include ablation of prostate, brain, gastrointestinal tract, capsule, breast, varicose veins, blood clots, skin wrinkles, cornea, teeth, and bone.