of 40 50 pounds per square inch this pressure in space 193 is readily transmitted through diaphragm 192 to the silicone oil in well 191 and hence through column 190 into space 165 the pressure provided by source 188 is in the order of 2 pounds per square inch higher than the pressure in system 196 in order to keep plate 161 flat and held against lens 162 through rod 163 element 199 in the transducer assembly is an insulating member to which element 172 is bolted by screw s 200 gasket 201 keeps the silicone oil contained in column 190 from reaching the coaxial cable 179 metal plate 182 is bolted to housing 164 around the outer periphery of plate 182 oil is kept in column 190 and well 191 by the use of o ring seal 203 positioned between housing 164 and plate 182 and by gasket 205 member 206 is bolted and sealed to plate 182 top metal plate 207 is bolted by screws 203 to housing 164 and sealed thereto through o rings 209 metal tube 195 is sealed to element 187 through seal 210 the coaxial cable 179 is water tight and sealed to top plate 207 through member 211 and o ring 212 in order to accomplish the task of producing lesions of any complex size or shape with intense focused ultrasound it is necessary to provide for ultrasound dosage conditions which produce individual focal lesions from which the complex volume can be generated which do not compromise tissue outside the intended focal lesions side and permit subsequent individual focal lesions in a.