High　intensity　focused　ultrasound　(　HIFU)　is　an　effective　technique　for　noninvasive　local　creating　coagulative　necrotic　lesions　in　deep　target　volumes　without　damage　to　the　overlaying　or　surrounding　tissues.　It　is　very　important　to　detect　and　evaluate　lesions　generated　by　HIFU　during　treatment　procedures.　This　study　describes　the　development　of　several　differential　ultrasonic　imaging　techniques　to　characterize　lesions　based　on　estimation　of　relative　changes　in　tissue　properties　derived　from　backscattered　RF　data.　A　single,　spherical　HIFU　transducer　was　used　to　produce　lesions　in　soft　tissues.　The　RF　signals　were　recorded　as　outputs　from　a　modi.　eddiagnosticultrasound　system.　After　some　preprocessing,　the　integrated　backscatter　values,　which　can　be　used　as　an　indicator　of　the　microstructure　and　backscattering　property　of　tissues,　were　calculated　before　and　after　HIFU　treatment.　The　differential　integrated　backscatter　values　were　subsequently　used　to　form　images　revealing　the　lesion　areas.　The　differential　attenuation　imaging　with　the　same　RF　data　was　also　performed,　which　has　been　proposed　by　a　few　researchers.　The　results　of　the　differential　integrated　backscatter　imaging　were　compared　with　that　of　the　differential　attenuation　imaging　and　the　former　method　offers　some　advantages　over　the　latter　method.　The　two　methods　above　are　both　based　on　spectrum　analysis　and　would　spend　much　computational　time.　Therefore,　some　simple　digital　differential　imaging　methods,　including　absolute　difference　(　AD),　sum　absolute　differences　(　SAD),　and　sum　squared　differences　(　SSD)　algorithms,　were　also　proposed　to　detect　HIFU-　induced　lesions.　However,　these　methods　cannot　provide　the　information　of　the　degree　of　tissue　damage.　Experiments　in　vitro　bovine　muscle　and　liver　validated　the　method　of　differential　integrated　backscatter　imaging　for　the　characterization　of　HIFU-　induced　lesions.　And　the　AD,　SAD,　and　SSD　algorithms　can　be　implemented　in　real-　time　during　HIFU　therapy　to　visualize　the　lesions.　(c)　2006　Elsevier　B.　V.　All　rights　reserved.