150 can be lowered and raised in a borehole 115 in earth formations 113 on an armored multiconductor cable 117 which passes over sheave wheel 122 and is controlled by surface equipment 130 cable displacement and therefore tool depth is measured by a depth gauge 124 casing or pipe 140 is set in the borehole and there may typically be cement not shown between the casing and the earth formations a primary purpose of the cement being to prevent migration of fluids between water and hydrocarbon bearing zones in a production zone the device 150 is provided with centralizers represented at 151 and has a rotatable subassembly or 34 sub 34 152 that is driven by a motor assembly not shown in the housing 153 of device 150 which drives the sub 152 via a rotating shaft and a rotating seal also not shown reference can be made to u s pat no 5 274 604 and to the publication of the assignee hereof 34 ultrasonic imager usi 34 schlumberger testing amp production services 1991 the rotatable sub 152 includes a focused transducer that directs pulse of ultrasound energy toward the casing and receives reflected echoes in general focusing reduces the sensitivity of the return echo to misalignment of the transducer with respect to the reflection surface the.