A system for ablation with acoustic feedback, the system comprising: a catheter (1, 61, 11, 102) which includes an elongated catheter body (1b, 61 b, 110) extending longitudinally between a proximal end and a distal end along a longitudinal axis; at least one ablation element disposed in a distal portion which is adjacent the distal end of the catheter body (1b, 61 b, 110) to ablate a targeted tissue region outside the catheter body (1b, 61b, 110); and a pulse- echo ultrasonic transducer disposed in the distal portion interior to the at least one ablation element and arranged to emit and receive an acoustic beam along a centroid in a beam direction, at a transducer beam angle of between about 30 degrees and about 60 degrees relative to a distal direction of the longitudinal axis at a location of intersection between the longitudinal axis and the beam direction of the centroid of the acoustic beam of the ultrasonic transducer, wherein the pulse-echo ultrasonic transducer transmits and receives acoustic pulses to provide lesion information in the targeted tissue region being ablated; an ablation power subsystem (105, 205) to provide ablation power to the at least one ablation element; an ultrasonic transmit and receive subsystem (106, 206) to operate the pulse-echo ultrasonic transducer to transmit and receive acoustic pulses; a control subsystem (104, 204) which includes a processor and one or more modules executable by the processor to control operation of the ablation power subsystem (105, 205) and the ultrasonic transmit and receive subsystem (106, 206); and a display (107, 207) to display information including the lesion information, characterised in that the one or more modules include a transducer detection information processing module to process transducer detected information from the pulse-echo ultrasonic transducer and to provide feedback, based on the processed transducer detected information, to be used to monitor or control ablation by the at least one ablation element, wherein the transducer detected information includes a detected lesion depth along a beam emanation direction; wherein the transducer detection information processing module includes a lesion depth correction module which converts the detected lesion depth along the beam direction to a corrected lesion depth in a normal direction which is perpendicular to the tissue surface in contact with the at least one ablation element. a catheter (1, 61, 11, 102) which includes an elongated catheter body (1b, 61 b, 110) extending longitudinally between a proximal end and a distal end along a longitudinal axis; at least one ablation element disposed in a distal portion which is adjacent the distal end of the catheter body (1b, 61 b, 110) to ablate a targeted tissue region outside the catheter body (1b, 61b, 110); and a pulse- echo ultrasonic transducer disposed in the distal portion interior to the at least one ablation element and arranged to emit and receive an acoustic beam along a centroid in a beam direction, at a transducer beam angle of between about 30 degrees and about 60 degrees relative to a distal direction of the longitudinal axis at a location of intersection between the longitudinal axis and the beam direction of the centroid of the acoustic beam of the ultrasonic transducer, wherein the pulse-echo ultrasonic transducer transmits and receives acoustic pulses to provide lesion information in the targeted tissue region being ablated; an ablation power subsystem (105, 205) to provide ablation power to the at least one ablation element; an ultrasonic transmit and receive subsystem (106, 206) to operate the pulse-echo ultrasonic transducer to transmit and receive acoustic pulses; a control subsystem (104, 204) which includes a processor and one or more modules executable by the processor to control operation of the ablation power subsystem (105, 205) and the ultrasonic transmit and receive subsystem (106, 206); and a display (107, 207) to display information including the lesion information, characterised in that the one or more modules include a transducer detection information processing module to process transducer detected information from the pulse-echo ultrasonic transducer and to provide feedback, based on the processed transducer detected information, to be used to monitor or control ablation by the at least one ablation element, wherein the transducer detected information includes a detected lesion depth along a beam emanation direction; wherein the transducer detection information processing module includes a lesion depth correction module which converts the detected lesion depth along the beam direction to a corrected lesion depth in a normal direction which is perpendicular to the tissue surface in contact with the at least one ablation element.