A probe for ultrasonic tissue treatment (such as liposuction) includes a body having a wall defining a lumen. A thickness of the wall decreases in a distal direction such that the lumen increases in cross section in the distal direction. The wall tapers to a smaller thickness in the distal direction. The wall steps down to a smaller thickness in the distal direction. The probe is cylindrical and an outer diameter of the probe remains constant while the thickness of the wall decreases.
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