A needle-like ultrasonic probe includes an inner needle received in a hollow, tubular outer needle for rotation about an axis thereof. The inner needle has a pointed distal end, and a notch is formed in an outer peripheral surface of that portion of the inner needle which is located adjacent to the distal end thereof. At least one ultrasonic transducer, as well as an acoustic lens for converging an ultrasonic wave, produced by the ultrasonic transducer, onto a point near to the outer peripheral surface of the inner needle, is provided in the notch. A filler, having an outer surface conforming to the outer peripheral surface of the inner needle, is fitted in the notch. With this construction, after the inner needle is smoothly stuck into a living tissue, even if it is rotated and axially moved, the living tissue is less affected or damaged by the inner needle.

An ultrasonic invasive instrument such as a biopsy needle has an ultrasonic transducer mounted at one end, with the transducer being electrically coupled to two conductors such as a stylet and central cannula forming the instrument body and transmitting signals from the transducer identifying the instrument's location in a field transmitted by an imaging scanner, the transducer being coupled to at least one of the conductors by an ohmic or capacitive coupling, with for example body fluids serving as the couplant material.

A piezoelectric element comprising a thin sheet piezoelectric element formed of a piezoelectric ceramic having PZT (PbZrO3.PbTiO3) as a main component with electrodes formed on the surfaces thereof, said thin sheet piezoelectric element being wrapped around a shaft to form a cylinder.

Novel intravascular, ultrasonic imaging catheters are provided which utilize thin layers of a flexible plastic material, such as PVDF, which can be spot polarized in active regions which are to serve as piezoelectric transducers. Thin layer metallic electrodes are deposited on opposing surfaces of these active regions. Strips of the appropriately configured material also having shielding and backing and/or core forming portions are spiral wound into a completed catheter. Alternatively, the catheters are fabricated from extruded PVDF tubing which may be formed around a central core which carries those electrodes which are to contact the inner surface of the extruded tube.

There is provided a small and inexpensive actuator which has a simple structure and can obtain a large displacement. When voltage is applied to electrodes 2a and 2b formed on an inner circumferential surface and an outer circumferential surface of a piezoelectric ceramic 1 wound like a coil, deformation occurs in such a direction that an inner circumferential side of the piezoelectric ceramic 1 wound like the coil is contracted, and an outer circumferential side is expanded. Accordingly, if one end portion of the piezoelectric ceramic 1 formed into the coil shape is fixed, the other end portion is rotated in accordance with the deformation of contracting the diameter of this coil.