Sonographically guided percutaneous interventions of the breast using a steerable ultrasound beam.

Abstract

P ercutaneous cyst aspiration, hookwire localization, fine-needle aspiration, and large-needle core biopsy of the breast are often performed with sonographic guidance. Successful and safe sonographically guided freehand intervention requires accurate needle placement. A favorable outcome is more likely when the shaft and tip of the needle are both well seen throughout the procedure. Transducer-mounted needle guides I I I. needles designed with echogenic surfaces, transducers with central apertures [2], and complex electronic guidance systems have been developed to assist such procedures. This report intr(xluces a novel application of electronic steering ofthe ultrasound beam, which is a simple technique that markedly enhances the visibility of needles used for sonographically guided interventions of the breast. The conventional arrangement for sonographically guided needle interventions resuits in an acute angle between the ultrasound beam and the needle that depends solely on the angle of the needle relative to the transducer (Fig. IA). Electronic beam steering is a technique for angling the ultrasound beam from a muitielement transducer array [3]. The individual piezoelectric elements are fired in sequence from one end of the transducer to the other rather than fired simultaneously. If the delay between the firing ofeach element is identical, the individual small wavefronts of each crystal combine to form a single large wavefront that is tilted at an angle to the standard beam axis (Fig. I B). The angle is determined by the delay between firings of the individual transducer elements. Beam steering considerably enhances the visibility of needles used for interventional procedures. Because it has a smooth, solid surface, a needle is an example of a specular reflector. The direction of the ultrasound echo reflecting off the surface of a specular reflector is established by the law of reflection: “the angle of incidence equals the angle of reflection” [31. Therefore, the closer the incident beam is to being perpendicular to the reflector (i.e., 900 to the needle), the stronger is the signal or echo that returns to the transducer [4].