A needle guidance system for biopsy and therapy using two-dimensional ultrasound.

Image-guided needle biopsies are currently used to provide a definitive diagnosis of breast cancer; however, difficulties in tumor targeting exist as the ultrasound (US) scan plane and biopsy needle must remain coplanar throughout the procedure to display the actual needle tip position. The additional time associated with aligning and maintaining this coplanar relationship results in increased patient discomfort. Biopsy procedural efficiency is further hindered since needle pathway interpretation is often difficult, especially for needle insertions at large depths that usually require multiple reinsertions. The authors developed a system that would increase the speed and accuracy of current breast biopsy procedures using readily available two-dimensional (2D) US technology. This system is composed of a passive articulated mechanical arm that attaches to a 2D US transducer. The arm is connected to a computer through custom electronics and software, which were developed as an interface for tracking the positioning of the mechanical components in real time. The arm couples to the biopsy needle and provides visual guidance for the physician performing the procedure in the form of a real-time projected needle pathway overlay on an US image of the breast. An agar test phantom, with stainless steel targets interspersed randomly throughout, was used to validate needle trajectory positioning accuracy. The biopsy needle was guided by both the software and hardware components to the targets. The phantom, with the needle inserted and device decoupled, was placed in an x-ray stereotactic mammography (SM) machine. The needle trajectory and bead target locations were determined in three dimensions from the SM images. Results indicated a mean needle trajectory accuracy error of 0.75 +/- 0.42 mm. This is adequate to sample lesions that are < 2 mm in diameter. Chicken tissue test phantoms were used to compare core needle biopsy procedure times between experienced radiologists and inexperienced resident radiologists using free-hand US and the needle guidance system. Cylindrical polyvinyl alcohol cryogel lesions, colored blue, were embedded in chicken tissue. Radiologists identified the lesions, visible as hypoechoic masses in the US images, and performed biopsy using a 14-gauge needle. Procedure times were compared based on experience and the technique performed. Using a pair-wise t test, lower biopsy procedure times were observed when using the guidance system versus the free-hand technique (t = 12.59, p < 0.001). The authors believe that with this improved biopsy guidance they will be able to reduce the "false negative" rate of biopsies, especially in the hands of less experienced physicians.