Comparison of Longitudinal-Mode and Longitudinal- Torsional Mode Ultrasonic Bone Biopsy Devices

Previous research by the authors has demonstrated the efficacy of an ultrasonic bone biopsy device that operates in a longitudinal (L)mode. Ultrasonic longitudinal-torsional (L-T)coupled vibration has proven successful in several applications including ultrasonic surgical devices. In this work, an L-mode ultrasonic bone biopsy device was geometrically modified by introducing helical slits to degenerate the longitudinal vibration into a composite L-T motion. The performance of the L-T biopsy needle device was then compared with the L-mode needle device based on their ability to penetrate animal bone samples. Finite element analysis was used to design the L-T needle. The depth and pitch of the helical slits were systematically modified in the FEA model with the aim of maximizing the achievable torsional displacement while ensuring sufficient frequency spacing between the L-T mode and the neighboring flexural modes. Experimental modal analysis (EMA)of the fabricated ultrasonic device was used to identify the modal parameters and validate the FEA model. Comparative penetration tests showed that to achieve penetration with the L-mode device, the operator was required to apply a slow backward and forward rotation as well as the small forward force, to maintain a forward motion and avoid imprinting of the needle tip. The resulting hole was slightly conical with some micro-damage on the hole surface. The L-T mode device, however, could penetrate the same animal bone sample only applying a small forward force, hence simplifying the procedure, increasing precision and resulting in a cylindrical, less damaged hole surface.

I. Introduction

A bone biopsy is an intrusive medical procedure used to diagnose an abnormality within the body. A small sample of bone is extracted and examined using microscopy to identify a bone disorder or establish the cause of discomfort. Generally, patients report moderate to severe pain levels for up to three to four days after a bone biopsy procedure is completed [1], [2]. For this procedure, the clinician usually uses a trephine needle and applies a large forward force, measured to be up to 400–600 N depending on the bone location. Additionally, lateral and twisting movements of the needle are required to penetrate the outer shell of the bone to retrieve the sample. Clinical studies have also found that the experience of the clinician significantly affects the pain levels experienced by the patient.