Elsevier

Medical Engineering & Physics

Volume 35, Issue 11, November 2013, Pages 1584-1590
Medical Engineering & Physics

Study of the effect of cannula rotation on tissue cutting for needle biopsy

https://doi.org/10.1016/j.medengphy.2013.05.001Get rights and content

Abstract

Needle biopsy is a medical procedure to extract tissue for diagnosis of cancer and other diseases. The quality of tissue samples acquired by needle biopsy greatly depends on the cutting forces of the cannula. The reduction of cutting forces is crucial for obtaining good tissue samples. There exist many factors that influence the cutting forces, some of which include the cannula tip geometry, translation speed, and rotation speed. In the present paper, the effects of rotating the cannula on tissue cutting for needle biopsy are studied. A fracture-mechanics-based approach is used to analyze the cutting forces. Analysis has shown that the cutting forces decrease with the increases in the slice/push ratio defined as the ratio of speed component parallel to the cutting edge/speed perpendicular to the cutting edge. Experiments are performed to demonstrate this phenomenon. Mathematical models of the slice/push ratio for bevel tip cannulas are formulated. The results are used to determine the optimal cannula rotation/translation speed and the desired tip geometry for needle biopsy. It is shown that a minimal slice/push ratio of 2 is recommended. A cannula with a large bevel angle is more suitable for rotational needle biopsy.

Introduction

Needle biopsy is a medical procedure to extract tissue for diagnosis of cancer and other diseases. End-cut needle biopsy, shown in Fig. 1, consists of an outer cannula (hollow needle) and an inner stylet (solid needle). To take a sample, both the cannula and stylet are first jointly inserted to the margin of the lesion. The cannula, which has a sharp cutting edge at the tip, then further advances to cut a tissue sample. The stylet and cannula, with the specimen, are then removed from the patient. The most common cannulas have either a circular cutting edge or a bevel angle with a circumferentially cutting edge, as illustrated in Fig. 1. It is crucial for a pathologist to acquire large and contiguous tissue samples in order to make an accurate diagnosis.

Needle biopsy is essentially a tissue cutting procedure, where the cannula is the cutting tool. The quality of tissue samples acquired by needle biopsy greatly depends on the cutting forces exerted by the cannula. Reduction in cutting forces is crucial in obtaining good tissue samples. Studies have shown that for a specific gauge needle lower cutting forces lead to larger biopsy samples [1]. It is well-known that the needle tip geometry has a direct influence on the insertion force. Much work has been conducted related to the solid needle tip geometry and insertion force [2], [3], [4], [5], [6], [7]. The effects of the cannula tip geometry on the cutting force and tissue sample length have been studied by Moore et al. [8], [9]. They found that the tip configuration of a cannula greatly affects the cutting force and tissue sample length for needle biopsy.

The idea of enhancing tissue cutting by rotating the cutting cannula has already been used for decades in skin punch biopsy, where the skin is incised by simultaneously rotating and pressing the punch's cutting edge into the tissue [10], [11]. Recently some breast biopsy devices apply rotation on the cannula to sever tissue. Commercially available rotational biopsy devices include the Mammotome biopsy systems (Devicor Medical Products Inc., Cincinnati, OH) and the Bard biopsy systems (C.R. Bard Inc., Tempe, AZ). The effect of needle rotation on the needle axial force has been investigated by Abolhassani et al. [12], [13], [14], [15], [16], [17] and Meltsner et al. [18]. The focus of their work was to improve needle placement accuracy in brachytherapy. Both needle axial force and tissue deformation were found to be reduced with needle rotation due to the reduction in the friction force along the needle's axial direction. However, no research has been conducted related to the interaction between the cannula cutting edge and tissue when rotating the cannula. Compared to non-rotational needle biopsy, rotating the cannula alters its cutting behavior. A cannula which is efficient for non-rotational needle biopsy may not be a good choice for rotational needle biopsy. Without understanding the cutting mechanics, it is difficult to determine the optimal cannula rotation/translation speed and the desired tip configuration.

The present work investigates the influence of cannula rotation on the cutting forces for needle biopsy. The objective is to determine the optimal rotation/translation speed and the desired tip configuration. The results from this work will serve as the basis for planning rotational needle biopsy and for the design of rotational needle biopsy devices and needles.

Section snippets

Cutting force model and slice/push ratio

It is a common experience that it is easier to cut with a combined “pressing down and slicing sideways” action rather than “pressing down alone”. Atkins et al. [19] studied the effect of slicing motion on the cutting forces using a fracture mechanics energy-based approach to explain why it is relatively difficult to cut when simply ‘pressing down’ but much easier to cut as soon as slicing action is introduced. It is expected that if external work is provided by the sideways motion of the

Results and discussion

Fig. 3 shows the axial force and torque for a cannula with a translation speed of va = 2 mm/s and rotation speed of vr = 1.6 mm/s. For a typical needle insertion procedure, there exists two distinct phases, as shown in Fig. 3. This phenomenon has also been observed by previous researchers [2], [4], [8], [25], [26], [27]. In the first phase, the needle deforms the tissue without cutting and the forces increase as the tissue deflects. In the second phase, the needle steadily cuts the tissue. During

Conclusions

The present paper studies the effect of rotating a cannula on tissue cutting for needle biopsy. A force model based on the fracture mechanics approach was proposed to analyze the effect of needle rotation on the cutting forces. It was found that the cutting forces depend on the slice/push ratio given by k = speed parallel to the cutting edge/speed perpendicular to the cutting edge. Increasing the slice/push ratio reduces the cutting forces. Experiments were performed to validate the cutting

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