Measurement of the Friction Force Inside the Needle in Biopsy

Abstract

Core needle biopsy (CNB) is widely used in active surveillance, which is the current standard of care for low risk prostate cancers. A longer biopsy sample length may improve the accuracy of diagnosis. To increase the biopsy sample length, the magnetic abrasive finishing (MAF) technique was applied to decrease the needle inner friction force, which may hinder the tissue from entering the lumen of the biopsy needle. To assess the effectiveness of these MAF polished needles as compared to the unpolished needles, a method to measure the three components of axial force during hollow needle insertion—tip cutting force, inner friction force, and outer friction force—was developed. Six tissue-mimicking samples of different lengths were used to find the linear relationship between the sum of the cutting force and inner friction force and the phantom length or contact length. Linear regression method was used to extrapolate and estimate the tip cutting force and the inner friction force. With this method, the difference between the inner friction force of the needles with and without polishing was found. The results showed that the unpolished needles had an inner friction force 40–50% higher and a tip cutting force 22% higher than their MAF polished counterparts. We also found that MAF polished needles had an average of 9% longer contact length between the sample and the inner wall than unpolished needles, indicating that a longer sample can be extracted at a lower friction force. The results of our investigation implied that reducing the inner surface roughness of a biopsy needle could reduce inner friction forces.