1. Field of the Invention
The invention relates to a biopsy needle. More particularly, the invention relates to a biopsy needle having a sample recess shaped and dimensioned to optimize operation of the biopsy needle. The invention also relates to a method for forming the recess.
2. Description of the Prior Art
Biopsy needles are currently available in gages ranging from 14 to 20. The biopsy samples are obtained using various methods. One of the commercially available designs employs a solid, pointed cannula inside of a slip-fitted outer cannula with a beveled leading end. The solid inner cannula contains a rectangular cavity, which collects the biopsy sample. The biopsy sample is removed from the tissue by inserting the biopsy needle into the tissue, uncovering the collection portion, that is, the rectangular cavity, and firing the outer cannula forward quickly using a spring. The portion of the tissue in the region of the sample collection rectangular cavity is torn from the surrounding tissue and collected in the rectangular cavity. Biopsy sample collection using this “brute force” approach results in trauma to the patient. A need exists, therefore, for a biopsy needle, that obtains the desired sample by cutting rather than tearing the sample from the surrounding tissue.
It is, therefore, an object of the present invention to provide a biopsy needle including an outer cannula and an inner cannula. The inner cannula includes a distal end and a proximal end. The outer cannula is shaped and dimensioned to closely circumscribe the inner cannula for movement relative thereto. The inner cannula further includes a sample recess at its distal end, the sample recess including a U-shaped cutting edge defined by
pn=xn cos θ
qN=xn sin θ
It is also an object of the present invention to provide an inner cannula of a biopsy needle manufactured in accordance with the method comprising setting a grinding wheel at an angle θ, relative to a longitudinal axis of the inner cannula and grinding the inner cannula with the grinding wheel to produce a sample recess having a cutting edge at an outside surface of the inner cannula as the grinding wheel moves through the inner cannula in a direction transverse to the longitudinal axis of the inner cannula. The cutting edge is defined as above.
Other objects and advantages of the present invention will become apparent from the following detailed description when viewed in conjunction with the accompanying drawings, which set forth certain embodiments of the invention.
The detailed embodiments of the present invention are disclosed herein. It should be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention.
With reference to
In general, the inner cannula 14 includes a distal end 16 and a proximal end 18. The distal end 16 is provided with a distal tip 20 and a sample recess 22 having a cutting edge 24. The distal tip 20 is a traditional point tip adapted to easily move through tissue with the creation of limited trauma.
As to the outer cannula 12, it also includes a distal end 26 having a sharpened distal tip 28 and a proximal end 30. The outer cannula 12 has a beveled, 360-degree cutting edge 32 at its distal tip 28. The leading, cutting edge 32 of the outer cannula 12 is beveled for a full 360 degrees. The outer cannula 12 is suitably spring driven to slide axially along the inner cannula 14 when triggered by the physician. The cutting edges 24, 32 of the inner cannula 14 and outer cannula 12 remove the biopsy sample by cutting the sample in scissor-like fashion as the spring-driven, outer cannula 12 slides axially along the inner cannula 14.
The proximal end 18 of the inner cannula 14 and the proximal end 30 of the outer cannula 12 are respectively coupled to an actuation mechanism 34 controlling movement of the outer cannula 12 relative to the inner cannula 14. In accordance with a preferred embodiment, the actuation mechanism 34 is a spring biased actuation mechanism as disclosed in U.S. Pat. No. 5,425,376 to Banys et al., which is incorporated herein by reference, although other actuation mechanisms may certainly be used without departing from the spirit of the present invention.
The biopsy needle 10 is preferably made of medical grade stainless steel although those skilled in the art will appreciate that it may be manufactured from other materials without departing from the spirit of the present invention.
In use, and with reference to
As briefly discussed above, the sample recess 22 is formed at the distal end 16 of the inner cannula 14. The sample recess 22 includes a forward wall 22a, a base 22b and a rearward wall 22c. The forward wall 22a includes a three dimensional, integral, biopsy sample cutting edge 24 which faces 180 degrees from the distal tip 20 of the inner cannula 14.
Referring to
The geometry of the “U” shaped cutting edge 24 depends on the values of the design parameters used. For any selected inner cannula 14 outer diameter (OD), the closed end of the “U” shaped cutting edge 24 can be ground to produce a relatively broad or a relatively sharp point 40 by changing the grinding angle, θ, shown in
A mathematical analysis was conducted to derive the equations necessary to design the three-dimensional “U” shaped cutting edge 24 for the inner cannula 14 of the biopsy needle 10.
When viewed from the perspective shown in
Referring to
pn=xn cos θ
qn=xn sin θ
One can also write the maximum value of xn and pn as:
max xn=ro−ri/sin θ
max pn=ro−ri/tan θ
The approximate, maximum value of qn is:
max qn=ro−ri
Those maximum values represent the values of pn, xn and qn at the base 22b of the sample recess 22 and the outer surface of the grinding wheel 36 forming the sample recess 22.
in±√{square root over ((2r0−xn sin θ)xn sin θ)}
From pn, qn, and in we can plot the three dimensional geometry of the “U” shaped cutting edge 24 on the inner cannula 14. For our purposes, a two-dimensional plot of pn vs. in shows the geometry of the “U” shaped cutting edge when viewed from above the inner cannula 14. The variation in cutting edge geometry is readily apparent from a plot of pn vs. in (see
S=h/sin θ
Now that a basic understanding of the sample recess geometry is appreciated, the preferred embodiments which optimize operation in accordance with the present invention are disclosed. To demonstrate the use of the design equations, the geometry of the biopsy needle “U” shaped cutting edge was calculated for three needle gages, namely 20 GA, 18 GA, and 14 GA. The 20 to 14 GA range covers the range of gages currently being used, with particularly heavy usage being noted with regard to the 18 GA size. In the three examples given below, the grinding wheel penetration is approximately to the centerline of the inner cannula. This was accomplished by setting the parameter ri to zero in the equations. The design parameters and the results are listed below:
The pn vs. in curves for the three examples showing the geometry of the cutting edge when viewed from above the inner cannula of the biopsy needle are given in
A comparison of the three pn vs. in curves is shown in
To demonstrate the influence of the angle, θ, in the three examples given above, the value of θ was set equal to 20° in all three examples. The results are as follows:
The length of the sample cavity, S, is 0.585″ for all three examples. The pn vs. in curves are given in
The results for all of the examples are summarized below:
From the results above, one sees that increasing the angle, θ, results in smaller values of max pn while maintaining the same values for max qn. The result is a stiffening of the cutting edge as θ increases. In addition, the size of biopsy sample recess, S, decreases as θ increases.
In the examples given, the value of ri was zero which brings the depth of the grind to the centerline of the inner cannula. Selecting values of ri greater than zero produces a grind which is above the centerline of the inner cannula which results in a biopsy needle point which is more resistant to bending.
For comparison purposes, the pn vs. in results for θ=10° and θ=20° were plotted in
Note that in the examples selected herein, the grinding depth was halfway through the inner cannula (i.e., ri=0). It is, however, contemplated, other grinding depths may be used to produce the cutting edge desired by selecting a value of ri between zero and the outer radius of the cannula, ro.
In operation, and as briefly discussed above, the biopsy needle 10 is inserted to the depth required and the outer cannula 12 is withdrawn and cocked. The portion of the tissue to be excised is in the region of the biopsy sample recess 22. When the outer cannula 12 is fired, the outer cannula 12 moves toward the distal tip 20 of the inner cannula 14. The portion of the tissue protruding into the biopsy sample recess 22 is cut off by the two cutting edges 24, 32 and is collected in the biopsy sample recess 22.
Referring to
Due to the cutting rather than tearing operation, biopsy samples cut with the present biopsy needle should produce less trauma to the patient.
While the preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention.
This application is based upon U.S. Provisional Application Ser. No. 60/610,542, entitled “BIOPSY NEEDLE”, which was filed Sep. 17, 2004.
Number | Date | Country | |
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60610542 | Sep 2004 | US |