Friction Transmission with Axial Loading and a Radiolucent Surgical Needle Driver
Conventional needle driving techniques are based on holding the needle head and not the barrel of the needle, the motion of the needle being induced by moving the support of the needle head. The above technique does not allow radiolucent constructions. Moreover, supporting the needle from its head tends to disadvantageously maximize the unsupported length of the needle, thus facilitating needle deflection under the insertion force.
An object of the present invention is to provide a simple and effective method and system for radiological image guidance in percutaneous surgery which overcome the disadvantages of the prior art.
The invention further pertains to a system for performing the method described above, comprising: a radiological image generating device for generating an image of a target anatomy of a patient to be operated on for determining a needle trajectory to be followed through the patient, the image generating device being positionable to generate an image of the target anatomy from a plurality of directions; and a needle insertion mechanism disposed adjacent the image generating device and having a needle adapted to be inserted into the patient and to be locked in a direction of the needle trajectory. The invention further pertains to a motion transmission mechanism comprising both an output shaft and an output shaft driver, which includes: a first rotational component having a first contact face and being adapted to rotate about a rotational axis; and a second rotational component coaxial with the first rotational component and having a second contact face facing the first contact face and spaced therefrom, the output shaft being spaced from the rotational axis and further being pressed between the contact faces thereby applying an axial force to each of the contact faces directed parallel to the rotational axis, the axial force effecting a frictional engagement of the output shaft with the contact faces, the second rotational component further being adapted to rotate about the rotational axis such that, when the rotational components rotate about the rotational axis, the frictional engagement of the output shaft with the contact faces effects a translational motion of the output shaft.
The simplicity of the method and system according to the present invention is achieved by combining the proven radiological image guidance procedures and devices of the prior art with a simple and cost-effective needle injection device which exhibits an extremely low radiological profile. The needle injection device further provides actuated needle motion in conjunction with a mechanical manipulator designed to be used in existing operating rooms without the necessity of additional computers or personnel.
Accordingly, the method and device of the present invention mimic and improve upon the surgeon's standard technique. The key advantages of the present invention are that it involves the use of a proven radiological needle alignment procedure, improves accuracy in comparison with purely manual needle positioning techniques, and enables lateral fluoroscopic monitoring of the needle without necessitating computer-based vision and robotic systems. The present invention results in a shortening of procedure durations, improves upon patient safety, ensures and improves upon equipment sterility, and reduces the radiation exposure of surgeons.
According to the present invention, a method and system are provided which, to an extent, mimic the surgical technique of superimposed registration used in the prior art and described above. Thus, the invention contemplates registering or aligning a C-arm and needle according to the prior art. However, in the accordance with the invention, the needle is mechanically locked so as to lock the needle axis along the desired needle trajectory by any suitable means, and preferably by a robotic manipulator. Thus, the needle trajectory according to the invention is memorized by a locked orientation of the needle proper, and not of the C-arm, thereby allowing the surgeon to position or "frog" the C-arm to obtain a lateral view of the target anatomy and needle. As a result, the insertion depth of the needle and the path of the needle during its insertion may be observed directly by the surgeon on the image provided by the laterally positioned C-arm. Direct observation of insertion depth advantageously allows the surgeon to compensate for soft tissue deflection of the target, such as the kidney, surrounding tissue. Thus, in comparison with prior art techniques, the method according to the present invention results in safer and more accurate percutaneous procedures.
A further advantage of the method according to the invention is that it does not require image correction and calibration. By superimposing the needle, the insertion site and the target, any image distortions are identical, and therefore, cancel each other. Moreover, the method of the present invention requires direct observation by only the surgeon involved, and hence does not necessitate image-processing that is computer based, thereby significantly reducing operative time and expense.
In order to drive the needle according to the present invention, a needle driver is provided which converts rotational to translational motion in a transmission element which is adapted to receive the barrel of the needle therein. Power is transmitted to the needle through friction forces from contact faces between which the needle is pressed. Thus, the novelty of the transmission resides in providing a mechanism in which a force is generated which extends in the direction of the axis of rotation and which is normal to the direction of friction forces thus leading to the conversion of the rotational motion to the translational motion mentioned above. The needle driver constructed according to the invention thus results in axial loading of the contact faces which is significantly larger than similarly sized radial loading systems of the prior art, yielding increased efficiency in the transmission of force and power. While mechanisms involving the conversion of rotational motion to translational motion through friction abound in the prior art, these systems involve the generation of a force which is oriented only radially with respect to the axis of rotation, and not axially with respect to this axis. On the other hand, the invention advantageously involves an axially loaded friction mechanism for converting rotational motion to translational motion.
Additionally, the needle driver according to the invention, by virtue of providing a construction where the needle is held by its barrel and not by its head, allows a radiolucent construction and advantageously decreases the unsupported length of the needle for substantially preventing needle deflection under the insertion force.
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