Funding Agency:

Carnegie Mellon University/NIH

Total Project Period:

5/01/11 - 4/30/12

Total Project Award:

$53,048

Principal Investigators:

Johnathan Engh, MD; Cameron Riviere, PhD (Carnegie Mellon University)

Project Summary:

Accuracy of needle placement is a matter of fundamental importance in brain interventions such as tumor surgery and deep brain stimulation (DBS), and there is a need for improvements in order to increase efficacy of treatment.

In response to this need, we have developed a computer-controlled system designed to steer a flexible needle through brain tissue, with proportional control of steering angle, using an elegantly simple technique of slowly rotating the needle in a “duty-cycled” fashion during insertion. The system can be used to reach targets deep in the brain, and can detour when needed in order to avoid damaging sensitive areas.

Preliminary testing of the system has been performed in vitro in a gelatin substrate and in human cadavers. The testing that has been performed to date has focused solely on efficacy in reaching a particular target.

There remain several unanswered needs, especially the development of means for tracking the tip of the flexible probe in vivo. However, before progressing to these questions, research is needed on several objectives in order to ensure the safety of the technique. The proposed project consists of the fundamental research needed in order to adapt the existing proof of concept for clinical safety. The specific aims of this proposal are as follows:

1. To adapt the tip geometry and the velocity envelope for safety in brain parenchyma. This will require finite element modeling of the needle tip geometry and the process of needle rotation in order to optimize the bevel angle, edge sharpness, rotation speed, and insertion speed of the probe in order to avoid damage to tissue. This aim will treat the tissue as homogeneous. Results of the work will be validated in fresh animal brain tissue in vitro.
2. To adapt the tip geometry and the velocity envelope for safety in contact with blood vessels. This aim will involve the addition of blood vessels to the previously homogeneous tissue model, and will again require finite element modeling of the needle tip geometry and the process of needle rotation in order to optimize the bevel angle, edge sharpness, rotation speed, and insertion speed of the probe, in order to avoid damage to blood vessels that are contacted during insertion. The goal will be to limit the likelihood of vessel damage to that exhibited by present clinical straight-probe brain needle designs. Results will be validated in fresh animal brain tissue in vitro.
3. To optimize the design and the velocity envelope to avoid tissue damage along the length of the curved needle trajectory. Unlike a straight probe, insertion of a flexible needle of course places acertain amount of stress along the outer curvature of the needle path. Therefore, in addition to the above work dealing specifically with the needle tip, it will be necessary to model the interaction between the flexible needle and the tissue all along the shaft, optimizing the design of the needle gauge and the velocity envelope to avoid tissue damage along the trajectory. This work will also serve to prevent the possibility of any “whirling” or “whipping” motion of the tip of the flexible needle as the shaft is rotated. We emphasize that while the particular needle design developed will be specific to brain tissue, the knowledge gained by the research described will be relevant to a wide variety of soft tissues, many of which potentially stand to benefit from the needle-steering technique.