The present invention pertains generally to medical instruments. More particularly, the present invention pertains to medical instruments which can be used with various imaging modalities. The present invention is particularly, but not exclusively, useful as a surgical probe that can be used in an MRI magnetic field without distorting the images obtained by the MRI system.
Magnetic Resonant Imaging (MRI) and similar systems are widely used to produce images of the internal structures of the human body. In some cases, images can be produced and used during a surgical procedure. In the event, images obtained can be used to position surgical equipment, including probes, relative to anatomical features. In addition, MRI imaging can be used to view, in near real time, the results of surgical procedures. For example, the image can provide information regarding process steps within a surgical procedure, such as the creation of an incision, the injection of a medicament, the cauterization of tissue, and the like.
With the above in mind, some materials, when immersed in the magnetic field generated during MRI imaging, interfere with the magnetic field and can cause distortions in the resulting MRI images. For example, when a probe is constructed from one of these interfering materials, the resultant MRI images tend to visually enlarge the probe and, thus, degrade the precision of the image. In particular, non-ferrous materials such as Aluminum and Titanium, which may be considered as candidates to construct surgical probes, can interfere with a magnetic field, resulting in artifacts that cause distortions in MRI images.
In addition to a material's effect on an MRI magnetic field, other factors must be considered during the selection of materials for construction of medical probes and similar equipment. For example, the selected materials must be biocompatible. This is particularly true for materials that are introduced into the body and placed in contact with tissue and other bodily fluids. In addition, the strength and stiffness of the material must often be considered. This can be especially true when a probe having a relatively large aspect ratio (i.e. a relatively long, thin probe) is contemplated. This is often the case because it is often desirable to reach deep within a bodily organ with as small an access orifice as possible. Moreover, failure of the probe to maintain rigidity during insertion and placement within the body can result in the probe being directed off course and missing the intended treatment location. For the case where the probe is also used to deliver a fluid to a treatment area, loss of rigidity can also adversely affect the flow of fluid through the relatively small diameter probe lumen.
In some instances, a probe may be used to transfer an electrical current to a treatment site, for example, to heat, excite, stimulate or cauterize tissue. For these types of procedures, a conductive path must be maintained along the length of the probe. This, in turn implies the use of a conductive material to construct the probe.
In light of the above it is an object of the present invention to provide a medical instrument made of materials that do not interfere with an MRI magnetic field or cause distortions in the resulting MRI images. Another object of the present invention is to provide surgical probes that are conductive, made of biocompatible materials, and are sufficiently rigid to allow the probe to be placed at an intended treatment location in the body. Still another object of the present invention is to provide a medical instrument, and corresponding methods for manufacturing and using the medical instrument, that are simple to implement, easy to use and comparatively cost effective.
In accordance with the present invention, a medical instrument that is impervious to a magnetic field includes an elongated probe section having a length (L) between a proximal probe section end and a distal probe section end. Structurally, the probe section includes a plurality of carbon fibers that is embedded in a medical grade, biocompatible epoxy resin. For the medical instrument, the probe section defines a longitudinal axis and is constructed with the carbon fibers arrayed along the axis to extend between the proximal end and the distal end of the probe section. In one embodiment, the carbon fibers in the probe section are arrayed with a substantially uniform density in a radial direction from the axis.
With the above described arrangement, the probe section is formed with sufficient structural rigidity to resist substantial off-axis deflection. In more quantitative terms, in a first embodiment, a relatively thin, substantially cylindrical probe section is contemplated having a probe section outer diameter (Do) in a range between 500 and 1,500 microns. In another embodiment, the probe section is tapered with a decreasing outer diameter (Do) in a direction from the proximal end to the distal end. For these embodiments, the probe section is constructed with a maximum predetermined off-axis deflection (dmax) of the distal probe section end relative to the proximal probe section end that is less than about 30% of the probe section length (dmax<0.3 L). For example, the probe section can be designed with a specified density of carbon fibers to provide the required structural rigidity.
Also for the medical instrument of the present invention, a handle is affixed to, and positioned to be coaxial with, the proximal end of the probe section. With this cooperative interaction of structure, the handle can be used to manipulate the probe section during a surgical procedure that is performed while the probe section is immersed within an MRI magnetic field. Specifically, for the present invention, it is envisioned that at least a portion of the probe section will be immersed in a homogenous magnetic field that is established by an MRI system to produce an MRI image.
In one embodiment of the present invention, the medical instrument includes a probe section that is formed with a lumen that extends along the probe section axis between the proximal and distal probe section ends. For this embodiment, the medical instrument can include a fluid source that is connected in fluid communication with the proximal end of the probe section. A pump is also provided that is connected with the fluid source to transfer a fluid from the fluid source and through the probe section lumen for expulsion of the fluid from the distal end of the probe section. For the embodiments where the probe section has a lumen, the inner diameter (Di) of the lumen is typically less than about 80% of the outer diameter (Do) of the probe section (Di/Do<0.8).
In one implementation of the present invention, the probe section can be constructed to provide a conductive pathway from the proximal probe section end to the distal probe section end. For example, this conductive pathway can extend through the carbon fibers. For this implementation, the medical instrument can include a voltage source that is connected to the distal end of the probe section by way of a switch. In use, the switch is operable to selectively send an electrical current from the voltage source through the carbon fibers in the probe section from the proximal end to the distal end of the probe section. For example, a current can be applied to internal tissue to treat the tissue, for example, by stimulation/excitation or cauterization.
The probe section of a surgical probe can be manufactured in accordance with the present invention by first orienting a plurality of carbon fibers along a linear axis. In one embodiment, the carbon fibers are oriented to establish a unidirectional composite material wherein the carbon fibers are aligned substantially parallel to the axis. In another embodiment, the carbon fibers are oriented to establish a helical pattern around the axis with each carbon fiber inclined with a positive pitch angle (+α1) relative to the axis. Once oriented, the carbon fibers are then embedded in an epoxy resin and the embedded fibers are wrapped within a woven material made of carbon fibers to produce an assembly. Next, the assembly is processed, e.g. by applying a selected temperature/pressure regimen, to cure the epoxy resin and create an elongated probe section. The handle can then be affixed to the proximal end of the probe section.
To manufacture a probe section having a lumen, a mandrel is first aligned along a linear axis and the carbon fibers are arrayed along the mandrel. Once arrayed, the carbon fibers are embedded in epoxy resin and the embedded fibers are wrapped within a woven material made of carbon fibers to produce an assembly. The assembly is then processed, e.g. by applying a selected temperature/pressure regimen to cure the epoxy resin and create an elongated probe section. The mandrel is then removed from the probe section after the curing step to form a lumen in the probe section.
The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which:
Referring initially to
To prepare the probe section 26b, the plurality of carbon fibers 36 are oriented along the linear axis 34 and embedded in the resin 38 to establish a unidirectional composite material. The embedded carbon fibers 36 are then wrapped within a woven material made of carbon fibers to produce the sheath 40. Next, the assembly is processed, e.g. by applying a selected temperature/pressure regimen, to cure the epoxy resin 38 and create the probe section 26b. The handle 28 (see
Referring back to
For the cylindrical probe section 26a-c shown in
Cross-referencing
The operation of the present invention can best be appreciated with cross-reference to
While the particular Carbon Fiber Medical Instrument as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.