Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-03-13
2002-10-22
Hoang, Tu Ba (Department: 3742)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C606S015000
Reexamination Certificate
active
06470205
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a medical device for insertion into an examination subject of the type having an elongated instrument body with a number of serially arranged rigid sections, respectively connected to one another via articulated joints so that the sections can be angled relative to one another.
2. Description of the Prior Art
Instruments of the above type can be catheters or endoscopes, for example. Using such an instrument it is possible to enter into the inside of the body of a patient via a very small body opening and to carry out different surgical measures. The instrument can be manually guided or automatically guided or by a robot. Since the instrument is no longer visible after it has been inserted into the body, it is necessary to exactly determine its position during the intervention in the patient and to fade the position information into preoperative or intraoperative patient images, so that the treating physician exactly knows where the instrument, and particularly the tip of the instrument, is situated. Conventionally, the positioning currently ensues using X-ray control, which normally makes only one projection direction available. For detecting the position, it is also known to use electromagnetic navigation systems, wherein sensor coils are integrated into the instrument tip. The sensor coils are localized via an external detection system in a coordinate system of the navigation system and are faded into previously obtained patient images after a coordinate transformation has been carried out. These known methods, however, have disadvantages. The radiation load on the patient is considerable during the determination of the position with X-ray control, and the determination of the position is quite difficult. The electromagnetic navigation system is susceptible to electromagnetic radiation and cannot be used in connection with other medical examination devices such as X-ray apparatuses, computed tomography devices or magnetic resonance apparatuses.
SUMMARY OF THE INVENTION
An object of the invention is to provide a medical instrument whose position in a subject body can be simply determined.
This object is inventively achieved in a medical instrument of the initially described type wherein at least one optical fiber that can be charged with light is conducted along the instrument body, with at least one fiber Bragg grating fashioned in a region adjacent each articulated joint.
An extremely accurately operating optical navigation system is realized by the optical fiber having at least one integrated fiber Bragg grating in the inventive instrument. A fiber Bragg grating is characterized by changing areas having different refractive indices. Such a grating acts as a wavelength-sensitive mirror having an extremely high reflective factor up to 99% and a half intensity width of below 0.05 nm. If light having a finite half intensity width is radiated through the optical fiber onto the fiber Bragg grating, a discrete, exactly defined wavelength of the light differing from the grating constant and the average effective refractive index of the grating is reflected back. If the joint position of the instrument is modified, a bending of the optical fiber and therefore of the fiber Bragg grating is also associated therewith, which causes an associated change of the reflective behavior and therefore of the reflected Bragg wavelength. As a result of this modification that can be detected by a suitable detection unit, or on the basis of the reflected wavelength modified as a result of the bending, the joint position can be extremely precisely determined in a particularly advantageous way. Since optical fibers are produced with diameters smaller than 100 &mgr;m, ths system therefore is extremely light and compact, and is advantageously insusceptible to electromagnetic radiation and therefore can be utilized in cooperation with other medical devices such as X-ray apparatuses, computed tomography apparatuses or magnetic resonance apparatuses. Since only the wavelength of the back-reflected light is important for determining the joint position, changes in intensity or polarization, which may be influenced by a dynamic conductor bending, therefore also have no effect on the measurement result. Overall, the inventive instrument enables the exact determination of the joint position with an extremely simple and compact structure and avoids the disadvantages of known devices.
In a further embodiment of the invention, a number of fiber Bragg gratings that are respectively allocated to the articulated joints are provided along the length of the optical fiber, each of these fiber Bragg gratings reflecting light of a grating specific wavelength range, the wavelength ranges of all fiber Bragg gratings of a optical fiber being different. Normally, a number of articulated joints are provided over the length of the instrument. In this embodiment, each articulated joint has a separate grating allocated thereto, which reflects in a specific wavelength range, so that the reflected light can be unambiguously allocated to a specific grating and therefore to a specific joint. For an unbent waveguide, the wavelength difference of the reflected light of two successively arranged gratings should be at least double the half intensity width of the grating reflected light of a single grating, particularly at least 1 nm. The reflected wavelength can be adjusted without a problem by correspondingly fashioning the grating. Each reflected light beam, therefore each Bragg peak, has a specific width that is determined by the formation of the grating. The difference should correspond to at least double the half intensity width of these Bragg peaks. The double of the half intensity width is normally situated between 100-200 pm. This difference value represents the lower limit. A difference of at least 1 nm is preferred in order to obtain a sufficient safety margin. The cited wavelength difference is sufficient with regard to the modification of the reflected wavelength of a grating between the extremes “maximal contraction” and “maximal expansion”, since the wavelength normally changes by less than 1 nm.
The articulated joints can be normally rotated around two orthogonal axes. In order to enable an exact determination of the position, it is expedient in this case when at least two optical fibers are provided, which are arranged at the instrument body at respective positions that are offset by 90°, and which each have a fiber Bragg grating fashioned at the regions adjacent to an articulated joint. Each of the two joint-related gratings supplies a specific signal dependent on the direction of the joint bending, so that the bend angle can be exactly calculated on the basis of the supplied signals.
In a further embodiment, four optical fibers can be provided, which are arranged at the instrument body at positions that are offset by 90°, and which each have at least one fiber Bragg grating fashioned at the regions adjacent to a link joint. This embodiment makes it possible to measure the difference between two opposite gratings. For example, if the joint is bent around an axis, the one grating is stretched and the other grating is compressed. On this basis, it can be recognized that a bend actually occurs in this case around this axis. Due to the bending, the two other gratings, which, as it were, are situated on the rotational axis, are also somewhat bent, but uniformly, so that both supply positive or negative signals. On the basis thereof, it can be unambiguously recognized that these two gratings do not experience a bending that is relevant for an angle modification, but they are merely bent together. It is thus possible to exactly determine the bending direction, particularly in the case of ball-and-socket joints.
A modification of the reflected wavelength can also be caused by temperature. Given increased temperature, the optical fiber expands and therefore the grating expands somewhat as well, whereas it somewhat contracts at a low temperatu
Bosselmann Thomas
Schuetz Oliver
Hoang Tu Ba
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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