Design of a Bending Section Endoscope
This article focuses on the design of a Bending Section Endoscope that can be used to perform medical procedures inside the body. It can also be used to monitor the health of the patient during these procedures.
The bending section of the insertion tube can be articulated to adjust its position in a desired direction within a selected body channel. This can reduce the risk of muscle layer damage during dissection.
Optical System
Endoscopes are a common medical instrument used to observe and treat various internal body structures. They typically have an elongated inserting portion which is inserted into the body cavity, and numerous accessories and ancillary instruments are connected to it, including sheaths, specialized imaging and treatment equipment, pumps for suction or insufflation, and image management systems.
A conventional approach for bending the distal tip of a flexible endoscope includes using coaxial wires that extend along the device, and pulling on the proximal end of one of these wires to bend the distal tip in the direction of that wire. This arrangement is problematic for long, very small diameter flexible endoscopes because the number of wires required to bend the distal tip in each orthogonal direction adds to the total length of the device, making it difficult to achieve a distal tip with a small enough diameter to be useful.
Consequently, a new bending technique has been developed that enables a user to selectively bend the distal tip in any of four orthogonal directions without adding wires to the device. The bending mechanism is made up of a helical extrusion that has a central lumen that extends radially outward from a proximal end of the extrusion, and a plurality of lumens that extend radially outward on diametrically opposite sides of the central lumen.
In exemplary embodiments of the invention, each of the plurality of lumens and each of the at least a pair of tension members is formed of one or more materials selected to have defined characteristics, such as a relatively high tensile strength, flexibility, toughness, and a low coefficient of friction. The helical path provided by each of the lumens and each of the at least the pair of tension members prevents distortion of the tether section between the distal tip and proximal end.
The exemplary embodiment shown in FIGS. 1A and 1B comprises two parallel members 10 and 12, which are bonded to each other. The members 10 and 12 are bonded so that when the members are bent, their relative paths do not change. This helps to ensure that the Bending Section Endoscope distal tip is not distorted when the tether section between the proximal end and the distal tip is bent.
Control Section
The control section is an important component of a Bending Section Endoscope. It is designed to steer the bending section in a desired manner and to maintain alignment of the individual vertebrae during insertion.
As a general rule, the control wires extend through apertures located on an inside surface of the vertebra and are selectively retracted or extended to turn the bending section a desired degree of bend in all directions. This is done using a combination of clearances for each of the four control wires through the apertures, and the thickness of a metal braid which covers the bending section.
One useful feature of the bending section is that the protrusions 43-46 which extend from the first and second surfaces are selected so that they are shaped to provide a uniform displacement of the control wires 69-70 through the apertures in a symmetrical manner with respect to the longitudinal bending axis 53. This is useful because the same displacement of the control wires would normally produce a different degree of bend in the left-right direction for wires 67 and 68, which are farther from the bending axis 53.
To further enhance torsional stability of the bending section, the inside surface of each of the four apertures 18 is generally planar. This allows the control wires 67-70 to move through each of the apertures without slipping or rubbing against each other.
Another feature of the bending section is that it is composed of a plurality of individual vertebrae 39 held together by control wires 67-70 extending through apertures 60-63 on each of these vertebrae. These control wires are not mechanically coupled to each other and, instead, the tension in the control wires 67-70 maintains the alignment of the vertebrae 39 during insertion.
In addition, the flat regions on the respective protrusions 45-46 of adjacent vertebrae 39 contact each other to provide a flat surface region which allows them to seat in a straight manner relative to an adjacent vertebra. This provides a more stable endoscope which is less likely to wear out.
The cable pulling system of an endoscope is a nonlinear response system which is prone to backlash, cable slackening and eventually reduced control. These effects can lead to delays in the insertion process and unresponsive tip steering. Fortunately, there are a variety of techniques for addressing these issues.
Insertion Tube
An insertion tube is a crucial part of the endoscope. It must have the perfect Bending Section Endoscope balance of flexibility, elasticity, column strength, and torquing ability for easy and safe insertion.
Obtaining this ideal combination is an art and science. It often involves months of clinical testing, and the final design is usually a compromise between these ideal characteristics.
One of the most common challenges for bending tubes is achieving torsional stability. Ideally, a heavy braid (generally providing 85% to 100% coverage) is used around the insertion tube to provide this desired torsional stability.
A polymetric jacket (typically black on gastroscopes or dark green on colonoscopes) is then wrapped over the metal braid and this assembly overlaid by the bending section to complete the insertion tube.
The bending section is constructed from many individual vertebrae, each of which are D-shaped in cross-section. The vertebrae have first and second pairs of protrusions extending from their surfaces to define a horizontal and vertical bending axis, respectively. The intersection of these bending axes defines the longitudinal bending axis.
In a preferred embodiment, the first pair of protrusions are shorter than the second pair. This is to compensate for the asymmetrical shape of the vertebrae, thereby ensuring symmetrical bending.
Another important consideration in a bending tube’s design is the ability to be curved in any direction. This can be achieved by angulation wires that run the length of the insertion tube and are firmly attached to the tip at various locations along the bending section. The wires are positioned in alternating up-and-down directions, with increasing bending angles, to achieve what is known as “up tip deflection” or “down tip deflection.”
To control the angulation of the insertion tube, a knob is located on the handle. The knob may be manipulated with the physician’s left hand to move the insertion tube in a desired direction, or by the right hand to pull on the angulation wires and cause the insertion tube to bend.
The insertion tube is also designed to accommodate the use of an air and water valve to inflate hollow cavities or provide suction to draw fluids or air into the biopsy channel within the insertion tube. The air and water valves are controlled by a valve on the control section of the endoscope.
Bending Section
The bending section of an endoscope provides the flexibility and control that physicians need to steer an endoscope in a desired direction. The ability to steer an endoscope tip is important for scope introduction, mucosal inspection, and interventional procedures. Without sufficient flexibility, these tasks can be difficult and unsafe for the physician. In addition, the bending section of the endoscope must be flexible enough to allow the tip to turn 180deg in any direction without losing control.
To achieve this, the bending section of the endoscope is made of non-round vertebrae. The individual vertebrae are D-shaped, with a planar portion and an arcuate portion. Each of the vertebrae includes a first pair of protrusions that extend from the first surface, defining a vertical bending axis and a second pair of protrusions that extend from a second surface, defining a horizontal bending axis.
At the apex of the protrusions, the vertebrae contact adjacent vertebrae in abutting contact, providing a flat surface region that allows the vertebrae to be positioned straight and in a stable orientation when the tension in the control wires is equal. This flat region is less likely to wear than a curved segment, which results in a more durable endoscope.
Additionally, the inside surfaces of the apertures are generally planar and not chamfered, which reduces torsional instability for the bending section. This may be especially beneficial when the endoscope is used in an abdominal environment, where it is difficult to maintain a stable torsional position.
As previously explained, the bending section of an endoscope can be selectively steered by extending and retracting control wires that extend through apertures in each individual vertebra. The control wires are selectively retracted and extended to bend the bending section, resulting in a controlled bending curve.
In one preferred embodiment, the apex of the protrusions is symmetrical about a longitudinal bending axis 53 that extends through the entire length of the bending section 32. The apex of the protrusions in each vertebra is shorter than the apex of the protrusions of adjacent vertebrae to achieve symmetrical bending.