Design of an endoscopic carrier with complete directional control

August 15, 2017 | Autor: Gerard Lachiver | Categoría: Engineering, Biomedical Engineering, Humans, Medical Electronics, Fiber Optic Technology, Endoscopes
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Annals o f Biomedieal Engineering, Vol. 7. pp. 345-355, 1979 Printed in the USA. All rights reserved.

0191-5649[79[030345-11 $2.00/0 Copyright 9 1979 Pergamon Press Ltd.

D E S I G N OF AN E N D O S C O P I C CARRIER WITH COMPLETE D I R E C T I O N A L C O N T R O L Gdrard Lachiver and Wolf D. Seufert Ddpartement de Biophysique, Facultd de Mgdecine Universitd de Sherbrooke Sherbrooke, Qudbec, Canada

An instrument is described in this article which will help flexible fiberoptic endoscopes negotiate the turns and loops in the large bowel, particularly those in sections that are only loosely suspended in the abdominal cavity and that are, therefore, difficult to pass. The principle o f operation o f this carrier as well as construction details are given and will demonstrate its advantages for gastroen teroscopy.

INTRODUCTION Bundles of glass fibers aligned in parallel can transmit images of a high resolution and brightness and are therefore widely used as endoscopes to examine body cavities. Several such instruments are available for the examination of the gastro-intestinal tract in particular, varying in length, caliber, and functional parameters according to the anatomical situation for which they are intended. Endoscopes for the lower digestive tract come in lengths of up to 2 m (approximately 6 ft) and their mean diameter is around 14 m m (about .55 in). They are used principally by physicians specialized in gastroenterology to inspect the intestinal wall for inflammatory processes, lesions, or signs of abnormal growth. The disproportionate increase p e r a n n u m in neoplastic degenerations of the bowel as compared to any other system is alarming (1). By far the greatest incidence of a cancerous degeneration of intestinal tissues is found in the descending colon and the next following sections, i.e., the sigmoid colon and the rectum (2, 3, 5). An examination with This work was presented in part at "Biosigma 78," International Conference on Signals and Images in Biology and Medicine, April 24-28, 1978, Paris. Requests for reprints may be sent to Wolf D. Seufert, D~partement de Biophysique, Facultd de M~decine, Universit~ de Sherbrooke, Sherbrooke, Qudbec J1H 5N4, Canada.

345

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G~rard Lachiver and Wolf D. Seufert

the fiberoptic endoscope of those parts o f the bowel that are n o t accessible to a rigid instrument is of great value for the early diagnosis of cancer. The flexible endoscopes presently in practice are advanced through the section to be examined by using its wall as a guide. Since the operator's thrust to pass the instrument hardly ever acts in the direction of the intestine's lumen, and since particularly the sigmoid colon is not tightly held by ligaments in the abdominal cavity, the advance of the endoscope can be difficult or take an undue amount of time, even in the hands of an experienced physician. We have designed a carrier to facilitate the passage of an endoscope including all probing and manipulating devices normally used with it. The carrier advances the scope in all directions with ease to negotiate flexures or pass constrictions in the intestinal canal since it is under the operator's complete control and, with his guidance, the endoscope follows always the lumen of the bowel. It does not have to be deflected off the intestine's wall in order to assure its continued passage. The carrier simulates the sequential activation of l o c o m o t o r muscles enabling snakes to wind around an obstruction in their path. We give details on the construction of a model which has the same diameter as a p r o t o t y p e intended for clinical trials in veterinary medicine and which is about twice the diameter of an instrument needed in human medicine. The model utilizes exactly the same mechanisms also to be employed in the p r o t o t y p e , and it functions to our complete satisfaction. DESIGN PRINCIPLES AND O P E R A T I O N The carrier is formed by a train of cylindrical segments with an outside diameter o f 30 mm. They are all identical and they are allowed to rotate about diametric axes perpendicular to the carrier's long dimension. To this end, the top and b o t t o m surfaces are sloped such that the sector between adjoining segments permits their approach through an angle of 12 ~ . The transverse axes of articulation are offset by 90 ~ so that the top surface of a segment can rotate with respect to the preceding one about an axis northsouth whereas the b o t t o m surface of the same segment rotates with the following one a b o u t an axis east-west (Fig. 1). Thus, a pair o f succeeding segments, odd- and even-numbered, constitute one directional unit. For example, 5 articulations in the same direction (even-odd) would have to close a b o u t axes E-W for the carrier to form a curve 60 ~ south, involving 5 directional units or 10 succeeding segments. A photograph o f the model carrier is given in Fig. 2. A central channel runs the entire length of the carrier to accept a fiberoptic endoscope. This channel will be made wider in relation to the outside diameter than in the model shown. In the p r o t o t y p e , the electronic leads coming out of the central channel are replaced b y slip-rings located on the diametric edges o f the segments' articulating surfaces. The physician directs the carrier as is desired, under view through the fiberscope, b y electrically

A Carrier For Encloscopes

34 7

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AXES E-W

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F I G U R E 1. A train of segments with their axes of rotation (not drawn to scale).

actuating 1 of 4 magnetic clutches per directional unit, situated in the cardinal compass positions in the articulating surfaces of adjoining segments. For example, segments 1-2 rotate about an axis N-S when the clutch magnets

348

Gdrard Lachiver and Wolf D. Seufert

F I G U R E 2. Overall aspect of the model carrier.

in position either E or W are brought to close; segments 2-3 rotate about axis E-W when either clutch N or S is actuated. A series of regularly spaced impulses constitutes the address signal and the clutch for a given direction in the leading unit engages and remains closed as long as these impulses are supplied. After a fixed delay, the signal is routed automatically to the next articulation of the same axis to there close the clutch magnet of the same coordinate position. In this way, the signal travels towards the tail end of the carrier, i.e., the end proximal to the operator. If, then, the carrier is made to advance with the same speed with which the segmental activation proceeds in a retrograde direction, the angle formed by the articulating segments will remain stationary and the sonde will follow the path prescribed by the leading segment. The carrier and the endoscope will

A Carrier For Endoscopes

349

therefore remain more or less centered; the intestinal wall sustains the weight of the instrument but is not used to find its direction. The intubation is performed with the endoscope placed in the carrier's central channel. The instrument is advanced from its proximal end with a constant speed furnished by a small motor through a frictional drive. A speed convenient for examination will be chosen, probably between .5 and 3 cm/sec, after further consultations with practicing endoscopists. We have an even and reliable mechanical advance with 3 rubber cylinders arranged in a triangle; the carrier is fed through its center. The speed of advance and the speed of the retrograde activation have to be identical. Minor differences can be eliminated by varying the supply voltage to the drive motor. A feedback system will match the two speeds automatically if this should prove to be of advantage in clinical trials. The operator brings the carrier to form a curve greater than the angle of one single articulation by supplying the activating signal for periods sufficiently long to engage the number of segments necessary for a given turn. The control signal spills over to activate the next articulation after a delay synchronized with the advancing speed. Any angle can be negotiated in multiples of the invariant articulation angle between segments. Fig. 2 illustrates that the carrier can be directed in 3 dimensions and that several curves of varying degrees can be called to follow one another in a rapid succession, in whichever direction desired and without mutual interference. The angular deflections remain separated by their initial intervals as they proceed in a retrograde direction. The carrier is steered for directions intermediate between the four cardinal points by resolving the course to be set into its component vectors. If one wanted to head, e.g., towards NE one would first activate the N magnetic clutch and then the E clutch immediately after that. The articulation between the leading segment and segment 2 would then lock in the N position first; the sonde advances and the magnetic clutch in the same quadrant of the next articulation with the same rotation axis will close as the signal follows the retrograde activation circuit. Meanwhile, clutch N of articulation 1 has disengaged and the leading clutch E receives its signal and closes. The resultant heading of the endoscope is NE. Other directions are set in the same way. A course N of NE requires an activation of two successive articulations towards N, followed by the activation of one towards E. More segments are participating when the sonde goes through a smaller directional change but the proportionally larger arc described is of no consequence for the carrier's function. The physician uses a small aircraft-type stick for directional control and an encoding circuit resolves any direction automatically into its vector components for him, to then address the lead clutches in the proper 9 time sequence. The thrust of the advancing drive determines how far the instrument can go before friction with the intestinal wall would impede progress. Only the momentarily closing segments are subject to frictional components that are not counteracted by the drive motor. The closing force of the clutches is

350

Gdrard Lachiver and Wolf D. Seufert

high enough (.2 to .4 N) to overcome friction in the short distance in which the rotating segments contact the intestinal wall. The outside of the carrier will be covered by a sheath of an inert polymer material with excellent insulating qualities. This envelope continues over the distal and proximal ends to become the lining of the central channel. At the distal end, it is doubled to form an inflatable ring around the leading segment's circumference. This cushion will hold the carrier gently and firmly in the intestinal canal on injection of a small volume of air, similar to the way in which a N~laton catheter is held in the urethra. The examining physician intubates the rectum and then guides the instrument's advance with the control stick, always under view through the scope. Once passage is completed, power to the carrier is interrupted. With the clutch magnets de-activated, the carrier becomes limp and is slowly withdrawn together with the fiberscope. It is during this phase that the intestinal wall is closely examined. The physician is free to use all ancillary instruments that come with the endoscope. In addition, he can withdraw the scope but leave the carrier in situ to then re-insert a different instrument, as the examination or therapeutic procedures require. Operations in several stages become feasible since the area where the first steps of an intervention took place is rapidly found again. CONSTRUCTION DETAILS In this chapter, we discuss construction and performance details pertaining to the operation of a carrier within the domain of distances and forces that are met in its use in conjunction with a conventional fiberoptic sigmoidoscope. Figure 3 shows a single segment with the incorporated clutch electromagnets. The magnet carrying the signal coil has the shape of the letter "U" and it is located in the top surface of a segment; its partner across the articulation gap is a bar magnet and it is not addressed. The magnets were machined from ferrite material code 3E2A possessing a very high magnetic perme-

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BOTTOM

F I G U R E 3. Three-way drawing of a segment showing the disposition of the clutch magnets (not drawn

to scale).

A Carrier For Endoscopes

351

ability (4). The segments are molded of an inert plastic that has the quality of retaining its volume and shape on repeated exposures to high temperature and humidity in an autoclave. Snap hinges of the same plastic will be formed integrally into the segmental body to provide the mechanical connection. Electrical contact will be assured through slip rings riding on the edge about which the segments rotate. Thus, the carrier is assembled from identical units that are easily replaced. Address Formatting

A block diagram of the address system components is given as Fig. 4. The operator's directional command passes first through a logic circuit which resolves an angle into its cardinal vector components and then supplies them in a time sequence to the electromagnetic clutches of the appropriate quadrants. The function generator forms the activating signal on reception of the directional impulse, and this signal is then propagated in a proximal direction on the retrograde activation circuit. The control stick can be moved in all directions of the compass and its motion is coupled to 2 potentiometers perpendicular to each other. The potentials registered are directly proportional to the angular position of the stick; a bank of comparators expresses this analog signal in digital form. In the application described here, we define 8 directions apart from the stick's central position. The coding circuit accepts the signals from the 4 comparators as entries and furnishes 8 directional outputs. The sequential generator provides its part of the decoding function at the rhythm of a clock. This assures that the directional commands are issued with the proper delay to consecutive articulations. An acute angle in the same direction is formed, e.g., by continuing the supply of impulses to the same clutch and holding it closed while others proximal have already engaged

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352

Gdrard Lachiver and Wolf D. Seufert

in the same direction. Since d u t c h magnets are available only for the cardinal points, intermediate headings are taken by bringing one vector component to activate its clutch and proceed retrograde while its partner is delayed momentarily before it is sent out. The impulses from the sequential generator trigger the formation of a signal to engage the clutch magnets and to perform the retrograde address. Figure 5 gives a timing diagram for the directional command NE. The directional coding circuit is shown in Fig. 6; it is contained in the operator's control box while the function generators are built directly into the segments as microcircuits.

The Electronics of Articulation The function generator has two tasks to perform" (a) it generates an address signal to close the clutch and to hold it engaged on receiving an im-

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FIGURE 5. Timing diagram for clutch activation. Example: carrier deflection NE. Subscripts refer to the segment number.

A Carrier For Endoscopes

353

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FIGURE 6. Directional coding circuit.

pulse from the coding circuit; (b) it sends this signal into the retrograde circuit to activate, after a delay, successive clutches of the same coordinates. The delay is calculated such that each consecutive articulation is closed as the carrier advances past the same reference point: forward advance and retrograde activation proceed at the same speed. It should be possible to bring the articulating surfaces of adjoining segments into contact over a distance given by twice the angle of segmental articulation in order to assure closure of even that clutch in a position diametrically opposite to the one just going out of operation. Furthermore, the tracking current has to contend with the stiffness of the sheaths as well as that of wires, instruments, or the fiber-bundle in the carrier's central channel. Once in contact, the current to hold the surfaces together should only be little higher than exacted by the combined elasticity of these components in order to keep the power requirements to a minimum. Consequently, the amplitude of the address signal is much higher during the first few milliseconds than during the remainder. The function generator is given as Fig. 7. Once a wave of deflection has passed the carrier must again become sufficiently flexible to adapt passively to the curvature of the channel in which it finds itself. In other words, only those articulations which momentarily obey the electric impulse traveling in a retrograde direction are rigidly linked and as soon as the train of signals has moved through this part the carrier is limp and pliable again. It rests supported by the wall of the tract and, there-

354

G~rard Lachiver and Wolf D. Seufert

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fore, the holding power of the magnets does n o t have to be as high as to support the weight o f the entire instrument. It is not necessary to hold a section of the carrier horizontally without support beyond, perhaps, a length of three or four segments. The dirigibility of our carrier as the principal design quality is not substantially affected when the carrier rests on a surface. The absolute and relative dimensions of the various elements constituting the carrier depend on the specific function for which it is intended. If it is to be used to facilitate the passage of a sigmoidoscope, the central channel's diameter should be around 15 mm and its outside diameter can be anywhere between 20 and 30 mm. A force of .43 N was developed across the 2.5 mm articulation gap between 2 segments in line when addressed b y a tracking

A Carrier For Endoscopes

355

current of 960 mA during 100 msec, and a force o f . 15 N across a 5 mm gap, the maximum distance when the opposite clutch in the same surface is closed. For the remainder of the signal's 3 sec duration the holding current is less than 50 mA. These values are more ttlan sufficient to operate the endoscope under the conditions given above. The carder is completely enclosed by inside and outside insulating sheaths continuing over both its ends so that the risk o f a current leak is minimal. It is constructed to conform to the regulations of the Canadian Standards Association regarding electromedical equipment.

CONCLUSION We are confident that our carrier will permit the examining physician to pass a flexible fiberoptic endoscope routinely through the sigmoid colon, without using its wall as a guide. This implies that the time to bring the endoscope to a desired destination can be predicted with a greater precision than is possible at present, and even when the endoscope is used by a physician who, because of a lesser case load, has not had the opportunity to acquire a high degree of proficiency with the instrument. REFERENCES 1. Bernard, D. Le cancer du crlon. La Vie m~dicale au Canada fran~ais 5:875-877, 1976. 2. Bokelmann, D. and R. M. Seufert. Chirurgische Onkologie des Kolon- und Rektumkarzinoms. Krebsgeschehen 6:142-149, 1976. 3. Ekelund, G. and J. E. Rosengren. Cancers multiples du crlon et du rectum. Ann. Gastroentdrol. H~patol. 12:461--470, 1976. 4. Ferroxcube Corporation. Ferroxcube Linear Ferrite Materials and Components. Saugerties, New York, 1976. 5. Kogama, Y. Fiberscopic examination of colo-rectal diseases. Am. J. Proctol. 25:51-59, 1974.

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