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oscopic Imaging and Instrumentation |
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It is important for the urologist to have a clear understanding of the characteristics of these highly technical instruments in order to make appropriate choices when purchasing these devices, and in understanding the methods of handling them in their clinical practice |
The goal of endoscopy is to access and treat organs, through natural or artificial orifices in the body
In1806 Philipp Bozzini desined the first endoscope it was made of hollow examining tubes with illumination by candle light directed by a mirror.
Optics
The traditional optics was made of series of precisely aligned thin lenses within a tube .The optical image is relayed from the distal end of the scope to the ocular lens where it can be viewed.
1960 Harold Hopkins developed the rod–lens system in which the air-containing spaces between the conventional series of lenses are replaced with glass rods with polished ends separated by small “air-lenses.”
The light reflecting off an object is detected by the objective lens at the distal tip and the image is transmitted via the rod–lens system back to the ocular lens where it is viewed by the surgeon’s eye or captured by a camera.
Advantiges of Hopkins system :
1- better light transmission
2- reduced image distortion 3- wider viewing angle
4- improved image brightness
The size, or the degree of magnification of the image is dependent on the diameter of the lenses, therefore a smaller caliber telescope, such as a ureteroscope, would have a smaller image than a larger caliber cystoscope
Disadvantiges of Hopkins system :
significant deterioration can occur when torque is placed on the scope, as during passage through the ureter. The lenses and air spacers may come out of alignment, and up to half of the image may disappear, leading to a crescent field defect, or a “half-moon” appearance. Further stress on the shaft may lead to permanent lens damage or misalignment.
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Light Source & cables the light source also underwent considerable modification : 1- candle light directed by a mirror 2-light bulb on the inner tip of the endoscope 3-fiberoptic cable that enabled the transmission of light from an outside Source using a halogen or xenon lamp Advantiges of Fiberoptic cables : 1-provided more illumination 2-cool light which made cystoscopy safer 3-it also made smaller profile scopes with larger irrigation and workin channels possible Types of light cables : 1-fluid-filled cables : more durable. 2-Fiberoptic cables, more commonly in use |
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Light cables vary in length from 6 to 12 feet and in diameter from 3.5 to 4.8 mm.
The light intensity carried by the light cable is inversely proportional to its length with approximately 10% loss for every foot of cable over 6 feet.
Although the light intensity increases with the thickness of the cable.
Broken and burned-out fibers decrease light transmission.
Broken fibers are easily recognized by seeing light shining sideways along the length of the cable or unilluminated fibers when the cable is viewed on end at low light levels. A light cable should be replaced when more than one-third of the fibers are broken or burn out
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The images transmitted by the endoscopes may be viewed directly from the eyepiece or indirectly on a television monitor using a video system Advantiges of Video System : 1- allow binocular vision 2-greater surgeon comfort 3-multiple persons can view the procedure Beamsplitter camera Video System |
The camera head contains a light-sensitive imaging chips called charged couple devices (CCDs).
How it work?
What is pixels ?
Single-chip cameras have one CCD to reproduce color and recreate an image. They are more compact and less expensive than the three-chip cameras (with three CCDs), which contain a prism to refract light into three primary colors (red, green, and blue). Each chip picks up one color, providing an image of better color quality. The three-chip cameras also provide better resolution
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Rigid Cystoscopes Advantiges of Rigid Cystoscopes : 1-better image quality 2-larger working channels 3-greater control 4-more durable Available sizes of Rigid Cystoscopes : from 8 to 12 Fr for pediatric endoscopes from16 to 25 Fr for adult endoscopes. Basic components of Rigid Cystoscopes : 1- the sheath 2-bridge, 3-obturator, 4-telescope. |
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Sheath It is the outer, most rigid part of the instrument It protects the telescopes which are delicate and expensive It provides a channel for introducing irrigation and working instruments The proximal end of the sheath has two irrigation ports, one for the entery of the irrigation medium and the other for its exit The distal end of the cystoscope sheath is cut away in a fenestration to permit the use of operative instruments and angled 70° and 30° cystoscopes. Because irrigation fluid leaks at the urethral meatus until the fenestrated tip is completely inserted, this design makes urethroscopy difficult. Unlike cystoscope sheaths, urethroscope sheaths are cut flush at the distal end, having no fenestration. This allows distention of the distal urethra and more complete visualization of the urethral walls. |
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Obturator Obturators can be introduced into the sheath to provide a smooth tip for insertion into the urethra. The closed obturator provides a solid intact tip for introduction of the instrument in a blind fashion. A visual obturator accommodates a telescope and fills the space between the telescope and the sheath to provide a smooth surface against the urethra and allows the sheath to be introduced under vision. |
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Bridge The bridge serves as a watertight connector between the telescope and the sheath. It may have one or two angled side-arms for introduction of instruments (e.g. biopsy or diathermy) into the irrigation-working channel. A deflecting bridge (Albarran bridge) may be inserted into the sheath to allow the use of flexible instruments , Deflection at the instrument tip is controlled with a wheel at the proximal end of the bridge. The Albarran bridge is particularly useful for directing a ureteral catheter into a ureteral orifice, a needle for injection (e.g. Botox). |
Telescope
The telescope carries the fiberoptic illuminating system which extends from the tip of the instrument to the point of attachment of the light bundle just beyond the eyepiece.
The light of the visual image is collected at the objective lens and transmitted through a rod–lens system to the eyepiece.
Cystoscopic telescopes are available with several viewing angles :
* 0° telescopes. to look directly forward good for urethroscopic viewing of the urethra and bladder neck
*30° telescope provides a forward oblique view the best view of the bladder base and the posterior wall
*70° telescope provides lateral view preferable for operative cystoscopy and allows inspection of the anterior-lateral walls, bladder dome, and ureteric orifices
*120° telescope provides retrograde view
Flexible Cystoscopes
Advantiges of Flexible Cystoscopes :
1- better access to visualizing all areas of the bladder 2-greater patient comfort (with local anasthesia )(in males) 3-less traumatic
Basic components of Flexible Cystoscopes :
1- the optical systems consist of flexible bundles that transmit light and images. The optical fibers are connected to a lens system that magnifies and focuses the image.
2-irrigation-working channels to accommodate irrigation and instruments.
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The tip of the scope can be deflected in either direction from 180 to 220° with a thumb control. * The flexible tip is about 15–18 Fr in diameter and 6–7 cm in length * The use of the working channel with operative instruments restricts the tip deflection. |
Ureteroscopes
The original ureteroscope was made by Richard Wolf Medical Instruments in 1979,
These ureteroscopes utilized the rod–lens optical system and were limited by their size and the lack of adequate instrumentation for stone fragmentation and removal. They were purely instruments for diagnosis and not for therapeutic efficacy.
The application of fiberoptic technology was the next major step in the development of ureteroscopes. This was based on the principle of total internal reflection; light traveling inside of an ultrathin glass fiber surrounded by a cladding with a lower refractory index can be transmitted over a long distance with minimal degradation.
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A coherent fiberoptic bundle contains thousands of individual fibers with identical orientation at the ends of each bundle so the exact image is transmitted to the eyepiece. Therefore the image obtained by fiberoptic bundles is not a single image but a composite matrix of each fiber within the bundle, giving it a “honeycomb” appearance |
Basic components of Rigid Ureteroscopes :
1-imaging and light transmission fiberoptic bundles,
Each scope contains a coherent fiberoptic bundle for image transmission and one or two larger noncoherent light transmitting fiberoptic bundles. In general, two sets of light transmission bundles provide a more even illumination and decreased shadowing.
2-working channel :
* one large channel for both instrumentation and irrigation,
* with two channels to separate instrumentation and irrigation (allow passage of a working instrument without diminution in the flow of the irrigant fluid.)
Available sizes of Rigid Ureteroscope
* Working length: 33- 43 cm * Tip size : 6- 8 fr
* proximal size :7.8- 13 fr Channel size : 2.3 -6.2 fr
Tip Design
* flush tips
*beveled,( triangular tip. Oval tip )
* facilitate insertion into the ureteral orifice
* decrease ureteral trauma
* allow smaller tip diameter,which rapidly enlarges to the distal
shaft size
Angle of visualisation
*0° angle most of the ureteroscopes
*9° angle for the visualization of instruments as they are advanced out of the working/irrigation channel
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Semirigid Ureteroscopes (miniscopes)
Advantiges of Semirigid Ureteroscopes :
1- The flexibility of the fiberoptic bundles allowed for the metal shaft to be flexed up to 2-in. off the vertical axis without significant image distortion.
2- reduction of the outside diameter of the endoscopes,while maintaining larger working channels and greater irrigation flow rate
3- ureteroscopes with small distal diameters allow inspection of the distal to midureter without routine dilation of the intramural ureter
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Flexible Ureteroscopes Basic components of Flexible Ureteroscopes: 1-imaging and light transmission fiberoptic bundles 2-working-irrigation channel 3-deflecting mechanism. |
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Scope Deflection * The active deflection of the tip of the flexible ureteroscope is manually controlled via a lever mechanism on the handle *Depending on the model, the tip may deflect from 130 to 270 degrees in either direction in the same plane |
*The scope may be designed with:
1-intuitive deflection in which the tip deflects in the same
direction as the movement of the thumb lever
2- counterintuitive deflection where the tip deflects in the opposite direction to the movement of the thumb lever.
Also the deflection may be:
1-primary
2-secondery as in “DUR-8 Elite” ureteroscope Deflection may be:
* Active
* Passive, passive deflecting segment is placed several centimeters proximal to the active deflectable segment it allows the scope to curl upon itself when the tip of the scope is reflected off the medial aspect of the renal pelvis for maneuvers into the lower pole infundibulum.
*the flow rate in the working-irrigation channel is affected by the degree of deflection
* Also ,the angle of active and passive deflection can be severely restricted by the presence of instruments in the working channel.this can be minimised with newer, smaller, and more malleable instruments
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Care and Sterilization 1-proper handling by holding these scopes near their eyepieces at the base while supporting the shaft 2-Cleaning with warm water and a nonabrasive detergent 3-Irrigation of the working channels, following each use 4-sterilized may be by : * gas (ethylene oxide) * soaking; in 2.4% glutaraldehyde (i.e., Cidex) 35% peroxyacetic acid (i.e., Steris,) * some may be autoclaved * plasma sterilization |
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Future Trends * The lenses can be replaced with small , high resolution cameras * Three-dimensional imaging may become possible if two CCD chips are used to create a stereoscopic vision. * Noninvasive virtual endoscopy from emerging compute tomography techniques may be used for noninvasive surveillance of the entire urinary tract This systems allow the operator to 'fly' through the urinar tract It will be more useful in : 1-when conventional cystoscopy is not applicable 2-when conventional cystoscopy is contraindicated 3-when close cystoscopic surveillance is required |
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It also can give idea about the nature of detected lesion by showing its size, shape ,vascular density “virtual biopsy
sensitivity of 90% and specificity of 94%
* wireless capsule endoscopy (WCE), in which a camera and a wireless radio transmitter are contained in a small capsule that is inserted into the urinary tract
In the future capsules could be modified to enable tissue biopsy and treatment, and even to deliver medication such as BCG or chemotherapy after bladder tumor resection.
*small robots built from novel materials, has already been demonstrated to be feasible
*Combining the molecular biologic techniques with endoscopy as in Raman probe endoscopy that use a specific powerful light to measure the molecular components of tissue in a qualitative and quantitative way providing “real time histopathology “ for early detection of cancer enoscopicaly.