Where Next for the Endoscope?

Ricardo A. Natalin; Jaime Landman

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In This Article

Digital Endoscopes

In 1970 Boyle and Smith created the charge-coupled device (CCD)—a chip that could store data in the form of electric charges within a grid for retrieval at a later time.[10] Although it soon became obsolete as a memory device, this ability of a CCD to transfer electric charges made it well suited to recording images as a grid of pixels.[11] The CCD chip's linearity of response, high sensitivity and instant image production were all advantageous over conventional film-based image capture. The complementary metal oxide semiconductor (CMOS) device—a low-cost alternative to expensive CCD chips—was patented in 1967. The CMOS chip offered reductions in cost and device size, and was more suitable than CCDs for mass production.[12]

A move from fiberoptic endoscopy to distal sensor or 'digital' image-based endoscopy based on CCD and CMOS chips is a natural result of the current and projected advantages of these technologies (Box 1). Contemporary distal sensor endoscopes are able to meet the diminutive size requirements of all but the very smallest endoscopes. Certainly, as distal sensor technology improves, endoscopes that employ this technology will match the size of contemporary fiberoptic endoscopes and will ultimately be smaller. Distal sensor endoscopes are already superior to flexible fiberoptic endoscopes in terms of weight.

The key characteristic of any endoscope is its optical fidelity, which includes both the ability to provide adequate light at the target site, and the ability to provide a high-quality representation of the target. The 30-year evolution of fiberoptic flexible endoscopes resulted in reasonable quality images. However, the finite diameter of image-carrying glass fibers made the pixelated 'screen door' effect an insurmountable problem for fiberoptic endoscopes. The first commercial distal sensor endoscope was the ACMI DCN-2010 digital flexible cystoscope (ACMI, Southborough, MA, USA), which was introduced in 2005. This cystoscope incorporated a digital camera and dual light-emitting diode (LED)-driven light carriers into the distal tip of the cystoscope, which reduced the need for cabling and the weight of the device. These measures increased the ergonomic compatibility of the device and facilitated its use.

Quayle and co-workers compared this first distal sensor cystoscope with three contemporary fiberoptic cystoscopes in vitro. In simulated adverse conditions, the distal sensor endoscopes provided superior optics.[13] Borin and colleagues compared a distal sensor, digital, flexible cystoscope with two standard fiberoptic endoscopes by studying contrast, resolution, and color discrimination. In 12 of 13 optical tests, the distal sensor cystoscope was superior to the fiberoptic cystoscopes. The authors noted that imaging with the distal sensor endoscope was improved by the ability to identify lesions as small as 1 mm at a greater distance than was possible with the fiberoptic endoscope.[14] They speculated that this optical advantage could potentially result in improved clinical evaluation, for example by increasing the sensitivity of surveillance cystoscopy.

Okhunov and colleagues conducted a prospective clinical comparison of distal-sensor and fiberoptic cystoscopes in over 1,000 patients who underwent office cystoscopy. The investigators evaluated the optics, clinical performance, and durability of these devices. All surgeons found the distal sensor endoscopes to be lighter and easier to handle, and the majority preferred these cystoscopes to the fiberoptic devices. Both subjective optical and functional metrics were significantly better with the distal sensor cystoscopes than with the fiberoptic ones. Distal sensor video imaging provided rapid and high-quality image capture. The images were easily stored and transferred by standard computer memory technologies. Both the fiberoptic and distal sensor cystoscopes were very durable with proper care.[15]

Evolution of distal sensor imaging has facilitated the construction of ever-smaller distal sensors, and the technology has been extended to other urologic endoscopes, such as ureteroscopes and nephroscopes. The quality of image captured by the contemporary digital ureteroscope is comparable to the image from a rigid Hopkins lens. However, distal sensor ureteroscopes offer superior illumination and resolution. Another advantage of digital imaging is the ability to digitally magnify an image up to 1.35 times its original size.[16]

Andonian and co-workers have evaluated the application of distal sensor imaging in a nephroscope. This device has a 15 Fr (5 mm) working channel, which enables the insertion of instruments such as forceps, lithotripsy probes and suction devices. The image produced has true color and retains good resolution.[17]

The superior optics of distal sensor ureteroscopes and nephroscopes is hypothesized to result in superior surgical performance. However, this theory has not yet been evaluated, and at present no evidence supports the superiority of distal sensor ureteroscopes in the clinical setting.

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