GreenLightTM procedure is an effective and economical way of treatment of benign prostate hyperplasia (BPH); there are almost a million of patients treated with GreenLightTM worldwide. During the surgical procedure, the surgeon or physician will rely on the monitoring video system to survey and confirm the surgical progress. There are a few obstructions that could greatly affect the image quality of the monitoring video, like laser glare by the tissue and body fluid, air bubbles and debris generated by tissue evaporation, and bleeding, just to name a few. In order to improve the physician’s visual experience of a laser surgical procedure, the system performance parameter related to image quality needs to be well defined. However, since image quality is the integrated set of perceptions of the overall degree of excellence of an image, or in other words, image quality is the perceptually weighted combination of significant attributes (contrast, graininess …) of an image when considered in its marketplace or application, there is no standard definition on overall image or video quality especially for the no-reference case (without a standard chart as reference). In this study, Subjective Quality Factor (SQF) and acutance are used for no-reference image quality evaluation. Basic image quality parameters, like sharpness, color accuracy, size of obstruction and transmission of obstruction, are used as subparameter to define the rating scale for image quality evaluation or comparison. Sample image groups were evaluated by human observers according to the rating scale. Surveys of physician groups were also conducted with lab generated sample videos. The study shows that human subjective perception is a trustworthy way of image quality evaluation. More systematic investigation on the relationship between video quality and image quality of each frame will be conducted as a future study.
We designed a cost effective, highly efficient diode-pumped and Q-switched 532nm laser with large laser output power range and fast laser output power switching from zero Watts to any user defined operating power by adjusting the pump diode current. It is well known that pump diodes used in the solid-state Nd:YAG lasers have center wavelength around 808nm or 885nm and will shift their center wavelength while changing its drive current. The pump diode wavelength shift can be large enough to move outside of the laser gain medium absorption band. This results in lower pump absorption efficiency and hence in lower overall system optical to optical conversion efficiency for some portion of the laser output power range. A few typical ways to minimize this wavelength-shift-caused lower pump absorption effect with their trade-offs have been discussed. We report the unique pump diode wavelength of 879nm and single Nd:YAG rod design for this laser system. This system has about 38% optical to optical (879nm to 532nm) conversion efficiency. The pump current can be adjusted to tune the laser output power to anywhere within the range of 20W to 300W. The laser output power responds within 2 seconds to this input current change, and does not result in Nd:YAG rod damage. Furthermore, a high pump light absorption efficiency is maintained.