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"A second issue is synchronization—how the vibration relates to the acoustic waves. We need to synchronize the vibrations to the acoustic wave form and now can do it with 11 microseconds precision, which is sufficient for us."
Deliyski uses the Phantom V7.3 digital camera from Vision Research (Wayne, N.J.) for his research. It gives him the capability of recording vocal folds in real time, at a speed of 6,668 frames-per-second (fps) at a full resolution of 800x600 pixels. For ascertaining the temporal precision, Deliyski records at 16,000 fps by reducing the Phantom V7.3's resolution to 320x320 pixels. Equipped with a 70° rigid endoscope and 300W constant Xenon light source, the V7.3 allowed the researcher to analyze the human vocal folds in ways never before possible, helping usher in a new era for laryngeal HSV.
"There are a number of factors that are critical in HSV, but paramount is the sensitivity of the high-speed digital camera's CMOS sensor," Deliyski says. "High intensity lighting could very well damage the vocal folds we are attempting to study, so the camera must have very high sensitivity and require little amounts of light. The proprietary Vision Research CMOS embedded in the Phantom V7.3 yielded the performance that this project required. The performance of the V7.3's sensor allowed our team to accurately record exceptionally rich detail that was never before available with previous stroboscopic or HSV systems."
Another challenge of this implementation was the weight of the camera. The ultra-high speeds require all hardware, including the memory, to be physically located inside the body of the camera. In order to compensate for the weight (3.18 kg), the device was attached to a camera crane model CamCrane 200 (Glidecam Industries, Inc., Kingston, Mass.). The camera weight was balanced, to appear weightless to the operator, while allowing most degrees of motion freedom by using a ballhead. Other than the weightlessness, the crane was found to significantly reduce the endoscopic motion and tilt, while also introducing a comfortable system to operate. Based on that experience, we recommended using a camera crane regardless of the weight of the camera.
In addition to this newly integrated HSV system, Deliyski's team is developing a whole new methodology for the analysis and clinical interpretation of the acquired images. The analyses include those that allow presenting the visual information that is hidden to the eye in a new and more intuitive way to the clinicians, and those that are fully automated, in which the results of the exam are presented in a quantitatively comparable form. The speed, spatial resolution and image quality of the recordings is critical for the accurate analysis of the human vocal folds. When it comes to HSV, color and spatial resolution are very important when identifying lesions, vascularities and tissue changes, as well as for accurately representing the edges of the vocal folds. Spatial resolution also is important to allow for a wide view angle necessary to examine the full anterior-posterior view of the vocal folds and their surrounding anatomic structures. The temporal resolution of a high-speed digital camera is essential for accurately displaying the mucosal wave produced by the vibration of the vocal folds and providing sharp edges, especially when viewing high-pitched samples.