somewhat limited, that any movement of the head clamp requires re-registration, and that the inherent accuracy was found to be somewhat lower than that of other methods. Marketed as the "ISG wand", this mechanical localizer was a critical component in the first regular applications of image-guided surgery .
Ultrasound Localization The first example of frameless navigation was a system developed by Roberts et al. . This system used a microscope both to register the images to the patient and to provide the guidance information. The localization system was based on ultrasonic spark-gap transducers. These emit a very short ultrasound pulse, which can be detected by three or more microphones in the operating room. The time delay for the sound pulse to reach each microphone gives a measure of distance and hence localizes the spark gap. Others have developed this technology for conventional pointer-based guidance . Some problems have been encountered owing to variations of the speed of sound with temperature and air flow. This localization system was implemented in the Picker Viewpoint system, but was subsequently replaced by optical tracking.
With either three linear cameras or two 2D cameras, if a point can be located in each view, the 3D location of the point relative to the cameras can be calculated. This is the basis of a number of tracking systems. The localized points are either active (bright infra-red-emitting diodes, IREDs) or passive (highly reflecting spheres). In smaller camera systems, such as the Polaris or IGT systems, each IRED can be localized with an accuracy of 0.2-0.4 mm. With the Optotrak -a larger and more expensive version - accuracy is 0.1-0.2 mm. The main difficulty with optical tracking is that line-of-sight between the cameras and tracked objects must be maintained. However, the high accuracy and stability of these systems have meant that optical tracking is now the technology of choice for most commercial image-guided surgery systems.
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The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.