To our knowledge, this study is the largest prospective, randomized, triple-blinded, and controlled pivotal clinical trial reported to date assessing a putative periodontal regenerative and wound healing therapy. The study demonstrated that the use of rhPDGF-BB was safe and effective in the treatment of periodontal osseous defects. Treatment with rhPDGF-BB stimulated a significant increase in the rate of CAL gain, reduced gingival recession at 3 months post-surgery, and improved bone fill as compared to a beta-TCP bone substitute at 6 months.

The human recognition probabilities of blurred rotationally symmetric shapes have been studied using computer generated images displayed in a 128x128 pixel area on a T.V. monitor.The shapes employed included a series of regular polygons, crosses and rectangles. These were blurred by convolution with two dimensional Gaussian functions which had standard deviations ranging from 0 to 29. Images of the blurred shapes were presented to observers in a random order and with a random extent of blurring. After each presentation the observer decided which of the shapes was most likely to be represented by the image displayed on the screen. A correlation has been found between the extent by which a shape may be blurred before it ceases to be recognizable and the difference between the original shape and a circle of the same area. This correlation has been expressed as an empirical relationship between the probability of recognition and the standard deviation of the Gaussian blurring function when the latter is normalised by a function which depends on the original shape and the one it is being confused with. This relationship has been applied to a series of irregular shapes to predict the amount of blurring required before they too cease to be recognizable. These predictions have been compared to experimental observations for the irregular shapes considered.The probability of recognizing an image may be used as a measure of image quality. The empirical relationship derived from this work could, therefore, form the basis of a new objective performance measure for thermal imaging systems.

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Current performance measures for thermal imagers relate only indirectly to human recognition. However, as the probability of recognizing an image may be used as a measure of image quality, the relationship described in this work could contribute to the formation of a new objective performance measure for thermal imaging systems.The human recognition probabilities of several degraded shapes have been evaluated using computer generated images displayed on a computer monitor. The shapes investigated, were blurred by convolving them with a range of two dimensional Gaussian functions. In subsequent trials, these blurred images were further degraded by sampling (in order to simulate the effect of detector arrays in an imager). Images of degraded shapes were presented to observers in a random order and with a random degradation. After each presentation the observer decided which was the most likely shape to represent the image displayed on the screen.A correlation has been found between the probability of recognition of a particular degraded shape and the relative contrast between the image of that shape and a similarly degraded circle of the same area. This is true whether the degradation is due to blurring alone or to blurring followed by sampling. LINTRODUCTIONSummary performance measures may be used to evaluate imaging systems and to optimise their design for specific applications. An ideal summary performance measure must include the observer's limitations. It must also be predictable from fundamental system parameters (such as optical transfer function, image signal-to-noise ratio, frame rate, magnification), be easily measurable and relate to the performance of the system as it is ultimately intended to be used '. There are many performance measures in common use (noise equivalent temperature difference (NETD), minimum resolvable temperature difference (MRTD), modulation transfer function (MTF)), all of which relate only indirectly to target recognition. Johnson (1958) attempted to overcome this limitation. He measured the resolution required by a human observer to perform the tasks of detection, orientation, recognition and identification in terms of the highest spatial frequency bar pattern adjacent to the target that was still resolvable in the image. Although attempts have been made to extend Johnson's work2' 3,his criteria still remains the most established, and universally employed.In order to improve existing performance measures, it is desirable to specify the effects of image degradation commonly introduced by infrared imaging devices, on human image recognition. In general, the information in the scene is first aberrated by the optical system, and subsequently distorted by the detector, electronics and the display. It is also subjected to both temporal and fixed pattern noise. 190 / SPIE Vol. 2470 0-8 194-1823-4/95/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 08/04/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx THE EFFECT OF DEGRADATJON BY GAUSSIAN BLURRING A...

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