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L. Wang, R. H. Silverman, H. O. Lloyd, D. J. Coleman; Very-High-Frequency Ultrasound Characterization of Particle Size in Anterior Uveitis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6213.
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To characterize anterior chamber inflammation with very-high-frequency ultrasound.
Patients with anterior uveitis were scanned with a prototype immersion arc-scan system utilizing a 35-MHz center frequency broadband ultrasound probe having a focal length of 12-mm and aperture of 6-mm. We digitized radiofrequency echo data of the entire anterior segment at a 250-MHz sample rate at 8-bits/sample and performed power spectrum analysis, subtracting the power spectrum of a glass-plate calibration target from the tissue power. Spectral parameter images were produced, in which pixel intensity represented spectral slope (dB/MHz), the frequency dependence of backscatter. Particle size was estimated using a model that assumed spherical Gaussian autocorrelation functions for scatterers and compensated for attenuation by the cornea. We produced histograms representing pixel count versus particle dimension.
Two patients (4 eyes) with prior diagnosis of anterior uveitis were scanned in a supine position. In one eye, particles with larger dimensions appear to be more prone to settling than smaller particles. The histogram of particle sizes showed a mean value of 29.8-microns, mode of 30.2-microns, and minimum of 20 microns. Distribution was highly skewed towards the larger-particle end, with exponentially decreasing numbers of particles as scatter dimension decreased.
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