Abstract
Purpose: :
To characterize anterior chamber inflammation with very-high-frequency ultrasound.
Methods: :
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.
Results: :
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.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • inflammation • anterior chamber