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Jeffrey A. Ketterling, Daniel Gross, Jonathan Mamou, Quan V Hoang, Ronald H Silverman; Improved detection of vitreous inhomogeneities using a 20-MHz, ultrasound annular array. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1692. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Clinical ophthalmic ultrasound has advanced very little over the last 20 years. Current commercial systems permit visualization of the anterior or posterior sections of the eye, but not the whole globe, without severe compromises on image quality. An increase in vitreous inhomogeneities (VH) is known to correlate with age and systemic diseases such as myopia and diabetic retinopathy, but quantifying VH throughout the vitreous with optical or ultrasound methods has not been possible. An annular-array ultrasound transducer permits visualization of the whole vitreous and provides the potential to quantify VH throughout the vitreous.
A custom, 20-MHz, annular-array ultrasound system with a hand-held probe was developed (Fig. 1a). The annular array had five elements, a 26-mm focal length and a 9-mm total aperture. After establishing that the acoustic output levels were within the FDA limits for ophthalmic imaging, human-subject scanning was performed and the raw, phase-resolved echo data, sampled at 125 MHz, were saved. Single-element 10- and 20-MHz probes were also used to scan in some patients. Eyes were scanned in the horizontal orientation and several image sequences were acquired. Regions of interest (ROIs), representing background noise and floaters within the vitreous, were manually segmented. The envelopes of the phase-resolved echo data were calculated and a threshold of six times the background noise was used to determine an area representing floaters within an ROI.
15 high-myopic patients (28 eyes) were scanned with the annular array (Fig. 1a). Of these, 5 patients (7 eyes) were also scanned with a single-element transducer. The signal-to-noise ratios of the floater regions were nearly the same (13 dB) for both scan types. For the annular-array scans, the average area of floaters was 0.68 ±0.6 mm2. The average area of floaters for the single-element patients was 0.13 ±0.08 mm2, over 4x less (p < 0.01). In nearly all of the annular-array scans, floaters were detected in the anterior-to-central region (Fig. 1b). The single-element system was not able to resolve this area of the eye (Fig. 1c).
These initial results show that, compared to current clinical ultrasound systems, an annular array is better able to detect VH, particularly in regions that current clinical systems or OCT cannot resolve.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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