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D Jackson Coleman, Ronald H Silverman, Mark J Rondeau, Stanley Chang; Signal Processing in High Resolution Ultrasonic Imaging of Tissue Characterization and Perfusion of the Choroid. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5856.
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© ARVO (1962-2015); The Authors (2016-present)
To develop quantitative ultrasound imaging techniques for monitoring of choroidal response to local and systemic medication using wavelet and choroidal perfusion analysis of phase-resolved ultrasound data.
Data were acquired on 56 subjects with age-related macular degeneration using a high frequency (20 MHz) ultrasound imaging immersion technique. Phase-resolve data were acquired at a 250 MHz sample rate (8-bit precision). Swept-mode data were acquired by acquisition of vectors spaced at 5-micron spatial intervals at a 2 msec temporal intervals, allowing tracking of choroidal perfusion using speckle-tracking techniques which measure sub-resolvable scatterers (e.g. blood cells). Wavelet analysis was performed on midband-fit (integrated backscatter) images produced by spectral domain methods. Choroidal thickness was also measured by OCT.
Interscale phase consistency, a parameter derived from wavelet analysis that is sensitive to boundary relationships (i.e. blood or fluid/ tissue boundaries) allowed development of classifiers for differentiation of normal choroid from geographic atrophy and exudative AMD. Swept-mode data allowed measurement of choroidal perfusion, which we characterized by determining the fractional area of choroid with detectable blood-flow. We found statistically significant differences in normal patients versus patients with AMD (ROC= 0.892±0.17). We also measured significant choroidal perfusion and thickness increase in patients given systemic sildenafil.
Advanced ultrasound imaging techniques can be useful combined with OCT measurement of choroidal thickness variation to study pharmacologic therapy of choroidal ischemia.
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