Abstract
Speckle noise significantly limits the information content provided by coherent optical imaging methods such as optical coherence tomography and its recent derivative, optical frequency-domain imaging (OFDI). In this paper, we demonstrate a novel OFDI system that simultaneously acquires hundreds of angularly resolved images, which can be compounded to reduce speckle noise. The system comprises an InGaAs line-scan camera and an interferometer, configured so that the elements of the detector array simultaneously capture light spanning a backscattering angular range of 32 degrees. On successive read-outs of the array, the wavelength of the laser source was stepped through a range of 130 nm centered at 1295 nm to concurrently generate 400 angle-resolved OFDI images. A theory of angle-resolved OFDI and the design equations of the system are presented. Incoherent averaging of the angle-resolved data is shown to yield substantial speckle reduction (as high as an 8 dB SNR improvement) in images of a tissue phantom and esophageal tissue ex vivo.
Highlights
Recent advances in optical frequency domain imaging (OFDI) have yielded systems capable of minimally-invasive cross-sectional imaging of biological tissue with both high frame-rates and high sensitivity [1,2,3]
As in optical coherence tomography (OCT), OFDI images are significantly confounded by speckle, which manifests as a grainy pattern within scattering regions
Angular diversity is a powerful method of speckle reduction and has hitherto been limited to averaging across a small number of angles
Summary
Recent advances in optical frequency domain imaging (OFDI) have yielded systems capable of minimally-invasive cross-sectional imaging of biological tissue with both high frame-rates and high sensitivity [1,2,3]. Many different methods have been proposed for mitigating the effects of speckle, including median filtering, phase-domain processing [4], frequency compounding [5], wavelet-based filtering [6], and I-divergence regularization [7]. While these methods have met with some success, most suffer the drawback of a loss of spatial resolution. The method of angular compounding, in which separate images acquired from different backscattering angles are averaged incoherently, does not necessarily involve that compromise. Compounded images from these studies still show high levels of speckle, which reflects the small number of detected angles employed. Using the method of angular compounding, we demonstrate high levels of speckle reduction without a substantial decrease in spatial resolution
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