MULTIMODAL IMAGING: OCT reaches further combined with fluorescence, ultrasound

An interdisciplinary team at the University of Arizona has combined OCT and laser-induced fluorescence (LIF) in a single endoscopy device—and reports higher sensitivity and specificity for distinguishing normal tissue from adenoma (benign glandular tumor) compared to either modality alone.1 While optical design is complicated by the large wavelength difference between the two systems, the researchers' new high-resolution endoscope, just 2 mm in diameter, can create focused beams from the ultraviolet to near-infrared. A reflective design ball lens operates achromatically over a large wavelength range, and employs total internal reflectance (TIR) at two faces and reflection at a third internal mirrored face. The 1:1 imaging system obtains theoretically diffraction-limited spots for both the OCT (1300 nm) and LIF (325 nm) channels.

Click to Enlarge
An OCT image, combined with spectroscopic autofluorescence information, depicts a colon. The peak emission intensity has been mapped to a false color scale, where blue = 430 nm and red = 490 nm. The autofluorescence emission is red-shifted in the region of the tumor, in the center of the image. (Image courtesy Jennifer Kehlet Barton, University of Arizona)

Meanwhile, researchers at the University of California–Irvine and the University of Southern California, having earlier reported what they believed to be the first probe to integrate OCT optical components with an ultrasound (US) transducer, have now used the device to demonstrate high-resolution coregistered intravascular imaging.2,3 The probe is based on a 50 MHz focused ring US transducer, with a centric hole for mounting the OCT probe. The coaxial US and light beams are steered by a mirror, mounted at the head of the hybrid probe 45° relative to the light and the ultrasound beams to change their propagation directions, to enable US/OCT imaging simultaneously. The scientists were able to improve the lateral resolution of US by using a focused ultrasonic beam. They used the integrated systems to image rabbit aorta in-vitro, and say that the combined US-OCT system demonstrated high resolution in visualizing superficial arterial structures while retaining the deep tissue penetration capability of ultrasonic imaging. "The results offer convincing evidence that the complementary natures of these two modalities may yield beneficial results that could not have otherwise been obtained," they report.4

The California researchers note that the approach could have a substantial impact on early detection and characterization of atherosclerosis. At least one commercial developer agrees: Volcano Corp., competitor to LightLab Imaging, which was the first company to receive FDA clearance for a cardiovascular system, in 2010 (see http://bit.ly/9ica4f), has a roadmap for combining OCT and IVUS in the same catheter (see http://bit.ly/i6PWJc).

1. R.W. Wall et al., Biomed. Opt. Express 2 (3): 421–430 (2011)
2. J. Yin et al., J. Biomed. Opt. 15, 010512, doi:10.1117/1.3308642 (2010)
3. X. Li et al., Appl. Phys. Lett. 97, 133702, doi:10.1063/1.3493659 (2010)
4. H.C. Yang, IEEE Trans. Ultrason. Ferroelect. Freq. Contr. 57 (12): 2839–2843, doi: 10.1109/TUFFC.2010.1758 (2010)

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