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U.S. Department of Health and Human Services

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Research Project: High Resolution Imaging with Optical Coherence Tomography

Optical coherence tomography (OCT) is a novel medical imaging modality which has been FDA-cleared for ophthalmic imaging and is under investigation for a number of other applications, including cardiovascular plaque assessment and mucosal cancer detection.  The hardware and software of OCT devices are quite complex, and have been rapidly evolving to improve image quality and incorporate quantitative measurement features.  To keep pace with these advances, we have been conducting research in the Optical Diagnostic Devices Laboratory to investigate the factors which impact OCT device performance and also develop bench test methods for device assessment.  Having standardized bench test methods enables rigorous and consistent pre- and post-market evaluation of OCT devices in a similar vein to long-standing medical imaging modalities. 

Enhanced OCT imaging with gold-silica nanoshells 

Nanoshells are a novel type of engineered nanoparticle which can strongly absorb and/or scatter light through the phenomenon of surface plasmon resonance.  In addition, cancer-targeting antibodies are readily attached to the gold surface of nanoshells, therefore offering a mechanism for molecular-specific imaging and treatment of cancer.  OCT image brightness is increased by the enhanced light scattering from nanoshells, as shown in Figure 1.  Such a brightness increase from a local region where nanoshells are attached to cancer cells can improve detectability of cancer surrounded by normal tissue.  We quantified the amount of nanoshells needed to yield meaningful contrast enhancement in a tissue-mimicking phantom1, as shown in Figure 2.

 

Figure 1: OCT images of two different tissue-mimicking phantoms with and without nanoshells.

 Figure 2: OCT enhancement by three different sizes of nanoshells.

 

Three-dimensional characterization of the OCT point spread function 

One of the most fundamental parameters for characterizing image quality is the point spread function (PSF), as this parameter defines spatial resolution in three dimensions.  Direct imaging of individual particles much smaller than the resolution limit permits characterization of the PSF in three dimensions. We have constructed and characterized a nanoparticle-embedded phantom (NEP)2, which comprises a sparse, homogeneous distribution of gold-silica nanoshells in a transparent silicone matrix, as shown in Figure 3.  The NEP enables the PSF to be characterized at various points in the OCT field of view, as shown in Figure 4.

 

 
Figure 3: OCT image of NEP showing locations of nanoparticles.
 


Figure 4: 3D renderings from individual nanoparticles at different depths in NEP

 

  

1 A Agrawal, S Huang, AWH Lin, MH Lee, JK Barton, RA Drezek, TJ Pfefer. Quantitative evaluation of optical coherence tomography signal enhancement with gold nanoshells.  J Biomed Opt 11(4), 041121 (2006). 

2 A Agrawal, TJ Pfefer, N Gilani, RA Drezek. Three-dimensional characterization of optical coherence tomography point spread functions with a nanoparticle-embedded phantom. Opt Lett 35(13), 2269-2271 (2010).