Optical Imaging Science and Technology

Optical coherence tomography (OCT) has dramatically extended the capabilities of optical imaging, by enabling high-resolution, label-free, biomedical diagnostics in vivo .  Yet, the need for rapid imaging in biomedical samples with micron-scale resolution in all three spatial dimensions, and over millimeter-scale volumes, (ideally single-shot volumetric imaging, without the need for serially-acquired images from multiple depths), remains a challenge.  New imaging capabilities are also needed for basic science investigations into the role of mechanical properties in tumor development and local invasion in vivo.  The up-and-coming area of optical coherence elastography (OCE) is well-positioned to help address this need, whilst, importantly, being compatible with translation to the clinic for diagnostic or therapy-monitoring applications.

Computational Image Formation. New image formation paradigms are made possible by recognizing that OCT combines the advantages of digital holography with the point-scanning benefits of confocal microscopy, allowing some traditional limitations of optical imaging to be overcome.  Computational focusing and aberration correction methods in digital holography are applicable, but the cross-talk issues that plague full-field holographic imaging with spatially coherent (e.g. laser) light are largely overcome by point-scanned acquisition.  In addition, the physics-based model for image formation in OCT has also been recognized to have close similarities to other imaging modalities, such as synthetic aperture radar, leading to a commonly applicable class of image reconstruction techniques.  By exploiting computational image formation we seek to further the boundaries of optical imaging science, particularly within the context of high-resolution 3D tomography of tissues and biological constructs.

Relevant papers

  1. Ralston, T.S., D.L. Marks, P.S. Carney, and S.A. Boppart, “Interferometric synthetic aperture microscopy”. Nature Physics, 3(2):129-134, 2007.
  2. Ralston T.S., Charvat G.L., Adie S.G., Davis B.J., P. Scott Carney and Boppart S.A., “Interferometric synthetic aperture microscopy: microscopic laser radar”, Optics and Photonics News, 21(6):32-38, 2010.
  3. Adie S.G., Graf B.W., Ahmad A., Carney P.S. and S.A. Boppart, “Computational adaptive optics for broadband optical interferometric tomography of biological tissue”, Proceedings of the National Academy of Sciences of the United States of America, 109(19):7175-80, 2012.
  4. Adie S.G., Shemonski N.D., Graf B.W., Ahmad A., Carney P.S. and S.A. Boppart, “Guide-star-based computational adaptive optics for broadband interferometric tomography”, Applied Physics Letters, 101(2): 221117, 2012.
  5. Ahmad A.†, Shemonski N.D.†, Adie S.G., Kim H., Hwu W.W., Carney P.S. and Boppart S.A., “Real-time in vivo computed optical interferometric tomography”, Nature Photonics, 7(6):444-48, 2013.

Optical coherence elastography. One hot area of development is OCE, which aims to image the mechanical properties of tissues in 3D.  OCE can provide a ‘high-resolution palpation’ capability of viscoelastic biological tissue by mechanically perturbing the sample and precisely imaging its response/displacement.  Additional advantages over manual palpation include the ability to control the temporal characteristics of the mechanical excitation, well into the audio-frequency regime, and the ability to perform mechanical spectroscopy in scattering tissues.  This opens up the possibility to perform mechanical spectroscopy (see Dynamic OCE and mechanical spectroscopy), thus providing an extra dimension of information by which to differentiate between different regions of tissue with distinct mechanical properties.  Other areas of development include the investigation of novel mechanical excitation methods, e.g. acoustic radiation force of focused ultrasound.

Optical coherence elastography combines mechanical excitation (‘palpation’) with high-resolution OCT imaging of the resulting displacements within the sample.  In the schematic above, the sample is resting on a plate (connected to a PZT rod to deliver mechanical excitation to the sample) and constrained from above by a glass window.

Relevant papers

  1. Schmitt, J.M., “OCT elastography: imaging microscopic deformation and strain of tissue”. Optics Express, 3(6):199-211, 1998.
  2. Adie S.G., Kennedy B.F., Armstrong J.J., Alexandrov S.A. and Sampson D.D., “Audio frequency in vivo optical coherence elastography”, Physics in Medicine and Biology, 54:3129-3139, 2009.
  3. Liang X., Adie S.G., John R. and Boppart S.A., “Dynamic spectral-domain optical coherence elastography for tissue characterization”, Optics Express, 18(13):14183-90, 2010.
  4. Adie S.G., Liang X., Kennedy B.F., John R., Sampson D.D. and S.A. Boppart, “Spectroscopic optical coherence elastography”, Optics Express, 18(25):25519-34, 2010.
  5. Kennedy B.F., Liang X., Adie S.G., Gerstmann D.K., Quirk B.C., Boppart S.A. and Sampson D.D., “In vivo three-dimensional optical coherence elastography”, Optics Express, 19(7):6623-34, 2011.