Feature Of The Week 9/26/10: Researchers from University of Maryland Demonstrated Multimodality Optical Coherence Tomography and Fluorescence Laminar Optical Tomography Imaging
Feature Of The Week 9/26/10: Multimodal imaging represents one of the current trends in the development of biophotonics imaging technologies for the integration of molecular and physiological information with structural information, enabling in vivo visualization and quantification of disease biomarkers and their progression over time. Multimodal imaging therefore improves the understanding of disease development, enables early diagnosis, and ultimately enhances treatment efficacy. This work presents an integration of optical coherence tomography (OCT) and fluorescence laminar optical tomography (FLOT), which combines the advantages of high-resolution structural imaging from OCT with high-sensitivity functional imaging from FLOT. This platform provides contextual structural information to help understanding the contrast provided by functional imaging.
Implementation of OCT/FLOT system was achieved by combining a swept-source OCT subsystem and a line-scanned FLOT (LS-FLOT) subsystem. The OCT swept source operated at a sweep rate of 16k A-scan/sec and generated a broadband spectrum of ~100nm FWHM centered at 1310 nm, providing an axial resolution of 10 micron in tissue. The OCT system delivered 4mW with a spot size of 15 micron on the sample. The sensitivity was measured as 95dB. On the other side, LS-FLOT was implemented by using a cylindrical lens to expand point illumination into a line. A CW laser diode at 670 nm was used as the excitation light source and combined with the OCT sample arm by a dichroic mirror. The fluorescence signal was separated from reflected excitation light by another dichroic mirror, filtered by a bandpass filter (700 +/- 10nm), and detected by an electron-multiplying CCD. The wavelength design was based on the near-IR dye Cy5.5 and can readily be adapted to image other fluorophores. The OCT/FLOT system shared a common galvanometer. The LS-FLOT used the galvanometer to achieve time-lapse 2D images recording. The recorded data (X-Y-T) were later to be reconstructed into depth-resolved 3D images (X-Y-Z). The reconstruction method applied Monte-Carlo simulation to acquire the knowledge of photon propagation in tissue. The imaging and reconstruction of tissue phantom validated the Monte-Carlo simulation and characterized the axial point spread function of the LS-FLOT. OCT/FLOT imaging of a human breast cancer xenograft model in vivo was later performed. OCT image clearly revealed the tumor boundary beneath the mouse skin layer. On the other hand, the co-registered FLOT image revealed the subcutaneous tumor with high molecular contrast that was otherwise invisible in OCT alone. Subsequent histology confirmed the existence and the sizes of tumor that were depicted by FLOT image. OCT/FLOT therefore represents a new and interesting multimodal imaging regime that could be useful for the investigation of tissue structure and function relationships. This system may open the window to diagnose small lesions which are located too deep for conventional microscopic imaging methods to detect, and too small for macroscopic imaging methods to resolve.
For more information see recent Article1 and Article2. Courtesy of Chao-Wei Chen and Yu Chen from the University of Maryland.