Broadband coherent anti-Stokes Raman scattering (CARS): a potential tool for atherosclerosis diagnostic imaging

Nonlinear optical imaging technologies offer some intriguing medical diagnostic applications. Examples include fast imaging of elastin and collagen distributions in diseased tissues using two-photon fluorescence (TPF) and second harmonic generation (SHG), respectively. The 3D sectioning capabilities and biochemical specificity that enable fast imaging in highly scattering biological media lie at the heart of the appeal of these nonlinear approaches for medical applications. One of these promising nonlinear techniques relies on the resonance enhancement of the third order nonlinear susceptibility by a vibrational mode of a molecule. Coherent Anti-Stokes Raman Scattering (CARS) can provide similar vibrational information as a spontaneous Raman spectrum. The technique has been shown to be orders of magnitude more sensitive than spontaneous Raman, with video rate imaging demonstrated recently. In this work, we investigate the potential use of broadband CARS spectroscopy and CARS imaging for biochemical analysis of arterial tissue. Biochemical imaging data from broadband CARS is compared with spontaneous Raman microspectroscopy. The broadband CARS system comprised of a single femtosecond-laser is presented in detail. Issues related to data analysis, the advantages and current limitations of the CARS technique in biodiagnostics are discussed.