Abstract. The specificity of molecular and functional photoacoustic (PA) images depends on the accuracy of the photoacoustic absorption spectroscopy. The PA signal is proportional to the product of the optical absorption coefficient and local light fluence; quantitative PA measurements of the optical absorption coefficient therefore require an accurate estimation of optical fluence. Light-modeling aided by diffuse optical tomography (DOT) can be used to map the required fluence and to reduce errors in traditional PA spectroscopic analysis. As a proof-ofconcept, we designed a tissue-mimicking phantom to demonstrate how fluence-related artifacts in PA images can lead to misrepresentations of tissue properties. To correct for these inaccuracies, the internal fluence in the tissue phantom was estimated by using DOT to reconstruct spatial distributions of the absorption and reduced scattering coefficients of multiple targets within the phantom. The derived fluence map, which only consisted of low spatial frequency components, was used to correct PA images of the phantom. Once calibrated to a known absorber, this method reduced errors in estimated absorption coefficients from 33% to 6%. These results experimentally demonstrate that combining DOT with PA imaging can significantly reduce fluence-related errors in PA images, while producing quantitatively accurate, high-resolution images of the optical absorption coefficient. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Local molecular and physiological processes can be imaged in vivo through perturbations in the fluorescence lifetime (FLT) of optical imaging agents. In addition to providing functional information, FLT methods can quantify specific molecular events and multiplex diagnostic and prognostic information. We have developed a fluorescence lifetime diffuse optical tomography (DOT) system for in vivo preclinical imaging. Data is captured using a time-resolved intensified charge coupled device (ICCD) system to measure fluorescence excitation and emission in the time domain. Data is then converted to the frequency domain, and we simultaneously reconstruct images of yield and lifetime using an extension to the normalized Born approach. By using differential phase measurements, we demonstrate DOT imaging of short lifetimes (from 350 ps) with high precision (+/-5 ps). Furthermore, this system retains the efficiency, speed, and flexibility of transmission geometry DOT. We demonstrate feasibility of FLT-DOT through a progressive series of experiments. Lifetime range and repeatability are first measured in phantoms. Imaging of subcutaneous implants then verifies the FLT-DOT approach in vivo in the presence of inhomogeneous optical properties. Use in a common research scenario is ultimately demonstrated by imaging accumulation of a targeted near-infrared (NIR) fluorescent-labeled peptide probe (cypate-RGD) in a mouse with a subcutaneous tumor.

New classes of synthetic chlorin and bacteriochlorin macrocycles are characterized by narrow spectral widths, tunable absorption and fluorescence features across the red and near-infrared (NIR) regions, tunable excited-state lifetimes (<1 to >10 ns) and chemical stability. Such properties make dyad constructs based on synthetic chlorin and bacteriochlorin units intriguing candidates for the development of NIR molecular imaging probes. In this study, two such dyads (FbC-FbB and ZnC-FbB) were investigated. The dyads contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. In both constructs, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of approximately (5 ps)(-1) and a yield of >99%. Thus, each dyad effectively behaves as a single chromophore with an exceptionally large Stokes shift (85 nm for FbC-FbB and 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (lambda(f) = 760 nm, Phi(f) = 0.19, tau approximately 5.5 ns in toluene). The long-wavelength transitions (absorption, emission) of each constituent of each dyad exhibit narrow (

Abstract:We have developed a laser speckle imaging method to reveal obscured subsurface inhomogeneities that cannot be seen under incoherent illumination. Speckle images of a scattering object were generated under coherent illumination using a laser. A sequence of speckle images was acquired with fixed exposure time and acquisition interval. The temporal statistics of each pixel in the image sequence was calculated and formed a new image. We demonstrate that such temporal speckle contrast images can reveal obscured subsurface objects. More importantly, by controlling image acquisition parameters, surface inhomogeneity can be eliminated in order to better bring to view the subsurface objects.

Abstract:We examined the expression of target optical properties in subsurface polarization imaging under linearly and circularly polarized illumination. Reflecting, scattering, and absorption targets were imaged in tissue mimic phantoms. The polarization gated images were compared with raw and unpolarized images to determine image enhancement as a function of target depth. The experimental results were also compared with MonteCarlo simulations to study the model's applicability. Our results indicated that polarization imaging provided a means to separate different optical targets where they would otherwise appear similar under unpolarized light.