Photoacoustic Fluorescence Tomography

1. Imaging Chamber filled with sound coupling medium
2. Studied sample
3. Orthogonal optical excitation from light delivered via fiber bundle from tunable laser
4. Epi-illumination from light delivered via fiber bundle from tunable laser
5. Curved photoacoustic multi-channel detector
6. Optical camera

PhotoSound patented the multi-modal PAFT technology enabling simultaneous acquisition of the signals from photoacoustic, fluorescent and bioluminescent sources at each rotational position of a studied live sample. Photoacoustic Tomography (PAT) enhanced with 3D fluorescence or bioluminescence imaging combines molecular sensitivity of optical imaging with resolution of ultrasound.

The multi-modality PAFT instrument brings in vivo molecular imaging to the level of highest fidelity enabling quantitative volumetric measurements and up to 10 times improvement in spatial resolution in comparison to state-of-the-art optical methods. Three-dimensional visualization of optically labeled biological structures and processes are performed with robust anatomical registration over skin, central/peripheral vasculature, and internal organs displayed with resolution of 100 μm. The instrument benefits from the exceptional molecular sensitivity provided by its optical detector. PAT enables functional imaging of volumetric blood content and oxygenation without a need for any contrast agent, as well as imaging of various NIR absorbing probes. Biomedical research areas such as cancer, toxicology, tissue engineering and regeneration, cardiovascular and developmental biology greatly benefit from PAFT technology providing in vivo tracking, mapping, and longitudinal studies of externally labeled or internally expressed light-emitting or absorbing molecular constructs.

The unique configuration of optical excitation induces simultaneous co-registered fluorescence and photoacoustic responses inside the interrogated object using the same optical excitation spectrum and the same spatial irradiation pattern. The direction of optical excitation is oriented orthogonal to photoacoustic and optical detectors. Such configuration is also well suited for bioluminescent tomography, which does not engage optical excitation. The major advantage of orthogonal photoacoustic projections is the minimal noise clutter from optical energy absorbed in superficial layers (e.g. skin) and bulk of the interrogated object, which otherwise dominates and masks smaller isotropic signals generated by internal tissues and organs. Orthogonal photoacoustic projections can be reconstructed into high-fidelity volumes showing internal anatomy and regions with induced optical contrast, while strong signals generated by the skin and bulk tissue propagate along the directions of optical excitation, and largely miss the photoacoustic detector. An additional epi-illumination photoacoustic arrangement, with the laser light irradiating the interrogated body from the side of the photoacoustic detector, provides high-fidelity imaging of skin and superficial structures in a separate co-registered dataset.

The major advantage of orthogonal fluorescence projections is significant reduction of background signals associated with transmitted or backscattered photons, which present a challenge in conventional trans-illumination and epi-illumination configurations of fluorescence, respectively. In the orthogonal configuration of fluorescence, the photons transmitted through and backscattered from the interrogated object will miss the detector’s aperture, while omni-directional sources of fluorescence can be detected from anywhere around the interrogated object.