Abstract
A high frame-rate near-infrared (NIR) tomography system was created to allow transmission imaging of thick tissues with spectral encoding for parallel source implementation. The design was created to maximize tissue penetration through up to 10 cm of tissue, allowing eventual use in human imaging. Eight temperature-controlled laser diodes (LD) are used in parallel with 1.5 nm shifts in their lasing wavelengths. Simultaneous detection is achieved with eight high-resolution, CCD-based spectrometers that were synchronized to detect the intensities and decode their source locations from the spectrum. Static and dynamic imaging is demonstrated through a 64 mm tissue-equivalent phantom, with acquisition rates up to 20 frames per second. Imaging of pulsatile absorption changes through a 72 mm phantom was demonstrated with a 0.5 Hz varying object having only 1% effect upon the transmitted signal. This subtle signal change was used to show that while reconstructing the signal changes in a tissue may not be possible, image-guided recovery of the pulsatile change in broad regions of tissue was possible. The ability to image thick tissue and the capacity to image periodic changes in absorption makes this design well suited for tracking thick tissue hemodynamics in vivo during MR or CT imaging.
Highlights
High speed near-infrared spectral tomography of tissue can be used to measure functional properties of tissues such as metabolism, hemodynamics and contrast agents to provide useful diagnostic information
This mode alone would make one charge-coupled device (CCD) keep exposing at a preset rate and only transfer the latest frame when the console was ready to receive, so no synchronization could be realized on multiple CCDs
This work has shown the feasibility of using this spectrally-encoded tomography system to do fast speed imaging through thick tissues, of the size required in clinical breast imaging [7,8,9,10]
Summary
High speed near-infrared spectral tomography of tissue can be used to measure functional properties of tissues such as metabolism, hemodynamics and contrast agents to provide useful diagnostic information. Simultaneous source delivery with frequency encoding [2] can be done considerably faster, but is limited by the overwhelming effect of closer strong signals dominating over the farther weaker signals that propagate through a few cm of tissue. This approach, while tremendously successful in subsurface imaging [3], cannot be realized in deep tissue tomography, because of the severe dynamic range variation seen in signals that propagate different distances in tissue. The system has the capacity to image through perhaps up to 8-10 cm of tissue, which would make it possible to be used to track hemoydnamics in peripheral limbs, breast tissue or part of the cranium
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