Zhiqiu Li

Dartmouth College, Hanover, NH, United States

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Publications (6)6.93 Total impact

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    ABSTRACT: A near-infrared (NIR) tomography system with spectral-encoded sources at two wavelength bands was built to quantify the temporal contrast at 20 Hz bandwidth, while imaging breast tissue. The NIR system was integrated with a magnetic resonance (MR) machine through a custom breast coil interface, and both NIR data and MR images were acquired simultaneously. MR images provided breast tissue structural information for NIR reconstruction. Acquisition of finger pulse oximeter (PO) plethysmogram was synchronized with the NIR system in the experiment to offer a frequency-locked reference. The recovered absorption coefficients of the breast at two wavelengths showed identical temporal frequency as the PO output, proving this multi-modality design can recover the small pulsatile variation of absorption property in breast tissue related to the heartbeat. And it also showed the system's ability on novel contrast imaging of fast flow signals in deep tissue.
    Proc SPIE 02/2011;
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    ABSTRACT: A near-IR (NIR) tomography system with spectral-encoded sources was built to quantify the temporal contrast in human breast tissue using guidance from magnetic resonance imaging. The systems were integrated with a custom breast coil interface to provide simultaneous acquisition. The NIR signal was synchronized to simultaneous finger pulse oximeter plethysmogram, which offered a frequency reference. A 0.1 s temporal delay of the absorption pulse within adipose tissue relative to fibroglandular tissue was found, in an initial human study, showing the potential for novel contrast imaging of fast flow signals in deep tissue.
    Optics Letters 12/2010; 35(23):3964-6. · 3.39 Impact Factor
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    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.
    Optics Express 08/2009; 17(14):12043-56. · 3.55 Impact Factor
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    ABSTRACT: A near-infrared (NIR) tomography system has been built to allow for imaging thick tissue at high frame rate. This tomography system uses a spectrally encoded source arrangement consisting of eight fibers coupled from temperature controlled single mode laser diode sources with about 1 nm spacing in their lasing wavelengths, having an overall spectrum confined to within 10 nm in the NIR region. Eight fiber-coupled, high-resolution, CCD based spectrometers were used to detect the intensities and decode their source origin locations. All detection CCDs were frame-synchronized using a computer controlled external TTL trigger circuit in order to preserve the temporal kinetics of the detected signals. A set of static heterogeneous phantom imaging was performed on a 64 mm thick resin phantom to verify the linearity and accuracy of the system and algorithm. Furthermore, to test the performance of this system at high frame rate, a dynamically varying absorption contrast study was realized by letting India ink diffuse into the phantom inclusion while continuously imaging it at 20 frames per second. The algorithm and the results from these phantom studies are presented. The 20 frames/second exposure rate and ability to image tissue beyond 60 mm thick makes this system perfect for potential clinical imaging of pulsatile hemodynamics in breast tumors.
    Proc SPIE 01/2009;
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    ABSTRACT: A NIR diffuse tomography system with spectrally-encoded sources allows simultaneous detection of all data. It can provide images of high-contrast, fast changes in tissue optical properties to be overlayed on the magnetic resonance breast scan. Article not available.
    Biomedical Optics; 03/2008
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    ABSTRACT: Video rate diffuse tomography can be implemented within the magnetic resonance breast exam. The following paper outlines the basics of a spectrally encoded source set up, being designed and tested for use in breast imaging within a specialized breast surface coil. The system design maximizes input power to the breast, while confining the spectrum to a 10 nm bandwidth of near-infrared light. The center spectral band can be varied, since it is supplied by a tunable Ti:Sapphire laser. The encoding of each source is achieved by splitting the signal into individual nanometer bands through a high resolution grating, and focusing the output of this into each source fiber. This source configuration then requires spectral detection at the output, and so each detection fiber is delivered to a high resolution spectrometer to resolve the detected intensities. Breast imaging with this system has some subtle dynamic range issues, which means that light from sources farthest from the detector pickup are likely not providing useful data, but the closest 4-6 fibers near each source can provide useful data. The implementation of this is being carried out within a magnetic resonance breast array, and initial testing of the signals is shown, along with diagrams and photographs of the system configuration.
    Proc SPIE 03/2008;