KEYWORDS: Cameras, 3D image processing, Hyperspectral imaging, Tissues, 3D image reconstruction, Imaging systems, 3D modeling, 3D acquisition, Calibration, Blood
Accurate and in vivo characterization of structural, functional, and molecular characteristics of biological tissue will facilitate quantitative diagnosis, therapeutic guidance, and outcome assessment in many clinical applications, such as wound healing, cancer surgery, and organ transplantation. We introduced and tested a multiview hyperspectral imaging technique for noninvasive topographic imaging of cutaneous wound oxygenation. The technique integrated a multiview module and a hyperspectral module in a single portable unit. Four plane mirrors were cohered to form a multiview reflective mirror set with a rectangular cross section. The mirror set was placed between a hyperspectral camera and the target biological tissue. For a single image acquisition task, a hyperspectral data cube with five views was obtained. The five-view hyperspectral image consisted of a main objective image and four reflective images. Three-dimensional (3-D) topography of the scene was achieved by correlating the matching pixels between the objective image and the reflective images. 3-D mapping of tissue oxygenation was achieved using a hyperspectral oxygenation algorithm. The multiview hyperspectral imaging technique was validated in a wound model, a tissue-simulating blood phantom, and in vivo biological tissue. The experimental results demonstrated the technical feasibility of using multiview hyperspectral imaging for 3-D topography of tissue functional properties.
We report a second derivative multispectral algorithm for quantitative assessment of cutaneous tissue oxygen saturation (StO2). The algorithm is based on a forward model of light transport in multilayered skin tissue and an inverse algorithm for StO2 reconstruction. Based on the forward simulation results, a parameter of a second derivative ratio (SDR) is derived as a function of cutaneous tissue StO2. The SDR function is optimized at a wavelength set of 544, 552, 568, 576, 592, and 600 nm so that cutaneous tissue StO2 can be derived with minimal artifacts by blood concentration, tissue scattering, and melanin concentration. The proposed multispectral StO2 imaging algorithm is verified in both benchtop and in vivo experiments. The experimental results show that the proposed multispectral imaging algorithm is able to map cutaneous tissue StO2 in high temporal resolution with reduced measurement artifacts induced by different skin conditions in comparison with other three commercial tissue oxygen measurement systems. These results indicate that the multispectral StO2 imaging technique has the potential for noninvasive and quantitative assessment of skin tissue oxygenation with a high temporal resolution.
Quantitative assessment of wound tissue ischemia, perfusion, and inflammation provides critical information for appropriate detection, staging, and treatment of chronic wounds. However, few methods are available for simultaneous assessment of these tissue parameters in a noninvasive and quantitative fashion. We integrated hyperspectral, laser speckle, and thermographic imaging modalities in a single-experimental setup for multimodal assessment of tissue oxygenation, perfusion, and inflammation characteristics. Algorithms were developed for appropriate coregistration between wound images acquired by different imaging modalities at different times. The multimodal wound imaging system was validated in an occlusion experiment, where oxygenation and perfusion maps of a healthy subject’s upper extremity were continuously monitored during a postocclusive reactive hyperemia procedure and compared with standard measurements. The system was also tested in a clinical trial where a wound of three millimeters in diameter was introduced on a healthy subject’s lower extremity and the healing process was continuously monitored. Our in vivo experiments demonstrated the clinical feasibility of multimodal cutaneous wound imaging.
The wound healing process involves the reparative phases of inflammation, proliferation, and remodeling. Interrupting
any of these phases may result in chronically unhealed wounds, amputation, or even patient death. Quantitative
assessment of wound tissue ischemia, perfusion, and inflammation provides critical information for appropriate
detection, staging, and treatment of chronic wounds. However, no method is available for noninvasive, simultaneous,
and quantitative imaging of these tissue parameters. We integrated hyperspectral, laser speckle, and thermographic
imaging modalities into a single setup for multimodal assessment of tissue oxygenation, perfusion, and inflammation
characteristics. Advanced algorithms were developed for accurate reconstruction of wound oxygenation and appropriate
co-registration between different imaging modalities. The multimodal wound imaging system was validated by an
ongoing clinical trials approved by OSU IRB. In the clinical trial, a wound of 3mm in diameter was introduced on a
healthy subject’s lower extremity and the healing process was serially monitored by the multimodal imaging setup. Our
experiments demonstrated the clinical usability of multimodal wound imaging.
Accurate and in vivo characterization of structural, functional, and molecular characteristics of biological tissue will
facilitate quantitative diagnosis, therapeutic guidance, and outcome assessment in many clinical applications, such as
wound healing, cancer surgery, and organ transplantation. However, many clinical imaging systems have limitations and
fail to provide noninvasive, real time, and quantitative assessment of biological tissue in an operation room. To
overcome these limitations, we developed and tested a multiview hyperspectral imaging system. The multiview
hyperspectral imaging system integrated the multiview and the hyperspectral imaging techniques in a single portable
unit. Four plane mirrors are cohered together as a multiview reflective mirror set with a rectangular cross section. The
multiview reflective mirror set was placed between a hyperspectral camera and the measured biological tissue. For a
single image acquisition task, a hyperspectral data cube with five views was obtained. The five-view hyperspectral image
consisted of a main objective image and four reflective images. Three-dimensional topography of the scene was achieved
by correlating the matching pixels between the objective image and the reflective images. Three-dimensional mapping of
tissue oxygenation was achieved using a hyperspectral oxygenation algorithm. The multiview hyperspectral imaging
technique is currently under quantitative validation in a wound model, a tissue-simulating blood phantom, and an in vivo
biological tissue model. The preliminary results have demonstrated the technical feasibility of using multiview
hyperspectral imaging for three-dimensional topography of tissue functional properties.
We developed a heat-sensitive microbubble (HSM) agent for intraoperative assessment of
thermal ablation margins in cancer ablation therapies. The HSM agent, comprising a core
of liquid perfluorocarbon (PFC) compound and a shell of biodegradable poly lactic-coglycolic
acid (PLGA), was fabricated using an emulsion evaporation method. In our
previous study, significant increase of ultrasound contrast was observed after heat
activation of HSMs. In this study, intraoperative ultrasonic assessment of thermal
ablation margins by HSMs was demonstrated in vivo in a pig model. HSMs were
delivered to the pig liver by portal vein injection. Liver ablation was done using a RF
ablation probe. Intraoperative ultrasound imaging with HSMs clearly delineated the
ablation margin. Fluorescence images of liver tissue samples confirmed the existence and
activation of HSMs. This result demonstrated that the HSM agent can be potentially
utilized as a multimodal contrast agent for intraoperative ultrasonic and fluorescence
assessment of thermal ablation margins in cancer ablation therapies.
Bevacizumab (Avastin) has been used as one of the anti-VEGF therapies to manage neovascular age-related macular degeneration (AMD). The drug delivery system for bevacizumab needs to be improved in order to decrease the frequency of injection and reduce the adverse effects. In our study, bevacizumab was conjugated with poly
(lactic-co-glycolic acid) (PLGA) microbubbles by activating carboxyl functional groups. The averaged size of microbubbles was estimated 1.055±0.258μm, allowing for ultrasound guided drug delivery. The binding efficiency between bevacizumab and microbubbles was evaluated in an enzyme-linked immunosorbent assay plate. The test results demonstrated the potential of using PLGA microbubbles to deliver bevacizumab with imaging guidance.
Many advantages of biomedical optical imaging modalities include low cost, portability, no radiation hazard, molecular
sensitivity, and real-time non-invasive measurements of multiple tissue parameters. However, clinical acceptance of
optical imaging is hampered by the lack of calibration standards and validation techniques. In this context, developing
phantoms that simulate tissue structural, functional, and molecular properties is important for reliable performance and
successful translation of biomedical optical imaging techniques to clinical applications.
Over the years, we have developed various tissue simulating phantoms to validate imaging algorithms, to optimize
instrument performance, to test contrast agents, and to calibrate acquisition systems. We also developed phantoms with
multimodal contrasts for co-registration between different imaging modalities. In order to study tissue dynamic changes
during medical intervention, we develop gel wax phantoms to simulate tissue optical and mechanical dynamics in
response to compression load. We also dispersed heat sensitive microbubbles in agar agar gel phantoms to simulate heatinduced
tissue coagulative necrosis in a cancer ablation procedure. The phantom systems developed in our lab have the
potential to provide standardized traceable tools for multimodal imaging and image-guided intervention.
Accurate assessment of wound oxygenation and perfusion is important for evaluating wound healing/regression and
guiding following therapeutic processes. However, many existing techniques and clinical practices are subjective and
qualitative due to background bias, tissue heterogeneity, and inter-patient variation. To overcome these limitations, we
developed a dual-modal imaging system for in vivo, non-invasive, real-time quantitative assessment of wound tissue
oxygenation and perfusion. The imaging system integrated a broadband light source, a high-resolution CCD camera, a
highly sensitive thermal camera, and a liquid crystal tunable filter. A user-friendly interface was developed to control all
the components systematically. Advanced algorithms were explored for reliable reconstruction of tissue oxygenation and appropriate co-registration between thermal images and multispectral images. Dual-mode oxygenation and perfusion imaging was demonstrated on both benchtop models and human subjects, and compared with measurements using other methods, such as Laser Doppler and tissue oximeter. The test results suggested that the dual-modal imaging system has the potential for non-contact real-time imaging of wound tissue oxygenation and perfusion.
Background: Accurate assessment of tumor boundaries and intraoperative detection of therapeutic margins are
important oncologic principles for minimal recurrence rates and improved long-term outcomes. However, many existing
cancer imaging tools are based on preoperative image acquisition and do not provide real-time intraoperative
information that supports critical decision-making in the operating room.
Method: Poly lactic-co-glycolic acid (PLGA) microbubbles (MBs) and nanobubbles (NBs) were synthesized by a
modified double emulsion method. The MB and NB surfaces were conjugated with CC49 antibody to target TAG-72
antigen, a human glycoprotein complex expressed in many epithelial-derived cancers. Multiple imaging agents were
encapsulated in MBs and NBs for multimodal imaging. Both one-step and multi-step cancer targeting strategies were
explored. Active MBs/NBs were also fabricated for therapeutic margin assessment in cancer ablation therapies.
Results: The multimodal contrast agents and the cancer-targeting strategies were tested on tissue simulating phantoms,
LS174 colon cancer cell cultures, and cancer xenograft nude mice. Concurrent multimodal imaging was demonstrated
using fluorescence and ultrasound imaging modalities. Technical feasibility of using active MBs and portable imaging
tools such as ultrasound for intraoperative therapeutic margin assessment was demonstrated in a biological tissue model.
Conclusion: The cancer-specific multimodal contrast agents described in this paper have the potential for intraoperative
detection of tumor boundaries and therapeutic margins.
We developed a novel dual-modal contrast agent for the structural and functional imaging of cancer. The contrast agent was fabricated by encapsulating indocyanine green (ICG) in poly(lactic-co-glycolic acid) (PLGA) microbubbles using a modified double-emulsion method. More stabilized absorption and fluorescence emission characteristics were observed for aqueous and plasma suspensions of ICG-encapsulated microbubbles. The technical feasibility of concurrent structural and functional imaging was demonstrated through a series of benchtop tests in which the aqueous suspension of ICG-encapsulated microbubbles was injected into a transparent tube embedded in an Intralipid phantom at different flow rates and concentrations. Concurrent fluorescence imaging and B-mode ultrasound imaging successfully captured the changes of microbubble flow rate and concentration with high linearity and accuracy. One potential application of the proposed ICG-encapsulated PLGA microbubbles is for the identification and characterization of peritumoral neovasculature for enhanced coregistration between tumor structural and functional boundaries in ultrasound-guided near-infrared diffuse optical tomography.
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