Joseph Angelo

qF-SSOP: real-time optical property corrected fluorescence imaging

Fluorescence imaging is well suited to provide image guidance during resections in oncologic and vascular surgery. However, the distorting effects of tissue optical properties on the emitted fluorescence are poorly compensated for on even the most advanced fluorescence image guidance systems, leading to subjective and inaccurate estimates of tissue fluorophore concentrations. Here we present a novel fluorescence imaging technique that performs real-time (i.e., video rate) optical property corrected fluorescence imaging. We perform full field of view simultaneous imaging of tissue optical properties using Single Snapshot of Optical Properties (SSOP) and fluorescence detection. The estimated optical properties are used to correct the emitted fluorescence with a quantitative fluorescence model to provide quantitative fluorescence-Single Snapshot of Optical Properties (qF-SSOP) images with less than 5% error. The technique is rigorous, fast, and quantitative, enabling ease of integration into the surgical workflow with the potential to improve molecular guidance intraoperatively.

Ultrafast optical property map generation using lookup tables

Imaging technologies working in the spatial frequency domain are becoming increasingly popular for generating wide-field maps of optical properties, enabling rapid analysis of tissue parameters. While acquisition methods have become faster and are now performing in real-time, processing methods remain slow, precluding real-time display of information. We present solutions that rapidly solve the inverse problem for extracting optical properties by use of advanced lookup tables (LUTs). We present methods and results based on a dense, linearly sampled lookup table and an analytical representation that generate maps of absorption and reduced scattering in ?10??ms, which is 100× faster than the standard method, with ?4% error compared to the Monte-Carlo simulation. Combined with real-time acquisition methods, the proposed techniques enable video-rate feedback of real-time property maps, enabling full video-rate guidance in the clinic.

Intraoperative Hemifacial Composite Flap Perfusion Assessment Using Spatial Frequency Domain Imaging: A Pilot Study in Preparation for Facial Transplantation.

BackgroundVascularized composite allotransplantation represents an important advancement in the field of reconstructive microsurgery and has continued to increase in popularity. The significant clinical morbidity associated with flap failure represents an important barrier to even more widespread use of these techniques. Early identification of vascular compromise has been associated with a higher salvage rate, yet most surgeons rely only on clinical assessment intraoperatively. Spatial frequency domain imaging (SFDI) presents a noncontact, objective measurement of tissue oxygenation over a large field of view. This study aims to evaluate the use of SFDI technology in hemifacial composite flap compromise as could occur during facial transplant. MethodsSix composite hemifacial flaps were created in three 35-kg Yorkshire pigs and continuously imaged using SFDI before, during, and after 15-minute selective vascular pedicle occlusion. Arterial and venous clamping trials were performed for each flap. Changes in oxyhemoglobin concentration, deoxyhemoglobin concentration, and total hemoglobin were quantified over time. ResultsThe SFDI successfully measured changes in oxygenation parameters in all 6 composite tissue flaps. Significant changes in oxyhemoglobin, deoxyhemoglobin, and total hemoglobin were seen relative to controls. Early and distinct patterns of alteration were noted in arterial and in venous compromise relative to one another. ConclusionsThe need for noninvasive, reliable assessment of composite tissue graft viability is apparent, given the morbidity associated with flap failure. The results of this study suggest that SFDI technology shows promise in providing intraoperative guidance with regard to pedicle vessel integrity during reconstructive microsurgery.

Application of semiempirical electronic structure theory to compute the force generated by a single surface-mounted switchable rotaxane

AbstractHerein we report a study of the switchable [3]rotaxane reported by Huang et al. (Appl Phys Lett 85(22):5391–5393, 1) that can be mounted to a surface to form a nanomechanical, linear, molecular motor. We demonstrate the application of semiempirical electronic structure theory to predict the average and instantaneous force generated by redox-induced ring shuttling. Detailed analysis of the geometric and electronic structure of the system reveals technical considerations essential to success of the approach. The force is found to be in the 100–200 pN range, consistent with published experimental estimates. Graphical AbstractA single surface-mounted switchable rotaxane

Decomposition of the Factors That Govern Binding Site Preference in a Multiple Rotaxane

A particularly interesting class of multiple rotaxanes consists of complexes where one long shaft threads two rings. If the shaft contains three or more potential binding sites for the rings, multiple co-conformations are possible. Such a complex is a molecular topological analogue to an abacus. Here we address the question, how does strength of ring binding to the shaft vary with respect to position on the shaft? Previous studies have found that a shaft with three binding sites exhibits strongest ring binding at the center site. Here a five-binding-site shaft is studied. We employ a novel method to partition the total energy of the system into contributions from intercomponent binding and intracomponent distortion. The method uses the output of quantum mechanical electronic structure calculations to determine fitting parameters in a set of coupled equations. The solution of the equations yields the energy partitioning and reveals the influence of long-range intercomponent interactions.

Accurate Prediction of Tissue Viability at Postoperative Day 7 Using Only Two Intraoperative Subsecond Near-infrared Fluorescence Images

Background: The ability to predict the future viability of tissue while still in the operating room and able to intervene would have a major impact on patient outcome. Although several objective methods to evaluate tissue perfusion have been reported, none to date has sufficient accuracy. Methods: In eight Sprague-Dawley rats, reverse McFarlane dorsal skin flaps were created. Continuous near-infrared fluorescence angiography using indocyanine green was performed immediately after surgery, for a total of 30 minutes. These dynamic measurements were used to quantify indocyanine green biodistribution and clearance, and to develop a simple metric that accurately predicted tissue viability at postoperative day 7. The new metric was compared to previously described metrics. Results: Reproducible patterns of indocyanine green biodistribution and clearance from the flap permitted quantitative metrics to be developed for predicting flap viability at postoperative day 7. Previously described metrics, which set the boundary between healthy and necrotic tissue as either 17 or 25 percent of peak near-infrared fluorescence at 2 minutes after indocyanine green injection, underestimated the area of necrosis by 75 and 48 percent, respectively. Our data suggest that both the shape and area of clinical necrosis occurring at postoperative day 7 can be predicted intraoperatively, with the boundary defined as near-infrared fluorescence intensities of 40 to 55 percent of peak fluorescence measured at 5 minutes. Conclusion: Two 750-msec intraoperative near-infrared fluorescence images obtained at time 0 and at 5 minutes after injection of indocyanine green accurately predicted skin flap viability 7 days after surgery.

Real-time imaging of tissue optical properties and surface profile using 3D-SSOP

Wide-field optical tissue characterization has a large clinical potential that is currently not exploited due to the lack of realtime imaging methods. In this work we propose 3D single shot optical properties imaging (3D-SSOP) a new acquisition and processing method for obtaining surface profile corrected tissue absorption and reduced scattering coefficient maps from a single image. A profile is projected that is sensitive to both optical properties and surface profile. With image processing, the two responses are separated and surface profile corrected tissue optical properties as with profile corrected spatial frequency domain imaging (3D-SFDI). Overall, 3D-SSOP estimates showed a small bias of -1.2% in both μa and μs in comparison with 3D-SFDI. Standard deviations on flat surfaces for 3D-SSOP were 7% (μa) and 17% (μs) lower than for 3D-SFDI. However, 3D-SSOP showed significant artifacts near edges, where spatial averaging caused inaccuracies in diffuse reflectance estimates, as well as the surface profile. In an in-vivo experiment of a hand optical property estimates were equivalent, but processing artifacts suppressed smaller details with 3D-SSOP. To our knowledge, this method is the first method to estimate surface profile corrected tissue optical properties from a single image. Therefore we expect this method to be an important step in bringing real-time wide-field tissue characterization to the operating room.

Depth-enhanced fluorescence imaging using masked detection of structured illumination

Abstract. There is a growing interest in imaging fluorescence contrast at depth within living tissues over wide fields of view and in real time. Most methods used to date to improve depth detection of fluorescence information involve acquisition of multiple images, postprocessing of the data using a light propagation model, and are capable of providing either depth-sectioned or tomographic fluorescence information. We introduce a method, termed masked detection of structured illumination, that allows the enhancement of fluorescence imaging at depth without postprocessing. This method relies on the scanning of a collimated beam onto a turbid medium and the physical masking of the point spread function on the detection arm before acquisition on a CCD camera. By preferentially collecting diffuse photons at a chosen source-detector range, this method enhances fluorescence information at depth and has the potential to form images without postprocessing and in real time.

A novel pilot animal model for the surgical prevention of lymphedema: the power of optical imaging

BACKGROUND Breast cancer-related lymphedema affects more than 400,000 survivors in the United States. In 2009, lymphatic microsurgical preventive healing approach (LYMPHA) was first described as a surgical technique to prevent lymphedema by bypassing divided arm lymphatics into adjacent veins at the time of an axillary lymph node dissection. We describe the first animal model of LYMPHA. METHODS In Yorkshire pigs, each distal hind limb lymphatic system was cannulated and injected with a different fluorophore (human serum albumin-conjugated indocyanine green or Evans Blue). Fluorescence-assisted resection and exploration imaging system was used to map the respective lymphangiosomes to the groin. Baseline lymphatic clearance of each hind limb lymphangiosome was obtained by measuring the fluorescence of each dye from centrally obtained blood samples. A lymphadenectomy versus lymphadenectomy with LYMPHA was then performed. The injections were then repeated to obtain clearance rates that were compared against baseline values. RESULTS Human serum albumin-conjugated indocyanine green and Evans Blue allowed for precise lymphatic mapping of each respective hind limb using fluorescence-assisted resection and exploration imaging. Lymphatic clearance from the distal hind limb dropped 68% when comparing baseline clearance versus after a groin lymphadenectomy. In comparison, lymphatic clearance dropped only 21% when comparing baseline clearance versus a lymphadenectomy with LYMPHA. CONCLUSIONS We describe the first animal model for LYMPHA, which will enable future studies to further evaluate the efficacy and potential limitations of this technique. Of equal importance, we demonstrate the power of optical imaging to provide real-time lymphatic clearance rates for each hind limb.

Real-time endoscopic oxygenation imaging using single snapshot of optical properties (SSOP) imaging (Conference Presentation)

With 50% of all interventional procedures in the US being minimally invasive, there is a need for objective tools to help guide surgeons in this challenging environment. Tissue oxygenation is a useful biomarker of tissue viability and suitable for surgical guidance. Here we present our efforts to perform real-time quantitative optical imaging through a rigid endoscope using Single Snapshot of Optical Properties (SSOP) imaging. In particular, in this work we introduce for the first time 3 dimensionally-corrected dual wavelength optical properties imaging using SSOP through an endoscope, allowing accurate oxygenation maps to be obtained on tissue simulating phantoms and in vivo samples. We compared the results with state-of-the-art wide-field spatial frequency domain imaging (SFDI). Overall, results from the novel endoscopic imaging system agreed within 10% in absorption, reduced scattering, and oxygenation. Moreover, we introduce here real-time, video-rate quantitative optical imaging with 3D profile correction through an endoscope. These results demonstrate the potential of endoscopic SSOP as an objective surgical guidance tool for the clinic.