Pulse Shaping Strategies for Nonlinear Interferometric Vibrational Imaging Optimized for Biomolecular Imaging

Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference. 2004  |  Pubmed ID: 17271537

Nonlinear interferometric vibrational imaging (NIVI) measures the temporal cross-correlation of anti-Stokes radiation from coherent anti-Stokes Raman scattering (CARS) processes to achieve increased sensitivity, stray light rejection, and nonresonant background rejection. Because the intensity of CARS radiation is proportional to the square of the molecular density of a target resonance, it is critical to maximize the recoverable signal for a given illumination level. Especially if one desires to measure several resonances, there can be a sensitivity as well as a speed advantage to measuring them simultaneously rather than serially. We discuss the methods of sample excitation that NIVI allows and their potential sensitivity advantages, as well as present experimental results demonstrating Raman signal recovery using these pulse sequences.

Nonlinear Optical Contrast Enhancement for Optical Coherence Tomography

Optics Express. Jan, 2004  |  Pubmed ID: 19471542

We present a new interferometric technique for measuring Coherent Anti-Stokes Raman Scattering (CARS) and Second Harmonic Generation (SHG) signals. Heterodyne detection is employed to increase the sensitivity in both CARS and SHG signal detection, which can also be extended to different coherent processes. The exploitation of the mentioned optical nonlinearities for molecular contrast enhancement in Optical Coherence Tomography (OCT) is presented.

Molecularly Sensitive Optical Coherence Tomography

Optics Letters. Mar, 2005  |  Pubmed ID: 15789714

Molecular contrast in optical coherence tomography (OCT) is demonstrated by use of coherent anti-Stokes Raman scattering (CARS) for molecular sensitivity. Femtosecond laser pulses are focused into a sample by use of a low-numerical-aperture lens to generate CARS photons, and the backreflected CARS signal is interferometrically measured. With the chemical selectivity provided by CARS and the advanced imaging capabilities of OCT, this technique may be useful for molecular contrast imaging in biological tissues. CARS can be generated and interferometrically measured over at least 600 microm of the depth of field of a low-numerical-aperture objective.

Spectroscopic Spectral-domain Optical Coherence Microscopy

Optics Letters. Apr, 2006  |  Pubmed ID: 16625909

The spectroscopic content within optical coherence tomography (OCT) data can provide a wealth of information. Spectroscopic OCT methods are frequently limited by time-frequency trade-offs that limit high spectral and spatial resolution simultaneously. We present spectroscopic spectral-domain optical coherence microscopy performed with a multimodality microscope. Restricting the spatial extent of the signal by using high-numerical-aperture optics makes high-resolution spectroscopic information accessible, facilitated with spectral-domain detection. Simultaneous acquisition of multiphoton microscopy images is used to validate tissue structure and localization of nuclei within individual cells.

High-spectral-resolution Coherent Anti-Stokes Raman Scattering with Interferometrically Detected Broadband Chirped Pulses

Optics Letters. May, 2006  |  Pubmed ID: 16642166

To achieve high-spectral-resolution multiplex coherent anti-Stokes Raman scattering (CARS), one typically uses a narrowband pump pulse and a broadband Stokes pulse. This is to ensure a correspondence between anti-Stokes and vibrational frequencies. We obtain high-resolution CARS spectra of isopropanol, using a broadband chirped pump pulse and a broadband Stokes pulse, by detecting the anti-Stokes pulse with spectral interferometry. With the temporally resolved anti-Stokes signal, we can remove the chirp of the anti-Stokes pulse and restore high spectral resolution while also rejecting nonresonant scattering.

Imaging Cellular Responses to Mechanical Stimuli Within Three-dimensional Tissue Constructs

Microscopy Research and Technique. Apr, 2007  |  Pubmed ID: 17262787

The cellular response to environmental cues is complex, involving both structural and functional changes within the cell. Our understanding of this response is facilitated by microscopy techniques, but has been limited by our ability to image cell structure and function deep in highly-scattering tissues or 3D constructs. A novel multimodal microscopy technique that combines coherent and incoherent imaging for simultaneous visualization of structural and functional properties of cells and engineered tissues is demonstrated. This microscopic technique allows for the simultaneous acquisition of optical coherence microscopy and multiphoton microscopy data with particular emphasis for applications in cell biology and tissue engineering. The capability of this technique is shown using representative 3D cell and tissue engineering cultures consisting of primary fibroblasts from transgenic green fluorescent protein (GFP) mice and GFP-vinculin transfected fibroblasts. Imaging is performed following static and dynamic mechanically-stimulating culture conditions. The microscopy technique presented here reveals unique complementary data on the structure and function of cells and their adhesions and interactions with the surrounding microenvironment.

Multispectral Photoacoustic Imaging of Fluorochromes in Small Animals

Optics Letters. Oct, 2007  |  Pubmed ID: 17909608

Fluorochromes have become essential reporter molecules in biological research. We show that the depth-resolved distribution of fluorochromes in small animals can be imaged with 25 fmol sensitivity and 150 microm spatial resolution by means of multispectral photoacoustic imaging. The major advantage of the multispectral approach is the sensitive differentiation of chromophores and fluorochromes of interest based on self-reference measurements, as evidenced in this study by resolving a commonly used fluorochrome (Alexa Fluor 750) in mouse. The suggested method is well suited for enhancing visualization of functional and molecular information in vivo and longitudinally.

In Vivo Imaging of Drosophila Melanogaster Pupae with Mesoscopic Fluorescence Tomography

Nature Methods. Jan, 2008  |  Pubmed ID: 18066071

We report a technique for fluorescence tomography that operates beyond the penetration limits of tissue-sectioning fluorescence microscopy. The method uses multi-projection illumination and photon transport description in opaque tissues. We demonstrate whole-body three-dimensional visualization of the morphogenesis of GFP-expressing salivary glands and wing imaginal discs in living Drosophila melanogaster pupae in vivo and over time.

Real-time Catheter Molecular Sensing of Inflammation in Proteolytically Active Atherosclerosis

Circulation. Oct, 2008  |  Pubmed ID: 18852366

To enable intravascular detection of inflammation in atherosclerosis, we developed a near-infrared fluorescence (NIRF) catheter-based strategy to sense cysteine protease activity during vascular catheterization.

Polarization-sensitive Optoacoustic Tomography of Optically Diffuse Tissues

Optics Letters. Oct, 2008  |  Pubmed ID: 18923605

Polarization is indicative of material anisotropy, a property that reveals structural orientation information of molecules inside the material. Herein we investigate whether polarization can be detected optoacoustically in scattering and absorbing tissues. Using a laboratory prototype of polarization-sensitive optoacoustic tomography, we demonstrate high-resolution reconstructions of dichroism contrast deep in optically diffusive tissue-mimicking phantoms. The technique is expected to enable highly accurate imaging of polarization contrast in tissues, far beyond the current capabilities of pure optical polarization-imaging approaches.

Real-time Assessment of Inflammation and Treatment Response in a Mouse Model of Allergic Airway Inflammation

The Journal of Clinical Investigation. Dec, 2008  |  Pubmed ID: 19033674

Eosinophils are multifunctional leukocytes that degrade and remodel tissue extracellular matrix through production of proteolytic enzymes, release of proinflammatory factors to initiate and propagate inflammatory responses, and direct activation of mucus secretion and smooth muscle cell constriction. Thus, eosinophils are central effector cells during allergic airway inflammation and an important clinical therapeutic target. Here we describe the use of an injectable MMP-targeted optical sensor that specifically and quantitatively resolves eosinophil activity in the lungs of mice with experimental allergic airway inflammation. Through the use of real-time molecular imaging methods, we report the visualization of eosinophil responses in vivo and at different scales. Eosinophil responses were seen at single-cell resolution in conducting airways using near-infrared fluorescence fiberoptic bronchoscopy, in lung parenchyma using intravital microscopy, and in the whole body using fluorescence-mediated molecular tomography. Using these real-time imaging methods, we confirmed the immunosuppressive effects of the glucocorticoid drug dexamethasone in the mouse model of allergic airway inflammation and identified a viridin-derived prodrug that potently inhibited the accumulation and enzyme activity of eosinophils in the lungs. The combination of sensitive enzyme-targeted sensors with noninvasive molecular imaging approaches permitted evaluation of airway inflammation severity and was used as a model to rapidly screen for new drug effects. Both fluorescence-mediated tomography and fiberoptic bronchoscopy techniques have the potential to be translated into the clinic.

Normalized Born Ratio for Fluorescence Optical Projection Tomography

Optics Letters. Feb, 2009  |  Pubmed ID: 19183644

We present a normalized Born approach for fluorescence optical projection tomography that takes into account tissue absorption properties. This approach can be particularly useful to study fluorochrome distribution within tissue. We use the algorithm to three-dimensionally reconstruct and characterize a fluorescein isothiocyanate containing absorptive phantom and an infarcted mouse heart previously injected with a fluorescent molecular probe.

Imaging of Mesoscopic-scale Organisms Using Selective-plane Optoacoustic Tomography

Physics in Medicine and Biology. May, 2009  |  Pubmed ID: 19369709

Mesoscopic-scale living organisms (i.e. 1 mm to 1 cm sized) remain largely inaccessible by current optical imaging methods due to intensive light scattering in tissues. Therefore, imaging of many important model organisms, such as insects, fishes, worms and similarly sized biological specimens, is currently limited to embryonic or other transparent stages of development. This makes it difficult to relate embryonic cellular and molecular mechanisms to consequences in organ function and animal behavior in more advanced stages and adults. Herein, we have developed a selective-plane illumination optoacoustic tomography technique for in vivo imaging of optically diffusive organisms and tissues. The method is capable of whole-body imaging at depths from the sub-millimeter up to centimeter range with a scalable spatial resolution in the order of magnitude of a few tenths of microns. In contrast to pure optical methods, the spatial resolution here is not determined nor limited by light diffusion; therefore, such performance cannot be achieved by any other optical imaging technology developed so far. The utility of the method is demonstrated on several whole-body models and small-animal extremities.

Transillumination Fluorescence Imaging in Mice Using Biocompatible Upconverting Nanoparticles

Optics Letters. Sep, 2009  |  Pubmed ID: 19724491

We report on a systematic study of upconverting fluorescence signal generation within turbid phantoms and real tissues. An accurate three-point Green's function, describing the forward model of photon propagation, is established and experimentally validated. We further demonstrate, for the first time to our knowledge, autofluorescence-free transillumination imaging of mice that have received biocompatible upconverting nanoparticles. The method holds great promise for artifact-free whole-body visualization of optical molecular probes.

Diffractionless Beam in Free Space with Adiabatic Changing Refractive Index in a Single Mode Tapered Slab Waveguide

Optics Express. Nov, 2009  |  Pubmed ID: 19997414

We propose a novel design to produce a free space diffractionless beam by adiabatically reducing the difference of the refractive index between the core and the cladding regions of a single mode tapered slab waveguide. To ensure only one propagating eigenmode in the adiabatic transition, the correlation of the waveguide core width and the refractive index is investigated. Under the adiabatic condition, we demonstrate that our waveguide can emit a diffractionless beam in free space up to 500 micrometers maintaining 72% of its original peak intensity. The proposed waveguide could find excellent applications for imaging purposes where an extended depth of field is required.

High Throughput Transmission Optical Projection Tomography Using Low Cost Graphics Processing Unit

Optics Express. Dec, 2009  |  Pubmed ID: 20052155

We implement the use of a graphics processing unit (GPU) in order to achieve real time data processing for high-throughput transmission optical projection tomography imaging. By implementing the GPU we have obtained a 300 fold performance enhancement in comparison to a CPU workstation implementation. This enables to obtain on-the-fly reconstructions enabling for high throughput imaging.

Intravascular Near-infrared Fluorescence Molecular Imaging of Atherosclerosis: Toward Coronary Arterial Visualization of Biologically High-risk Plaques

Journal of Biomedical Optics. Jan-Feb, 2010  |  Pubmed ID: 20210433

New imaging methods are urgently needed to identify high-risk atherosclerotic lesions prior to the onset of myocardial infarction, stroke, and ischemic limbs. Molecular imaging offers a new approach to visualize key biological features that characterize high-risk plaques associated with cardiovascular events. While substantial progress has been realized in clinical molecular imaging of plaques in larger arterial vessels (carotid, aorta, iliac), there remains a compelling, unmet need to develop molecular imaging strategies targeted to high-risk plaques in human coronary arteries. We present recent developments in intravascular near-IR fluorescence catheter-based strategies for in vivo detection of plaque inflammation in coronary-sized arteries. In particular, the biological, light transmission, imaging agent, and engineering principles that underlie a new intravascular near-IR fluorescence sensing method are discussed. Intravascular near-IR fluorescence catheters appear highly translatable to the cardiac catheterization laboratory, and thus may offer a new in vivo method to detect high-risk coronary plaques and to assess novel atherosclerosis biologics.

Imaging of Molecular Probe Activity with Born-normalized Fluorescence Optical Projection Tomography

Optics Letters. Apr, 2010  |  Pubmed ID: 20364226

Optical projection tomography is a new ex vivo imaging technique that allows imaging of whole organs in three dimensions at high spatial resolutions. In this Letter we demonstrate its capability to tomographically visualize molecular activity in whole organs of mice. In particular, eosinophil activity in asthmatic lungs is resolved using a Born-normalized fluorescence optical projection tomography and employing a near-IR molecular probe. The possibility to achieve molecularly sensitive imaging contrast in optical projection tomography by means of targeted and activatable imaging reporter agents adds a new range of capabilities for investigating molecular signatures of pathophysiological processes and a wide variety of diseases and their development.

Hybrid PET-optical Imaging Using Targeted Probes

Proceedings of the National Academy of Sciences of the United States of America. Apr, 2010  |  Pubmed ID: 20385821

Fusion imaging of radionuclide-based molecular (PET) and structural data [x-ray computed tomography (CT)] has been firmly established. Here we show that optical measurements [fluorescence-mediated tomography (FMT)] show exquisite congruence to radionuclide measurements and that information can be seamlessly integrated and visualized. Using biocompatible nanoparticles as a generic platform (containing a (18)F isotope and a far red fluorochrome), we show good correlations between FMT and PET in probe concentration (r(2) > 0.99) and spatial signal distribution (r(2) > 0.85). Using a mouse model of cancer and different imaging probes to measure tumoral proteases, macrophage content and integrin expression simultaneously, we demonstrate the distinct tumoral locations of probes in multiple channels in vivo. The findings also suggest that FMT can serve as a surrogate modality for the screening and development of radionuclide-based imaging agents.

WNT5A/JNK and FGF/MAPK Pathways Regulate the Cellular Events Shaping the Vertebrate Limb Bud

Current Biology : CB. Nov, 2010  |  Pubmed ID: 21055947

The vertebrate limb is a classical model for understanding patterning of three-dimensional structures during embryonic development. Although decades of research have elucidated the tissue and molecular interactions within the limb bud required for patterning and morphogenesis of the limb, the cellular and molecular events that shape the limb bud itself have remained largely unknown.

In-vivo Two-photon Imaging of the Honey Bee Antennal Lobe

Biomedical Optics Express. 2010  |  Pubmed ID: 21326643

Due to the honey bee's importance as a simple neural model, there is a great need for new functional imaging modalities. Herein we report on the development and new findings of a combined two-photon microscope with a synchronized odor stimulus platform for in-vivo functional and morphological imaging of the honey bee's olfactory system focusing on its primary centers, the antennal lobes (ALs). Our imaging platform allows for simultaneously obtaining both morphological measurements of the AL's functional units, the glomeruli, and in-vivo calcium recording of their neural activities. By applying external odor stimuli to the bee's antennae, we were able to record the characteristic glomerular odor response maps. Compared to previous works where conventional fluorescence microscopy was used, our approach has been demonstrated to offer all the advantages of multi-photon imaging, providing substantial enhancement in both spatial and temporal resolutions while minimizing photo-damages. In addition, compared to previous full-field microscopy calcium recordings, a four-fold improvement in the functional signal has been achieved. Finally, the multi-photon associated extended penetration depth allows for functional imaging of profound glomeruli.

Searching for Anatomical Correlates of Olfactory Lateralization in the Honeybee Antennal Lobes: a Morphological and Behavioural Study

Behavioural Brain Research. Aug, 2011  |  Pubmed ID: 21402106

The honeybee, Apis mellifera L. (Hymenoptera: Apidae), has recently become a model for studying brain asymmetry among invertebrates. A strong lateralization favouring the right antenna was discovered in odour learning and short-term memory recall experiments, and a lateral shift favouring the left antenna for long-term memory recall. Corresponding morphological asymmetries have been found in the distribution of olfactory sensilla between the antennae and confirmed by electrophysiological odour response measurements in isolated right and left antennae. The aim of this study was to investigate whether a morphological asymmetry can be observed in the volume of the primary olfactory centres of the central nervous system, the antennal lobes (ALs). Precise volume measurements of a subset of their functional units, the glomeruli, were performed in both sides of the brain, exploiting the advantages of two-photon microscopy. This novel method allowed minimal invasive acquisition of volume images of the ALs, avoiding artefacts from brain extraction and dehydration. The study was completed by a series of behavioural experiments in which response asymmetry in odour recall following proboscis extension reflex conditioning was assessed for odours, chosen to stimulate strong activity in the same glomeruli as in the morphological study. The volumetric measurements found no evidence of lateralization in the investigated glomeruli within the experimental limits. Instead, in the behavioural experiments, a striking odour dependence of the lateralization was observed. The results are discussed on the basis of recent neurophysiological and ethological experiments in A. mellifera.

Indocyanine Green Enables Near-infrared Fluorescence Imaging of Lipid-rich, Inflamed Atherosclerotic Plaques

Science Translational Medicine. May, 2011  |  Pubmed ID: 21613624

New high-resolution molecular and structural imaging strategies are needed to visualize high-risk plaques that are likely to cause acute myocardial infarction, because current diagnostic methods do not reliably identify at-risk subjects. Although molecular imaging agents are available for low-resolution detection of atherosclerosis in large arteries, a lack of imaging agents coupled to high-resolution modalities has limited molecular imaging of atherosclerosis in the smaller coronary arteries. Here, we have demonstrated that indocyanine green (ICG), a Food and Drug Administration-approved near-infrared fluorescence (NIRF)-emitting compound, targets atheromas within 20 min of injection and provides sufficient signal enhancement for in vivo detection of lipid-rich, inflamed, coronary-sized plaques in atherosclerotic rabbits. In vivo NIRF sensing was achieved with an intravascular wire in the aorta, a vessel of comparable caliber to human coronary arteries. Ex vivo fluorescence reflectance imaging showed high plaque target-to-background ratios in atheroma-bearing rabbits injected with ICG compared to atheroma-bearing rabbits injected with saline. In vitro studies using human macrophages established that ICG preferentially targets lipid-loaded macrophages. In an early clinical study of human atheroma specimens from four patients, we found that ICG colocalized with plaque macrophages and lipids. The atheroma-targeting capability of ICG has the potential to accelerate the clinical development of NIRF molecular imaging of high-risk plaques in humans.

Accurate Measurement of Pancreatic Islet Beta-cell Mass Using a Second-generation Fluorescent Exendin-4 Analog

Proceedings of the National Academy of Sciences of the United States of America. Aug, 2011  |  Pubmed ID: 21768367

The hallmark of type 1 diabetes is autoimmune destruction of the insulin-producing β-cells of the pancreatic islets. Autoimmune diabetes has been difficult to study or treat because it is not usually diagnosed until substantial β-cell loss has already occurred. Imaging agents that permit noninvasive visualization of changes in β-cell mass remain a high-priority goal. We report on the development and testing of a near-infrared fluorescent β-cell imaging agent. Based on the amino acid sequence of exendin-4, we created a neopeptide via introduction of an unnatural amino acid at the K(12) position, which could subsequently be conjugated to fluorophores via bioorthogonal copper-catalyzed click-chemistry. Cell assays confirmed that the resulting fluorescent probe (E4(×12)-VT750) had a high binding affinity (~3 nM). Its in vivo properties were evaluated using high-resolution intravital imaging, histology, whole-pancreas visualization, and endoscopic imaging. According to intravital microscopy, the probe rapidly bound to β-cells and, as demonstrated by confocal microscopy, it was internalized. Histology of the whole pancreas showed a close correspondence between fluorescence and insulin staining, and there was an excellent correlation between imaging signals and β-cell mass in mice treated with streptozotocin, a β-cell toxin. Individual islets could also be visualized by endoscopic imaging. In short, E4(×12)-VT750 showed strong and selective binding to glucose-like peptide-1 receptors and permitted accurate measurement of β-cell mass in both diabetic and nondiabetic mice. This near-infrared imaging probe, as well as future radioisotope-labeled versions of it, should prove to be important tools for monitoring diabetes, progression, and treatment in both experimental and clinical contexts.

A Multimodal Approach for Tracing Lateralisation Along the Olfactory Pathway in the Honeybee Through Electrophysiological Recordings, Morpho-functional Imaging, and Behavioural Studies

European Biophysics Journal : EBJ. Nov, 2011  |  Pubmed ID: 21956452

Recent studies have revealed asymmetries between the left and right sides of the brain in invertebrate species. Here we present a review of a series of recent studies from our laboratories, aimed at tracing asymmetries at different stages along the honeybee's (Apis mellifera) olfactory pathway. These include estimates of the number of sensilla present on the two antennae, obtained by scanning electron microscopy, as well as electroantennography recordings of the left and right antennal responses to odorants. We describe investigative studies of the antennal lobes, where multi-photon microscopy was used to search for possible morphological asymmetries between the two brain sides. Moreover, we report on recently published results obtained by two-photon calcium imaging for functional mapping of the antennal lobe aimed at comparing patterns of activity evoked by different odours. Finally, possible links to the results of behavioural tests, measuring asymmetries in single-sided olfactory memory recall, are discussed.

Intraoperative Near-infrared Fluorescent Cholangiography (NIRFC) in Mouse Models of Bile Duct Injury: Reply

World Journal of Surgery. Mar, 2011  |  Pubmed ID: 20645091

Deep Tissue Optical and Optoacoustic Molecular Imaging Technologies for Small Animal Research and Drug Discovery

Current Pharmaceutical Biotechnology. Jan, 2012  |  Pubmed ID: 22216767

For centuries, biological discoveries were based on optical imaging, in particular microscopy but also several chromophoric assays and photographic approaches. With the recent emergence of methods appropriate for bio-marker in vivo staining, such as bioluminescence, fluorescent molecular probes and proteins, as well as nanoparticle-based targeted agents, significant attention has been shifted toward in vivo interrogations of different dynamic biological processes at the molecular level. This progress has been largely supported by the development of advanced tomographic imaging technologies suitable for obtaining volumetric visualization of bio-marker distributions in small animals at a whole-body or whole-organ scale, an imaging frontier that is not accessible by the existing tissue-sectioning microscopic techniques due to intensive light scattering beyond the depth of a few hundred microns. Major examples of such recently developed optical imaging modalities are reviewed here, including bioluminescence tomography (BLT), fluorescence molecular tomography (FMT), and optical projection tomography (OPT). The pharmaceutical imaging community has quickly appropriated itself of these novel forms of optical imaging, since they come with very compelling advantages, such as quantitative three-dimensional capabilities, direct correlation to the biological cultures, easiness and cost-effectiveness of use, and the use of safe non-ionizing radiation. Some multi-modality approaches, combining light with other imaging modalities such as X-Ray CT or MRI, giving the ability to acquire both an optical contrast reconstruction along with a hi-fidelity anatomical images, are also reviewed. A separate section is devoted to the hybrid imaging techniques based on the optoacoustic phenomenon, such as multispectral optoacoustic tomography (MSOT), which are poised to leverage the traditional contrast and specificity advantages of optical spectrum by delivering an ever powerful set of capabilities, including real-time operation and high spatial resolution, not affected by the scattering nature of biological tissues.

PET/MRI of Inflammation in Myocardial Infarction

Journal of the American College of Cardiology. Jan, 2012  |  Pubmed ID: 22222080

The aim of this study was to explore post-myocardial infarction (MI) myocardial inflammation.