Publications – Page 4

February 15, 2019September 30, 2019

Optoacoustic image reconstruction and system analysis for finite-aperture detectors under the wavelet-packet framework.

In optoacoustic tomography, detectors with relatively large areas are often employed to achieve high detection sensitivity. However, spatial-averaging effects over large detector areas may lead to attenuation of high acoustic frequencies and, subsequently, loss of fine features in the reconstructed image. Model-based reconstruction algorithms improve image resolution in such cases by correcting for the effect of the detector’s aperture on the detected signals. However, the incorporation of the detector’s geometry in the optoacoustic model leads to a significant increase of the model matrix memory cost, which hinders the application of inversion and analysis tools such as singular value decomposition (SVD). We demonstrate the use of the wavelet-packet framework for optoacoustic systems with finite-aperture detectors. The decomposition of the model matrix in the wavelet-packet domain leads to sufficiently smaller model matrices on which SVD may be applied. Using this methodology over an order of magnitude reduction in inversion time is demonstrated for numerically generated and experimental data. Additionally, our framework is demonstrated for the analysis of inversion stability and reveals a new, nonmonotonic dependency of the system condition number on the detector size. Thus, the proposed framework may assist in choosing the optimal detector size in future optoacoustic systems.[Read more…]

Fig.Optoacoustic reconstructions of a mouse’s head from limited view (180 deg) experimental data obtained using (a) BP, (b) IMMI, (c) IMMI-FAD, and (d) GWP-IMMI-FAD.

Yiyong Han, Vasilis Ntziachristos, Amir Rosenthal. J. of Biomedical Optics, 21(1), 016002 (2016). https://doi.org/10.1117/1.JBO.21.1.016002

February 15, 2019September 30, 2019

High-Throughput Sparsity-Based Inversion Scheme for Optoacoustic Tomography

The concept of sparsity is extensively exploited in the fields of data acquisition and image processing, contributing to better signal-to-noise and spatio-temporal performance of the various imaging methods. In the field of optoacoustic tomography, the image reconstruction problem is often characterized by computationally extensive inversion of very large datasets, for instance when acquiring volumetric multispectral data with high temporal resolution. In this article we seek to accelerate accurate model-based optoacoustic inversions by identifying various sources of sparsity in the forward and inverse models as well as in the single- and multi-frame representation of the projection data. These sources of sparsity are revealed through appropriate transformations in the signal, model and image domains and are subsequently exploited for expediting image reconstruction. The sparsity-based inversion scheme was tested with experimental data, offering reconstruction speed enhancement by a factor of 40 to 700 times as compared with the conventional iterative model-based inversions while preserving similar image quality. The demonstrated results pave the way for achieving real-time performance of model-based reconstruction in multi-dimensional optoacoustic imaging.[Read more…..]

Fig.3d maximum intensity projections of the volumetric dataset showing a 3d angiogram of a human finger obtained by cross-sectional scan in the z direction. (a) Photograph of the finger and reconstructions obtained with (b) LSQR-15, (c) WP-o, and (d) PCA-wp-T are shown.

Christian Lutzweiler, Stratis Tzoumas, Amir Rosenthal, Vasilis Ntziachristos, Daniel Razansky. Published in: IEEE Transactions on Medical Imaging ( Volume: 35 , Issue: 2 , Feb. 2016 ).

January 29, 2019September 30, 2019

Quantitative intravascular biological fluorescence-ultrasound imaging of coronary and peripheral arteries in vivo.

Aims
(i) to evaluate a novel hybrid near-infrared fluorescence—intravascular ultrasound (NIRF-IVUS) system in coronary and peripheral swine arteries in vivo; (ii) to assess simultaneous quantitative biological and morphological aspects of arterial disease.
Methods and results
Two 9F/15MHz peripheral and 4.5F/40MHz coronary near-infrared fluorescence (NIRF)-IVUS catheters were engineered to enable accurate co-registrtation of biological and morphological readings simultaneously in vivo. A correction algorithm utilizing IVUS information was developed to account for the distance-related fluorescence attenuation due to through-blood imaging. Corrected NIRF (cNIRF)-IVUS was applied for in vivo imaging of angioplasty-induced vascular injury in swine peripheral arteries and experimental fibrin deposition on coronary artery stents, and of atheroma in a rabbit aorta, revealing feasibility to intravascularly assay plaque structure and inflammation. The addition of ICG-enhanced NIRF assessment improved the detection of angioplasty-induced endothelial damage compared to standalone IVUS. In addition, NIRF detection of coronary stent fibrin by in vivo cNIRF-IVUS imaging illuminated stent pathobiology that was concealed on standalone IVUS. Fluorescence reflectance imaging and microscopy of resected tissues corroborated the in vivo findings.
Conclusions
Integrated cNIRF-IVUS enables simultaneous co-registered through-blood imaging of disease related morphological and biological alterations in coronary and peripheral arteries in vivo. Clinical translation of cNIRF-IVUS may significantly enhance knowledge of arterial pathobiology, leading to improvements in clinical diagnosis and prognosis, and helps to guide the development of new therapeutic approaches for arterial diseases.[Read more…]

Intravascular cNIRF-IVUS imaging with the 4.5F/40MHz catheter reveals the value of IVUS-based distance correction of the NIRF signal in blood. In vivo cNIRF-IVUS imaging of a swine carotid artery was performed following local injection of an NIR fluorophore into the artery wall. Panels (A), (B) and (C) illustrate the in vivo cNIRF image, the corresponding longitudinal IVUS image, and the FRI image of the resected artery, respectively. (D) A 3D representation of the lumen and arterial wall NIR fluorescence signal rendered based on the in vivo cNIRF-IVUS image stack. Insets (C1–C3) show representative examples of the cross-sectional cNIRF-IVUS images corresponding to pullback positions C1, C2, and C3 in (B), (C), and (D). The cNIRF signal in C1, C2, and C3 is fused onto the interior of the IVUS catheter and also replicated at the exterior (outlined with red dotted lines) of the IVUS image. (E) Serial imaging of the same vessel region demonstrates that the raw NIRF signal (top row) is affected by variable intraluminal catheter position that changes the distance between the NIR fluorescence source and imaging catheter detector, leading to fluctuations in the measured NIRF signal. Note that applying the NIRF distance correction (bottom row) substantially improved the reproducibility of the NIRF image and reduced the variability due to changes in catheter position. (F) Quantitative assessment of the improvement of the reproducibility by NIRF distance correction: black dots correspond to the maximum NIRF signal vs. pullback position, and the blue line indicates the average distribution function. Distance correction improved the correspondence between NIRF signals from all three pullbacks from R2 = 0.89 to R2 = 0.96.

Dmitry Bozhko, Eric A Osborn, Amir Rosenthal, Johan W Verjans, Tetsuya Hara, Stephan Kellnberger, Georg Wissmeyer, Saak V Ovsepian, Jason R McCar. European Heart Journal – Cardiovascular Imaging, Volume 18, Issue 11, 1 November 2017, Pages 1253–1261.

February 17, 2019September 30, 2019

Histopathological evaluation of thrombus in patients presenting with stent thrombosis. A multicenter European study: a report of the prevention of late stent thrombosis by an interdisciplinary global European effort consortium.

Background
Stent thrombosis (ST) is a rare but serious complication following percutaneous coronary intervention. Analysis of thrombus composition from patients undergoing catheter thrombectomy may provide important insights into the pathological processes leading to thrombus formation. We performed a large-scale multicentre study to evaluate thrombus specimens in patients with ST across Europe.

Methods
Patients presenting with ST and undergoing thrombus aspiration were eligible for inclusion. Thrombus collection was performed according to a standardized protocol and specimens were analysed histologically at a core laboratory. Serial tissue cross sections were stained with haematoxylin–eosin (H&E), Carstairs and Luna. Immunohistochemistry was performed to identify leukocyte subsets, prothrombotic neutrophil extracellular traps (NETs), erythrocytes, platelets, and fibrinogen.

Results
Overall 253 thrombus specimens were analysed; 79 (31.2%) from patients presenting with early ST, 174 (68.8%) from late ST; 79 (31.2%) were from bare metal stents, 166 (65.6%) from drug-eluting stents, 8 (3.2%) were from stents of unknown type. Thrombus specimens displayed heterogeneous morphology with platelet-rich thrombus and fibrin/fibrinogen fragments most abundant; mean platelet coverage was 57% of thrombus area. Leukocyte infiltrations were hallmarks of both early and late ST (early: 2260 ± 1550 per mm2 vs. late: 2485 ± 1778 per mm2; P = 0.44); neutrophils represented the most prominent subset (early: 1364 ± 923 per mm2 vs. late: 1428 ± 1023 per mm2; P = 0.81). Leukocyte counts were significantly higher compared with a control group of patients with thrombus aspiration in spontaneous myocardial infarction. Neutrophil extracellular traps were observed in 23% of samples. Eosinophils were present in all stent types, with higher numbers in patients with late ST in sirolimus-and everolimus-eluting stents.

Conclusion
In a large-scale study of histological thrombus analysis from patients presenting with ST, thrombus specimens displayed heterogeneous morphology. Recruitment of leukocytes, particularly neutrophils, appears to be a hallmark of ST. The presence of NETs supports their pathophysiological relevance. Eosinophil recruitment suggests an allergic component to the process of ST.[Read more….]

Fig. Leukocyte accumulation in stent thrombus specimens. (A) Leukocyte accumulation in human stent thrombus specimens. Left images: Haematoxylin–eosin staining (n = 253). Arrows indicate granulocytes, arrowheads indicate mononuclear cells. Right images: immunofluorescence staining of neutrophil elastase to identify neutrophils (n = 229). Nuclei are counterstained with Hoechst. Bars, 200 µm (upper row) and 50 µm (bottom row); (B) Quantification of leukocytes and neutrophils in early (n = 67) vs. late (n = 162) stent thrombosis (leukocytes: P = 0.44; neutrophils: P = 0.81); (C) Leukocytes and neutrophils in stent thrombosis from drug-eluting stents (n = 149) and bare metal stents (n = 73) and in thrombi aspirated from patients with spontaneous myocardial infarction (spont. myocardial infarction; n = 104) (P < 0.05 for drug-eluting stents vs. spont. myocardial infarction and bare metal stents vs. spont. myocardial infarction). Shown are mean + SD, each symbol in (B) and (C) represents one individual patient.

++These authors contributed equally to this work.
Julia Riegger, Robert A. Byrne, Michael Joner, Sue Chandraratne, Anthony H. Gershlick, Jurrien M. ten Berg, Tom Adriaenssens, Giulio Guagliumi, Thea C. Godschalk, Franz-Josef Neumann, Dietmar Trenk, Laurent J. Feldman, Philippe Gabriel, Steg Walter Desmet, Fernando Alfonso, Alison H. Goodall, Roman Wojdyla, Dariusz Dudek, Vanessa Philippi, Sheryl Opinaldo, Anna Titova, Nikesh Malik, James Cotton, Darshni A. Jhagroe, Antonius A.C.M. Heestermans, Peter Sinnaeve, Paul Vermeersch, Christian Valina, Christian Schulz, Adnan Kastrati, Steffen Massberg the Prevention of Late Stent Thrombosis by an Interdisciplinary Global European Effort (PRESTIGE) Investigators On Behalf of the Prevention of Late Stent Thrombosis by an Interdisciplinary Global European Effort (PRESTIGE) Investigators,Tom Adriaenssens, Ian Buysschaert, Mickaël Chausson, Dries De Cock, Jo Dens, Emanuele Barbato, Walter Desmet, Sandrine Gautier, Paul Vermeersch, Peter Sinnaeve, Helene Abergel, Laurent Feldman, Martine Jandrot-Perrus, Didier Letourneur, Pierre Mangin, Véronique Olivier, Caroline Roques, Robert A. Byrne, Sue Chandraratne, Matthias Gratz, Michael Joner, Adnan Kastrati, Elisabeth Kennerknecht, Ildiko Konrad, Tobias Koppara, Steffen Massberg, Franz-Josef Neumann, Vasilis Ntziachristos, Sheryl Opinaldo, Vanessa Philippi, Julia Riegger, Amir Rosenthal, Alexander Rzany, Christian Schulz, Kristin Steigerwald, Tomohiso Tada, Anna Titova, Dietmar Trenk, Christian Valina, Andreas Vogelsang, Erion Xhepa, Chiara Bernelli, Micol Coccato, Giulio Guagliumi, Kenichi Komukai, Vasile Sirbu, Garry Kerch, Giovanni Amoroso, Jurriën ten Berg, Willem J.M. Dewilde, Thea C. Godschalk, Antonius A.C.M. Heestermans, Darshni A. Jhagroe, Joanne J. Wykrzykowska, Mark H.M. Winkens, Dariusz Dudek, Łukasz Rzeszutko, Roman Wojdyla, Wojciech Zasada, Fernando Alfonso, Javier Cuesta, Miguel Medina, Colin Berry, James Cotton, Nick Curzen, Margaret McEntegart, Robert Gerber, Anthony Gershlick, Alison H. Goodall, Simon Hetherington, Jonathan Hill, Damian Kelly, Nikesh Malik, Keith Oldroyd, Helen Routledge, Joanne Shannon, Venkatesan Suresh, Azfar Zahman.

European Heart Journal, Volume 37, Issue 19, 14 May 2016, Pages 1538–1549, https://doi.org/10.1093/eurheartj/ehv419

January 28, 2019September 30, 2019

Sensitive interferometric detection of ultrasound for minimally invasive clinical imaging applications.

Miniaturized optical detectors of ultrasound represent a promising alternative to piezoelectric technology and may enable new minimally invasive clinical applications, particularly in the field of optoacoustic imaging. However, the use of such detectors has so far been limited to controlled lab environments, and has not been demonstrated in the presence of mechanical disturbances, common in clinical imaging scenarios. Additionally, detection sensitivity has been inherently limited by laser noise, which hindered the use of sensing elements such as optical fibers, which exhibit a weak response to ultrasound. In this work, coherence‐restored pulse interferometry (CRPI) is introduced – a new paradigm for interferometric sensing in which shot‐noise limited sensitivity may be achieved alongside robust operation. CRPI is implemented with a fiber‐based resonator, demonstrating over an order of magnitude higher sensitivity than that of conventional 15 MHz intravascular ultrasound probes. The performance of the optical detector is showcased in a miniaturized all‐optical optoacoustic imaging catheter.[Read more….]

Fig1. Experimental demonstration of ultrasound detection in turbulent water using coherence restored pulse interferometry (CRFI) with passive demodulation. (a) Schematic description of the setup used to test CRPI for detecting ultrasound under a strong external disturbance. (b) The resonance shift measured with the passive‐demodulation scheme when the water pump was on. The inset shows one of the ultrasound signals measured under the volatile environmental conditions.

Amir Rosenthal, Stephan Kellnberger, Dmitry Bozhko, Andrei Chekkoury, Murad Omar, Daniel Razansky, Vasilis Ntziachristos. Volume8, Issue3, May 2014, Pages 450-457

December 12, 2018September 30, 2019

Fiber interferometer for hybrid optical and optoacoustic intravital microscopy

The addition of optoacoustic sensing to optical microscopy may supplement fluorescence contrast with label-free measurements of optical absorption, enhancing biological observation. However, the physical dimensions of many optoacoustic systems have restricted the implementation of hybrid optical and optoacoustic (O2A) microscopy to imaging thin samples in transmission mode or to ex-vivo investigations. Here we describe a miniaturized optoacoustic sensor, based on a ?-phase-shifted fiber Bragg grating embedded in an acoustic cavity, which is virtually invisible to the optical path and can be seamlessly integrated into any conventional optical microscope. The new sensor enables, for the first time to our knowledge, entirely optical O2A intravital microscopy in epi-illumination mode, demonstrated by label-free optoacoustic and second-harmonic generation images of a mouse abdomen and ear. Our technique greatly simplifies the integration of acoustic detection in standard microscopes and could therefore make optoacoustic microscopy more accessible to the biomedical community. [Read More…]

Fig. 5. Schematic depiction of the O2A microscopy setup: A standard inverted microscope with laser sources for optoacoustic and non-linear optical imaging is combined with galvanometric mirrors for fast laser raster scanning. The sensor is mounted on the microscope objective, with a tunable CW laser coupled to the embedded ?-FBG. The inset shows the 3D printed platform supporting an anesthetized mouse and mounted on a ??? positioning stage. DM, dichroic mirror; BP, bandpass filter; PH, pinhole; ND, neutral density filter; BS, beam splitter; PMT, photomultiplier tube; OA, optoacoustic; DAQ, data acquisition card.

Authors: Rami Shnaiderman, Georg Wissmeyer, Markus Seeger, Dominik Soliman, Hector Estrada, Daniel Razansky, Amir Rosenthal, and Vasilis Ntziachristos, “Fiber interferometer for hybrid optical and optoacoustic intravital microscopy,” Optica 4, 1180-1187 (2017)

December 11, 2018September 30, 2019

Model-based image reconstruction in optoacoustic tomography

The effect of limited tomographic coverage on the quality of the reconstructed image [13]. (a) A reconstruction of a cylindrical phantom with a square inclusion from full-view experimental data. (b) Model-based reconstruction with no regularizarion when only 130º of the projection data is used. (c) Back-projection reconstruction of the phantom in the limited-view scenario. (d) Regularized model-based reconstruction of the phantom in the limited-view scenario.

Optoacoustic tomography is a powerful hybrid bioimaging method which retains rich optical contrast and diffraction-limited ultrasonic resolution at depths of varying from millimeters to several centimeters in biological tissue irrespective of photon scattering. Optoacoustic imaging is commonly performed with high power optical pulses whose absorption leads to instantaneous temperature increase, thermal expansion and, subsequently, to the generation of a pressure field proportional to the distribution of the absorbed energy. For tomographic data acquisition, the optoacoustically generated waves are detected on a surface surrounding the imaged region. Recovery of the initially generated pressure distribution from the detected tomographic projections, and hence of the optical energy deposition in the tissue, constitutes the inverse problem of optoacoustic tomography, which is often solved using closed-form inversion formulae. However, those closed-form solutions are only exact for ideal detection geometries, which often do not accurately represent the experimental conditions. Model-based image-reconstruction techniques represent an alternative approach to solving the inverse problem that can significantly reduce image artifacts associated with approximated analytical formulae and significantly enhance image quality in non-ideal imaging scenarios. In the model-based reconstruction, a linear forward model is constructed to accurately describe the experimental conditions of the imaging setup. Inversion is performed numerically and may include regularization when the projection data is insufficient. This chapter demonstrates the benefits of the model-based reconstruction approach and describes numerically efficient methods for its implementation.
[Read More…]

Fig. 5 A comparison between back-projection and model-based reconstructions of a mouse heart in a 3D limited view scenario. The reduction of streak aritifacts in the model-based reconstruction
is readily seen in the images.

A. Rosenthal, D. Razansky, V. Ntziachristos, „Model-based image reconstruction in optoacoustic tomography,“ in Computer Vision in Medical Imaging, edited by C.H. Chen; World Scientific Publishing, October 2013.

December 11, 2018September 30, 2019

Improving quantification of intravascular fluorescence imaging using structural information

iNIRF system schematic. Excitation and emission light are coupled into a fibre which can be inserted in a catheter system through a rotational and translational stage, to allow fibre rotation and pull-back. The front end of the fibre is modified using a 45° prism so that fluorescence readings are obtained perpendicular to the translation axis.

Intravascular near-infrared fluorescence (iNIRF) imaging can enable the in vivo visualization of biomarkers of vascular pathology, including high-risk plaques. The technique resolves the bio-distribution of systemically administered fluorescent probes with molecular specificity in the vessel wall. However, the geometrical variations that may occur in the distance between fibre-tip and vessel wall can lead to signal intensity variations and challenge quantification. Herein we examined whether the use of anatomical information of the cross-section vessel morphology, obtained from co-registered intravascular ultrasound (IVUS), can lead to quantification improvements when fibre-tip and vessel wall distance variations are present. The algorithm developed employs a photon propagation model derived from phantom experiments that is used to calculate the relative attenuation of fluorescence signals as they are collected over 360° along the vessel wall, and utilizes it to restore accurate fluorescence readings. The findings herein point to quantification improvements when employing hybrid iNIRF, with possible implications to the clinical detection of high-risk plaques or blood vessel theranostics.
[Read More…]

Fig. 3 Experiment for validation of the algorithm: (a) phantom schematic: two straws containing the same concentration of fluorescent dye at different distances from the catheter; (b) iNIRF longitudinal image of the straws A and B and cross-section formation of a particular pullback position of interest; (c) corresponding IVUS cross-section of the straws and their corresponding edges; (d) iNIRF cross-section overlaid on the segmented IVUS cross-section is used for the correction of the iNIRF signal; (e) correction of the iNIRF image along the entire pullback.

G.Mallas, D. H. Brooks, A. Rosenthal, R.N.Nudelman, A. Mauskapf, F.A.Jaffer and V. Ntziachristos, “Improving quantification of intravascular fluorescence imaging using structural information,” Phys. Med. Biol. Vol. 57, pp. 6395–6406 (2012).

December 11, 2018September 25, 2019

Intravascular multispectral optoacoustic tomography of atherosclerosis: prospects and challenges

Intravascular optoacoustic imaging of lipids in human aorta using the 1210 nm wavelength

The progression of atherosclerosis involves complex changes in the structure, composition and biology of the artery wall. Currently, only anatomical plaque burden is routinely characterized in living patients, whereas compositional and biological changes are mostly inaccessible. However, anatomical imaging alone has proven to be insufficient for accurate diagnostics of the disease. Multispectral optoacoustic tomography offers complementary data to anatomical methods and is capable of imaging both tissue composition and, via the use of molecular markers, the biological activity therein. In this paper we review recent progress in multispectral optoacoustic tomography imaging of atherosclerosis with specific emphasis on intravascular applications. The potential capabilities of multispectral optoacoustic tomography are compared with those of established intravascular imaging techniques and current challenges on the road towards a clinically viable imaging modality are discussed.
[Read More…]

Fig. 1 Intravascular multispectral optoacoustic tomography of gold nanoparticle-bearing macrophages in rabbit aorta.
(A) Intravascular ultrasound image and (B) optoacoustic image acquired at 700 nm of an atherosclerotic rabbit aorta injected with gold nanoparticle-bearing macrophages. The arrows indicate the locations where injection was performed. (C) The normalized spectral optoacoustic response obtained in a small section on the aorta, where injection was performed. (D) Multispectral optoacoustic tomography image corresponding to the recovered spectrum overlaid onto the intravascular ultrasound image revealing the injected regions.

A. Rosenthal, F. A. Jafferand V. Ntziachristos, „Intravascular multispectral optoacoustic tomography of atherosclerosis: prospects and challenges,” Imaging Med., Vol. 4, pp. 299-310 (2012).

December 11, 2018September 30, 2019

In vivo Near Infrared Fluorescence (NIRF) Intravascular Molecular Imaging of Inflammatory Plaque, a Multimodal Approach to Imaging of Atherosclerosis

Schematic demonstrating protease-mediated activation of the nanosensor, Prosense/VM110.

In vivo Near Infrared Fluorescence (NIRF) Intravascular Molecular Imaging of Inflammatory Plaque, a Multimodal Approach to Imaging of Atherosclerosis

The vascular response to injury is a well-orchestrated inflammatory response triggered by the accumulation of macrophages within the vessel wall leading to an accumulation of lipid-laden intra-luminal plaque, smooth muscle cell proliferation and progressive narrowing of the vessel lumen. The formation of such vulnerable plaques prone to rupture underlies the majority of cases of acute myocardial infarction. The complex molecular and cellular inflammatory cascade is orchestrated by the recruitment of T lymphocytes and macrophages and their paracrine effects on endothelial and smooth muscle cells.

Molecular imaging in atherosclerosis has evolved into an important clinical and research tool that allows in vivo visualization of inflammation and other biological processes. Several recent examples demonstrate the ability to detect high-risk plaques in patients, and assess the effects of pharmacotherapeutics in atherosclerosis.4 While a number of molecular imaging approaches (in particular MRI and PET) can image biological aspects of large vessels such as the carotid arteries, scant options exist for imaging of coronary arteries. The advent of high-resolution optical imaging strategies, in particular near-infrared fluorescence (NIRF), coupled with activatable fluorescent probes, have enhanced sensitivity and led to the development of new intravascular strategies to improve biological imaging of human coronary atherosclerosis.

Fig. 1 Schematic of 2D NIRF Catheter To extend the clinical potential of a 1D NIRF sensing approach, we constructed a novel 2-D NIRF-catheter for intravascular imaging. The custom-built catheter consists of an optical fiber (125 micron diameter housed in polyethylene tubing: 2.9F) that illuminates using a 750 nm laser excitation source. Laser light is emitted at a 90 degree angle relative to fiber axis. The system utilizes two automated motors (rotational and translational) to enable concomitant 360 degree imaging and longitudinal pullback to obtain true 2D imaging. Images used with permission from reference 11.

Near infrared fluorescence (NIRF) molecular imaging utilizes excitation light with a defined band width (650-900 nm) as a source of photons that, when delivered to an optical contrast agent or fluorescent probe, emits fluorescence in the NIR window that can be detected using an appropriate emission filter and a high sensitivity charge-coupled camera. As opposed to visible light, NIR light penetrates deeply into tissue, is markedly less attenuated by endogenous photon absorbers such as hemoglobin, lipid and water, and enables high target-to-background ratios due to reduced autofluorescence in the NIR window. Imaging within the NIR ‘window’ can substantially improve the potential for in vivo imaging.

Inflammatory cysteine proteases have been well studied using activatable NIRF probes, and play important roles in atherogenesis. Via degradation of the extracellular matrix, cysteine proteases contribute importantly to the progression and complications of atherosclerosis. In particular, the cysteine protease, cathepsin B, is highly expressed and colocalizes with macrophages in experimental murine, rabbit, and human atheromata. In addition, cathepsin B activity in plaques can be sensed in vivo utilizing a previously described 1-D intravascular near-infrared fluorescence technology, in conjunction with an injectable nanosensor agent that consists of a poly-lysine polymer backbone derivatized with multiple NIR fluorochromes (VM110/Prosense750, ex/em 750/780nm, VisEn Medical, Woburn, MA) that results in strong intramolecular quenching at baseline. Following targeted enzymatic cleavage by cysteine proteases such as cathepsin B (known to colocalize with plaque macrophages), the fluorochromes separate, resulting in substantial amplification of the NIRF signal. Intravascular detection of NIR fluorescence signal by the utilized novel 2D intravascular NIRF catheter now enables high-resolution, geometrically accurate in vivo detection of cathepsin B activity in inflamed plaque.

In vivo molecular imaging of atherosclerosis using catheter-based 2D NIRF imaging, as opposed to a prior 1-D spectroscopic approach, is a novel and promising tool that utilizes augmented protease activity in macrophage-rich plaque to detect vascular inflammation. The following research protocol describes the use of an intravascular 2-dimensional NIRF catheter to image and characterize plaque structure utilizing key aspects of plaque biology. It is a translatable platform that when integrated with existing clinical imaging technologies including angiography and intravascular ultrasound (IVUS), offers a unique and novel integrated multimodal molecular imaging technique that distinguishes inflammatory atheromata, and allows detection of intravascular NIRF signals in human-sized coronary arteries.
[Read More…]

M. A. Calfon, A. Rosenthal, G. Mallas, A. Mauskapf, R. N. Nudelman, V. Ntziachristos, F. A. Jaffer, „In vivo Near Infrared Fluorescence (NIRF) Intravascular Molecular Imaging of Inflammatory Plaque, a Multimodal Approach to Imaging of Atherosclerosis,” J. Vis. Exp., Issue 54 (2011).