Multi-Parametric Standardization of Fluorescence Imaging Systems Based on a Composite Phantom.

OBJECTIVE: Fluorescence molecular imaging (FMI) has emerged as a promising tool for surgical guidance in oncology, with one of the few remaining challenges being the ability to offer quality control and data referencing. This paper investigates the use of a novel composite phantom to correct and benchmark FMI systems. METHODS: This paper extends on previous work by describing a phantom design that can provide a more complete assessment of FMI systems through quantification of dynamic range and determination of spatial illumination patterns for both reflectance and fluorescence imaging. Various performance metrics are combined into a robust and descriptive "system benchmarking score," enabling not only the comprehensive comparison of different systems, but also for the first time, correction of the acquired data. RESULTS: We show that systems developed for targeted fluorescence imaging can achieve benchmarking scores of up to 70%, while clinically available systems optimized for indocyanine green are limited to 50%, mostly due to greater leakage of ambient and excitation illumination and lower resolution. The image uniformity can also be approximated and employed for image flat-fielding, an important milestone toward data referencing. In addition, we demonstrate composite phantom use in assessing the performance of a surgical microscope and of a raster-scan imaging system. CONCLUSION: Our results suggest that the new phantom has the potential to support high-fidelity FMI through benchmarking and image correction. SIGNIFICANCE: Standardization of the FMI is a necessary process for establishing good imaging practices in clinical environments and for enabling high-fidelity imaging across patients and multi-center imaging studies.

Cardiovascular optoacoustics: From mice to men - A review.

Imaging has become an indispensable tool in the research and clinical management of cardiovascular disease (CVD). An array of imaging technologies is considered for CVD diagnostics and therapeutic assessment, ranging from ultrasonography, X-ray computed tomography and magnetic resonance imaging to nuclear and optical imaging methods. Each method has different operational characteristics and assesses different aspects of CVD pathophysiology; nevertheless, more information is desirable for achieving a comprehensive view of the disease. Optoacoustic (photoacoustic) imaging is an emerging modality promising to offer novel information on CVD parameters by allowing high-resolution imaging of optical contrast several centimeters deep inside tissue. Implemented with illumination at several wavelengths, multi-spectral optoacoustic tomography (MSOT) in particular, is sensitive to oxygenated and deoxygenated hemoglobin, water and lipids allowing imaging of the vasculature, tissue oxygen saturation and metabolic or inflammatory parameters. Progress with fast-tuning lasers, parallel detection and advanced image reconstruction and data-processing algorithms have recently transformed optoacoustics from a laboratory tool to a promising modality for small animal and clinical imaging. We review progress with optoacoustic CVD imaging, highlight the research and diagnostic potential and current applications and discuss the advantages, limitations and possibilities for integration into clinical routine.

Neoatherosclerosis: from basic principles to intravascular imaging.

Development of new atherosclerotic lesions within the neointima of stented vessels has been recognized as a novel disease manifestation of atherosclerosis (neoatherosclerosis), often manifesting as in-stent restenosis (ISR) or in-stent thrombosis (ST). The pathobiology of this entity is still not fully understood and definite diagnosis is challenging owing to limitations in resolution of contemporary intravascular imaging modalities and lack of consequent histopathology correlation studies. Yet, intravascular imaging has emerged as the gold standard for the diagnosis of in-stent pathologies, the most routinely used modalities being intravascular ultrasound (IVUS) and optical coherence tomography (OCT). In this review, we will give a concise summary about the basic understanding and histological findings of neoatherosclerosis. We will focus on the description of in-vivo findings using IVUS and OCT, discussing advantages and pitfalls. Furthermore, recent developments regarding innovative molecular imaging techniques for a more precise and advanced examination of neoatherosclerotic plaques will be discussed.

Optoacoustic sensing of hematocrit to improve the accuracy of hybrid fluorescence-ultrasound intravascular imaging.

Hybrid intravascular fluorescence-ultrasound imaging is emerging for reading anatomical and biological information in vivo. By operating through blood, intravascular near-infrared fluorescence (NIRF) detection is affected by hemoglobin attenuation. Improved quantification has been demonstrated with methods that correct for the attenuation of the optical signal as it propagates through blood. These methods assume an attenuation coefficient for blood and measure the distance between detector and the vessel wall by observing the intravascular ultrasound images. Assumptions behind the attenuation employed in correction models may reduce the accuracy of these methods. Herein, we explore a novel approach to dynamically estimate optical absorption by using optoacoustic (photoacoustic) measurements. Adaptive correction is based on a trimodal intravascular catheter that integrates fluorescence, ultrasound and optoacoustic measurements. Using the novel catheter, we show how optoacoustic measurements can determine variations of blood absorption, leading to accurate quantification of the detected NIRF signals at different hematocrit values.

Importance of Ultrawide Bandwidth for Optoacoustic Esophagus Imaging.

Optoacoustic (photoacoustic) endoscopy has shown potential to reveal complementary contrast to optical endoscopy methods, indicating clinical relevance. However operational parameters for accurate optoacoustic endoscopy must be specified for optimal performance. Recent support from the EU Horizon 2020 program ESOTRAC to develop a next-generation optoacoustic esophageal endoscope directs the interrogation of the optimal frequency required for accurate implementation. We simulated the frequency response of the esophagus wall and then validated the simulation results with experimental measurements of pig esophagus. Phantoms and fresh pig esophagus samples were measured using two detectors with central frequencies of 15 or 50 MHz, and the imaging performance of both detectors was compared. We analyzed the frequency bandwidth of optoacoustic signals in relation to morphological layer structures of the esophagus and found the 50 MHz detector to differentiate layer structures better than the 15 MHz detector. Furthermore, we identify the necessary detection bandwidth for visualizing esophagus morphology and selecting ultrasound transducers for future optoacoustic endoscopy of the esophagus.

Flow-mediated dilatation test using optoacoustic imaging: a proof-of-concept.

Label-free multispectral optoacoustic tomography (MSOT) has recently shown superior performance in visualizing the morphology of human vasculature, especially of smaller vessels, compared to ultrasonography. Herein, we extend these observations towards MSOT interrogation of macrovascular endothelial function. We employed a real-time handheld MSOT scanner to assess flow-mediated dilatation (FMD), a technique used to characterize endothelial function. A data processing scheme was developed to quantify the dimensions and diameter changes of arteries in humans and determine wall distensibility parameters. By enabling high-resolution delineation of the blood-vessel wall in a cross-sectional fashion, the findings suggest MSOT as a capable alternative to ultrasonography for clinical FMD measurements.

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.