Sensitivity and depth penetration of continuous wave versus frequency-domain photon migration near-infrared fluorescence contrast-enhanced imaging

Theoretical Study on Spectrum and Luminescence Mechanism of Cy5.5 and Cy7.5 Dye Based on Density Functional Theory (DFT)

Cy5.5 and 7.5 are the most commonly used NIR 2-region fluoresceins, which have good luminescence properties and important biomedical tracer applications. In this paper, their molecular non-covalent interactions, UV-Vis absorption spectra, main bond lengths, electrostatic potential distributions, frontier molecular orbitals (HOMO and LUMO) and energy gaps were calculated by density functional theory (DFT). We found that the differences in the luminescence properties and energy gaps of Cy5.5 and Cy7.5 molecules may be caused by the length of the conjugated chains between the two aromatic rings in the molecule. By calculating the relevant molecular characteristics, this paper can provide ideas and theoretical basis for the relevant modification and application, as well as the development of new fluorescent dyes.

A rapid dynamic in vivo near-infrared fluorescence imaging assay to track lung vascular permeability after acute radiation injury

To develop a dynamic in vivo near-infrared (NIR) fluorescence imaging assay to quantify sequential changes in lung vascular permeability-surface area product (PS) in rodents. Dynamic NIR imaging methods for determining lung vascular permeability-surface area product were developed and tested on non-irradiated and 13 Gy irradiated rats with/without treatment with lisinopril, a radiation mitigator. A physiologically-based pharmacokinetic (PBPK) model of indocyanine green (ICG) pulmonary disposition was applied to in vivo imaging data and PS was estimated. In vivo results were validated by five accepted assays: ex vivo perfused lung imaging, endothelial filtration coefficient (Kf) measurement, pulmonary vascular resistance measurement, Evan's blue dye uptake, and histopathology. A PBPK model-derived measure of lung vascular permeability-surface area product increased from 2.60 ± 0.40 [CL: 2.42-2.78] mL/min in the non-irradiated group to 6.94 ± 8.25 [CL: 3.56-10.31] mL/min in 13 Gy group after 42 days. Lisinopril treatment lowered PS in the 13 Gy group to 4.76 ± 6.17 [CL: 2.12-7.40] mL/min. A much higher up to 5× change in PS values was observed in rats exhibiting severe radiation injury. Ex vivo K_f (mL/min/cm H₂O/g dry lung weight), a measure of pulmonary vascular permeability, showed similar trends in lungs of irradiated rats (0.164 ± 0.081 [CL: 0.11-0.22]) as compared to non-irradiated controls (0.022 ± 0.003 [CL: 0.019-0.025]), with reduction to 0.070 ± 0.035 [CL: 0.045-0.096] for irradiated rats treated with lisinopril. Similar trends were observed for ex vivo pulmonary vascular resistance, Evan's blue uptake, and histopathology. Our results suggest that whole body dynamic NIR fluorescence imaging can replace current assays, which are all terminal. The imaging accurately tracks changes in PS and changes in lung interstitial transport in vivo in response to radiation injury.

Performance test methods for near-infrared fluorescence imaging

PURPOSE

Near-infrared fluorescence (NIRF) imaging using exogenous contrast has gained much attention as a technique for enhancing visualization of vasculature using untargeted agents, as well as for the detection and localization of cancer with targeted agents. In order to address the emerging need for standardization of NIRF imaging technologies, it is necessary to identify the best practices suitable for objective, quantitative testing of key image quality characteristics. Toward the development of a battery of test methods that are rigorous yet applicable to a wide variety of devices, we have evaluated techniques for phantom design, measurement, and calculation of specific performance metrics.

METHODS

Using a NIRF imaging system for indocyanine green imaging, providing excitation at 780 nm and detection above 830 nm, we explored methods to evaluate uniformity, field of view, spectral crosstalk, spatial resolution, depth of field, sensitivity, linearity, and penetration depth. These measurements were performed using fluorophore-doped multiwell plate and high turbidity planar phantoms, as well as a 3D-printed multichannel phantom and a USAF 1951 resolution target.

RESULTS AND CONCLUSIONS

Based on a wide range of approaches described in medical and fluorescence imaging literature, we have developed and demonstrated a cohesive battery of test methods for evaluation of fluorescence image quality in wide-field imagers. We also propose a number of key metrics that can facilitate direct, quantitative comparison of device performance. These methods have the potential to facilitate more uniform evaluation and inter-comparison of clinical and preclinical imaging systems than is typically achieved, with the long-term goal of establishing international standards for fluorescence image quality assessment.

Comparison of fluorescence optical imaging, ultrasonography and clinical examination with magnetic resonance imaging as a reference in active rheumatoid arthritis patients

BACKGROUND

Fluorescence optical imaging with indocyanine-green enhancement (FOI) is a new imaging modality for the assessment of hand arthritis. The objective of this study was to compare performance profiles of clinical examination (CE), US and FOI using MRI as a reference in the same active rheumatoid arthritis (RA) patients.

METHODS

CE, US, FOI and MRI were performed on six subjects with active RA. Each sequence of FOI was divided into three phases based on indocyanine-green dynamics and the joints were graded semi-quantitatively. Sensitivities and specificities of CE, US and FOI were calculated using the RAMRIS synovitis score >0 as a reference in a total of 30 joints (the second to fifth metacarpophalangeal (MCP) joints and the wrist of the clinically dominant hand).

RESULTS

FOI showed sensitivities and specificities, respectively, of 85% and of 94% for Phase-1 and 69% and 94% for Phase-2. Sensitivities and specificities were 100% and 35% for CE (tender or swollen), 92% and 41% for gray scale US, and 77% and 100% for color-Doppler US.

CONCLUSIONS

The performance characteristics of FOI in detection of synovitis in patients with active RA are comparable to those of US and more specific than CE. FOI has a potential as an assessment modality of RA.

Methods for detecting host genetic modifiers of tumor vascular function using dynamic near-infrared fluorescence imaging

Vascular supply is a critical component of the tumor microenvironment (TME) and is essential for tumor growth and metastasis, yet the endogenous genetic modifiers that impact vascular function in the TME are largely unknown. To identify the host TME modifiers of tumor vascular function, we combined a novel genetic mapping strategy [Consomic Xenograft Model] with near-infrared (NIR) fluorescence imaging and multiparametric analysis of pharmacokinetic modeling. To detect vascular flow, an intensified cooled camera based dynamic NIR imaging system with 785 nm laser diode based excitation was used to image the whole-body fluorescence emission of intravenously injected indocyanine green dye. Principal component analysis was used to extract the spatial segmentation information for the lungs, liver, and tumor regions-of-interest. Vascular function was then quantified by pK modeling of the imaging data, which revealed significantly altered tissue perfusion and vascular permeability that were caused by host genetic modifiers in the TME. Collectively, these data demonstrate that NIR fluorescent imaging can be used as a non-invasive means for characterizing host TME modifiers of vascular function that have been linked with tumor risk, progression, and response to therapy.

Depth sensitivity of frequency domain optical measurements in diffusive media

The depth sensitivity functions for AC amplitude, phase (PH) and DC intensity signals have been obtained in the frequency domain (where the source amplitude is modulated at radio-frequencies) by making use of analytical solutions of the photon diffusion equation in an infinite slab geometry. Furthermore, solutions for the relative contrast of AC, PH and DC signals when a totally absorbing plane is placed at a fixed depth of the slab have also been obtained. The solutions have been validated by comparisons with gold standard Monte Carlo simulations. The obtained results show that the AC signal, for modulation frequencies < 200 MHz, has a depth sensitivity with similar characteristics to that of the continuous-wave (CW) domain (source modulation frequency of zero). Thus, the depth probed by such a signal can be estimated by using the formula of penetration depth for the CW domain (Sci. Rep.6, 27057 (2016)). However, the PH signal has a different behavior compared to the CW domain, showing a larger depth sensitivity at shallow depths and a less steep relative contrast as a function of depth. These results mark a clear difference in term of depth sensitivity between AC and PH signals, and highlight the complexity of the estimation of the actual depth probed in tissue spectroscopy.

Fluorescence to highlight the urethra: a human cadaveric study

Background

Urethral injury is a complication feared by surgeons performing transanal TME (TaTME) or abdominoperineal excision (APE) procedures. Injury during TaTME occurs when the prostate is inadvertently mobilised or as a direct injury similar to the direct injury during the perineal dissection of APE procedures. We performed a proof of principle study to assess the feasibility of using indocyanine green (ICG) to fluoresce the urethra in human cadavers.

Methods

Indocyanine green at varying doses was mixed with Instillagel and infiltrated into the urethra of male human cadavers. The urethra was exposed through either a perineal incision or by mobilisation of the prostate during a TaTME dissection and fluorescence observed using a PINPOINT laparoscope (NOVADAQ). Brightness was assessed on the images using ImageJ (National Institute of Health).

Results

Eight cadavers were included in the study. Fluorescence was visualised in the urethra in all eight cadavers. Minimal dissection was required to obtain fluorescence transperineally. In one cadaver, the urethra was demonstrated under fluorescence using a simulated TaTME with additional fluorescence also being observed in the prostate. There was no correlation between brightness and dosing.

Conclusions

This novel proof of principle study demonstrates a simple way in which the urethra may be easily identified preventing it from injury during surgery.

Electronic supplementary material

The online version of this article (doi:10.1007/s10151-017-1615-y) contains supplementary material, which is available to authorized users.

Near-Infrared Fluorescence-Enhanced Optical Tomography

Fluorescence-enhanced optical imaging using near-infrared (NIR) light developed for in vivo molecular targeting and reporting of cancer provides promising opportunities for diagnostic imaging. The current state of the art of NIR fluorescence-enhanced optical tomography is reviewed in the context of the principle of fluorescence, the different measurement schemes employed, and the mathematical tools established to tomographically reconstruct the fluorescence optical properties in various tissue domains. Finally, we discuss the recent advances in forward modeling and distributed memory parallel computation to provide robust, accurate, and fast fluorescence-enhanced optical tomography.

Indocyanine green-enhanced fluorescence for assessing parathyroid perfusion during thyroidectomy

Identification of the parathyroid glands during thyroid surgery may prevent their inadvertent surgical removal and thus provide a better postoperative quality of life. Nevertheless, the most common "technique" for intraoperative evaluation of perfusion of parathyroid gland tissues during thyroid surgery is visual inspection of the physical condition of tissues, e.g., their color and bleeding edges. Another technique is measurement of intact parathyroid hormone. Recently, indocyanine green-enhanced fluorescence has been used in various surgical techniques, particularly laparoscopic surgery, to improve visualization and to provide detailed anatomical information. Fluorescent optical guidance helps surgeons to avoid inadvertent tissue injury while enhancing procedural efficiency. This technique has potential use for evaluating perfusion of the parathyroid gland in real-time intraoperative angiography.

From shadow to light: visualization of extrahepatic bile ducts using image-enhanced laparoscopy

BACKGROUND

Correct recognition of the extrahepatic bile ducts is thought to be crucial to reduce the risk of bile duct injuries during various laparoscopic procedures. Image-enhanced laparoscopy techniques, utilizing various optical modalities other than white light, may help in detecting structures "hidden" underneath connective tissue.

METHODS

A systematic literature search was conducted of studies describing image-enhanced laparoscopy techniques for visualization of the extrahepatic bile ducts.

RESULTS

In all, 29 articles met inclusion criteria. They describe various techniques in the animal or human setting, including autofluorescence imaging, drug-enhanced fluorescence imaging, infrared thermography, and spectral imaging. This review describes these various techniques and their results.

CONCLUSION

Image-enhanced laparoscopy techniques for real-time visualization of extrahepatic bile ducts are still in its infancy. Out of the techniques currently described, indocyanine green-enhanced near-infrared fluorescence laparoscopy has the most mature results, but other techniques also appear promising. It can be expected that in the future, image-enhanced laparoscopy might become a routine adjunct to any white-light laparoscopic operation near the hepatic hilum.

Indocyanine green (ICG) fluorescent cholangiography during robotic cholecystectomy: results of 184 consecutive cases in a single institution

BACKGROUND/AIM

Laparoscopic cholecystectomy is currently the gold standard treatment for gallstone disease. Bile duct injury is a rare and severe complication of this procedure, with a reported incidence of 0.4% to 0.8% and is mostly a result of misperception and misinterpretation of the biliary anatomy. Robotic cholecystectomy has proven to be a safe and feasible approach. One of the latest innovations in minimally invasive technology is fluorescent imaging using indocyanine green (ICG). The aim of this study is to evaluate the efficacy of ICG and the Da Vinci Fluorescence Imaging Vision System in real-time visualization of the biliary anatomy.

METHODS

A total of 184 robotic cholecystectomies with ICG fluorescence cholangiography were performed between July 2011 and February 2013. All patients received a dose of 2.5 mg of ICG 45 minutes prior to the beginning of the surgical procedure. The procedures were multiport or single port depending on the case.

RESULTS

No conversions to open or laparoscopic surgery occurred in this series. The overall postoperative complication rate was 3.2%. No biliary injuries occurred. ICG fluorescence allowed visualization of at least 1 biliary structure in 99% of cases. The cystic duct, the common bile duct, and the common hepatic duct were successfully visualized with ICG in 97.8%, 96.1%, and 94% of cases, respectively.

CONCLUSIONS

ICG fluorescent cholangiography during robotic cholecystectomy is a safe and effective procedure that helps real-time visualization of the biliary tree anatomy.

Non-invasive fluorescence imaging under ambient light conditions using a modulated ICCD and laser diode

One limitation of fluorescence molecular imaging that can limit clinical implementation and hamper small animal imaging is the inability to eliminate ambient light. Herein, we demonstrate the ability to conduct rapid non-invasive, far-red and near-infrared fluorescence imaging in living animals and a phantom under ambient light conditions using a modulated image intensified CCD (ICCD) and a laser diode operated in homodyne detection. By mapping AC amplitude from three planar images at varying phase delays, we show improvement in target-to-background ratios (TBR) and reasonable signal-to-noise ratios (SNR) over continuous wave measurements. The rapid approach can be used to accurately collect fluorescence in situations where ambient light cannot be spectrally conditioned or controlled, such as in the case of fluorescent molecular image-guided surgery.

Real-time near-infrared (NIR) fluorescent cholangiography in single-site robotic cholecystectomy (SSRC): a single-institutional prospective study

BACKGROUND

Bile duct injury is a rare but serious complication of laparoscopic cholecystectomy and the primary cause is misinterpretation of biliary anatomy. This may occur more frequently with a single-incision approach due to difficulties in exposing and visualizing the triangle of Calot. Intraoperative cholangiography was proposed to overcome this problem, but due to multiple issues, it is not used routinely. Indocyanine green (ICG) near-infrared (NIR) fluorescent cholangiography is non invasive and provides real-time biliary images during surgery, which may improve the safety of single-incision cholecystectomy. This study aims to evaluate the efficacy and safety of this technique during single-site robotic cholecystectomy (SSRC).

METHODS

Patients presenting with symptomatic biliary gallstones without suspicion of common bile duct stones underwent SSRC with ICG-NIR fluorescent cholangiography using the da Vinci Fluorescence Imaging Vision System. During patient preparation, 2.5 mg of ICG was injected intravenously. During surgery, the biliary anatomy was imaged in real time, which guided dissection of Calot's triangle. Perioperative outcomes included biliary tree visualizations, operative time, conversion and complications rates, and length of hospital stay.

RESULTS

There were 45 cases between July 2011 and January 2012. All procedures were completed successfully; there were no conversions and at least one structure was visualized in each patient. The rates of visualization were 93 % for the cystic duct, 88 % for the common hepatic duct, and 91 % for the common bile duct prior to Calot's dissection; after Calot's dissection, the rates were 97 % for all three ducts. Mean hospital stay was 1.1 days and there were no bile duct injuries or any other major complications.

CONCLUSION

Real-time high-resolution fluorescent imaging to identify the biliary tree anatomy during SSRC using the da Vinci Fluorescence Imaging Vision System was safe and effective.

Validating the Sensitivity and Performance of Near-Infrared Fluorescence Imaging and Tomography Devices Using a Novel Solid Phantom and Measurement Approach

With the aid of indocyanine green (ICG), lymphatic architecture and function in both mice and humans has been successfully imaged non-invasively using near-infrared (NIR) fluorescence imaging devices. Maximal measurement sensitivity of NIR fluorescence imaging devices is needed for “first-in-humans” molecularly targeting NIR fluorescence agents that are brighter than non-specific ICG. In this study, we developed a solid phantom and measurement approach for the quantification of excitation light leakage and measurement sensitivity of NIR fluorescence imaging devices. The constructed solid phantom, consisting of quantum dots impregnated onto specularly reflective surface, shows long-term stability and can be used as a traceable fluorescence standard. With the constructed solid phantom, the intensified CCD (ICCD)-based device demonstrated more than 300% higher measurement sensitivity compared to the Electron Multiplying CCD (EMCCD) based device when integration time was maintained less than 1.0 s.

Intraoperative assessment of biliary anatomy for prevention of bile duct injury: a review of current and future patient safety interventions

Background

Bile duct injury (BDI) is a dreaded complication of cholecystectomy, often caused by misinterpretation of biliary anatomy. To prevent BDI, techniques have been developed for intraoperative assessment of bile duct anatomy. This article reviews the evidence for the different techniques and discusses their strengths and weaknesses in terms of efficacy, ease, and cost-effectiveness.

Method

PubMed was searched from January 1980 through December 2009 for articles concerning bile duct visualization techniques for prevention of BDI during laparoscopic cholecystectomy.

Results

Nine techniques were identified. The critical-view-of-safety approach, indirectly establishing biliary anatomy, is accepted by most guidelines and commentaries as the surgical technique of choice to minimize BDI risk. Intraoperative cholangiography is associated with lower BDI risk (OR 0.67, CI 0.61–0.75). However, it incurs extra costs, prolongs the operative procedure, and may be experienced as cumbersome. An established reliable alternative is laparoscopic ultrasound, but its longer learning curve limits widespread implementation. Easier to perform are cholecystocholangiography and dye cholangiography, but these yield poor-quality images. Light cholangiography, requiring retrograde insertion of an optical fiber into the common bile duct, is too unwieldy for routine use. Experimental techniques are passive infrared cholangiography, hyperspectral cholangiography, and near-infrared fluorescence cholangiography. The latter two are performed noninvasively and provide real-time images. Quantitative data in patients are necessary to further evaluate these techniques.

Conclusions

The critical-view-of-safety approach should be used during laparoscopic cholecystectomy. Intraoperative cholangiography or laparoscopic ultrasound is recommended to be performed routinely. Hyperspectral cholangiography and near-infrared fluorescence cholangiography are promising novel techniques to prevent BDI and thus increase patient safety.

Formation of near-infrared fluorescent nanoparticles for medical imaging

Aims: Indocyanine green (ICG) is a US FDA-approved near-infrared fluorescent, water-soluble dye used for diagnostics in vitro and in vivo. The aim of this study was to develop insoluble nanoparticles based on a cationic polymer, ICG and a targeting molecule. The particles are intended for oral administration in the colon, having fluorescence in near-infrared, thus enabling remote detection. Materials & methods: An aqueous dispersion of particles formed from Eudragit-RS by simple precipitation method possessing a mean size of approximately 100 nm and zeta potential of +16 mV was produced. Results: These particles are capable of binding both ICG and fluorescein isothiocyanate–IgG via noncovalent interactions. These composite particles retain the emission characteristics of the fluorescent precursors and also exhibit potential specific recognition ability. The particles were stable in intestinal fluid and are composed only of materials that are FDA approved. Conclusion: The nanoparticles may be suitable for in vivo imaging and therapy by oral delivery systems.

Reduction of excitation light leakage to improve near-infrared fluorescence imaging for tissue surface and deep tissue imaging

PURPOSE

Fluorescence-enhanced optical imaging using near-infrared (NIR) light developed for in vivo molecular targeting and reporting of various diseases provides promising opportunities for diagnostic imaging. However, the measurement sensitivity of NIR fluorescence (NIRF) optical imaging systems is limited by the leakage of the strong backscattered excitation light through rejection filters. In this article, the authors present a systematic method for improving sensitivity and validating the NIRF optical imager currently used for clinical imaging of human lymphatic function.

METHODS

The proposed systemic method consists of an appropriate filter combination and a collimation optics adapted to an NIRF optical imager. The spectral contributions were first assessed due to the excitation light backscattered from the tissue and from non-normal-incidence of the excitation light on the optical filters used in the authors' NIRF clinical imaging system. Then two tests were conducted to assess the system with and without the components of appropriate filters combination and collimation optics using: (1) a phantom to evaluate excitation light leakage as a function of target depth and (2) deployment in an actual human study.

RESULTS

The phantom studies demonstrate as much as two to three orders of magnitude reduction in the transmission ratio, indicating that the excitation light leakage can be reduced upon using the appropriate filter combination and collimation optics while an in vivo investigatory human study confirms improved imaging.

CONCLUSIONS

The method for reducing the excitation light leakage is presented for validating collected signals for fluorescence imaging.

Near-Infrared Fluorescence Imaging in Humans with Indocyanine Green: A Review and Update

Near-infrared (NIR) fluorescence imaging clinical studies have been reported in the literature with six different devices that employ various doses of indocyanine green (ICG) as a non-specific contrast agent. To date, clinical applications range from (i) angiography, intraoperative assessment of vessel patency, and tumor/metastasis delineation following intravenous administration of ICG, and (ii) imaging lymphatic architecture and function following subcutaneous and intradermal ICG administration. In the latter case, NIR fluorescence imaging may enable new discoveries associated with lymphatic function due to (i) a unique niche that is not met by any other conventional imaging technology and (ii) its exquisite sensitivity enabling high spatial and temporal resolution. Herein, we (i) review the basics of clinical NIR fluorescence imaging, (ii) survey the literature on clinical application of investigational devices using ICG fluorescent contrast, (iii) provide an update of non-invasive dynamic lymphatic imaging conducted with our FDPM device, and finally, (iv) comment on the future NIR fluorescence imaging for non-invasive and intraoperative use given recent demonstrations showing capabilities for imaging following microdose administration of contrast agent.

Molecular imaging with optics: primer and case for near-infrared fluorescence techniques in personalized medicine

We compare and contrast the development of optical molecular imaging techniques with nuclear medicine with a didactic emphasis for initiating readers into the field of molecular imaging. The nuclear imaging techniques of gamma scintigraphy, single-photon emission computed tomography, and positron emission tomography are first briefly reviewed. The molecular optical imaging techniques of bioluminescence and fluorescence using gene reporter/probes and gene reporters are described prior to introducing the governing factors of autofluorescence and excitation light leakage. The use of dual-labeled, near-infrared excitable and radio-labeled agents are described with comparative measurements between planar fluorescence and nuclear molecular imaging. The concept of time-independent and -dependent measurements is described with emphasis on integrating time-dependent measurements made in the frequency domain for 3-D tomography. Finally, we comment on the challenges and progress for translating near-infrared (NIR) molecular imaging agents for personalized medicine.

In vivo measurement of vascular modulation in experimental tumors using a fluorescent contrast agent

We compared the effectiveness of three optical techniques based on fluorescence imaging and spectroscopy with indocyanine green (ICG) contrast agent to evaluate in vivo the disruption of the active vasculature induced by a vascular targeting agent. The blood perfusion of the MDA-MB-435 tumor model transplanted in nude mice was estimated from the signal of the contrast agent measured immediately after its systemic injection in mice. Optical measurements were performed using a fluorescence imaging setup and a fiber-based time correlated single photon counting (TCSPC) apparatus. This latter apparatus was used to measure the tumor fluorescence in transmittance geometry and the change in the basal optical absorption induced by the contrast agent, thus providing an alternative estimation of the blood content in the tumor. Mice were divided into four groups. Three groups were treated with different doses of the vascular disrupting agent ZD6126, the fourth group (control group) received the drug vehicle only. Optical measurements were carried out 3 h after pharmacologic treatment. After 24 h, mice were killed, tumors were excised and the extent of necrosis was evaluated with standard histologic analysis. On fluorescence imaging ICG emission from tumors of mice treated with ZD6126 significantly was lower compared with the emission from control mice. The histologic sections also showed a significantly higher amount of necrosis in tumors of treated mice. Both these findings, which correlate with each other, indicate an effective vascular shutdown induced by the drug. However, ICG fluorescence measured with the TCSPC apparatus in transmittance geometry and the estimate of the change in optical absorption did not allow a statistically significant differentiation between treated and control groups.

A comparison between a time domain and continuous wave small animal optical imaging system

We present a phantom study to evaluate the performance of the eXplore Optix (Advanced Research Technologies-GE Healthcare), the first commercially available time-domain tomography system for small animal fluorescence imaging, and compare its capabilities with the widely used IVIS 200 (Xenogen Corporation-Caliper) continuous wave planar imaging system. The eXplore Optix, based on point-wise illumination and collection scheme, is found to be a log order more sensitive with significantly higher detection depth and spatial resolution as compared with the wide-area illumination IVIS 200 under the conditions tested. A time-resolved detection system allows the eXplore Optix to measure the arrival time distribution of fluorescence photons. This enables fluorescence lifetime measurement, absorption mapping, and estimation of fluorescent inclusion depth, which in turn is used by a reconstruction algorithm to calculate the volumetric distribution of the fluorophore concentration. An increased acquisition time and lack of ability to image multiple animals simultaneously are the main drawbacks of the eXplore Optix as compared with the IVIS 200.

Targeted photothermal lysis of the pathogenic bacteria, Pseudomonas aeruginosa, with gold nanorods

Increases in the prevalence of antibiotic resistant bacteria require new approaches for the treatment of infectious bacterial pathogens. It is now clear that a nanotechnology-driven approach using nanoparticles to selectively target and destroy pathogenic bacteria can be successfully implemented. We have explored this approach by using gold nanorods that have been covalently linked to primary antibodies to selectively destroy the pathogenic Gram-negative bacterium, Pseudomonas aeruginosa. We find that, following nanorod attachment to the bacterial cell surface, exposure to near-infrared radiation results in a significant reduction in bacterial cell viability.

Fluorescence diffuse optical tomography with functional and anatomicala prioriinformation: feasibility study

Fluorescence diffuse optical tomography (FT) is an emerging molecular imaging technique that can spatially resolve both fluorophore concentration and lifetime parameters. In this study, we investigate the performance of a frequency-domain FT system for small inclusions that are embedded in a heterogeneous background. The results demonstrate that functional and structural a priori information is crucial to be able to recover both parameters with high accuracy. The functional a priori information is defined by the absorption and scattering maps at both excitation and emission wavelengths. Similarly, the boundaries of the small inclusion and different regions in the background are utilized as the structural a priori information. Without a priori information, the fluorophore concentration of a 5 mm inclusion in a 40 mm medium is recovered with 50% error, while the lifetime cannot be recovered at all. On the other hand, when both functional and structural information are available, the true lifetime can be recovered and the fluorophore concentration can be estimated only with 5% error. This study shows that a hybrid system that can acquire diffuse optical absorption tomography (DOT), FT and anatomical images in the same setting is essential to be able to recover the fluorophore concentration and lifetime accurately in vivo.

Effects of residual fluorescence on time-resolved signals simulated with the finite element method in biological tissues

A computational model based on finite element method is derived to examine how the simulated time-dependent signals are related to the presence of residual fluorescence in biological media surrounding a fluorescent object. We apply a subtraction technique on recorded data when imperfect uptake of fluorescing agent into the tumor is considered. We show the limits of the subtracting method for low target: background fluorescent absorption contrast by extracting the time to reach the half maximum and analyzing the maximum of the time-resolved signals versus target depth.

Influence of excitation light rejection on forward model mismatch in optical tomography

Fluorescence enhanced tomography for molecular imaging requires low background for detection and accurate image reconstruction. In this contribution, we show that excitation light leakage is responsible for elevated background and can be minimized with the use of gradient index (GRIN) lenses when using fibre optics to collect propagated fluorescence light from tissue or other biological media. We show that the model mismatch between frequency-domain photon migration (FDPM) measurements and the diffusion approximation prediction is decreased when GRIN lenses are placed prior to the interference filters to provide efficient excitation light rejection. Furthermore, model mismatch is correlated to the degree of excitation light leakage. This work demonstrates the importance of proper light filtering when designing fluorescence optical imaging and tomography.

Fully adaptive FEM based fluorescence optical tomography from time-dependent measurements with area illumination and detection

Using an area-illumination and area-detection scheme, we acquire fluorescence frequency domain measurements from a tissue phantom with an embedded fluorescent target and obtain tomographic reconstructions of the interior fluorescence absorption map with an adaptive finite element based scheme. The tissue phantom consisted of a clear acrylic cubic box (512 ml) filled with 1% Liposyn solution, while the fluorescent targets were 5 mm diameter glass bulbs filled with 1 microM Indocyanine Green dye solution in 1% Liposyn. Frequency domain area illumination and detection employed a planar excitation source using an expanded intensity modulated (100 MHz) 785 nm diode laser light and a gain modulated image intensified charge coupled device camera, respectively. The excitation pattern was characterized by isolating the singly scattered component with cross polarizers and was input into a dual adaptive finite element-based scheme for three dimensional reconstructions of fluorescent targets embedded beneath the phantom surface. Adaptive mesh refinement techniques allowed efficient simulation of the incident excitation light and the reconstruction of fluorescent targets buried at the depths of 1 and 2 cm. The results demonstrate the first clinically relevant noncontact fluorescence tomography with adaptive finite element methods.

Subnanosecond-resolution phase-resolved fluorescence imaging technique for biomedical applications

Characterization of fluorescence emissions from cells often leads to conclusive results in the early detection of cellular abnormalities. Cellular abnormalities can be characterized by their difference in the fluorescence lifetime, which may be less than nanoseconds. A sensitive frequency domain technique, also called a phase-resolved fluorescence imaging technique, is proposed in which fluorescence emissions at the same wavelengths can more effectively be separated with subnanosecond resolution in their lifetime difference. The system configuration is optimized by incorporating even-step phase shifting in the homodyne-assisted signal-processing concept along with the phase-resolved fluorescence technique to eliminate the dc offsets of emission. Experiments are carried out with simulated samples composed of two fluorescence emissions of the same wavelength but with different lifetime values. Suppression of either of the fluorescence emissions by selective imaging of the other validates the superiority of the proposed technique. Hence, this technique can potentially be applied in the early detection of cellular abnormalities.

Fluorescence-enhanced optical tomography of a large tissue phantom using point illumination geometries

We demonstrate fluorescence-enhanced optical imaging of single and multiple fluorescent targets within a large (approximately 1081 cm3) phantom using frequency-domain photon migration measurements of fluorescence collected at individual points in response to illumination of excitation light at individual points on the boundary. The tissue phantom was filled with a 1% lipid solution with and without 0.01 microM Indocyanine Green (ICG) and targets consisted of vials filled with the 1% lipid containing 1-2.5 microM ICG. Measurements were acquired using a modulated intensified CCD imaging system under different experimental conditions. For 3-D image reconstruction, the gradient-based penalty modified barrier function (PMBF) method with simple bounds constrained truncated Newton with trust region method (CONTN) was used. Targets of 0.5, 0.6, and 1.0 cm3 at depths of 1.4-2.8 cm from the phantom surface were tomographically reconstructed. This work demonstrates the practicality of fluorescence-enhanced tomography in clinically relevant volumes.

Quality analysis of in vivo near-infrared fluorescence and conventional gamma images acquired using a dual-labeled tumor-targeting probe

The cyclic peptide, cyclopentapeptide cyclo(lys-Arg-Gly-Asp-phe) (c(KRGDf)), which is known to target alpha(v)beta3 integrin, is dual-labeled with a radiotracer, (111)indium, for gamma scintigraphy as well as with a near-infrared dye, IRDye800, for continuous-wave (cw) imaging of alpha(v)beta3 positive human M21 melanoma in xenografts. Twenty-four hours after administration of the dual-labeled peptide at a dose equivalent to 90 microCi of (111)In and 5 nmol of near-infrared (NIR) dye, whole-body gamma scintigraphy and cw imaging was conducted. Image acquisition time was 15 min for the gamma scintigraphy images and 800 ms for the optical images acquired using an NIR sensitive intensified charge-coupled device. The results show that while the target-to-background ratio (TBR) of nuclear and optical imaging were similar for surface regions of interest and consistent with the origin of gamma and NIR radiation from a common targeted peptide, the signal-to-noise ratio (SNR) was significantly higher for optical than nuclear imaging. Furthermore, an analysis of SNR versus contrast showed greater sensitivity of optical over nuclear imaging for the subcutaneous tumor targets. While tomographic reconstructions are necessary to probe TBR, SNR, and contrast for interior tissues, this work demonstrates for the first time the direct comparison of molecular optical and planar nuclear imaging for surface and subsurface cancers.

Improved Excitation Light Rejection Enhances Small-Animal Fluorescent Optical Imaging

Small-animal fluorescence-enhanced imaging involves the detection of weak fluorescent signals emanating from nanomolar to picomolar concentrations of exogenous or endogenously produced fluorophore concurrent with the rejection of an overwhelmingly large component of backscattered excitation light. The elimination of the back-reflected excitation light of the collected signal remains a major and often unrecognized challenge for further reducing the noise floor and increasing sensitivity of small-animal fluorescence imaging. Herein, we show that the combination of three-cavity interference and holographic super notch filters with appropriate imaging lenses to collimate light improves rejection of excitation light, enabling more accurate imaging. To assess excitation leakage, the “out-of-band ( S(Λ x))” to “in-band ( S(Λ m)– S(Λ x))” signal ratio from phantom studies and the target-to-background ratio (TBR) from in vivo animal imaging was acquired with and without collimating optics. The addition of collimating optics resulted in a 51% to 75% reduction in the ratio of ( S(Λ x))/( S(Λ m)– S(Λ x)) for the phantom studies and an improvement of TBR from 11% to 31% and of signal-to-noise ratio from 11% to 142% for an integrin-targeting conjugate in human glioma xenografts.

Detection of single and multiple targets in tissue phantoms with fluorescence-enhanced optical imaging: feasibility study

PURPOSE

To evaluate the feasibility of reconstructing single and multiple targets by using fluorescence-enhanced tomography of a breast tissue phantom.

MATERIALS AND METHODS

Frequency-domain fluorescence measurements were performed in cup-shaped tissue phantoms of clinically relevant size (diameter, 10 cm) in which single or multiple 0.5-1.0-cm(3) targets that contained micromolar concentrations of indocyanine green with 1:0 and 100:1 target-to-background (T:B) contrast ratios had been embedded. Rapid acquisition of time-dependent fluorescent light measurements was performed at the phantom surface in response to point illumination of excitation light by using a gain-modulated intensified charge-coupled device detection system. Boundary surface measurements were used to tomographically reconstruct the interior targets located with various experimental conditions.

RESULTS

Single 1.0-cm(3) targets located between 1.43 and 2.82 cm deep from the phantom surface at a T:B contrast ratio of 100:1 and three approximately 0.55-cm(3) targets located about 1.30 cm deep at a T:B contrast ratio of 1:0 were reconstructed with minimal or no artifacts by using boundary surface fluorescence measurements and an approximate extended Kalman filter algorithm.

CONCLUSION

It is feasible to detect single or multiple fluorescent targets in tissue phantoms of clinically relevant size by using fluorescence-enhanced optical tomography.

Comparison of Two Tricarbocyanine-Based Dyes for Fluorescence Optical Imaging

Optical technologies are evolving in many biomedical areas including the biomedical imaging disciplines. Regarding the absorption properties of physiological molecules in living tissue, the optical window ranging from 700 to 900 nm allows to use fluorescent dyes for novel diagnostic solutions. Here we investigate the potential of two different carbocyanine-based dyes fluorescent in the near infrared as contrast agents for in vivo imaging of subcutaneously grown tumours in laboratory animals. The primary aim was to modify the physicochemical properties of the previously synthesized dye SIDAG to investigate the effect on the in vivo imaging properties.

Tomographic fluorescence imaging in tissue phantoms: a novel reconstruction algorithm and imaging geometry

A novel image reconstruction algorithm has been developed and demonstrated for fluorescence-enhanced frequency-domain photon migration (FDPM) tomography from measurements of area illumination with modulated excitation light and area collection of emitted fluorescence light using a gain modulated image-intensified charge-coupled device (ICCD) camera. The image reconstruction problem was formulated as a nonlinear least-squares-type simple bounds constrained optimization problem based upon the penalty/modified barrier function (PMBF) method and the coupled diffusion equations. The simple bounds constraints are included in the objective function of the PMBF method and the gradient-based truncated Newton method with trust region is used to minimize the function for the large-scale problem (39919 unknowns, 2973 measurements). Three-dimensional (3-D) images of fluorescence absorption coefficients were reconstructed using the algorithm from experimental reflectance measurements under conditions of perfect and imperfect distribution of fluorophore within a single target. To our knowledge, this is the first time that targets have been reconstructed in three-dimensions from reflectance measurements with a clinically relevant phantom.

Optical tomographic imaging of small animals

Diffuse optical tomography is emerging as a viable new biomedical imaging modality. Using visible and near-infrared light this technique can probe the absorption and scattering properties of biological tissues. The main applications are currently in brain, breast, limb and joint imaging; however, optical tomographic imaging of small animals is attracting increasing attention. This interest is fuelled by recent advances in the transgenic manipulation of small animals that has led to many models of human disease. In addition, an ever increasing number of optically reactive biochemical markers has become available, which allow diseases to be detected at the molecular level long before macroscopic symptoms appear. The past three years have seen an array of novel technological developments that have led to the first optical tomographic studies of small animals in the areas of cerebral ischemia and cancer.

Diagnostic imaging of breast cancer using fluorescence-enhanced optical tomography: phantom studies

Molecular targeting with exogenous near-infrared excitable fluorescent agents using time-dependent imaging techniques may enable diagnostic imaging of breast cancer and prognostic imaging of sentinel lymph nodes within the breast. However, prior to the administration of unproven contrast agents, phantom studies on clinically relevant volumes are essential to assess the benefits of fluorescence-enhanced optical imaging in humans. Diagnostic 3-D fluorescence-enhanced optical tomography is demonstrated using 0.5 to 1 cm(3) single and multiple targets differentiated from their surroundings by indocyanine green (micromolar) in a breast-shaped phantom (10-cm diameter). Fluorescence measurements of referenced ac intensity and phase shift were acquired in response to point illumination measurement geometry using a homodyned intensified charge-coupled device system modulated at 100 MHz. Bayesian reconstructions show artifact-free 3-D images (3857 unknowns) from 3-D boundary surface measurements (126 to 439). In a reflectance geometry appropriate for prognostic imaging of lymph node involvement, fluorescence measurements were likewise acquired from the surface of a semi-infinite phantom (8x8x8 cm(3)) in response to area illumination (12 cm(2)) by excitation light. Tomographic 3-D reconstructions (24,123 unknowns) were recovered from 2-D boundary surface measurements (3194) using the modified truncated Newton's method. These studies represent the first 3-D tomographic images from physiologically relevant geometries for breast imaging.

Fluorescence-enhanced optical imaging in large tissue volumes using a gain-modulated ICCD camera

A novel image-intensified charge-coupled device (ICCD) imaging system has been developed to perform 3D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. The imager is unique since it (i) employs a large tissue-mimicking phantom, which is shaped and sized to resemble a female breast and part of the extended chest-wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diffusion model predictions are compared to experimental measurements using two different referencing schemes under two different experimental conditions of perfect and imperfect uptake of fluorescent agent into a target. From these experimental measurements, three-dimensional images of fluorescent absorption were reconstructed using a computationally efficient variant of the approximate extended Kalman filter algorithm. The current work represents the first time that 3D fluorescence-enhanced optical tomographic reconstructions have been achieved from experimental measurements of the time-dependent light propagation on a clinically relevant breast-shaped tissue phantom using a gain-modulated ICCD camera.