Jessica A. Carr

Next-generation in vivo optical imaging with short-wave infrared quantum dots

For in vivo imaging, the short-wavelength infrared region (SWIR; 1000–2000 nm) provides several advantages over the visible and near-infrared regions: general lack of autofluorescence, low light absorption by blood and tissue, and reduced scattering. However, the lack of versatile and functional SWIR emitters has prevented the general adoption of SWIR imaging by the biomedical research community. Here, we introduce a class of high-quality SWIR-emissive indium-arsenide-based quantum dots (QDs) that are readily modifiable for various functional imaging applications, and that exhibit narrow and size-tunable emission and a dramatically higher emission quantum yield than previously described SWIR probes. To demonstrate the unprecedented combination of deep penetration, high spatial resolution, multicolor imaging and fast-acquisition-speed afforded by the SWIR QDs, we quantified, in mice, the metabolic turnover rates of lipoproteins in several organs simultaneously and in real time as well as heartbeat and breathing rates in awake and unrestrained animals, and generated detailed three-dimensional quantitative flow maps of the mouse brain vasculature.

Continuous injection synthesis of indium arsenide quantum dots emissive in the short-wavelength infrared

With the emergence of applications based on short-wavelength infrared light, indium arsenide quantum dots are promising candidates to address existing shortcomings of other infrared-emissive nanomaterials. However, III–V quantum dots have historically struggled to match the high-quality optical properties of II–VI quantum dots. Here we present an extensive investigation of the kinetics that govern indium arsenide nanocrystal growth. Based on these insights, we design a synthesis of large indium arsenide quantum dots with narrow emission linewidths. We further synthesize indium arsenide-based core-shell-shell nanocrystals with quantum yields up to 82% and improved photo- and long-term storage stability. We then demonstrate non-invasive through-skull fluorescence imaging of the brain vasculature of murine models, and show that our probes exhibit 2–3 orders of magnitude higher quantum yields than commonly employed infrared emitters across the entire infrared camera sensitivity range. We anticipate that these probes will not only enable new biomedical imaging applications, but also improved infrared nanocrystal-LEDs and photon-upconversion technology.

Shortwave infrared fluorescence imaging with the clinically approved near-infrared dye indocyanine green

Significance Imaging in the shortwave IR (SWIR) spectral window allows the observation of processes deep within living animals. Recent studies have shown that SWIR imaging enables unprecedented imaging opportunities, including contact-free monitoring of vital signs, generation of microvasculature blood flow maps, real-time metabolic imaging, and molecularly targeted imaging. Yet, whereas bright SWIR fluorophores have been developed for preclinical research settings, applications in the clinic have been held back by the conventional belief that no clinically approved fluorophore is available. Here, we show that indocyanine green, a clinically approved near-IR dye, exhibits a remarkable amount of SWIR emission, which enables state-of-the-art SWIR imaging with direct translation potential into clinical settings, and even outperforms other commercially available SWIR emitters. Fluorescence imaging is a method of real-time molecular tracking in vivo that has enabled many clinical technologies. Imaging in the shortwave IR (SWIR; 1,000–2,000 nm) promises higher contrast, sensitivity, and penetration depths compared with conventional visible and near-IR (NIR) fluorescence imaging. However, adoption of SWIR imaging in clinical settings has been limited, partially due to the absence of US Food and Drug Administration (FDA)-approved fluorophores with peak emission in the SWIR. Here, we show that commercially available NIR dyes, including the FDA-approved contrast agent indocyanine green (ICG), exhibit optical properties suitable for in vivo SWIR fluorescence imaging. Even though their emission spectra peak in the NIR, these dyes outperform commercial SWIR fluorophores and can be imaged in the SWIR, even beyond 1,500 nm. We show real-time fluorescence imaging using ICG at clinically relevant doses, including intravital microscopy, noninvasive imaging in blood and lymph vessels, and imaging of hepatobiliary clearance, and show increased contrast compared with NIR fluorescence imaging. Furthermore, we show tumor-targeted SWIR imaging with IRDye 800CW-labeled trastuzumab, an NIR dye being tested in multiple clinical trials. Our findings suggest that high-contrast SWIR fluorescence imaging can be implemented alongside existing imaging modalities by switching the detection of conventional NIR fluorescence systems from silicon-based NIR cameras to emerging indium gallium arsenide-based SWIR cameras. Using ICG in particular opens the possibility of translating SWIR fluorescence imaging to human clinical applications. Indeed, our findings suggest that emerging SWIR-fluorescent in vivo contrast agents should be benchmarked against the SWIR emission of ICG in blood.

Using the shortwave infrared to image middle ear pathologies

Significance Imaging with shortwave infrared (SWIR) light has great potential for visualizing biological structures previously undetectable with visible light. To demonstrate the clinical potential of SWIR imaging, we developed a medical otoscope sensitive to SWIR light. We show that the unique transmission of SWIR light through tissue improves resolution of anatomical structures lying behind thin tissue membranes like the ear drum. We therefore significantly improve imaging of underlying middle ear anatomy. SWIR imaging also allows identification of disease characterized by fluid accumulation, as in the diagnosis of otitis media. With successful diagnosis of otitis media estimated at 51% for US pediatricians, objectifying this diagnosis could curb the antibiotic resistance associated with an estimated 2 million overdiagnoses each year. Visualizing structures deep inside opaque biological tissues is one of the central challenges in biomedical imaging. Optical imaging with visible light provides high resolution and sensitivity; however, scattering and absorption of light by tissue limits the imaging depth to superficial features. Imaging with shortwave infrared light (SWIR, 1–2 μm) shares many advantages of visible imaging, but light scattering in tissue is reduced, providing sufficient optical penetration depth to noninvasively interrogate subsurface tissue features. However, the clinical potential of this approach has been largely unexplored because suitable detectors, until recently, have been either unavailable or cost prohibitive. Here, taking advantage of newly available detector technology, we demonstrate the potential of SWIR light to improve diagnostics through the development of a medical otoscope for determining middle ear pathologies. We show that SWIR otoscopy has the potential to provide valuable diagnostic information complementary to that provided by visible pneumotoscopy. We show that in healthy adult human ears, deeper tissue penetration of SWIR light allows better visualization of middle ear structures through the tympanic membrane, including the ossicular chain, promontory, round window niche, and chorda tympani. In addition, we investigate the potential for detection of middle ear fluid, which has significant implications for diagnosing otitis media, the overdiagnosis of which is a primary factor in increased antibiotic resistance. Middle ear fluid shows strong light absorption between 1,400 and 1,550 nm, enabling straightforward fluid detection in a model using the SWIR otoscope. Moreover, our device is easily translatable to the clinic, as the ergonomics, visual output, and operation are similar to a conventional otoscope.

Packing resonant hexagons in fullerenes

A fullerene graph G is a plane cubic graph such that every face is bounded by either a hexagon or a pentagon. A set H of disjoint hexagons of G is a resonant set (or sextet pattern) if G-V(H) has a perfect matching. A resonant set is a forcing set if G-V(H) has a unique perfect matching. The size of a maximum resonant set is called the Clar number of G. In this paper, we show the Clar number of fullerene graphs with a non-trivial cyclic 5-edge-cut is (n-20)/10. Combining a previous result obtained in Kardos et al. (2009), it is proved in this paper that a fullerene has the Clar number at least (n-380)/61. For leapfrog fullerenes, we show that the Clar number is at least n/6-n/5. Further, it is shown that the minimum forcing resonant set has at least two hexagons and the bound is tight.

Absorption by water increases fluorescence image contrast of biological tissue in the shortwave infrared

Significance Shortwave infrared (SWIR) fluorescence imaging is a tool for visualizing biological processes deep within tissue or living animals. Our study shows that the contrast in a SWIR fluorescence image is primarily mediated by the absorptivity of the tissue, and can therefore be tuned through deliberate selection of imaging wavelength. We show, for example, that, in 3D tissue phantoms and in brain vasculature in vivo in mice, imaging at SWIR wavelengths of the highest water absorptivity results in the greatest fluorescence contrast. We further demonstrate, in microscopy of ex vivo mouse liver tissue, that imaging at wavelengths of high tissue absorptivity can also increase imaging penetration depth, and use a theoretical contrast model to explain this effect. Recent technology developments have expanded the wavelength window for biological fluorescence imaging into the shortwave infrared. We show here a mechanistic understanding of how drastic changes in fluorescence imaging contrast can arise from slight changes of imaging wavelength in the shortwave infrared. We demonstrate, in 3D tissue phantoms and in vivo in mice, that light absorption by water within biological tissue increases image contrast due to attenuation of background and highly scattered light. Wavelengths of strong tissue absorption have conventionally been avoided in fluorescence imaging to maximize photon penetration depth and photon collection, yet we demonstrate that imaging at the peak absorbance of water (near 1,450 nm) results in the highest image contrast in the shortwave infrared. Furthermore, we show, through microscopy of highly labeled ex vivo biological tissue, that the contrast improvement from water absorption enables resolution of deeper structures, resulting in a higher imaging penetration depth. We then illustrate these findings in a theoretical model. Our results suggest that the wavelength-dependent absorptivity of water is the dominant optical property contributing to image contrast, and is therefore crucial for determining the optimal imaging window in the infrared.

Initial findings of shortwave infrared otoscopy in a pediatric population

OBJECTIVE To evaluate the feasibility of Shortwave infrared (SWIR) otoscopy in a pediatric population and establish differences with visible otoscopy. METHODS Pediatric patients 3 years of age and older seen in the otolaryngology clinic with an audiogram and tympanogram obtained within a week of the visit were recruited for video otoscopy using visible light otoscopy and SWIR otoscopy. Videos were rated by two otolaryngologists based on ability to identify the promontory, ability to identify the ossicular chain and presence or absence of middle ear fluid. RESULTS A total of 74 video recordings of ears were obtained in 20 patients. We obtained interpretable images in 63/74 (85.1%) ears. There was no statistical significance between ability to perform SWIR otoscopy versus white light video otoscopy as indicated by a p-value of 0.376. There was high inter-rater agreement for identification of both the promontory and the ossicular chain with Kappa values of 0.81 and 0.92 respectively. There was statistical significance between SWIR otoscopy and visible otoscopy in the ability to image the promontory (p = 0.012) and the ossicular chain (p = 0.010). Increased contrast of middle ear fluid was seen in SWIR otoscopy when compared to visible otoscopy. CONCLUSION SWIR otoscopy is feasible in a pediatric population and could offer some advantages over visible light otoscopy such as better visualization of the middle ear structures through the tympanic membrane and increased contrast for middle ear effusions.

A short-wave infrared otoscope for middle ear disease diagnostics (Conference Presentation)

Otitis media, a range of inflammatory conditions of the middle ear, is the second most common illness diagnosed in children. However, the diagnosis can be challenging, particularly in pediatric patients. Otitis media is commonly over-diagnosed and over-treated and has been identified as one of the primary factors in increased antibiotic resistance. We describe the development of a short-wave infrared (SWIR) otoscope for objective middle ear effusion diagnosis. The SWIR otoscope can unambiguously detect the presence of middle ear fluid based on its strong light absorption in the SWIR. This absorption causes a stark, visual contrast between the presence and absence of fluid behind the tympanic membrane. Additionally, when there is no middle ear fluid, the deeper tissue penetration of SWIR light allows the SWIR otoscope to better visualize middle ear anatomy through the tympanic membrane than is possible with visible light. We demonstrate that in healthy, adult human ears, SWIR otoscopy can image a range of middle ear anatomy, including landmarks of the entire ossicular chain, the promontory, the round window niche, and the chorda tympani. We suggest that SWIR otoscopy can provide valuable diagnostic information complementary to that provided by visible pneumotoscopy in the diagnosis of middle ear effusions, otitis media, and other maladies of the middle ear.