Laura M. Higgins

Characterization of thin poly(dimethylsiloxane)-based tissue-simulating phantoms with tunable reduced scattering and absorption coefficients at visible and near-infrared wavelengths

Abstract. Optical phantoms are used in the development of various imaging systems. For certain applications, the development of thin phantoms that simulate the physical size and optical properties of tissue is important. Here, we demonstrate a method for producing thin phantom layers with tunable optical properties using poly(dimethylsiloxane) (PDMS) as a substrate material. The thickness of each layer (between 115 and 880  μm) was controlled using a spin coater. The reduced scattering and absorption coefficients were controlled using titanium dioxide and alcohol–soluble nigrosin, respectively. These optical coefficients were quantified at six discrete wavelengths (591, 631, 659, 691, 731, and 851 nm) at varying concentrations of titanium dioxide and nigrosin using spatial frequency domain imaging. From the presented data, we provide lookup tables to determine the appropriate concentrations of scattering and absorbing agents to be used in the design of PDMS-based phantoms with specific optical coefficients. In addition, heterogeneous phantoms mimicking the layered features of certain tissue types may be fabricated from multiple stacked layers, each with custom optical properties. These thin, tunable PDMS optical phantoms can simulate many tissue types and have broad imaging calibration applications in endoscopy, diffuse optical spectroscopic imaging, and optical coherence tomography, etc.

Design and characterization of a handheld multimodal imaging device for the assessment of oral epithelial lesions

Abstract. A compact handpiece combining high resolution fluorescence (HRF) imaging with optical coherence tomography (OCT) was developed to provide real-time assessment of oral lesions. This multimodal imaging device simultaneously captures coregistered en face images with subcellular detail alongside cross-sectional images of tissue microstructure. The HRF imaging acquires a 712×594  μm2 field-of-view at the sample with a spatial resolution of 3.5  μm. The OCT images were acquired to a depth of 1.5 mm with axial and lateral resolutions of 9.3 and 8.0  μm, respectively. HRF and OCT images are simultaneously displayed at 25 fps. The handheld device was used to image a healthy volunteer, demonstrating the potential for in vivo assessment of the epithelial surface for dysplastic and neoplastic changes at the cellular level, while simultaneously evaluating submucosal involvement. We anticipate potential applications in real-time assessment of oral lesions for improved surveillance and surgical guidance.

Snapshot 3D optical coherence tomography system using image mapping spectrometry

A snapshot 3-Dimensional Optical Coherence Tomography system was developed using Image Mapping Spectrometry. This system can give depth information (Z) at different spatial positions (XY) within one camera integration time to potentially reduce motion artifact and enhance throughput. The current (x,y,λ) datacube of (85×356×117) provides a 3D visualization of sample with 400 μm depth and 13.4 μm in transverse resolution. Axial resolution of 16.0 μm can also be achieved in this proof-of-concept system. We present an analysis of the theoretical constraints which will guide development of future systems with increased imaging depth and improved axial and lateral resolutions.

Line-scanning confocal microscopy for high-resolution imaging of upconverting rare-earth-based contrast agents.

Rare-earth (RE) doped nanocomposites emit visible luminescence when illuminated with continuous wave near-infrared light, making them appealing candidates for use as contrast agents in biomedical imaging. However, the emission lifetime of these materials is much longer than the pixel dwell times used in scanning intravital microscopy. To overcome this limitation, we have developed a line-scanning confocal microscope for high-resolution, optically sectioned imaging of samples labeled with RE-based nanomaterials. Instrument performance is quantified using calibrated test objects. NaYF4 : Er,Yb nanocomposites are imaged in vitro, and in ex vivo tissue specimens, with direct comparison to point-scanning confocal microscopy. We demonstrate that the extended pixel dwell time of line-scanning confocal microscopy enables subcellular-level imaging of these nanomaterials while maintaining optical sectioning. The line-scanning approach thus enables microscopic imaging of this emerging class of contrast agents for preclinical studies, with the potential to be adapted for real-time in vivo imaging in the clinic.

Surveillance nanotechnology for multi-organ cancer metastases

The identification and molecular profiling of early metastases remains a major challenge in cancer diagnostics and therapy. Most in vivo imaging methods fail to detect small cancerous lesions, a problem that is compounded by the distinct physical and biological barriers associated with different metastatic niches. Here, we show that intravenously injected rare-earth-doped albumin-encapsulated nanoparticles emitting short-wave infrared light (SWIR) can detect targeted metastatic lesions in vivo, allowing for the longitudinal tracking of multi-organ metastases. In a murine model of human breast cancer, the nanoprobes enabled whole-body SWIR detection of adrenal-gland microlesions and bone lesions that were undetectable via contrast-enhanced magnetic resonance imaging as early as three and five weeks post-inoculation, respectively. Whole-body SWIR imaging of nanoprobes functionalized to differentially target distinct metastatic sites and administered to a biomimetic murine model of human breast cancer resolved multi-organ metastases that showed varied molecular profiles in the lungs, adrenal glands and bones. Real-time surveillance of lesions in multiple organs should facilitate pre- and post-therapy monitoring in preclinical settings.Rare-earth-doped albumin-encapsulated nanoparticles emitting short-wave infrared light enable whole-body real-time tracking of metastatic lesions in multiple organs in mice.

Small animal imaging platform for quantitative assessment of short-wave infrared-emitting contrast agents

We report the design, calibration, and testing of a pre-clinical small animal imaging platform for use with short-wave infrared (SWIR) emitting contrast agents. Unlike materials emitting at visible or near-infrared wavelengths, SWIR-emitting agents require detection systems with sensitivity in the 1-2 μm wavelength region, beyond the range of commercially available small animal imagers. We used a collimated 980 nm laser beam to excite rare-earth-doped NaYF4:Er,Yb nanocomposites, as an example of a SWIR emitting material under development for biomedical imaging applications. This beam was raster scanned across the animal, with fluorescence in the 1550 nm wavelength region detected by an InGaAs area camera. Background adjustment and intensity non-uniformity corrections were applied in software. The final SWIR fluorescence image was overlaid onto a standard white-light image for registration of contrast agent uptake with respect to anatomical features.

Rare-earth doped nanocomposites enable multiscale targeted short-wave infrared imaging of metastatic breast cancer

We are investigating the ability of targeted rare earth (RE) doped nanocomposites to detect and track micrometastatic breast cancer lesions to distant sites in pre-clinical in vivo models. Functionalizing RE nanocomposites with AMD3100 promotes targeting to CXCR4, a recognized marker for highly metastatic disease. Mice were inoculated with SCP-28 (CXCR4 positive) and 4175 (CXCR4 negative) cell lines. Whole animal in vivo SWIR fluorescence imaging was performed after bioluminescence imaging confirmed tumor burden in the lungs. Line-scanning confocal fluorescence microscopy provided high-resolution imaging of RE nanocomposite uptake and native tissue autofluorescence in ex vivo lung specimens. Co-registered optical coherence tomography imaging allowed assessment of tissue microarchitecture. In conclusion, multiscale optical molecular imaging can be performed in pre-clinical models of metastatic breast cancer, using targeted RE-doped nanocomposites.

Early detection and longitudinal imaging of cancer micrometastases using biofunctionalized rare-earth albumin nanocomposites

Success of personalized medicine in cancer therapy depends on the ability to identify and molecularly phenotype tumors. Current clinical imaging techniques cannot be integrated with precision molecular medicine at the level of single cells or microlesions due to limited resolution. In this work we use molecularly targeted infrared emitting optical probes to identify and characterize metastatic microlesions prior to their detection with clinically relevant imaging modalities. These contrast agents form the basis of an in vivo optical imaging system capable of resolving internal microlesions, filling a critical unmet need in cancer imaging.

High-Resolution Imaging of Molecularly Targeted Rare-Earth Based Nanocomposites

We describe the development and testing of a line-scanning confocal microscope and integrated confocal / optical coherence tomography system for imaging biological cells and tissues labeled with molecularly-targeted rare-earth-doped nanocomposites.

High-resolution, 3-D imaging of lumpectomy tissue using optical coherence tomography

Pathology image guidance may enhance the effectiveness of adjuvant radiation treatment by identifying high-risk regions that would benefit from escalated radiation dose and low-risk regions at which little to no radiation dose is necessary. We present 3-D high-resolution optical coherence tomography (OCT) images of breast lumpectomy specimens. Formalin-fixed, paraffin-embedded lumpectomy tissue specimens and mouse breast glands were imaged with OCT in the form of multiple series of 2-D axial depth scans. The computationally-combined series of 2D images forms a reconstructed volume. Ongoing studies will establish whether these images can capture features comparable to the corresponding pathology for localized adjuvant radiation treatment planning.