In September 2016 I started work as a postdoctoral researcher in Darren Roblyer's Biomedical Optical Technologies lab. My work here is focused on developing new techniques and improving current diffuse optical imaging techniques to address clinical needs in cancer monitoring. I am currently working on projects related to high-speed digital Diffuse Optical Spectroscopic Imaging (dDOSI) as well as Spatial Frequency Domain Imaging (SFDI).
OpenSFDI: an open source guide for building an SFDI system
Building imaging systems is hard. Many publications do a great job describing their imaging systems, but it's less common to share the "tricks of the trade" that researchers learn along the way. I developed an open source guide to building your own spatial frequency domain imaging system called openSFDI. The website guides you through building an SFDI system step-by-step with pictures. It includes software and a guide to data processing developed by Rolf Saager. Hopefully by making SFDI more accessible it will become more popular and widely used. This work was recently published in the Journal of Biomedical Optics.
Hypotrochoidal scanning for depth resolved DOS images
Diffuse optics is nice because it is safe. But the downside is the images are blurry which makes them more difficult to interpret than X-rays or CT scans. Here, I've developed a novel scanning system that rotates a source fiber and a detector fiber in a pattern called a hypotrochoid. I was inspired by the "teacup" rides at amusement parks which carries riders around multiple hypotrochoids.
The plot on the right shows that the source detector separation varies smoothly over a wide range. At short source/detector separations the surface of the tissue is probed, while at longer source/detector separations deeper layers are interrogated. Using the high speed acquisition along with this scanning paradigm we are able to obtain pseudo-depth-resolved diffuse optical images that are similar to ultrasound. Unlike, ultrasound, however, these images carry information about the metabolism of the tissue which would be useful for monitoring breast cancer and in neurologic applications. This work has been accepted for publication at Optics Letters, but has not yet been published. (top)
Spatial Frequency Domain Imaging is a widefield imaging technique to measure tissue absorption and scattering. These images can be used to determine absolute concentrations of tissue chromophores such as oxy-hemoglobin, deoxy-hemoglobin, lipids, and water. My work focuses on extending the spectral richness of SFDI to increase the accuracy of chromophore extractions. The additional information may be useful for non-invasively monitoring the response of tumors to chemotherapy or for the needle-free measurement of lipid species in the blood.
By temporally modulating different wavelengths of light while collecting a video of the sample the individual wavelengths can be separated using a Fourier transform of each pixel of the image. This technique allows rapid acquisition of multiple wavelengths and, importantly, renders the SFDI images insensitive to the ambient light. Automatic ambient light rejection makes Temporally Modulated (TM) SFDI suitable for use in operating rooms and hospitals where light levels may be constantly changing. This work was published in the Journal of Biomedical Optics in 2017. (top)
My PhD thesis research focused on using the interaction between light and silk fibroin for applications in biomedicine. Silk is a natural material that can be implanted in the body without evoking an immune response. It is also transparent and can conform to nano-scale structures, making it a useful optical material. Finally, silk can stabilize fragile substances such as DNA and enzymes. This combination of properties make silk fascinating to work with.
I have been investigating the possibility of using silk as a platform for ablative 3D micromachining. My aim is to take advantage of the large 3-photon cross-section of silk to ablate small volumes of material without use of an exogenous photoinitiator. This work explores the potential to create 3D structures within a silk hydrogel and the investigation of how cells respond to them in vitro and in vivo. This technique could potentially be applied to pre-vascularization of tissue constructs for use in artificial organs. This work was published in PNAS in September, 2015. (top)
Simulating multiphoton absorption
The utility of multiphoton micromachining in silk to guide cells is described above. In order to optimize material removal I've developed an R program to rapidly simulate the energy absorbed due to multiphoton absorption in a material. The simulation requires knowledge of the beam waist, pulse energy, temporal pulse width, pulse repetition frequency, and multiphoton absorption cross-section of the material under investigation. From this information, a map of energy absorption can be generated. Using this map we were able to determine that the energy needed to denature a single silk molecule is around 60 pJ by comparing the simulated void volumes to measured void volumes. The accuracy of this model implies that multiphoton micromachining in silk using infrared light is purely due to 3-photon absorption, and does not rely on the diffusion of heat or other photoproducts to produce the void. (top)
Biocompatible silk waveguides
I have been working on creating an all silk optical fiber suitable for implantation. Encapsulating a silk film inside a silk gel results in a core/cladding structure suitable for light guidance. The film can be formed around a glass fiber taper for convenient coupling with conventional optical systems. Biocompatible waveguides have tremendous potential for sensing and imaging deep within the body. This work was published in Biomedical Optics Express in 2015. (top)
Photocrosslinking of silk with riboflavin
My search for a biocompatible photocrosslinker that would work with silk fibroin eventually led to this project in which riboflavin is used in conjunction with blue or UV light to transform the liquid silk into a gel. This material could possibly be used in opthalmology. (top)
Multiphoton absorption of silk fibroin
I used the Z-scan technique to determine the multi-photon absorption of silk fibroin to 810 nm light. Through this simple technique (illustrated above) we found that the multiphoton absorption in silk is much larger than its amino acid composition would suggest and that the tryptophan residues of the protein are primarily responsible for the observed absorption. This work was published in late 2013. (top)