The Chrisp Compact Visible-SWIR Spectrometer (CCVIS) was developed by MIT Lincoln Laboratory as a high performance, low Size-Weight-Power (SWAP) slit-based hyperspectral sensor that provides comparable performance to current fielded units but more than an order smaller in packaging volume. The design takes advantage of a flat, immersed grating and a color-corrected catadioptric layout to provide >25mm slit length operating from 380-2500nm. We show results from our efforts to design and build an environmentally robust variant which undergoing Technology Readiness Level 6 testing for future spaceflight.
We compare the optical performance, alignment sensitivity, and thermal stability of a Non-Uniform Rational B-Spline (NURBS) freeform telescope design to two more conventional design forms with the goal of facilitating acceptance of this new optical surface for aerospace applications. We present the designs of three three-mirror anastigmat (TMA) wide field (4°) telescopes with identical first order optical design parameters. These TMAs consist of a conventional design using off-axis aspheric mirrors, a freeform design using off-axis Zernike polynomial surfaces, and a freeform design using NURBS surfaces. Of the three, the NURBS design gives the best image quality and lowest geometrical design residual. The three designs have similar misalignment sensitivities and sensitivity to thermal soaks, countering a common misconception that freeform designs are more sensitive to misalignment than conventional designs.
Globally, colorectal cancer was the second leading cause of cancer death in 2020. Research suggests that collagen, a major structural protein, plays a pivotal role in cancer development and metastasis, and by extension, subject prognosis. Collagen surrounding tumor cells undergoes structural changes that can be quantitatively studied with second harmonic generation (SHG), a subset of multiphoton microscopy (MPM). MPM as an imaging modality is difficult to implement in an endoscope because of the complex and expensive miniaturized scanning components required. Endoscope complexity can be greatly reduced by implementing a simpler, non-synchronized scanning mechanism. This study investigates whether non-imaging, randomly sampled SHG intensity measurements are sufficient to distinguish normal tissue from tumor/tumor-adjacent tissue. Unstained tumor, normal, and adjacent formalin-fixed, paraffin-embedded thin sections from 12 colorectal cancer subjects were imaged using a multiphoton microscope with 850nm excitation and 400-430nm emission band, constant power, and consisting of 1024x1024 pixels over 425x425μm. SHG signal from collagen fibers was isolated by grayscale thresholding, and the grayscale mean of the thresholded image was calculated. Then, random supra-threshold pixels in the image were selected. The mean SHG signal from normal samples was significantly greater than adjacent samples (p = 0.014) and cancer samples (p = 0.007). For both tumor and adjacent comparisons to normal tissue, p value becomes reliable after randomly sampling only 1000 pixels. This study suggests that reliable diagnostic information may be obtained through simple non-imaging, random-sampling SHG intensity measurements. A simple endoscope with this capability could help identify suspicious masses or optimum surgical margins.
Multimodal imaging is an advantageous method to increase the accuracy of disease classification. As an example, we and others have shown that optical coherence tomography images and fluorescence spectroscopy contain complementary information that can increase the sensitivity and specificity for cancer detection. A common challenge in multimodal imaging is image co-registration. The different images are often taken with separate imaging setups, making it challenging to precisely image the same tissue area or co-register the images computationally. To solve this problem, we have developed a co-registered multimodal imaging system that images the same tissue location with reflectance, multi-photon, and optical coherence microscopy. The co-registration mechanism is a dual-clad fiber that integrates with a scanning microscope or scanning endoscope, collecting all three signals using the same optical path. In the current implementation, optical coherence tomography utilizes a 1300 nm super luminescent diode, multi-photon signals are excited by a custom femtosecond 1400 nm fiber laser producing two- and three-photon signals in the 460-900 nm band, and reflectance imaging operates at 561 nm. The system separates the different signals using fiber wavelength division multiplexers, a dual-clad fiber coupler, and dichroic mirrors to deliver the different signals to the corresponding detector. This wavelength selection enables the system to work passively, meaning that there is no need for devices such as filter wheels. Using the scanning microscope configuration, we have obtained multimodal images of ex-vivo ovine ovary tissue.
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