The amount of light backscattered from neural tissues changes as a function of activation and is the basis of intrinsic optical signal (IOS). Typically IOS is observed by looking at darkfield scatter with a CCD camera. The retina is a calculating portion of the central nervous grey matter with an optical quality window, and is likewise easily stimulated optically. Therefore the retina makes a natural model for observing neural interactions with optical tools. Optical coherence tomography (OCT) is an imaging modality that provides depth resolved maps of the amount of light backscattered from tissue that has wide clinical use for observing structural defects associated with ophthalmic disease. It is therefore also natural to use OCT as means to observe intrinsic optical signal in the retina. Indeed, OCT has recently been used to observe an increase in backscatter at the level of the outer photoreceptor segment after bleaching light stimulation in an excised rabbit retina. We are currently attempting to translate this result towards a diagnostic technique for photoreceptor dysfunction in human patients. Currently patient motion and physiological noise present barriers that must be overcome with increases in technological and experimental sophistication. This proceeding reviews current understanding of retinal intrinsic optical signal and discusses its measurement challenge.
Optical coherence tomography, optical coherence microscopy, reflectance confocal microscopy, and darkfield
microscopy all derive contrast from the intensity of endogenous tissue scatter. We have imaged excised mouse colon
tissue with these complimentary technologies to make conclusions about structural origins of scatter in the mouse
colonic mucosa observed with endoscopic OCT. We find hyperintense scattering both from the cytoplasm of epithelial
cells and from the boundary between epithelia and the lamina propria. We find almost no scatter from the portion of
epithelial cells containing the nucleus. These observations substantiate explanations for the appearance of colonic crypts
and the luminal surface.
Purpose: Optical coherence tomography (OCT) is a minimally invasive, depth-resolved imaging tool that can be
commissioned for small diameter endoscopic applications for imaging mouse models of colorectal cancer. In this study,
we utilized ultrahigh resolution OCT (UHR OCT) to serially image the lower colon of azoxymethane (AOM) treated A/J
mouse models of CRC, monitor the progression of neoplastic transformations, and determine if OCT is capable of
identifying early disease.
Experimental Design: Thirteen AOM treated A/J and two control A/J mice were surveyed at four timepoints (8, 14, 22,
and 26 weeks post AOM treatment) using a prototype 2.0 mm diameter UHR OCT endoscope-based system that
achieved resolutions of 3.2 um axial and 4.4 um lateral. Histological samples were obtained at the final imaging
timepoint serving as the gold standard.
Results: Gross and histological assessment of the excised colonic tissue revealed at least one tumor in all 13 AOM
treated mice, with most mice developing multiple tumors. In the corresponding OCT images, a progression from healthy
thin mucosa to adenoma appearing as large, structurally disorganized masses was visualized over the imaging time
points correlating to the locations of the grossly visualized tumors.
Conclusions: This study indicates that UHR OCT enables accurate identification of disease and non-destructive
visualization of CRC progression in the lower colon of mice.
Depth dependent broadening of the axial point spread function due to dispersion in the imaged media, and algorithms for postprocess correction have been previously described for both time domain and frequency domain optical coherence tomography. Homogeneous media dispersion artifacts disappear when frequency domain samples are uniformly spaced in circular wavenumber, as opposed to uniform sampling in optical frequency. In this paper, we explicate the source of this point spread broadening and simulate its magnitude in aqueous media. We conclude with a suggestion for interferometric k-triggering which accounts for dispersion in the media.
Endoscopic ultrahigh-resolution optical coherence tomography (OCT) enables collection of minimally invasive cross-sectional images in vivo, which may be used to facilitate rapid development of reliable mouse models of colon disease as well as assess chemopreventive and therapeutic agents. The small physical scale of mouse colon makes light penetration less problematic than in other tissues and high resolution acutely necessary. In our 2-mm diameter endoscopic time domain OCT system, isotropic ultrahigh-resolution is supported by a center wavelength of 800 nm and full-width-at-half-maximum bandwidth of 150 nm (mode-locked titanium:sapphire laser) combined with 1:1 conjugate imaging of a small core fiber. A pair of KZFSN5/SFPL53 doublets provides excellent color correction to support wide bandwidth throughout the imaging depth. A slight deviation from normal beam exit angle suppresses collection of the strong back reflection at the exit window surface. Our system achieves axial resolution of 3.2 µm in air and 4.4-µm lateral spot diameter with 101-dB sensitivity. Microscopic features too small to see in mouse tissue with conventional resolution systems, including colonic crypts, are clearly resolved. Resolution near the cellular level is potentially capable of identifying abnormal crypt formation and dysplastic cellular organization.
Mouse models are increasingly important for studying human GI pathology. OCT provides minimally
invasive, cross-sectional images that indicate the thickness and scattering density of underlying tissue. We have
developed endoscopic ultrahigh resolution OCT (UHR-OCT) to imaging mouse colon in vivo. The reduced scale of the
mouse colon makes tissue light penetration much less problematic, and high resolution acutely necessary. Higher lateral
resolution requires a departure from the traditional cemented GRIN lens design. We support the need for better
chromatic aberration than can be achieved by a GRIN lens using commercial raytracing software. We have designed and
built a 2mm diameter endoscopic UHR-OCT system achromatized for 770-1020nm for use with a Titanium:sapphire
laser with 260 nm bandwidth at full-width-half-maximum centered at 800 nm while achieving a 4.4um lateral spot
dimension at focus. A pair of KZFSN5/SFPL53 doublets provides excellent primary and secondary color correction to
maintain wide bandwidth through the imaging depth. A slight deviation from normal beam exit angle suppresses
collection of the strong back reflection at the exit window surface. The novel design endoscope was built and
characterized for through focus bandwidth, axial resolution, signal to noise, and lateral spot dimension. Performance is
demonstrated on in vivo mouse colon. Ultrahigh-resolution images of mouse tissue enable the visualization of
microscopic features, including crypts that have previously been observed with standard resolution OCT in humans but
were too small to see in mouse tissue. Resolution near the cellular level is potentially capable of identifying abnormal
crypt formation and dysplastic cellular organization.
Mouse models are increasingly important for studying human GI pathology. OCT provides minimally invasive, cross-sectional images that indicate the thickness and scattering density of underlying tissue. We have developed endoscopic ultrahigh resolution OCT (UHR-OCT) for the purpose of in vivo imaging in mouse colon. The reduced scale of the mouse colon makes tissue light penetration much less problematic, and high resolution acutely necessary. Higher lateral resolution requires a departure from the traditional cemented GRIN lens design. We support the need for better chromatic aberration than can be achieved by a GRIN lens using commercial raytracing software. We have designed and built a 2mm diameter endoscopic UHR-OCT system achromatized for 770-1020nm for use with a Titanium:sapphire laser with 260 nm bandwidth at full-width-half-maximum centered at 800 nm while achieving a 4.4um lateral spot dimension at focus. A pair of KZFSN5/SFPL53 doublets provides excellent primary and secondary color correction to maintain wide bandwidth through the imaging depth. A slight deviation from normal beam exit angle suppresses collection of the strong back reflection at the exit window surface. The novel design endoscope was built and characterized for through focus bandwidth, axial resolution, signal to noise, and lateral spot dimension. Performance is demonstrated on a variety of ex vivo tissues and in situ mouse colon. Ultrahigh-resolution images of mouse tissue enable the visualization of microscopic features, including crypts that have previously been observed with standard resolution OCT in humans but were too small to see in mouse tissue. Resolution near the cellular level is potentially capable of identifying abnormal crypt formation and dysplastic cellular organization.
Optical Coherence Tomography (OCT) and Laser Induced Fluorescence Spectroscopy (LIF) have separately been found to have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models of human disease is unknown. We combine the two modalities to survey the GI tract of a variety of mouse strains and sample dysplasias and inflammatory bowel disease (IBD) of the small and large intestine. Segments of duodenum and lower colon 2.5 cm in length and the entire esophagus from 10 mice each of two colon cancer models (ApcMin and AOM treated A/J) and two IBD models (Il-2 and Il-10) and 5 mice each of their respective controls were excised. OCT images and LIF spectra were obtained simultaneously from each tissue sample within 1 hour of extraction. Histology was used to classify tissue regions as normal, Peyer’s patch, dysplasia, adenoma, or IBD. Features in corresponding regions of OCT images were analyzed. Spectra from each of these categories were averaged and compared via the student's t-test. Features in OCT images correlated to histology in both normal and diseased tissue samples. In the diseased samples, OCT was able to identify early stages of mild colitis and dysplasia. In the sample of IBD, the LIF spectra displayed unique peaks at 635nm and 670nm, which were attributed to increased porphyrin production in the proliferating bacteria of the disease. These peaks have the potential to act as a diagnostic for IBD. OCT and LIF appear to be useful and complementary modalities for imaging mouse models.
We develop a dual-modality device that combines the anatomical imaging capabilities of optical coherence tomography (OCT) with the functional capabilities of laser-induced fluorescence (LIF) spectroscopy. OCT provides cross-sectional images of tissue structure to a depth of up to 2 mm with approximately 10-µm resolution. LIF spectroscopy provides histochemical information in the form of emission spectra from a given tissue location. The OCT subsystem utilizes a superluminescent diode with a center wavelength of 1300 nm, whereas a helium cadmium laser provides the LIF excitation source at wavelengths of 325 and 442 nm. Preliminary data are obtained on eight postmortem aorta samples, each 10 mm in length. OCT images and LIF spectra give complementary information from normal and atherosclerotic portions of aorta wall. OCT images show structures such as intima, media, internal elastic lamina, and fibrotic regions. Emission spectra ratios of 520/490 (325-nm excitation) and 595/635 (442-nm excitation) could be used to identify normal and plaque regions with 97 and 91% correct classification rates, respectively. With miniaturization of the delivery probe and improvements in system speed, this dual-modality device could provide a valuable tool for identification and characterization of atherosclerotic plaques.
An endoscopic system that provides simultaneous cross-sectional imaging and fluorescence spectroscopy is described. The first application of this device was the investigation of mouse colon cancer in vivo. This system combined optical coherence tomography (OCT), which provided high-resolution cross-sectional structural information in the form of a two-dimensional image, and laser induced fluorescence (LIF), which yielded histochemical information about the tissue. The design challenge and solution of packaging these two systems with widely different optical requirements are described in detail. The illumination geometry of the endoscope was similar to earlier published OCT and LIF catheter endoscope designs. However, several unique design challenges encountered in combining these two systems have been addressed. The use of a rodprism to reduce the asymmetry in the OCT beam caused by a cylindrical window is presented. Materials selection for use with wavelengths from 325nm - 1310nm presented a challenge usually avoided in OCT endoscopes. Preliminary mouse colon data collected with this endoscopic device is compared with previous experiments performed by researchers in our lab working with an earlier bulk-optic, combined OCT-LIF system.
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