SignificanceAn unmet need is recognized for early detection and diagnosis of neurological diseases. Many psychological markers emerge years after disease onset. Mitochondrial dysfunction and corresponding neurodegeneration occur before onset of large-scale cell and tissue pathology. Early detection of subcellular morphology changes could serve as a beacon for early detection of neurological diseases. This study is on bacterial colonies, Bacillus subtilis, which are similar in size to mitochondria.AimThis study investigates whether morphological changes can be detected in Bacillus subtilis using scattering angle resolved optical coherence tomography (SAR-OCT).ApproachThe SAR-OCT was applied to detect scattering angle distribution changes in Bacillus subtilis. The rod-to-coccus shape transition of the bacteria was imaged, and the backscattering angle was analyzed by recording the distribution of the ratio of low- to medium angle scattering (L/M ratio). Bacillus orientation at different locations in colonies was analytically modeled and compared with SAR-OCT results.ResultsSignificant differences in the distribution of backscattering angle were observed in Bacillus subtilis transitioning from rod-to-coccus shapes. In Bacillus subtilis, the C-parameter of the Burr distribution of the SAR-OCT-derived L/M ratio was significantly smaller in coccus compared with rod-shaped bacteria. SAR-OCT-derived L/M ratio varied with bacterial position in the colony and is consistent with predicted orientations from previous studies.ConclusionsStudy results support the potential of utilizing SAR-OCT to detect bacterial morphological changes.
Optical coherence tomography (OCT) retinal imaging contributes to understanding central nervous system (CNS)
diseases because the eye is an anatomical “window to the brain” with direct optical access to nonmylenated retinal
ganglion cells. However, many CNS diseases are associated with neuronal changes beyond the resolution of standard
OCT retinal imaging systems. Though studies have shown the utility of scattering angle resolved (SAR) OCT for particle
sizing and detecting disease states ex vivo, a compact SAR-OCT system for in vivo rodent retinal imaging has not
previously been reported. We report a fiber-based SAR-OCT system (swept source at 1310 nm ± 65 nm, 100 kHz scan
rate) for mouse retinal imaging with a partial glass window (center aperture) for angular discrimination of backscattered
light. This design incorporates a dual-axis MEMS mirror conjugate to the ocular pupil plane and a high collection
efficiency objective. A muring retina is imaged during euthanasia, and the proposed SAR-index is examined versus time.
Results show a positive correlation between the SAR-index and the sub-cellular hypoxic response of neurons to
isoflurane overdose during euthanasia. The proposed SAR-OCT design and image process technique offer a contrast
mechanism able to detect sub-resolution neuronal changes for murine retinal imaging.
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