Hyperspectral, Time-Resolved, Fluorescence Imaging System for Large Sample Sizes: Part I. Development of a High-Energy Line-Illumination Source

To reduce the risk of foodborne illnesses, produce fields are visually surveyed prior to harvest for signs of fecal contamination. To improve the efficacy of surveys, a hyperspectral, line-scan, laser-induced fluorescence imaging system was developed. The goal is to incorporate the imaging system into a field-deployable apparatus to survey produce fields. The system includes a gated intensified camera, a spectral adapter, a 355 nm pulsed laser, and a Powell lens that is used to expand the laser beam into a line-illumination source. Software was developed to facilitate alignment of the Powell lens with the laser beam and the resulting line-illumination profile with the line-imaging field. Comparisons were made of uniformity and efficiency measures for regions within illumination profiles that corresponded to the camera field of view for the Powell lens and previously developed simple and homogenizing expansion optics. Spatial and temporal uniformity measures were similar for the Powell and homogenizing optics, and both were better than for simple optics; however, total efficiency was better for Powell compared to homogenizing optics at 28.5% and 3.0%, respectively. After spectral calibrations, theoretical and measured spectral peaks of five fluorescent standards were identical. Images of apples and spinach artificially contaminated with dilutions of dairy manure demonstrated high contrast. By selecting appropriate gate timing parameters, it was possible to create images in which responses from contamination sites were still evident but responses from normal surfaces were effectively extinguished. These results demonstrate that the system has potential to be used to detect sites of fecal contamination in produce fields. Keywords: Fecal detection, Fluorescence imaging, Food safety, Machine vision, Powell lens.