D3496: X-ray phase-contrast imaging for larvae-in-fruit infestation inspections

This research is a Stanford-USDA APHIS collaboration on using tri-signature X-ray phase-contrast imaging (X-PCI) for fruit infestation inspections. Currently, imported fruits are mostly manually dissected for labor-intense inspection. Traditional attenuation-based X-ray imaging perceives no differences between high-water-content insects and high-water-content fruits, which makes it impractical for plant inspection. A novel inspection tool, tri-signature X-PCI has two extra orthogonal imaging channels—phase-contrast imaging and dark-field imaging, in addition to attenuation-based imaging. Phase-contrast imaging displays diffraction-based material properties, providing a 1000x more sensitive measuring tool than attenuation-based imaging. Dark-field imaging from small-angle X-ray scattering emphasizes texture of tiny objects such as digestive systems of insects.



Many insects and their host fruits are of high water content (70 – 96%). Our preliminary tests focused on whether water can make insects invisible in X-rays. Our results showed that as soon as we put pupae of spotted wing drosophila in water, they are invisible in the traditional attenuation-based X-ray imaging. However, the phase-contrast and dark-field images unveiled the pupae "hidden" in water. The results encouraged us to pursue a new pathway for plant infestation inspections. We continue to investigate whether various kinds and stages of insects can be detectable in water and in fruits using tri-signature X-ray phase-contrast imaging. Using micro phase-contrast computed tomography, we are quantitively measuring X-ray attenuation, diffraction, and scattering material properties in various insects and fruits. We aim to improve and speed up plant and fruit inspections at US customs borders and in the food industry using X-ray phase-contrast imaging technology.