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Real-time GHz Ultrasonic Imaging of Nematodes at Microscopic Resolution

Nematodes are worm-like multi-cellular animals that are known to cause damage to the roots, stems, and foliage of plants. They are responsible for billions of dollars’ worth of damage per year in the crop industry worldwide [1]. Plant-pest management should accurately detect and identify nematodes to carry out necessary action in the farm before any damages occur. Several identification methods of nematodes are based on biochemical, morphological, and molecular features [2]. Most of these require extraction and processing of soil samples, chemical analysis, Polymerase Chain Reaction (PCR), enzymes extraction, and other complex biochemical processing [3-6]. These processes can be time-consuming, laborious, and requires specialized facilities/laboratories to perform analysis. Similarly, several imaging techniques previously used to visualize and study nematodes include visible light, thermal, hyperspectral, and atomic force microscopes [7,8]. Most of these microscopy techniques are expensive and bulky. In addition, several limitations among these techniques arise due to the impermeability of light in soil. Ultrasound imaging has been frequently used in medical diagnostic processes where the frequency used ranges from 2 – 15 MHz. In this work, we propose high frequency (1.8 GHz) ultrasonic imaging as a potential tool to visualize and study microscopic pests such as nematodes. In previous work, we demonstrated the use of this GHz ultrasonic imager array to sense nematodes in air, water, and soil [9]. This work further analyzes the reflected echo data to extract spatial features of two different nematode species (Steinernema carpocapsae and Steinernema feltiae). The ultrasonic imaging modality enables measurements of acoustic impedance and phase shifts allowing potential differentiation between various nematode species. Furthermore, the high frequency ultrasonic imaging approach can be a powerful tool to visualize, as well as detect microscopic pests at a very high sampling rate.