Development of an ultrasound microscope combined with optical microscope for multiparametric characterization of a single cell

A rapid rice blast detection and identification method based on crop disease spores' diffraction fingerprint texture

BACKGROUND

Rice blast fungus is a worldwide disease, and it is one of the most serious rice diseases in the north and south rice fields in China. The initial symptoms of rice blast are not obvious, and the speed of transmission is fast. Manual identification is time-consuming and laborious. At present, it is a great challenge to realize rapid and accurate early identification of rice blast.

RESULTS

In this paper, an identification method based on crop disease spores' diffraction fingerprint texture for rice blast was studied; this method utilizes the light field and texture features of diffraction images. To verify the reliability of the model that we proposed, we selected two methods of manual identification and machine recognition to compare and detect rice blast spores. The experimental results show that the identification of light diffraction characteristics is not only higher than the traditional manual recognition by microscope (increased by more than 0.3%), but also faster after neural network training (increased by more than 90%). The diffraction recognition method used in this study, based on crop disease spores' diffraction fingerprint texture, can be completed in a few seconds, and its test accuracy is 97.18%.

CONCLUSION

The proposed method, a rapid rice blast detection and identification method based on crop disease spores' diffraction fingerprint texture, has certain advantages compared with the existing manual identification by microscope. This method can be applied to the recognition of rice blast in agricultural research. © 2020 Society of Chemical Industry.

Optical Resolution Photoacoustic Microscopy With Fast Laser Scanning and Fixed Photoacoustic Detector

Photoacoustic (PA) imaging is rapidly progressing imaging modality in which very short pulsed laser causes thermal expansion to generate PA signal. In previous PA microscope systems, relatively long time was required for image acquisition because they required mechanical scan of the PA transducer. The objective of the present study is to develop fast laser scanning optical resolution photoacoustic microscopy (OR-PAM) with fixed PA signal detector to realize very high frame rate PA imaging. Q-switched Nd:YAG laser with the wavelength of 532 nm, pulse width of 5.5 ns and pulse repetition rate of up to 50 kHz was equipped in the system. Low frequency PA detector was comprised of a glass prism configuring acoustic focusing and a polymethyl methacrylate (PMMA) prism with 5 MHz PZT (lead zirconate titanate) transducer. High frequency PA detector was comprised of the same glass prism and a glass prism with ZnO (zinc oxide) thin film transducer. Galvano scanner operating in the air was controlled by a microcomputer to scan laser beam. PA signal was detected with the fixed PA detector thus realized the frame rate of 5 fps for C-mode equivalent to 500 fps for B-mode. The lateral resolution of the low frequency system was found to be 11.6 μm and the blood vessel on the surface of cod roe was clearly visualized. The system may be applicable for imaging blood flow and vascular dynamics of micro vessel.

Correction of phase rotation in pulse spectrum method for scanning acoustic microscopy and its application to measurements of cells

Scanning acoustic microscopy (SAM) can measure the mechanical properties, such as sound speed, thickness, and density, of biological tissues, by using the pulse spectrum method. However, the estimation method needs to be modified because of increases in the center frequency of acoustic transducers. In this paper, we proposed a new estimation method combining a time-of-flight method by Wiener filtering with the pulse spectrum method. First, an optimal control parameter β for Wiener filter was chosen based on a simulation by k-wave MATLAB toolbox. Setting the thickness of a layer to be 1.95 μm, a bias error between the estimated and true thickness was 0.0016% and the control parameter β was chosen to be 0.01 based on the simulated result and previous research. Next, the thickness of a film sample was measured by the time-of-flight method with Wiener filtering and was compared with an optically-measured thickness to confirm the estimation accuracy. Thickness was estimated to be 18.3 ± 0.025 μm at a center frequency of 120 MHz and agreed with the optically-measured thickness. Finally, the parameter n, the number of phase rotation in Gaussian plane, is calculated from the thickness and sound speed, and the pulse spectrum method with the correction of the parameter n is applied to the cellular measurements. Also, the mechanical properties estimated by the proposed method was compared with these by the conventional method.

A method for the design of ultrasonic devices for scanning acoustic microscopy using impulsive signals

Scanning acoustic microscopy (SAM) using impulsive signals is useful for characterization of biological tissues and cells. The operating center frequency of an ultrasonic device strongly depends on the performance characteristics of the device if the measurement is conducted by using impulsive signals. In this paper, a method for the design of ultrasonic devices for SAM using impulsive signals was developed. A new plane-wave model was introduced to calculate frequency characteristics of loss of ultrasonic devices by taking into account the conversion loss at the ultrasonic transducer, the transmission loss at the acoustic anti-reflection coating, and the propagation loss in the couplant. Ultrasonic devices were fabricated with a ZnO ultrasonic transducer using two acoustic lenses with aperture radii of 1.0 mm and 0.5 mm, respectively. The frequencies at which measured losses became minima corresponded to the calculation results by the plane-wave model. This numerical calculation method is useful for designing ultrasonic devices for acoustic microscopy using impulsive signals.