Ultrasound computed tomography (USCT) is a 3D imaging tool, especially for breast screening. Sound-speed tomography as one imaging modal of USCT is widely studied by researchers because of its great clinical potential for early breast cancer detection. Sound-speed reconstruction methods include ray-based methods and wave-based methods. In this study, a ray-based method for sound speed reconstruction: Fresnel volume tomography (FVT) is implemented. We use Limitedmemory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) optimization algorithm to solve the large and sparse equation for the inversion step. Considering the great computation burden in the L-BFGS inversion process, two kinds of acceleration schemes: CPU parallel and GPU parallel schemes are used and evaluated by in vitro experiment. The corresponding acceleration ratios are 5.3 and 18.6 for the 512×512 sound speed image reconstruction, compared to CPU serial computation.
Scanning probe acoustic microscope (SPAM) can be used to acquire the morphology image as well as the non-destructive internal structures acoustic image. However, the observations of the morphology image as well as the internal structures acoustic image of liver cancer cells in SPAM are few. In this paper, we cultured 4 different types of liver cancer cells on the silicon wafer and coverslip to observe their morphology images as well as acoustic images in SPAM, and made a preliminary study of the 8 types of cells specimens (hereinafter referred to as the silicon specimens and coverslips specimens). The experimental measurement results showed that some cellular pseudopodium were observed in the morphology images of the coverslip specimens while no such cellular pseupodium were appeared in the morphology images of the silicon specimens, which concluded that the living liver cancer cells were less likely to grow on the silicon wafer. SPAM provides a rapid and sensitive visual method for studying the morphology and internal structures of the cancer cells. The proposed method can be also used to obtain the morphology and internal information in both solid and soft material wafers, such as silicon and cells, with the resolution of nanometer scale.
Acquiring nondestructive internal structures acoustic image as well as the morphology images using scanning probe acoustic microscope (SPAM) is a challenge and no known metrology tools to identify the ultrasonic internal resolution and detectable depth of SPAM in a nondestructive way. Monitoring these defects necessitates the identification of their technical parameters of SPAM. In this paper, the specific materials (test phantoms) were designed and processed so that the ultrasound internal resolution of SPAM in nondestructive imaging of the embedded or buried substructures as well as the morphology images were measured. Experimental results demonstrated the successful identification of embedded or buried defects under the test phantom with the resolution of 50nm for SPAM as well as the detectable depth of more than 100μm.
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