Three Megapixel Ultrasonic Microscope Imaging

Acoustic microscopy is a modality that utilizes mechanical properties as the imaging contrast. Imaging large areas is desirable for biological samples which often have features that span large areas (>1 mm2). Here we use our custom-made coded excitation scanning acoustic microscope (CESAM) for large area scanning: we visualized two bioactive glass (S53P4) bone substitutes in a rabbit femur, the new bone formation in the bioactive glass, as well as the surrounding bone after implantation. In this study we used 375 MHz central frequency transducer and a 300 to 500 MHz linear chirp with a gaussian envelope. The sample was scanned in 10 different focus layers, each 10 μm apart from each other. These 10 layers were aligned using 2D-cross correlation. In the final image. The reconstruction was done by picking the A-line in focus for each pixel. We discuss the method for large area scanning with focus layer alignment. We show that it reduces the sample flatness requirements. Absolute acoustic impedance values were calculated from the measured data via acoustic impedance calibration [6]. We demonstrated that our device is capable of 250+ mm2area imaging with 10 μm XY-stepping, with sample surface height variation of over 100 μm.