Speaker
Description
Based on our earlier experience with the first clinically applicable 3D USCT system, we now realized our new pseudo-randomly sampled 3D USCT device (3D USCT III). It contains 2304 transducers arranged in a semispherical aperture (Fig. 1 (a)). The aperture diameter and shape, the transducer opening angle, the bandwidth and active area of the transducers as well as the front-end electronics and data acquisition system were improved. The system is expected to increase the field of view (FOV), the image contrast and considerably reduce measurement and read out time. In this work we present first imaging results obtained with the new system.
After acquiring approx. 10 million A-Scans using all emitter-receiver-combinations, we reconstructed reflectivity images using synthetic aperture focusing technique. For signal processing we applied matched filtering, local maximum detection and convolution with an optimal pulse of adaptable width. Transmission images were reconstructed using straight and bent ray-based tomography in an algebraic reconstruction with total variation regularization. To assess the image quality we imaged several phantoms including a steel sphere and metal thread for reflectivity imaging and a custom built phantom made from gelatin with spherical inclusions of different size made from PVC. Furthermore we imaged first volunteers.
Resulting images are shown in Fig.1 (b) and (c). Initial assessment of the point spread function in reflectivity images using the metal thread phantom resulted in nearly isotropic maximum resolution of 0.26 mm. The mean reconstructed speed of sound of the main body of the gelatin phantom was 1531.3 m/s compared to 1530 m/s measured as ground truth. The mean attenuation averaged over frequency was 0.62 dB/cm compared to 0.42 dB/cm measured as ground truth. For the largest inclusion of diameter 2.2 cm, the speed of sound was 1436.1 m/s (1430 m/s ground truth) and the attenuation 6.1 dB/cm (5.9 dB/cm ground truth). The smallest inclusion of 0.8 cm diameter is visible both in sound speed and attenuation imaging.
In conclusion, the speed of sound and attenuation images show promising quality and good quantitative reproduction of the ground truth values given the ray-based reconstruction. Reflectivity images show improved contrast over the previous 3D USCT system due to pseudorandom sampling and a PSF near the theoretical resolution limit. We expect to increase the image quality further after successfully completing system calibration. Currently we are working on preparation of the system for a clinical study.
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