Ultrasonics. Real-time pulse-echo scanners. Phantom with cylindrical, artificial cysts in tissue-mimicking material & method for evaluation & periodic testing of 3D-distributions of void-detectability ratio (VDR) Ultrasonics, Ultrasonic devices, Scanners, Ultrasonic medical apparatus, Ultrasound scanners, Patient scanners, Image processing (computer), Real-time systems, Clinical investigation instruments, Test equipment, Data acquisition, Data processing, Signal-to-noise ratio, Testing