Measurement procedure of a 3D USCT: semi-spherical water filled measurement container lined with ultrasound transducer arrays in cylindrical housings (transducer elements as green dots). Centrally placed a simple object (red). Spherical wave emitted (semi-transparent blue), all other transducers gather data. Wave-front interacts with object and re-emits a secondary wave (semi-transparent purple). Repeated iteratively for all transducers.<unk>  use ultrasound waves for creating images. In the first measurement step a defined ultrasound wave is generated with typically Piezoelectric ultrasound transducers, transmitted in direction of the measurement object and received with other or the same ultrasound transducers. While traversing and interacting with the object the ultrasound wave is changed by the object and carries now information about the object. After being recorded the information from the modulated waves can be extracted and used to create an image of the object in a second step. Unlike X-ray or other physical properties which provide typically only one information, ultrasound provides multiple information of the object for imaging: the attenuation the wave's sound pressure experiences indicate on the object's attenuation coefficient, the time-of-flight of the wave gives speed of sound information, and the scattered wave indicates on the echogenicity of the object (e.g. refraction index, surface morphology, etc.). Unlike conventional ultrasound sonography, which uses phased array technology for beamforming, most USCT systems utilize unfocused spherical waves for imaging. Most USCT systems aiming for 3D-imaging, either by synthesizing ("stacking") 2D images or by full 3D aperture setups. Another aim is quantitative imaging instead of only qualitative imaging. The idea of<unk>  goes back to the 1950s with analogue compounding setups, in the mid 1970s the first "computed" USCT systems were built up, utilizing digital technology. The<unk> " in the USCT concept indicates the heavy reliance on computational intensive advanced digital signal processing, image reconstruction and image processing algorithms for imaging. Successfully realization of USCT systems in the last decades was possible through the continuously growing availability of computing power and data bandwidth provided by the digital revolution.
Ultrasound computer tomography
Ultrasound transmission tomography
Medicine chest
Medicine chest 
X-ray image intensifier
Operation of computed tomography
Digital X-ray radiogrammetry
G-arm medical imaging