To ease the comprehension of the Advanced Ultrasound Imaging Toolbox, it is essential for the reader to understand the theory behind the libraries and the possible range of applications.
This Beamformer works with 3D data input axial, lateral, and elevation, captured from ultrasound transducers to produce a visible image of the region impinged by ultrasonic waves. There are two modalities specific of this library: Synthetic Aperture Imaging (SA from now on), and Plane Wave Imaging (PW form now on). The Beamformer however can be used with other imaging technique such as flow imaging.
In ultrasound medical imaging, beamforming captures the spatial distribution of the acoustic waves pressure field amplitude in the volume of interest elaborating the signals generated by an ultrasonic transducer, reflected by an anatomic part as scattered waves, and received by the same ultrasonic transducer, for the purpose of generating images.
There are several parameters that affect the final image quality:
Spatial resolution: The smallest spatial distance for which two scatterers can be distinguished in the final image. Spatial resolution can be either axial (along the direction of propagation of the ultrasound wave), lateral, or elevation resolution (along the plane to which the direction of propagation is perpendicular). This feature is normally expressed in mm.
Temporal resolution: The time interval between two consecutive images. This feature is normally expressed in Hz.
Contrast: The capability to visually delineate different objects, for example, different tissue types, in the generated images. This feature is generally expressed in dB, and it is a relative measure between image intensities.
Penetration depth: The larger depths for which a sufficiently high signal-to-noise ratio (SNR) level can be maintained. This feature is normally expressed in cm.
Array aperture: The physical sizes of the surface representing the combined distribution of active and passive ultrasound sensors: in other words, the array footprint. The array aperture is defined by the number of ultrasound sensors (elements), their sizes, and their distribution. This feature is generally expressed in cm2.
Field of view (FOV): The sizes of the area represented by the obtained images. This feature is generally expressed in cm2 or cm3.
All such features are correlated and interdependent.