Medical ultrasonics: adaptive time gain compensation in diagnostic imaging

Large errors can occur with time gain compensation (TGC) which is set up manually since one gain function is unlikely to be appropriate for all scan lines and the operator may not have sufficient time or experience to optimise it. Adaptive TGC offers the benefit of improved images which are less operator dependentThe clinical application of simple adaptive TGC in abdominal and obstetric ultrasound is described.Recent developments in diqital electronics allow powerful methods of gain control to be implemented. A microcomputer controlled system has been built to investigate various methods of adaptive TGC. The microcoputer is interfaced to a real-time scanner from which it can collect echo data. The echo data is processed by programs written in a combination of assembly language and Fortran IV, and the microcomputer can then set up a unique TGC function for each scan line in the image. The design and construction of the microcomputer system are described. Several algorithms for adaptive TGC have been developed. These range from the derivation of a single gain function applied across the whole image to more sophisticated algorithms which apply a unique TGC function to each scan line and are capable of detecting regions of low attenuation.The algorithms were tested using tissue equivalent phantoms, and clinically in routine abdominal and obstetric scanning. The results were compared with those of a skilled operator setting up the TGC by hand. The performance of the algorithms was also investigated using computer simulations. The clinical results show that adaptive TGC is capable of producing consistently better images than a skilled operator setting the TGC manually.Further developments of adaptive TGC are considered - in particular, the implementation of a hard-wired system which would operate in real-time and the development of an interactive gain control system