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 dependent
The 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
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