The invention relates to a method of improving the precision of a medical
nuclear SPECT or PET image in which notably a nuclear sectional image (n)
can be superposed on a two-dimensional ultrasound image (u). For the
superposition that nuclear sectional image (n.sub.0) which exhibits the
best correspondence with a free-hand ultrasound image (u) is chosen from
a three-dimensional nuclear image (2). In order to determine this
sectional image, an evaluation index f(n,u) is calculated, on the basis
of an estimated value (1), for differently situated nuclear sectional
images (n). This index assigns a positive value to positions of
structures (heart muscle tissue etc.) which correspond in the two images,
a neutral value to structures which are represented only in the
ultrasound image (u) and a negative value to structures which are
represented only in the nuclear sectional image (n). The nuclear
sectional image (n.sub.0) having the highest value of the evaluation
index is subsequently displayed so as to be superposed on the ultrasound
image. In a generalized form the method can also be carried out in
conjunction with three-dimensional ultrasound images.