  The J-PET detector being developed at Jagiellonian University, is a Positron
Emission Tomograph composed of the long strips of polymer scintillators. At the
same time it is a detector system which will be used for studies of the decays
of positronium atoms. The shape of photomultiplier signals depends on the
hit-time and hit-position of the gamma quantum. In order to take advantage of
this fact a dedicated sampling front-end electronics which enables to sample
signals in voltage domain with the time precision of about 20 ps and novel
reconstruction method based on the comparison of examined signal with the model
signals stored in the library has been developed. As a measure of the
similarity we use the Mahalanobis distance. The achievable position and
time-resolution depends on number and values of the threshold levels at which
the signal is sampled. A reconstruction method, as well as preliminary results
are presented and discussed.
