  In this article, a new method for the reconstruction of hit-position and
hit-time of photons in long scintillator detectors is investigated. This
research is motivated by the recent development of the positron emission
tomography scanners based on plastic scintillators. The proposed method
constitutes a new way of signal processing in Multi-Voltage-Technique. It is
based on the determination of the degree of similarity between the registered
signals and the synchronized model signals stored in a library. The library was
established for a set of well defined hit-positions along the length of the
scintillator. The Mahalanobis distance was used as a measure of similarity
between the two compared signals. The method was validated on the experimental
data measured using two-strips J-PET prototype with dimensions of 5x9x300
mm$^3$. The obtained Time-of-Flight (TOF) and spatial resolutions amount to
325~ps (FWHM) and 25~mm (FWHM), respectively. The TOF resolution was also
compared to the results of an analogous study done using Linear Fitting method.
The best TOF resolution was obtained with this method at four pre-defined
threshold levels which was comparable to the resolution achieved from the
Mahalanobis distance at two pre-defined threshold levels. Although the
algorithm of Linear Fitting method is much simpler to apply than the
Mahalanobis method, the application of the Mahalanobis distance requires a
lower number of applied threshold levels and, hence, decreases the costs of
electronics used in PET scanner.
