Most of the crystal identification (CI) or Depth-Of-Interaction (DOI) measurement schemes for phoswich detectors are based on pulse shape discrimination [7], [18]. This approach is very sensitive to noise and mostly limited to photopeak signals for efficient discrimination. To overcome this problem, a fully digital method, based on an adaptive filtering scheme, has been proposed [19]. This method, which is better known as AutoRegressive model with eXogenous variable (ARX), is able to discriminate crystals even with lowenergy Compton events. Although this method is very accurate, it is computationally expensive and not really tailored for realtime processing. Simplified versions of the ARX technique with recursive algorithms, such as Least Mean Square (LMS) or Recursive Least Square (RLS) [14], and non recursive algorithms, such as Wiener [13] estimation, are more appropriate for real time digital processing. Prior to the real-time implementation of the algorithm, an analysis of the DAQ chain characteristics in the polezero domain (Z-trans- form) must be done. This analysis consists in building a model by replacing each part of the front-end electronic (Fig. 9) by filters in the Z-domain as depicted in Fig. 10.