Abstract
The ability of properly localizing the cancerous cells is mainly dependent on the capability of a Positron Emission Tomographic (PET) scanner to distinguish between the time-correlated true γ-rays pairs from the random and scattered ones. It requires an effective energy thresholding and time stamping of the moment when the γ-rays interact with the crystal scintillators. In this context a novel method of timestamp calculation is suggested. It is based on a process of interaction detection and its conversion to electrical signals. These pulses are digitized and selected via en energy thresholding. Later on they are processed with a signal leading edge selector, a two stage hybrid interpolator and a multi threshold discriminator. The digitization process reduces the signal temporal resolution which affects the precision of digital timestamp calculators. This inadequacy is treated by up-sampling the selected signal part with a smart combination of the optimized Weighted Least Square Interpolator (WLSI) and the Simplified Linear Interpolator (SLI). The signal selection process allows focusing on the relevant signal part and avoids the unnecessary operations during the post-interpolation process. Moreover, the hybrid nature allows the devised interpolator to achieve a suitable temporal resolution with a comparable precession at a reduced computational complexity as compared to the counter computationally complex mono interpolator based solutions. Finally the timestamp of up-sampled signal is calculated by using an amplitude compensated multi threshold discriminator. The process of calibrating the WLSI coefficients and the discriminator thresholds is described. The system functionality is verified with the help of an experiment. Results have shown that the proposed system results in a Full-Width at Half-Maximum (FWHM) coincidence timing resolution of 49.4 picoseconds. It aptitudes for the realization of submillimetric resolution three dimensional tomographs.