Optimizing timing performance of CdTe detectors for PET

Abstract

Despite several attractive properties, the poor timing performance of compound semiconductor detectors such as CdTe and CdZnTe has hindered their use in commercial PET imaging systems. The standard method of pulse timing with such detectors is to employ a constant-fraction discriminator at the output of a timing filter which is fed by the pulses from a charge-sensitive preamplifier. The method has led to a time resolution of about 10 ns at full-width at half-maximum (FWHM) with 1 mm thick CdTe detectors. This paper presents a detailed investigation on the parameters limiting the timing performance of Ohmic contact planar CdTe detectors with the standard pulse timing method. The jitter and time-walk errors are studied through simulation and experimental measurements and it is revealed that the best timing results obtained with the standard timing method suffer from a significant loss of coincidence events (~50%). In order to improve the performance of the detectors with full detection efficiency, a new digital pulse timing method based on a simple pattern recognition technique was developed. A time resolution of 3.29 ± 0.10 ns (FWHM) in the energy range of 300-650 keV was achieved with an Ohmic contact planar CdTe detector (5 × 5 × 1 mm). The digital pulse processing method was also used to correct for the charge-trapping effect and an improvement in the energy resolution from 4.83 ± 0.66% to 2.780 ± 0.002% (FWHM) at 511 keV was achieved. Further improvement of time resolution through a moderate cooling of the detector and the application of the method to other detector structures are also discussed.

A General-Purpose Digital Pulse Shape Discrimination Algorithm

“…The cosine similarity was initially used for the PSD of CdTe detectors by employing several peak-sensing ADCs [18]. It has been also used in digital domain for the discrimination of neutrons and γ-rays with liquid scintillation detectors [19], and recently, for the correction of time-walk error in pulse timing with CdTe detectors [20]. In all these attempts, the cosine similarity was calculated between the sampled pulses and a pulse template from the concerned detector.…”

Proceedings of the Second International Symposium on Radiation Detectors and Their Uses (ISRD2018)

“…The algorithm of the digital differentiator can be found in Ref. [5]. Then, the ion component is obtained by the subtraction of the electron component from the whole signal waveform.…”