Experimental study of the response of 1–5 mm thick CdTe/CZT detectors inside strong magnetic field

摘要

In this study, we experimentally investigated the detailed charge collection process in CdTe ERPC detectors that are operated inside a strong magnetic field for MRI-compatible SPECT imaging system. As one of the key objectives, we quantitatively assessed the effect of the Lorenz force on the migration of charge carriers and signal induced inside the detector bulk. During the study, the ERPC detectors were set on a non-magnetic gantry that can be rotated inside a 3T MR scanner. Two collimations were used to form incident gamma ray events traveling onto the detector with known incident points and angles. One of them is a highly machined Tungsten collimator and the other one is the nine-pinhole aperture. Multiply studies were performed using the same experimental detection setup with and without the magnetic field to estimate the charge collection behavior in MRI environment. In addition, the detector coupled with collimator was placed at the different angular position in SPECT scanning to evaluate the second-order distortions caused by the inhomogeneity of the magnetic field. Meanwhile, we used a Monte Carlo simulation model to reproduce the charge collection behavior with and without presence of magnetic field. This accurate modeling of the ERPC detectors energy response helps to compensate the event-positioning error induced by the strong magnetic field and also evaluate effects of several physics factors in charge collection. Through this process, we derived an accurate system response function for the MRI-compatible SPECT system, which allows us to achieve ultrahigh spatial resolution of images obtained inside the MRI.