Evaluation of a MR-compatible CZT detector

Multimodality imaging is increasingly relevant in many clinical and preclinical fields. PET/CT and SPECT/CT studies, for instance, generally provide more information than the same imaging modalities taken separately. This synergistic effect, obtained by combining anatomical and functional information, also would be desirable for magnetic resonance imaging (MRI), a nonionizing modality that provides excellent spatial resolution and soft-tissue contrast. The development of a PET/MRI or SPECT/MRI system however represents a significant technological challenge, in part due to the effect of the strong MRI magnetic field on the PET/SPECT detection subsystem. This environment complicates the use of photomultiplier tubes (PMTs) and rather favors solid-state detection technologies. As a proof of principle, we have studied the behavior of a MR-compatible CdZnTe (CZT) detector, a room-temperature semiconductor already used in some SPECT systems. The detector, made from a single 5x5x2 mm³ CZT crystal, was coupled to a Cremat CR-110 preamplifier with nonmagnetic connectors. The whole detector/preamplifier assembly was tested within a static magnetic field while the radiation detector electronics remained outside the magnet room. We measured the energy resolution of the detector from ⁵⁷Co spectra both inside and outside the magnet. The results suggest that the static magnetic field does not affect the energy resolution of the CZT detector, making it a good candidate for the development of a MRI device combining a nuclear medicine imaging subsystem.