Low-level Radioactive Contamination Detected by a High-sensitivity Cadmium-Zinc-Telluride SPECT System Despite Background-level Survey Measurements

A 76-year-old woman underwent myocardial perfusion Single Photon Emission Computed Tomography (SPECT) using a high-sensitivity cadmium-zinc-telluride camera after administration of 8 mCi 99m Tc Methoxyisobutylisonitrile (MIBI). An unexpected diffuse peripheral count distribution was observed. No specific contamination event was identified, and surveys of the detector surface and patient table remained at background levels. Persistent counts on source-free blank imaging despite decontamination initially suggested a possible technical issue. However, serial blank acquisitions demonstrated progressive count reduction consistent with 99m Tc physical decay, supporting low-level residual 99m Tc contamination. This case demonstrates that high-sensitivity cadmium-zinc-telluride systems may detect low-level contamination not identified by conventional survey measurements.