PURPOSE: CD38 is a glycoprotein highly specific to multiple myeloma (MM). Therapeutics using antibodies targeting CD38 have shown promising efficacy. However, the efficient stratification of patients who may benefit from daratumumab (Dara) therapy and timely monitoring of therapeutic responses remain significant clinical challenges. To address these issues, we developed a novel nanobody-based PET tracer, [ MATERIALS AND METHODS: We prepared a new PET imaging probe based on a CD38-targeted nanobody CD3813, [ RESULTS: TOHP-CD3813 retained a high affinity for CD38 with a KD of 0.0826 nmol/L. [ CONCLUSIONS: [