Abstract Here, positronium imaging is presented to determine cardiac myxoma (CM) extracted from patients undergoing urgent cardiac surgery due to unexpected atrial masses. Positronium is an atom build from an electron and a positron, produced copiously in intra-molecular voids during the PET imaging. CM, the most common cardiac tumor in adults, accounts for 50-75% of benign cardiac tumors. We aimed to assess if positronium serves as a biomarker for diagnosing CM. Perioperative examinations and histopathology staining in six patients confirmed the primary diagnosis of CM. We observed significant differences in the mean positronium lifetime between tumor and normal tissues, with an average value of 1.92(02) ns and 2.72(05) ns for CM and the adipose tissue, respectively. Our findings, combined with positronium lifetime imaging, reveals the novel emerging positronium biomarker for cardiovascular imaging. One-Sentence Summary Positronium may serve as an imaging biomarker for cancer diagnostics.

Developing a Novel Positronium Biomarker for Cardiac Myxoma Imaging