We used a single-layer 3D positioning Compton camera (M400 from H3D, Michigan) and demonstrated imaging of Ac-225 daugthers (Bi-213 and Fr-221) in a mouse phantom filled with a low activity concentration.

Reference: Compton Imaging of Ac-225 in Pre-Clinical Phantoms with a 3D-Positioning CZT Camera - Das, Mehrdel, Goodman, Streicher, Seo, and Caravaca (2025). IEEE Transactions on Radiation and Plasma Medical Sciences PP (99): 1–1.

We used a CZT detector without a collimator to dramatically increase gamma-ray detection efficiency and achieve nanocurie activity quantification in regions of interest defined by CT anatomical segmentation.

Reference: A technique to quantify very low activities in regions of interest with a collimatorless detector - J. Caravaca, K. N. Bobba, S. Du, R. Peter, G. T. Gullberg, A. P. Bidkar, R. R. Flavell, Y. Seo, IEEE Transactions on Medical Imaging, vol. 43, no. 8, pp. 2745-2757, Aug. 2024, doi: 10.1109/TMI.2024.3377142 (2024)