Mesenchymal stem cells (MSCs) are highly promising therapeutic agents. However, unknown biodistribution upon transplantation limits the understanding of their therapeutic effects. This limitation particularly affects advanced and more precise intraarterial routes of cell delivery. Intra-arterial delivery of cellular therapies might be highly beneficial due to the first-pass effect, lowering total cell dose; however, imaging might be instrumental in achieving high precision. Magnetic labeling was used for this purpose, but it interferes with diagnostic MRI and has low specificity on follow-up scans. Radiolabeling and PET imaging may address both drawbacks, although radiolabeling conditions were never studied systematically, and efficiencies needed to be higher to adapt methods of low-dose intra-arterial interventions. We hypothesize that radiolabeling of human mesenchymal stem cells might be beneficial by yielding higher sensitivity over a longer period and will provide quantitative results.