Polymeric micelles in nanomedicine are often cross‐linked to prevent disintegrationin vivo. This typically requires clinically problematic chemicals or laborious procedures. In addition, cross‐linking may interfere with advanced release strategies. Despite this, it is often not investigated whether cross‐linking is necessary for efficient drug delivery. We used positron emission tomography (PET) imaging with64Cu to demonstrate general methodology for real‐timein vivoinvestigations of micelle stability. Triblock copolymers with 4‐methylcoumarin cores of ABC‐type (PEG‐PHEMA‐PCMA) were functionalized in the handle region (PHEMA) with CB‐TE2A chelators. Polymeric micelles were formed by dialysis and one half was core cross‐linked (CL) by UV light and the other half was not (nonCL). Both CL and nonCL were radiolabeled with64Cu and comparedin vivoin tumor‐bearing mice, with free64Cu as control. Accumulation in relevant organs was quantified by region of interest analysis on PET images andex vivocounting. It was observed that CL and nonCL showed limited differences in biodistribution from each other, whereas both differed markedly from control (free64Cu). This demonstrated that 4‐methylcoumarin core micelles may form micelles that are stable in circulation even without cross‐linking. The methodology presented here where individual unimers are radiolabeled is applicable to a wide range of polymeric micelle types.