Fiducial markers for MR histological correlation in ex vivo or short-term in vivo animal experiments: A screening study

Purpose: To test injectable fiducial markers for magnetic resonance (MR) histological correlation in ex vivo or in vivo animal experiments. Materials and Methods: A total of 35 potential markers were tested ex vivo in pork muscle. The end-points were: 1) visibility, size, and shape on MR images and at macroscopic examination; 2) 24-hour stability; and 3) microscopic appearance. Selected markers were injected in vivo (rabbit's muscle and breast tumor tissue) to test their three-hour in vivo stability and their potential toxicity. Finally, different dilutions of the two best markers were assessed again through the same screening tests to determine whether their size on MR images could be customized by dilution. Results: Two fluid acrylic paints containing inorganic pigments were found to be potentially interesting markers. On MR images, they created well-defined susceptibility artifacts. The markers made with iridescent bronze paint (iron oxide coated mica particles) were readily visible on microscopy and their size on MR images could be customized by dilution. The iridescent stainless steel paint (iron, chromium, nickel) created ex vivo the smallest markers in tissue but needed colloidal iron staining to be visible on microscopy and could not be easily diluted. Conclusion: Fluid acrylic paints are potentially interesting markers for MR histological correlation. Further studies are needed to assess their long-term properties.