Simultaneous PET/MR imaging has recently been introduced to the clinic and dual PET/MR imaging probes are rare and of growing interest. We have developed a strategy for producing multimodal probes based on a carbon nanotube platform without the use of chelating ligands. Materials and Methods: Gd3+ and 64Cu2+ ions were loaded into ultra-short single-walled carbon nanotubes (US-tubes) by sonication. Normal, tumor-free athymic nude mice were injected intravenously with the probe and imaged over 48 hrs. Results and Conclusions: The probe was stable for up to 24 hrs when challenged with PBS and mouse serum. PET imaging also confirmed the stability of the probe in vivo for up to 48 hrs. The probe was quickly cleared from circulation, with enhanced accumulation in the lungs. Stable encapsulation of contrast agents within US-tubes represents a new strategy for the design of advanced imaging probes with variable multimodal imaging capabilities.