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Despite their apparent similarities, MRI and PET machines operate fundamentally differently. PET reveals the distribution of a small amount of radioactive substance within the body, while MRI provides detailed images of the structure of organs and tissues. The Werner Siemens Imaging Center in Tübingen has pioneered the development of unique devices that can perform both MRI and PET and are already being used in patient care. The remaining challenge was to create a contrast agent that works for both imaging techniques. PET uses radioactive fluorine-18 for its signal, whereas MRI uses gadolinium-containing contrast agents to enhance the visibility of human tissues and organs. Thanks to the efforts of an international research team, a solution has now been achieved. "Our solution is a cleverly designed molecule that contains both gadolinium and the radioactive fluorine-18," explains Dr. Jan Kretschmer of the Werner Siemens Imaging Center at the University of Tübingen. He is one of the two lead authors of the study, which was published in the scientific journal Angewandte Chemie. 

"For a simultaneous PET/MRI scan, mixing two separate contrast agents is typically challenging because an MRI needs a lot more contrast molecules than a PET. We have resolved this issue by substituting radioactive fluorine-18 atoms for some non-radioactive fluorine atoms in a gadolinium-based MRI contrast agent," explains Kretschmer. It's impressive that in less than 30 minutes, the researchers can create enough of this medical probe to test five subjects. Moreover, the chemical's stability in the body is quite promising for potential clinical applications.

More accurate diagnoses through precise and personalized imaging 

"The molecule is easy to use and has a wide range of applications. It has all the properties of current MRI contrast agents and provides a precise PET signal. This adds another level of information, improves accuracy, and opens up new diagnostic applications," says Dr. Miloslav Polášek from the Institute of Organic Chemistry and Biochemistry at the Academy of Science in Prague. Previous attempts by other scientists resulted in molecules that were too complex to manufacture, severely limiting their practical use. Therefore, this novel molecule has the potential to outperform rival strategies in real-world applications.

Trials on mouse models demonstrated the initial success of combining contrast agents in medical imaging for precise diagnostics. Researchers unexpectedly discovered renal issues in an apparently healthy mouse during a combined PET/MRI scan. The researchers in Tübingen observed that the right kidney retained the contrast agent longer than the left kidney, as observed by the MRI. The PET signal allowed researchers to quantify the amount of accumulated contrast agent and identify early inflammation in the right kidney. All this is done simultaneously in a single non-invasive scan session. "In the future, a single examination could not only determine a patient's illness but also the disease's type, stage, and aggressiveness," highlights Professor André Ferreira Martins of the Werner Siemens Imaging Center at the University of Tübingen. Until now, this process required two separate exams. Although PET and MRI scans with contrast are generally safe, they are very time-consuming and lack spatially resolved precision. Remy Chiaffarelli, a doctoral student at the Werner Siemens Imaging Center and the study's principal co-author, emphasizes that "a combined examination could significantly reduce the duration of the diagnostic workflow, the number of appointments and simplify medical decisions by personalizing the medical diagnostic."

The new hybrid contrast agent molecule has already been patented, and the researchers are looking for potential investors. How the new procedure can be used in a clinical context is now being further investigated in Tübingen.

Title of the original publication:
A Macrocyclic Hybrid PET/MRI Probe for Quantitative Perfusion Imaging In Vivo
Link: https://onlinelibrary.wiley.com/doi/10.1002/anie.202409520
DOI: 10.1002/anie.202409520

Experts: 

Dr. Jan Kretschmer & Remy Chiaffarelli
Werner Siemens Imaging Center
University of Tübingen
University Hospital of Tübingen