When the radiology department at the University Hospital of Geneva was approached in 2008 by a major international medical imaging company looking for a site to test its new imaging modality, it seemed like science fiction had become reality. The company had combined a magnetic resonance imaging (MRI) functionality with that of positron emission tomography (PET) into one single system capable of scanning the entire body. In this article Prof O. Ratib describes the installation of Europe’s first PET/MRI at the University Hospital of Geneva and the early results that are being produced by the new system, its benefits as well as its future potential.
by Prof. O. Ratib
It has been a long-held belief that combining an MRI scanner and a PET scanner would be technically impossible due to the incompatibility of the ultra-sensitive electronics of PET scanners with the powerful magnetic field generated by the MRI. Recent technological advances (see side-bar) have however now made such an integrated system a reality — the University Hospital of Geneva in Switzerland now houses Europe’s first combined full-body PET /MR system.
We performed the first scan in April 2010 and by the end of the April we had performed 25 patient examinations. Initially, we concentrated on oncology cases of patients originally scheduled for a PET-CT study and we compared the results of the PET-MR studies with the PET-CT data. We believe the new combined PET-MRI technique will significantly improve our diagnostic accuracy in areas where patients already undergo separate PET and MR studies as part of their workup such as in prostate cancers, breast cancer and head and neck cancers. Our early results show that bringing the two modalities together improves the quality and accuracy of diagnoses. The molecular imaging provided by PET in conjunction with the anatomy and tissue characterisation of MRI will enable us to see the function and metabolism of tissue more precisely than ever before.
The clinical cases we have examined so far have already shown the advantages of being able to perfectly superimpose the PET over MRI images to detect lesions. Previously, this has not been possible because the two studies took place at different times, different conditions and different patient positions.
The results of the early cases examined so far by PET/MRI compare favourably with more traditional PET-CT studies performed in the same patients. PET-MR provided identical PET quality with the added value of perfectly matched MR images. These encouraging results confirm that both modalities function perfectly together and provide diagnostic quality results when used together in a hybrid system. The studies we performed so far showed that they benefitted from additional high definition MRI sequences providing soft tissue characterisation that is not possible with CT images of traditional PET-CT scanners.
Advantages of combined PET/MRI for patients
There are many immediate advantages for patients with the new system. Generally, patients receiving MRI and PET scans as part of their clinical work-up and follow-up undergo these two studies hours or even days apart, frequently requiring separate visits to the clinic. Now we can provide both studies and repeat scans, such as an MRI focus on areas identified in the PET scan, in one single visit. And for both patients and staff, MRI has the advantage of there being no exposure to ionising radiation, which is a particularly important benefit for our pediatric patients.
Combined PET/CT scanners have only been available in the past decade and they have already made a significant impact. However, we believe that PET/MR is the next quantum leap in imaging technology. Even though the PET/MR combination is promising for both cardiology and neurology applications, in Geneva we have decided to focus on the benefits it provides in oncology.
Although personalised medicine has been discussed at symposia for years, PET/MR may help us close the gap between science fiction and reality by providing a means to track whether a drug is reaching a tumor and monitor on a cellular level whether it’s working and tailor the treatment plan for each patient accordingly.
Installation of the new system
Developing the combined PET/MRI system was certainly an exciting and challenging project, but the work did not end with the development of the system itself. Like many hospitals, the University Hospitals of Geneva has infrastructure restrictions so it was difficult to find a suitable and large enough space within the hospital for the system or a way of transporting the new system to the hospital. In addition, construction of any new building to accommodate the new system could of course not disturb or interfere with the surrounding infrastructure of the hospital.
Fortunately, a small Swiss company was able to design a room-size container where the system was pre-installed. The unit was then transported directly to the hospital building and the container positioned adjacent to the outside wall of the building. The only actual construction that was needed was a door between the building and the new container container.
Whole-body PET/MR in the US
In parallel to the installation of the first PET/MRI in Europe in the University Hospital of Geneva, Switzerland, another combined system from Philips Healthcare was installed in the Translational and Molecular Imaging Institute (TMII) of the Mount Sinai Hospital in New York City, NY, USA. Founded in 1852, the Mount Sinai Medical Center is a 1,171-bed, tertiary-care teaching facility internationally acclaimed for excellence in clinical care. As a leader in cardiology research, Mount Sinai is specifically interested in PET/MR since the combination is expected to provide a more advanced understanding of the processes taking place in vascular beds. Multimodality imaging synergistically enhances the power of the separated modalities by automatically combining functional and anatomical information. The use of PET/MR scanners instead of PET/CT scanners would not only reduce the extra radiation dose to the patient but would also offer higher soft tissue contrast, allowing better visualisation and understanding of the underlying disease.
Under the leadership of Prof Zahi A. Fayad, who is the Professor of Radiology and Medicine (Cardiology) at Mount Sinai and is also Director of the Translational and Molecular Imaging Institute, the Mount Sinai Medical Center is currently performing a clinical and a preclinical study to test the performance of the new PET/MR scanner. The preliminary images are already showing promising and valuable results and Prof. Fayad and colleagues will soon begin a study to profile the development of vulnerable/high-risk atherosclerotic plaque in patients with high risk
of cardiovascular disease.
The author
Osman Ratib, MD, PhD, FAHA,
Professor and Chief of Nuclear Medicine,
Department of Radiology,
University Hospital of Geneva,
Geneva, Switzerland
