A milestone in diagnostic imaging – With Biograph mMR, Siemens turns the dream of molecular MR imaging into reality for the first time
Since the mid-80s, physicians and medical physicists have been dreaming of the tremendous possibilities offered simultaneously by magnetic resonance imaging (MRI) and positron emission tomography (PET) in an integrated whole-body system. This technological milestone was made possible through the vast experience of two Siemens business units – Magnetic Resonance and Molecular Imaging in close cooperation with its clinical partners for the pre-development and clinical application (University Hospital of Tuebingen, University Hospital “Klinikum rechts der Isar” of the Technical University of Munich, Massachusetts General Hospital in Boston, Section for MR Imaging (Prof. Dr. Harald H. Quick, PhD) at the “Institut für Medizinische Physik” (Institute of Medical Physics, IMP) of Friedrich-Alexander-University of Erlangen-Nuremberg).
“With simultaneous MR-PET hybrid imaging, we open the door to entirely new diagnostic and technical possibilities in medical imaging,” says Prof Dr Harald H Quick, Head of the Section for MR Imaging at the IMP Erlangen.
The Biograph mMR is a very sophisticated and elegant integration of the two imaging modalities (MR and PET). This realises for the first time the vision of simultaneous acquisition of MR and PET data across the whole body, leading to better diagnosis and management of the patient.
Clinical utility of hybrid systems is seen in the combination of functional information (e.g. PET) and anatomic structures (e.g. CT, MRI) into a single image. MRI provides superior soft-tissue contrast along with functional information as in MR spectroscopy, diffusion imaging, perfusion imaging, and functional MRI (fMRI). Further, no radiation exposure helps in preventing long term cell damage in young children and patients with repeat follow-ups.
There were numerous physical and technical preconditions and challenges, which hampered the development of hybrid MR/ PET scanners for a long time. Siemens with its innovative concept of utilising new generation assembly consisting of APDs (Avalanche Photodiodes) over the conventional PMT (Photomultiplier Tube) could overcome the hurdle of a simultaneous MR/ PET. These are not only insensitive to magnetic field but also have a small footprint to be cased within the MR gantry. Siemens MR systems with 70 cm bore are hence a pre-requisite for the above integration.
|The PET unit of Biograph mMR has the largest axial PET field of view in the industry of 25.8 cm. This offers an advantage of fewer bed positions need to be acquired during whole-body examinations. Again with industry best crystal dimension of 4 mm x 4 mm x 20 mm [NEMA 2007] and sensitivity of 13.2 cps/kBqz it sets entirely new standards for PET imaging. In addition, the large solid angle covered allows for a very high volume sensitivity which translates directly into low-noise images.|
Biograph mMR also houses the state-of-the-art 3T MRI system with the same gradient specification as all other premium 3T MR scanners from Siemens (45 mT/m, 200 T/m/s). Together with the Biograph mMR specific coils (Siemens Tim (Total imaging matrix) coil technology) especially optimised for simultaneous MR and PET imaging, it is possible to perform not only the standard imaging sequences, but also all the advanced functional MR sequences that you want to combine with PET imaging, all this across the whole body and, thanks to Tim coil technology, without changing coils or repositioning the patient.
One advantage of an integrated system as compared to two separate systems is that it requires about 50 percent less space. With a total of 33 m2, the footprint is similar to that of a conventional 3T MR scanner. In addition to its low space requirement, an integrated system also offers considerable advantages in clinical operation. Acquiring a single exam with an integrated system, controlled by one technologist via one control unit, dispenses with the necessity of coordinating two examination dates for two systems in different departments. This saves the hospital unnecessary work and leads to faster examination results for patients.
Simultaneous MR and PET imaging also opens up entirely new possibilities with regard to image quality and thus diagnosis is precise. Its uniqueness lies in precise spatial and temporal registration of anatomical, functional and metabolic image data, simultaneous acquisition of PET and MR data for attenuation correction, MR gating for motion correction in the PET data.
Physicians expect to make inroads in several important areas using simultaneous PET/ MR. Overall, PET/MR may be the modality that ushers in a new era for personalised medicine. According to Bruce R. Rosen, MD, PhD, Massachusetts General Hospital, Boston, as individualised medicine is on rise the PET/MR is the first stepping stone towards a long term goal for better patient care. Thus, the dream of molecular MR imaging also becomes reality for those who
are to profit from it – mostly patients.