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Institute of Neuroscience and Medicine

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Combination of MRI and PET

It is the combination of magnetic resonance imaging (MRI) and positron emission tomography (PET) merged in this so far unique device which opens up new perspectives for researchers.

The hybrid device with a field strength of 9.4 tesla provides high-resolution images of the brain structure which simultaneously show the functional activities occurring in the healthy and diseased brain. This device enables scientists for the first time to simultaneously analyse the structure and function of the brain down to the molecular level. While MRI differentiates between different types of tissue in the brain, PET makes the physiological and biochemical activities of the brain visible.

Simultaneous MR-PETImages of the brain obtained using magnetic resonance tomography (left) and through positron emission tomography (right). With the new device, the two techniques can be combined (middle).

New Technology for Combining the Two Techniques

The combination of the two techniques in one device creates methodological and technical challenges for the developers of "9komma4": conventional PET detectors are incompatible with magnetic fields because they use photomultipliers.

Electrons (negatively charged) produced during the measurements would be deflected in the strong MRI environment and no signal would be measurable. For this reason, developers of the device – scientists at Forschungszentrum Jülich and Siemens Healthcare – trust a new technology, so-called avalanche photodiodes.

Although they also measure a flow of electrons caused by light particles, this occurs within a semiconductor layer system in which the electrons cover sections that are hardly longer than a few atomic distances: too short to be disturbed by the magnetic field. Not only are Jülich scientists constructing this device together with Siemens; they are also developing the measuring method.

9.4 Tesla MR-PET ScannerDevelopers of the device invented a new technology known as avalanche photodiodes, which allows MRI and PET techniques to be combined.