The first device to simultaneously perform a positive emission tomography (PET) scan and a magnetic resonance imaging (MRI) scan has been cleared by the FDA.

Until now, clinicians could only use a PET and computed tomography (CT) scanner to image the body. The Siemens Biograph mMR system uses MRI rather than CT to produce detailed images of the organs, soft tissues, bone, and other internal structures. Because MRI creates images based mainly on the concentration of water in the body, it can produce greater detail of nearly all the internal structures of the body compared with CT, which uses x-rays to make images. PET scans, for their part, employ a radioactive chemical tracer injected into the bloodstream to detail how body organs and tissue are actually functioning.

The Biograph mMR system offers a significantly lower radiation dose than a PET/CT system: Although the PET radiation dose remains unchanged, the entire ionizing radiation dose from the CT scan is eliminated because MRI does not use ionizing radiation.

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Another advantage of the simultaneous scanning is that it allows two tests to run at the same time without having to move the patient to a different system, as pointed out by Alberto Gutierrez, PhD, director of the Office of In Vitro Diagnostic Device Evaluation and Safety in the FDA’s Center for Devices and Radiological Health. “Minimizing changes in a patient’s position between tests allows [providers] to compare images more easily and helps them get the most accurate information possible,” noted Gutierrez in the FDA’s announcement of its approval of the device (

Persons with pacemakers, defibrillators, or other implanted electronic devices that are not specifically indicated for use in the MRI environment should not be scanned with the Biograph mMR system because the strong magnetic fields of the MRI component may interfere with the function of those instruments.