Hybrid MRI/PET Imaging System Effective for Tumor Detection

Nancy A. Melville

June 13, 2011

June 13, 2011 (San Antonio, Texas) — State-of-the-art hybrid imaging technology that combines positron emission tomography (PET) and magnetic resonance imaging (MRI) has the promise of emerging as the new gold standard for delivering precise diagnostic imaging, according to research presented here at the Society for Nuclear Medicine (SNM) 2011 Annual Meeting.

The PET/computed tomography (CT) scan is currently the most popular hybrid molecular imaging technology in use; however, CT images, which use x-ray technology, are not as sensitive as MRI in soft tissue contrast. MRI demonstrates improved imaging for areas such as the brain, head and neck, and pelvis.

In the first-ever study demonstrating the clinical use of integrated PET/MRI technology (Biograph mMR), researchers from Germany performed PET/CT scans and subsequent MRI/PET scans on 11 patients with oncologic diagnoses.

The scans were performed using standard clinical protocols. Attenuation correction for the images was performed using CT data for the PET/CT scans, and using segmented Dixon-MR sequences for the MRI/PET scans.

A comparison showed that the MRI/PET scans provide high-quality data that are comparable to those from the PET/CT scans, with no significant differences in ratios of tracer-uptake for the lung, liver, spleen, and bone.

All tumor lesions that were detected with PET/CT (n = 13) could also be identified with MRI/PET. No significant differences were observed between the 2 hybrid technologies for uptake ratios in tumor lesions.

"We think the new imaging modality may offer unique opportunities, particularly in regard to oncologic diagnostic imaging of the entire body," said lead author Alexander Drzezga, MD, from the Technische Universität München, in Munich, Germany.

Dr. Drzezga reported that his team is currently following 22 patients and the results are remaining consistent with the preliminary findings.

PET imaging systems have not been combined with MRI in the past because PET technology was not compatible with the high magnetic field of MRI. However, advances in PET design have made the 2 technologies more compatible, explained Michael M. Graham, MD, PhD, professor of radiology and radiation oncology and director of nuclear medicine at the University of Iowa College of Medicine in Iowa City.

"What has occurred over the decade has been a gradual improvement in photodiode methodology," said Dr. Graham, SNM president in 2009/10.

"It's now feasible to make high-quality PET scan technology without photomultiplier tubes, and instead use 'avalanche' photodiodes," he said. "This allows for a relatively thin PET scanner that can fit into the bore of an MRI device."

The study's findings offer promising evidence of the potential of MRI/PET in the future of diagnostic imaging, he added.

"What is extraordinarily encouraging is that the new PET works well and works within an MRI machine. The study shows that the image quality is comparable with the PET scanner, and allows a combination with MRI."

"It's a very nice demonstration of the feasibility of this methodology. and I think that we will see this technology proliferate over the next few years."

Last week, the US Food and Drug Administration cleared for marketing the Siemens Biograph mMR system, which can simultaneously run a PET scan and an MRI scan.

The study received research support from Deutsche Forschungsgemeinschaft. Dr. Drzezga's reports financial relationships with and serving as an advisor for Bayer and Schering. Dr. Graham has disclosed no relevant financial relationships.

Society for Nuclear Medicine (SNM) 2011 Annual Meeting: Abstract 262. Presented June 6, 2011.


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