BREAKING NEWS

University of California, Davis
March 6, 2008MRI/PET SCANNER COMBO

Two kinds of body imaging -- positron emission tomography (PET) andmagnetic resonance imaging (MRI) -- have been combined for the firsttime in a single scanner.

MRI scans provide exquisite structural detail but little functionalinformation, while PET scans -- which follow a radioactive tracer inthe body -- can show body processes but not structures, said SimonCherry, professor and chair of biomedical engineering at UC Davis.Cherry's lab built the scanner for studies with laboratory mice, forexample in cancer research.

"We can correlate the structure of a tumor by MRI with the functionalinformation from PET, and understand what's happening inside atumor," Cherry said.

Combining the two types of scan in a single machine is difficultbecause the two systems interfere with each other. MRI scanners relyon very strong, very smooth magnetic fields that can easily bedisturbed by metallic objects inside the scanner. At the same time,those magnetic fields can seriously affect the detectors andelectronics needed for PET scanning. There is also a limited amountof space within the scanner in which to fit everything together,Cherry noted.

Scanners that combine computer-assisted tomography (CAT) and PETscans are already available, but CAT scans provide less structuraldetail than MRI scans, especially of soft tissue, Cherry said. Theyalso give the patient a dose of radiation from X-rays.

The photomultiplier tubes used in conventional PET machines are verysensitive to magnetic fields. So the researchers used a newtechnology -- the silicon avalanche photodiode detector -- in their machine. They were able to show that the scanner could acquire accurate PET and MRI images at the same time from test objects and mice.

The other authors on the paper, published online March 3 by the journal Proceedings of the National Academy of Sciences, are UC Davis graduate student Ciprian Catana, now at the Martinos Center for Biomedical Imaging, Harvard University; postdoctoral researcher Yibao Wu and Jinyi Qi, assistant professor of biomedical engineering, both at UC Davis; Daniel Procissi, Caltech; Bernd Pichler, University of Tubingen, Germany; and Russell Jacobs from the Beckman Institute, California Institute of Technology. Another paper by Cherry, Jacobs and UC Davis Associate Professor Angelique Louie reviewing the opportunities and challenges for combined PET/MRI was published in the Feb. 2008 issue of the Proceedings of the IEEE. The work was supported by grants from the National Institutes of Health.

Additional information: Discuss this story on our blog, Egghead.

Media contact(s):

Simon Cherry, Biomedical Engineering
(530) 754-9419
srcherry@ucdavis.edu

Andy Fell, UC Davis News Service
(530) 752-4533
ahfell@ucdavis.edu

View this story on the Web here.