Novel PET/MR scanner enters development pipeline

British researchers say they have found an effective way to combine PET and MR in one system. They intend to get a prototype animal imaging model up and running by the end of 2005 to prove their claim.

The system will be based on a 1T split-coil magnet developed and patented at the University of Cambridge. Researchers highlighted the clinical potential of their integrated PET/MR design at a seminar entitled Imaging and Healthcare: The Future Horizon, held Oct. 19 at Churchill College in Cambridge, U.K.

The bespoke MRI magnet, which was manufactured by Magnex Scientific and installed at the university in 2003, features an 8-cm gap to accommodate other imaging equipment. The plan is to obtain funding to build a micro-PET system inside the magnet, allowing simultaneous PET/MR image acquisition in an animal research system by the end of next year. A human prototype system is also in development and could be ready as early as 2007.

It will cost an estimated £1 million to build the prototype animal research system, including equipment and personnel costs. The Cambridge team submitted a funding application in October to the government-run Engineering and Physical Sciences Research Council in Swindon, U.K. Researchers say they are confident the application will be approved and they can begin building the system in conjunction with industry partners, notably CTI Concorde Microsystems of Knoxville, TN. If their application for funding fails, they will seek backing from other sources with the goal of sticking to their development timetables.

Previously developed PET/MR scanners have involved the placement of relatively crude PET detectors inside a standard clinical MR scanner. They have been capable of imaging only one slice at a time. The proposed Cambridge system promises whole-volume imaging capability, according to Richard Ansorge, senior lecturer in physics at the University of Cambridge.

"The use of standard hospital magnets severely limits the possible designs of the PET system that can be accommodated inside," he said. "We believe our concept is unique in using a specially designed MRI magnet."

The clinical value of combining images from different modalities to show anatomic structure as well as metabolic function has been well documented. The introduction of PET/CT scanners energized the positron imaging marketplace around the world, particularly the U.S.

But to date, the industry has given short shrift to the combination of PET and MR. A major barrier has been the difficulty of operating the photomultiplier tubes (PMTs) associated with PET, needed to count photons, in a magnetic field, Ansorge said. The problem may be challenging but not impossible to overcome. PET scintillators can be positioned in a high magnetic field and linked via fiber optics to PMTs placed far enough away to avoid adverse effects from the magnet's field.

PET/MR would offer simultaneous acquisition of information about structure and function without the radiation dose drawback of PET/CT, said Dr. Adrian Carpenter, director of the Wolfson Brain Imaging Centre at the University of Cambridge. This could prove advantageous in cancer screening, among other applications.

"PET is exquisitely sensitive for finding lesions at low radiation dose - but you need good anatomic images to find out where the lesions are," Carpenter said. "The problem with the current combination of CT and PET is that you cannot use CT on normal volunteers and you cannot use it as a screening tool."

Cambridge researchers say equipment manufacturers are interested in the concept but want to see actual images to assess the capability of such a scanner.