An MRI-compatible PET scanner has been built by the biomedical engineering lab at the University of California (UC) Davis for biomedical research applications to allow data from both modalities to be acquired simultaneously.
MRI scans provide exquisite structural detail but little functional information, while PET scans -- which follow a radioactive tracer in the body -- can show body processes but not structures, said Simon Cherry, professor and chair of biomedical engineering at UC Davis. Cherry's lab built the scanner for studies with laboratory mice for cancer research.
"We can correlate the structure of a tumor by MRI with the functional information from PET, and understand what's happening inside a tumor," Cherry said.
Combining the two types of scan in a single machine is difficult because the two systems interfere with each other. MRI scanners rely on strong, smooth magnetic fields that can easily be disturbed by metallic objects inside the scanner. At the same time, those magnetic fields can seriously affect the detectors and electronics needed for PET scanning. There is also a limited amount of space within the scanner in which to fit everything together, Cherry said.
Scanners that combine computed tomography (CT) and PET scans are already available, but CT scans provide less structural detail than MRI scans, especially of soft tissue, Cherry said. They also give the patient a dose of radiation from x-rays, he added.
According to a paper published online March 4 in Proceedings of the National Academy of Sciences, researchers used 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, Cherry said.
“Experiments demonstrate no effect of the MRI system on the spatial resolution of the PET system and <10% reduction in the fraction of radioactive decay events detected by the PET scanner inside the MRI. The signal-to-noise ratio and uniformity of the MR images, with the exception of one particular pulse sequence, were little affected by the presence of the PET scanner. In vivo simultaneous PET and MRI studies were performed in mice. Proof-of-principle in vivo MR spectroscopy and functional MRI experiments were also demonstrated with the combined scanner,” the authors wrote.
The work was supported by grants from the National Institutes of Health.