Positron emission tomography (PET) and magnetic resonance imaging (MRI) have been combined for the first time in a single scanner, built for work with laboratory mice. The machine was developed by the lab of Simon Cherry in the Department of Biomedical Engineering.

MRI scans are great for structural detail, especially soft tissue, while PET scans can show what is happening inside the body but don’t tell you much about structure. By putting the two methods together in a single machine, you could get real-time information about structure and function. For example, you might locate a tumor within the body and see what parts of the tumor are actively growing and which are dying.

Combining the two types of scan in a single machine is difficult because the two systems interfere with each other. MRI scanners rely on very strong, very 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.

The researchers replaced the photomultiplier tubes usually used in PET scanners with a new technology, silicon avalanche photodiode detectors that are far less sensitive to magnetic fields.

So far they’ve used the machine to image test objects, and experimental tumors in mice.

Papers describing the work are published in Proceedings of the National Academy of Sciences and Proceedings of the IEEE.