For the first time at UC Davis, two types of imaging – positron emission tomography (PET) and magnetic resonance imaging (MRI) – have been combined into a single scanner.
Both are medical imaging techniques used to see inside the body. MRIs use radio waves to excite the water molecules in the body to show a detailed image of the body but do not show how the body part is functioning, explains Simon Cherry, professor of biomedical engineering and director of the Center for Molecular and Genomic Imaging.
PET scans use trace amounts of radioactive material injected in the patient in order to see how well the body functions. For example, there is sugar in cancer cells, and since cancer cells divide rapidly, they need a lot of glucose. Small amounts of radioactive glucose can be injected in the patient, and the accumulated amount of glucose can be seen on the PET scans to determine where the cancer is concentrated.
The task of combing the two types of imaging is a very difficult process, and a project that Cherry and his lab have worked on for the last 10 years.
The MRI relies on very strong, very uniform magnetic fields placed on the part intended of the patient. A PET scanis placed inside a MRI messes up the magnetic field. PET scans also emit radioactive waves and can interfere (with the MRI ), Cherry said. The detectors conventionally used in PET scanners will not work in magnetic fields 10 times the earth’s magnetic fields, and the MRI uses magnetic fields thousands more, so [the PET scan] needs to be changed to be compatible with the MRI.
We built a PET scanner that is compatible with the MRI and carefully shielded from a commercial MRI. We basically build new PET technology that can be put in the MRI.
The successful fusion of the MRI and PET scans not only benefits patients by saving them from having to take two imaging scans, but theresulting scanner also brings great advancement to research in the biomedical field.
It gives us exciting technology with which to see images in both humans and animals, and gain a better understanding [of] disease and treatment, Cherry said. The body is dynamic. Taking pictures at two different times, you often miss what is happening. Taking two pictures at the same time, aligned, is very helpful in improving the quality of scientific information.
The two-in-one scanner at UC Davis is one of a handful of machines that are available around the world and has been used for animal studies by Cherry and his lab.
Our approach lab specializes in doing imaging for animal models of disease, and we do a lot of tests on animals first, Cherry said. A lot might translate to humans. The question now is ‘How can we really use it for imaging that has never been done before?’ said Cherry.
In 2006, German-based engineering company Siemens was able to develop the first prototype of a MRI and PET combined scanner that was able to show images of the human brain.
According to a press release by Siemens, the technology will open new doors in understanding the pathologies and progression of various neurological disorders like Alzheimer’s, Parkinson’s, epilepsy, depression and schizophrenia.
MRI and PET scans are still relatively new technologies that are advancing quickly. The first full body PET scanner was used in 1977, and now over 400 PET scanners are used worldwide. The first commercially produced MRI scanner was available in 1980, and now there are over 10,000 machines worldwide according to doemedicalsciences.org.
WENDY WANG can be reached at campus@californiaaggie.com.
