 |
||||
Home > News and Events > News Releases > News Releases Archive News Releases: April - June 2008
Dr. Simon Cherry Seeking to exploit the best features of two different bioimaging systems, researchers in Dr. Simon Cherry’s molecular imaging lab at the University of California Davis (UC Davis), are combining two very familiar technologies—positron emission tomography (PET) and magnetic resonance imaging (MRI)—to create a more versatile imaging tool. With collaborative contributions from Dr. Russell Jacob’s team at the California Institute of Technology and Dr. Bernd Pichler of Tubingen University in Germany, results of this tandem PET/MRI research, which is sponsored by NIBIB, indicate this new technology could lead to improvements in many aspects of health care, as well as in basic research. Both imaging systems have unique strengths that compliment each other. For example, PET is much more sensitive than MRI. Because it can zero in on very faint signals emitted by radioactively labeled sugar molecules that enter cancer cells, PET is often used to locate tumors. On the other hand, one of MRI’s strengths is its ability to produce clearly defined images of anatomical structures and soft tissues, which can provide critical information such as changes in the size of a tumor following treatment. This team imaging approach has potential to help new treatments get from the laboratory to the patient’s point of care in less time. Dr. Cherry explains, “These two technologies are powerful allies in the evaluation of new medical therapies in animal models where the detailed information they provide on the distribution and action of a drug can help improve the success of the translation of new therapies into the clinic.” Today, many physicians use data from these two imaging modalities to evaluate anatomy, physiology, cellular metabolism, molecular targets and pathways, and even gene expression. This information helps build a strong foundation of evidence for biological or medical evaluation that helps doctors determine, and monitor, a medical course of action. Moreover, these systems allow clinicians to peer deep into the body without performing surgery or other invasive techniques. With all this in mind, one might ask why researchers have not previously combined these modalities, especially given the success of other combined imaging systems such as PET and x-ray computed tomography (CT). The answer to that question lies in the many ways that the two systems can interfere with each other and distort the images that are recorded. For example the detectors used in most PET scanners are extremely sensitive to magnetic fields and will not operate inside the strong magnetic field of an MRI scanner. Furthermore, in order to obtain a clear MRI image, its magnetic field must be stable and uniform, but the mere placement of PET detectors within the scanner can disrupt the magnetic field. For these reasons, PET and MRI scans have previously been done independently, but the problem in using these imaging systems independently is that the process of accurately weaving both sets of information together can be very difficult. The process works fairly well in applications such as brain imaging where there is little potential for movement or change in position, but the true challenge arises in locations such as the chest or abdomen where movement can be problematic, and if MRI and PET data cannot be matched or “registered” perfectly, interpretation of images can be difficult. Furthermore, much important biological information would be revealed about dynamic processes if we had the ability to observe such events using both systems at the same time. Therefore, development of a dual system capable of providing simultaneous PET and MRI scans is a great benefit in situations where movement is inevitable, and it also provides the added benefit of real-time, dual-imaging observations of physiological processes. Realizing the tremendous benefits of such a system, researchers at UC Davis have designed a new integrated PET/MRI scanner that positions a PET scanner within the MRI scanner, while also minimizing the interference between the two systems by employing special materials and clever design strategies. For example, the new integrated PET system’s data is decoded using special solid-state detectors (developed by Radiation Monitoring Devices, Inc., with NIH and Department of Energy Small Business Innovation Research funding) that can tolerate the strong magnetic fields inside the MRI. Detectors are also shielded by a high-frequency copper laminate and kept at a constant, cool negative 10 degrees Celsius (14 degrees Fahrenheit) to optimize results. Additionally, the short optical fiber bundles are positioned precisely to further minimize interference. A convenient feature of the new system is that the PET scanner insert fits many commercially available MRI systems and can be easily removed from the MRI scanner so that the units can be used separately, if necessary. Initial studies have clearly demonstrated the promise of the PET/MRI technology, and Dr. Cherry predicts, “While the technology will continue to improve and mature, the spotlight will now shift to finding unique ways to use this integrated technology to learn new things about the biology of disease and the best way to use PET/MRI for early diagnosis and to monitor treatment response.” Researchers already predict that the new system has the potential to greatly enhance our understanding of the origins and evolution of disease processes, such as cancer, Alzheimers, and bone disease. It will also help monitor the effectiveness of cancer treatments, locate metastases in soft tissues, and give clues about tumor physiology and the immune system’s ability to fight cancer. Dual-modality imaging can yield data that automatically match up in time and space because both PET and MRI imaging scans of the same body regions are done at exactly the same time. Even in brain tissues where independent use of these technologies has been very useful, the new system can do more, such as PET analysis of glucose metabolism while MRI images evaluate constriction or dilation of blood vessels. As for nurturing this fledgling technology to its full potential, this collaborative research team is already working on it. The integrated PET/MRI system is now being used for preclinical research, and the UC Davis team is developing ways to further improve on their prototype technology by increasing the spatial resolution and sensitivity of the PET component. So even just as the nuptial ceremonies are coming to a close and the union of these imaging systems is sealed, investigators are brainstorming about the many possibilities for its future. And just like Dr. Charles Townes’s famous invention, the laser, the full potential of PET/MRI integration will only be realized as its offspring emerge from the pipeline of this new wave of technology, arriving as creative new technologies in their own right in the healthcare of our future. If you would like to learn more about Genomic Imaging research at UC Davis, see Dr. Cherry's web site at: http://www.bme.ucdavis.edu/profiles/cherry.html JuneJune 18: NIST/NIH Micromagnets Show Promise as Colorful "Smart Tags" for Magnetic Resonance ImagingBOULDER, Colo.—Customized microscopic magnets that might one day be injected into the body could add color to magnetic resonance imaging (MRI), while also potentially enhancing sensitivity and the amount of information provided by images, researchers at the National Institute of Standards and Technology (NIST) and National Institutes of Health (NIH) report. The new micromagnets also could act as “smart tags” identifying particular cells, tissues, or physiological conditions, for medical research or diagnostic purposes.
As described in the June 19 issue of Nature,* the NIST and NIH investigators have demonstrated the proof of principle for a new approach to MRI. Unlike the chemical solutions now used as image-enhancing contrast agents in MRI, the NIST/NIH micro-magnets rely on a precisely tunable feature—their physical shape—to adjust the radio-frequency (RF) signals used to create images. The RF signals then can be converted into a rainbow of optical colors by computer. Sets of different magnets designed to appear as different colors could, for example, be coated to attach to different cell types, such as cancerous versus normal. The cells then could be identified by tag color. “Current MRI technology is primarily black and white. This is like a colored tag for MRI,” says lead author Gary Zabow, who designed and fabricated the microtags at NIST and, together with colleagues at the National Institute of Neurological Disorders and Stroke, part of NIH, tested them on MRI machines. The micromagnets also can be thought of as microscopic RF identification (RFID) tags, similar to those used for identifying and tracking objects from nationwide box shipments to food in the supermarket. The device concept is flexible and could have other applications such as in enabling RFID-based microscopic fluid devices (microfluidics) for biotechnology and handheld medical diagnostic toolkits. The microtags would need extensive further engineering and testing, including clinical studies, before they could be used in people undergoing MRI exams. The magnets used in the NIST/NIH studies were made of nickel, which is toxic but was relatively easy to work with for the initial prototypes. But Zabow says they could be made of other magnetic materials, such as iron, which is considered non-toxic and is already approved for use in certain medical agents. Only very low concentrations of the magnets would be needed in the body to enhance MRI images. Each micromagnet consists of two round, vertically stacked magnetic discs a few micrometers in diameter, separated by a small open gap in between. Researchers create a customized magnetic field for each tag by making it from particular materials and tweaking the geometry, perhaps by widening the gap between the discs or changing the discs’ thickness or diameter. As water in a sample flows between the discs, protons acting like twirling bar magnets within the water’s hydrogen atoms generate predictable RF signals—the stronger the magnetic field, the faster the twirling—and these signals are used to create images. The open sandwich design allows the movement or diffusion of water through the micromagnet, producing a signal that may be thousands of times stronger than that produced by a similarly sized, but stationary, volume of water. The diffusion effectively increases local MRI sensitivity, which in a future clinical setting could lead to practical benefits such as faster imaging, images that are richer with information, or reduced dose requirements for these contrast agents. The NIST/NIH test results show that changing magnet geometry results in significant shifts in the frequency signals. Thanks to their physical attributes, the magnets can be designed to have more tunable properties than conventional injectable MRI contrast agents. MRI contrast agents enhance images by altering the magnetic field seen by hydrogen nuclei in water. Conventional contrast agents are chemically synthesized whereas the new micromagnets are microfabricated. This allows for greater control and range of the modified magnetic field, greatly enhancing sensitivity. Furthermore, unlike the molecular chemical “soups” that make up many of the contrast agents, each micromagnet potentially could be individually detected for imaging purposes. The magnets also could be designed to be turned on and off by, for example, filling the gap between the discs to block water passage. The gap could be filled with something that dissolves when exposed to certain substances or conditions, Zabow says. The micromagnets can be made using conventional microfabrication techniques and are compatible with standard MRI hardware. Advanced lithography techniques of the kind used to make sophisticated computer chips might be used to make the tags even smaller, approaching the nanometer scale, according to the paper. The magnets could make medical diagnostic images as information-rich as the optical images of tissue samples now common in biotechnology, which already benefits from a variety of colored markers such as fluorescent proteins and tunable quantum dots. NIH has filed a provisional patent application on the micromagnets. NIH support for Zabow’s work was funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) through the NIST/NIH-NIBIB National Research Council Joint Associateship Program. The program seeks to recruit physicists into biomedical research in order to improve technologies like MRI. As a non-regulatory agency, NIST promotes U.S. innovation and industrial competitiveness by advancing measurement science, standards and technology in ways that enhance economic security and improve our quality of life. The National Institutes of Health (NIH)—The Nation's Medical Research Agency—includes 27 institutes and centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov. *G. Zabow, S. Dodd, J. Moreland, A. Koretsky. 2008. Micro-engineered local field control for high-sensitivity multispectral MRI. Nature. June 19. |
, or see, "Simultaneous in vivo positron emission tomography and magnetic resonance imaging" at: 
 |
 |
Department of Health and Human Services |
 |
National Institutes of Health |
 |
