Over the last decade, hybrid imaging has become a standard of care in radiology, cardiology, nuclear medicine and oncology. Integrated scanning systems offer a number of advantages for physicians and patients.
Take for example PET/CT. In just a few short years since its introduction on the market, PET/CT has emerged as the gold standard of oncological imaging. “Hybrid PET/CT systems help clinicians see how functional data can be integrated into structural information,” notes Gary Small, MD, director of the University of California at Los Angeles Center on Aging in California. This best-of-both worlds approach improves on both modalities as it adds critical functional data to anatomical CT images. And it boosts the utility of PET. Physicians are more likely to accept combined scanners such as PET/CT systems than stand-alone PET scanners because they are more familiar with CT and less familiar with PET imaging, says Small. On the patient side, hybrid systems offer one-stop shopping; there is an economy of effort in obtaining the necessary imaging data as patients don’t need to undergo two separate scans. Despite the demonstrated power of PET/CT, there is room for additional mergers between conventional imaging modalities. Wedding PET and MRI, for example, could provide a number of key benefits in both oncological and neurological imaging.
Replacing the CT portion of the scanner with MRI delivers improved soft-tissue contrast and eliminates the ionizing radiation of the CT scan. In addition, MR/PET studies could be simultaneously acquired rather than sequentially acquired as in PET/CT. As a result, the MR data could be used for respiratory gating of PET data. The upshot? Hybrid MR/PET systems could play a significant role in oncology imaging. MR/PET applications, however, extend beyond oncology. The neurological community also is interested in the hybrid systems.
Small explains the current role of PET and MRI in the research realm. Researchers regularly use both types of studies; PET and MRI produce different, but complementary, datasets. MRI yields higher resolution images that display structural details and volumes. PET, on the other hand, is a lower resolution study that allows researchers to hone in and examine function in an area of interest.
The current MR/PET processes are labor-intensive, time-consuming and far from ideal. UCLA researchers merge PET and MRI data, using software to co-register the data and analyze the region of interest in a single plane and create 3D surface projections of plaques, tangles and cortical thinning, but they do not fuse the separate datasets. A hybrid MR/PET scanner could improve the process as it eliminates the need to take images on two separate scanners and superimpose them after acquisition.
The potential of MR/PET is intriguing, says Small. “It could aid in the early detection and prevention of Alzheimer’s disease and other dementias. We know that changes in structure and function precede the onset of clinical symptoms. Earlier identification may allow physicians to prescribe preventative treatment of delay onset of the disease. This combined MR/PET approach is very promising,” concludes Small.
Despite the potential of the hybrid MR/PET system, it remains a work-in-progress. Engineers need to overcome several technical challenges including replacing photomultipliers in PET scanners with semi-conductors and solving electromagnetic incompatibilities between PET and MR systems. Nevertheless, Siemens Medical Solutions has developed a prototype MR/PET scanner and researchers plan to begin investigating the system to determine how well it interacts with PET isotopes in a clinical research setting this fall. In the next several years, researchers should determine its clinical viability and role in the medical imaging continuum. Stay tuned.