Software Allows Virtual PET/MRI Fusion
It was a difficult, but not uncommon, neuroradiology case: A patient suffered seizures, but had, a year before, been cleared of the possibility of epilepsy by a radiologist looking at an MRI study of the patient’s brain. The persistence of the symptoms suggested that the initial diagnosis had been incorrect, so Meng Law, MD, professor of radiology and director of neuroradiology at the Keck School of Medicine at the University of Southern California (USC), Los Angeles, compared an MRI scan with a PET scan to look for the more subtle lesions that are characteristic of the disease.
Meng Law, MD
“In patients with epilepsy, the lesions are often very subtle,” Law says. “The MRI was done a year ago and read as being normal by a colleague, and the PET scan, done recently, showed very subtle abnormalities.” The technology required to obtain MRI and PET images simultaneously is not yet available in clinical practice, so Law fused the images virtually, using 3D visualization software from FUJIFILM Medical Systems USA Inc, Stamford, Connecticut. Law has been using the product, which will be demonstrated at this year’s RSNA meeting and released in early 2010, as part of a clinical trial. “Separately, there was really no way to find the abnormality,” he recalls. “It wasn’t until we used the 3D application to fuse the two images that we saw valuable information.”
PET/MRI fusion image of lesions indicating epilepsy.
Law explains that even if simultaneous MRI/PET acquisition technology did become available in the future, using software to fuse two images from different modalities is more cost effective than investing in new high-tech imaging equipment. “It’s useful to have this software so you don’t need that very expensive technology,” he observes. “If you have this software, you can essentially save $4 million or $5 million, because to have both technologies working together simultaneously represents a huge technological challenge.” There are other cost benefits as well: “This patient would have gone on to have multiple surgeries to try to determine where this lesion was in the brain,” Law says, “whereas we can easily locate the lesion with the 3D application, avoiding a surgical craniotomy.” Clinical Conundrums Diagnosing epilepsy is only one of several clinical scenarios in which the ability to create a virtual fusion of PET and MRI images could be useful, Law notes. “Besides epilepsy, you could use PET/MRI fusion for stroke imaging, for brain-tumor imaging, and for multiple sclerosis,” he says. “Today, we had a spine patient for whom we might potentially fuse PET with MRI.” Though PET/MRI fusion is still primarily used as a research tool, Law hopes that in the future, as the technique becomes more substantiated by research, its use will be more widespread. “The technique is still under investigation, so there’s not a lot of real outcome data,” he says, “but anecdotally, we’ve seen that these tools can have a strong impact on patient care.” The Synapse 3D application also enables users to create perfusion maps of the brain quickly, facilitating more rapid characterization of angiogenesis in brain tumors; by fusing perfusion and diffusion images of stroke patients’ brains, the software also optimizes identification of the ischemic penumbra. “This application completes these processes very quickly,” Law notes. “Normally, this kind of image interpretation would require a separate workstation. I’m not aware of many PACS workstations that can do this very powerful postprocessing very efficiently.” PACS Integration The 3D application will be available with FUJIFILM’s Synapse PACS platform, providing easy access to the 3D toolset. Law explains that this yields particular benefits for neuroradiology because almost all cases require some form of 3D interpretation. “Most PACS can do a very basic multiplanar reconstruction, but that’s a very basic image-manipulation tool,” he says. “We’re using the more advanced applications on a daily basis in neuroimaging. That’s where the future of imaging’s going to be, and it’s useful to have a PACS that can do that.” Law explains that the postprocessing time required for many neuroradiology studies can hinder workflow, an issue that PACS integration solves by eliminating the need to transfer data between workstations—and thus, between servers. “Ordinarily, most of these advanced applications would take a few minutes to do on a workstation,” he says, “but transferring the data to a workstation involves not only a second computer, but sometimes also a second server. To have everything on one PACS server saves anywhere from a few minutes to an hour, depending on the level of connectivity and bandwidth in your institution.” PACS integration also eliminates the need for the radiologist physically to change work areas, saving valuable space and time. “Having everything on a single workstation saves space, and the transfer of data between the 3D application and the PACS is much more efficient,” Law says. “For neuroimaging, where we’re using 3D applications in almost every single case, having everything on the same screen, rather than having to move physically to a different workstation or a different desk, is obviously a huge advantage.” Currently, Law and his team at USC are using not only the 3D fusion application, but also the MR angiography, CT angiography, diffusion, and perfusion applications; a research project is underway that uses the 3D application for calcium scoring in the brain to predict stroke. Future Applications Law and his colleagues have been investigating the use of the application for several clinical scenarios, including PET/MRI fusion in imaging patients with epilepsy, in time-resolved angiography, and in diffusion tensor and fiber tracking in patients with multiple sclerosis. He particularly emphasizes the potential of PET/MRI fusion to enhance the care of patients with epilepsy, noting, “These patients become challenging to manage, and there is a potential for high morbidity.” He continues, “The surgeon may resect a part of the brain that’s normal in an attempt to find the lesion, or may open up the brain and put in subdural grids. Those are costly outcomes that result from not having adequate imaging and 3D processing tools.” Law and his team are developing a paper to demonstrate the utility of PET/MRI fusion in these cases. Law also recently demonstrated PET/MRI fusion for oncological imaging of the brain at a meeting of the International Cancer Imaging Society, held in Salzburg, Austria, in October. “They’re very interested in novel cancer-imaging techniques in neuro-oncology,” he says. “We demonstrated how PET imaging was able to confirm that a patient’s tumor probably was not recurrent in a case where the MRI wasn’t conclusive.”
PET/MRI fusion image of a malignancy in the brain.
Law has demonstrated the software to his fellow clinicians with promising results. “We’ve demonstrated the software to the epilepsy neurologist and the neurosurgeons, and it’s certainly been very beneficial to them in terms of avoiding surgery and increasing their diagnostic and therapeutic confidence,” he says. “They can decide whether a patient needs surgery or radiation therapy based on the software, whereas before, it has been a bit of a challenge to make those decisions.” Cat Vasko is editor of and associate editor of Radiology Business Journal.