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For other articles and previous issues click here. April 10, 2006
Planning Ahead — Clinical Uses for fMRI Functional magnetic resonance imaging (fMRI), a noninvasive tool for measuring brain function, has been around since the early 1990s. Over the last decade, it has been regarded largely as a research tool and has not been widely employed in clinical environments. However, experts in the technique believe fMRI has a number of promising clinical applications and that it is likely to become a leading imaging tool of the future as neuroradiologists become more familiar with the technology. Experts predict the growing use of fMRI in at least three clinical areas: • mapping of critical areas in patients undergoing brain surgery; • early identification of psychiatric and central nervous system (CNS) disorders; and • measurement of the effects of therapies on neurodegenerative and neurodevelopmental disorders. Michael Schulder, MD, vice chairman and professor in the department of neurosurgery at New Jersey Medical School, has been using fMRI as a surgical planning tool for many years. His first paper on the topic was published in the Journal of Neurosurgery in September 1998. For his group and others, he says, “it’s not an exotic technology any more.” He believes it should be a routine part of the preoperative evaluation and intraoperative management of patients undergoing brain surgery for various reasons. Schulder requires that patients undergo an fMRI exam before he operates on a brain tumor. He needs to know the tumor’s proximity of the surgical field to what is known as the eloquent cortex—the areas of the brain that, if injured, will result in a major impairment such as paralysis, blindness, or loss of language function. Before the advent of fMRI, Schulder relied on anatomic criteria of routine scans. “Those are reliable up to a point,” he says. “But because of variations in individuals’ anatomy and physiology, as well as the changes brought on by intracranial lesions of different kinds, the anatomical criteria themselves are not sufficient for critical decisions before and during brain surgery.” The fMRI exam is not replacing any previous techniques, Schulder notes. Rather, it is adding vital information when operating on brain tumors, whether they’re benign or malignant. Schulder uses fMRI for preoperative planning. “You may decide whether or not to operate on a patient based on where his or her tumor is in relation to eloquent cortex.” Also, he says, the information provided by fMRI could determine how aggressively a tumor is treated. “You may modify your surgery, one way or another. You may become more or less aggressive if you know with certainty where important areas of brain function are located in relationship to the tumor.” fMRI can be brought into the operating room in an interactive fashion, using a technique pioneered by Schulder and colleagues in neuroradiology. “You can bring this data into surgical planning computers so that you can very precisely locate an area of the brain during surgery and know whether this is the area showing activity during the fMRI exam.” Epilepsy Surgery to treat epilepsy can be performed only if the exact area of the brain causing epilepsy can been identified. Also, surgeons must be confident that the surgical removal of this part of the brain will not affect the patient’s ability to function. The current standard for obtaining this information is the Wada test, named after physician Juhn Wada, who developed it. The Wada test requires the injection of an anesthetic into the right or left internal carotid artery. An alternative, Schulder says, is fMRI and the diffusion tensor imaging (DTI) scanning technique to provide the same information needed in these cases. The advantage is that fMRI and DTI are noninvasive. DTI measures the actual movement of water molecules in the brain rather than just measuring the amount of energy given off by the water molecules as fMRI does. The technique is based on the idea that water moves along the easiest route available. In the brain, the easiest route is along the major nerve pathways. In areas of the brain where there is any disruption to those nerve pathways, the water will diffuse more randomly—which is what the DTI technique detects. “When you combine fMRI and DTI, you can get a comprehensive map of the brain that includes not just areas where movement originates—where language is perceived or vision is perceived—but also the nerve fibers that connect to those different areas,” Schulder says. The combination of fMRI and DTI is very exciting, he says. “The path for making this kind of surgery safer and smarter is before us.” Diagnosing
CNS Disease Currently, physicians often can’t diagnose neurological diseases such as AD or Parkinson’s until symptoms are clearly evident. By the time symptoms are obvious, the disease has been progressing for years and it is almost too late to start a therapeutic approach that would slow its course, says Catherine Elsinger, PhD, director of research and clinical operations at Neurognostics, Inc. in Milwaukee. Neurognostics, Inc. specializes in developing clinical applications for fMRI in the areas of presurgical brain mapping and longitudinal assessment and management of CNS disorders. The company develops products and services to help facilitate fMRI’s transition into the clinical setting. In the near future, Elsinger says, fMRI could be used to map brain function changes in people who are genetically predisposed to neurological disorders such as Huntingdon’s Disease or AD. “Particularly in Huntingdon’s Disease, you can see changes on functional MR images of the brain long before you see changes in structural changes in the brain,” she says. “These are people who are 10 to 15 years away from developing full blown Huntingdon’s, and are still at a point where a potential therapy might slow the progression of their disorder.” Evidence is growing that the pathological process associated with AD begins decades prior to diagnosis. If AD could be detected before it became obvious, people likely to develop the disease could be treated, which may delay the onset of the disease perhaps up to 10 years, Elsinger says. More than one half of individuals with mild cognitive impairment, characterized as isolated memory dysfunction, will develop AD. Unfortunately, it is not currently possible to tell whether patients with mild impairment will develop progressive dementia, Elsinger says. Early
Change Currently, PET and SPECT are being used to understand neural activity associated with brain pathology. The techniques are also being used to investigate the effects of potential drug therapies. However, many PET and SPECT techniques measure resting brain activity and, unlike fMRI, do not measure the brain’s response to cognitive or motor behaviors that stress neural systems directly affected by disease, Elsinger says. Likewise, Elsinger says, current technologies used to test the efficacy of drugs designed to treat CNS disorders are paper-and-pencil tests. “They have been shown to have limited reliability and sensitivity,” she says, making it harder for pharmaceutical companies to push new agents through the discovery process. fMRI, on the other hand, can provide quantitative measures of the effectiveness of drugs and possibly offer results that are not only more sensitive but also more reliable and reproducible. Reimbursement
Issues Currently, there is no Current Procedural Terminology (CPT) code for fMRI, and CPT codes are almost always a prerequisite to having a third-party payor cover and pay service providers for a medical procedure, Borimsky says. However, Borimsky says CPT codes for fMRI studies are likely to be published by early next year. According to the American Journal of Neuroradiology, the CPT editorial committee looked at a set of fMRI codes in fall 2005. Borimsky expects several codes to be based on the complexity of the exam and who is performing it. He says a single imaging code could be used for brain mapping studies where an fMRI test does not require a neurological or neuropsychological evaluation and is conducted within the radiology department. However, if a more complex cognitive test is administered, where a neuropsychological and cognitive evaluation by a neurologist or neuropsychiatrist is required, a different set of codes may be used for test administration (imaging components) and interpretation of the results (cognitive components). Once CPT codes for fMRI are published, Borimsky says, third-party payors will have to decide whether to cover the procedure. Generally, private-sector payors follow the coverage procedures of Medicare. A good sign is that members of the American Society of Neuroradiology were recently asked to complete a Relative Value Update Committee survey from the Centers for Medicare & Medicaid Services (CMS). The results will ultimately determine the rate at which Medicare and other payors reimburse for the procedures, says Borimsky. He expects that fMRI’s transition from research to the clinical setting will be similar to that of other imaging modalities such as PET. PET was introduced in the early 1970s, and, like fMRI, quickly became a new and exciting research utility. “It was not until the 1980s that commercially oriented, and, by extension, clinically oriented, imaging device vendors introduced PET scanners and PET imaging services became available in healthcare facilities,” Borimsky says. Reimbursement came after research studies demonstrated PET’s clinical utility in the diagnosis and treatment of breast, lung, and colon cancers; lymphoma; and melanoma. In 2004, the CMS approved PET reimbursement for limited indications in AD. “The decision was based on research results that used PET to show notable changes in the neural activity in a particular cohort of Alzheimer’s patients,” Borimsky says. Clinical
Studies Schulder says he has found that the limitations of the use of fMRI have more to do with the complexity of the technology than the reimbursement issues. “When you’re doing an fMRI,” he says, “you’re almost always doing a regular anatomical MR study, whether for surgical planning or to check on changes in the intracranial lesion. The anatomical MR will be reimbursable.” An fMRI takes more time than the anatomical MR study, but most of that is postprocessing, he says. Because the information the fMRI provides is so valuable, most surgeons will gladly do it to have the data available, Schulder says. “The value of the studies is so high that, at least for surgical planning purposes, the amount of time is not prohibitive.” However, Schulder says, once fMRI moves from the research and surgical planning realm to use as a marker for disorders such as AD or Parkinson’s, it may no longer be practical for it to be performed “in this sort of ad hoc or boutique basis.” With so many affected by AD and Parkinson’s, reimbursement will be necessary and inevitable, he says. fMRI technology can provide fascinating insights into how the brain functions in healthy individuals as well as those with CNS disorders, Elsinger says. Given the advantages fMRI offers over existing imaging technologies, it will inevitably change how diagnostic care is provided and therapeutic agents are administered. — Beth W. Orenstein, a freelance health
writer living in Northampton, Pa., is a regular contributor to Radiology
Today.
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