The Big Picture
After much anticipation, an artfully orchestrated arrival and careful calibration, the 7.0 Tesla Magnetic Resonance Imaging (MRI) is up and running. The 7T is part of a new generation of ultra-high field MRI instruments and one of the first to be installed in a clinical setting for future use. With more than double the strength and resolution of the current state-of-the-art 3T MRI, the 7T offers clinical insights that have not been possible until now, particularly focusing on neurodegenerative and musculoskeletal diseases.
While national and state level approvals are needed before the first patient can be seen in the clinical setting, principal investigators at BWH are already putting the machine to good use. During this time, researchers will be able to leverage the unique capabilities of the 7T, using the machine to visualize anatomical details through high quality image scans that could give them a clearer picture of the origins and consequences of diseases, with implications for both diagnostics and treatment options.
The 7T is one of only a few of its kind available to investigators that will capture critical structures and pathologies that were barely visible in the past. Earlier this month, at a scientific symposium organized by the Department of Radiology, investigators had a chance to share their research with the community, and show what researchers can accomplish with the addition of this new technology.
Rohit Bakshi, MD, MA, Department of Neurology
Bakshi described how the Partners Multiple Sclerosis (MS) Center will collaborate with the BWH Radiology Department to use the 7T for the investigation of MS, and ultimately, for clinical care. The benefits of the 7T device will likely include a more accurate diagnosis of MS and improved monitoring of treatment response. The 7T will allow detection of the central vein sign to help determine if the patient’s lesions are associated with MS. The 7T is also uniquely sensitive to cortical lesions, spinal cord involvement and other features that are key to identifying patients who are experiencing disease progression and may need their therapy changed. According to Bakshi, 7T MRI unit at BWH should have an immediate impact on research happening at the Partners Multiple Sclerosis Center, and may eventually help improve patient care and attract patient referrals from other institutions in the region.
Ellen J. Bubrick, MD, Department of Neurology
Bubrick, whose work focuses on treating epilepsy, sees tremendous potential in the 7T for clinical use. She believes it will provide more accurate diagnoses, evaluate patients with uncontrolled seizures and identify who may be eligible for epilepsy surgery. To better understand and test just how well the 7T can help clinicians diagnose and plan treatment, Bubrick has been evaluating the 7T’s ability to detect lesions in the brain. Investigators saw a big leap in improvement of lesion detection when they began using the 3T in place of the 1.5T, finding that greater field strength increased detection and often improved surgical decision making. “The clues were always there; we just haven’t been able to see them,” said Bubrick.
Alexandra Golby, MD, Department of Neurosurgery
As co-director of the Advanced Multimodality Image Guided Operating (AMIGO) suite, Golby sees possibilities for the 7T in a variety of applications, including informing surgical decision-making and improving patient care. Biomarkers developed on the 7T could be validated using tissue samples taken in AMIGO, and further, images made possible by the 7T may one day eliminate the need for traditional biopsies in some patients. Currently, surgeons face the challenge of pseudoprogression – a phenomenon that can make a tumor appear worse on MRI after treatment when, in reality, the tumor isn’t growing. “Pseudoprogression makes everyone nervous,” said Golby. She anticipates that the 7T may help eliminate this uncertainty as researchers find clearer ways to monitor response or progression after treatment.
Alexander Lin, PhD, Department of Radiology
Lin, director of the Center of Clinical Spectroscopy, spoke about neurospectroscopy, a widely applicable technique that compares the chemical composition of normal brain tissue with abnormal tissue. Repetitive head injuries, as would be seen on a football field, can cause metabolic disruption. The 7T’s increased chemical resolution will allow Lin to measure brain metabolism after brain trauma and other conditions, like Alzheimer’s disease, allowing researchers to distinguish chemicals – such as glutamate versus glutamine – in a way that hasn’t been possible until now. He anticipates that similar techniques can be applied to studies of schizophrenia and the neurobiology of chronic traumatic stress to assess how chemical changes affect the brain.
Stephan Maier, MD, PhD, Department of Radiology
Though the 7T’s signal-to-noise ratio permits higher resolution, image distortions grow proportionally with field strength and resolution, and single-shot Echo-planer Imaging (EPI), which typically is used to obtain diffusion-weighted images of individual slices, is not practical at a high resolution due to severe distortions as well. Maier’s team proposes multi-shot rather than single-shot diffusion imaging methods, or field of view reduction, and uses line scan diffusion imaging (LSDI) which permits the ultimate field of view reduction to an image of a single line. The team is using this technique to evaluate nerve fiber architecture in greater detail within a section of the brain called the cerebral cortex. In future research this technique could be applied to diseases that affect nerve fiber architecture such as MS.
Vitaly Napadow, PhD, Department of Radiology (MGH)
Vagus nerve stimulation (VNS) has been used as a nervous system therapy for multiple cardiovascular disorders, including hypertension, coronary artery disease and heart failure. However, VNS is an invasive procedure and has been associated with complications. Napadow and colleagues are interested in mapping non-invasive pathways that could be stimulated to modify the activity of the heart. In humans, 7T functional MRI (fMRI) will provide enhanced resolution to evaluate the response of the brainstem and higher regions of the brain (specifically, the hypothalamus) to stimulation of the auricular branch of the vagus (ABVN), the only branch of this nerve that distributes to the skin. The team hopes to gather pivotal information regarding potential effects on cardiovascular physiology.
Sonia Pujol, PhD, Department of Radiology
Deep brain stimulation (DBS) is an established treatment for Parkinson’s disease, but its exact mechanism of action remains unknown. Pujol and her co-author Rees Cosgrove, MD, of the Department of Neurosurgery, propose that patient-specific mapping of the brain white matter fibers could help illuminate how DBS works and what changes may be taking place in the subthalamic nucleus and white matter connections of the brain. Specifically, the team plans to compare images from the 7T and 3T, use these images to identify white matter fibers of interest and, ultimately, standardize evaluation of white matter tracts reconstruction at 7T and 3T. Their preliminary results, based on 3T imaging, have been published earlier this year. “I’m excited to see if the 7T helps us resolve complex tracts in the deep parts of the brain,” said Pujol. “In the long term, we hope to perform patient-specific white matter mapping in Parkinson’s disease.”
Yanmei Tie, PhD, Department of Neurosurgery
Tie and her colleagues plan to use the 7T to investigate easy paradigms (resting-state and movie-watching) fMRI for mapping language function for surgical planning. These paradigms can benefit neurosurgical patients, particularly those who cannot perform the conventional task-based fMRI. Originally developed for use with the 3T, Tie’s technique may offer increased functional sensitivity and spatial specificity of language maps when the team can leverage the 7T. They plan to compare the language maps they generate using the 7T versus 3T, and would like to examine both healthy subjects and brain tumor patients.