In the field of neuroimaging research, MR imaging has a critical role enabling scientists to study the structure and function of the brain non-invasively. Its use continues to grow in neurodegenerative and psychiatric diseases, as well as developmental disorders.
SIGNA™ Premier leads the way in neuroimaging research with its best-in-class clinical translation system and 70 centimeter bore. Designed for research and beyond, SIGNA™ Premier is GE HealthCare’s most powerful 3.0T system with the robust SuperG gradients and 146 channel TDI RF chain that delivers 60 cm performance in a wide-bore scanner. SIGNA™ Premier is used in many major neuro research projects, including the National Institute of Health’s (NIH) Human Connectome Project, which has mapped the neural pathways that underlie human brain function, and the NIH ABCD (Adolescent Brain Cognitive Development) Study, the largest long-term study of brain development and child health in the US.
In the study of brain connectivity, diffusion tensor imaging (DTI) is critical. According to Suchandrima Banerjee, PhD, Senior Global Director of Neuro MRI at GE HealthCare, DTI is very gradient intensive, meaning it needs high gradient amplitude to get a short enough echo for high b-value diffusion, which ensures good signal in diffusion-weighted images.
“This is where SIGNA™ Premier really shines,” Dr. Banerjee says. “Now, with the combination of AIR™ Recon DL, we are seeing extraordinary results for diffusion tractography.”
GE HealthCare is expanding its collaboration with researchers on these techniques to determine if brain connectivity studies can be completed in shorter scan times or potentially improve neurosurgical planning. Shorter scan times are even more important when studying children and patients with developmental or psychiatric disabilities who may not be able to tolerate lying motionless for long periods of time, or who may be claustrophobic, confused or irritable due to the gradient noise or the proximity of the MR bore.
In functional MRI (fMRI), the temporal stability of SIGNA™ Premier is beneficial for conducting studies of the whole brain in 15 minutes.
Researchers connect on fMRI research
At the Catholic University of Louvain (UCLouvain) in Belgium, Laurence Dricot, Ir, PhD, is the Chief Research Logistician and Platform Manager for the Neuroimaging Platform (NIMA). NIMA performs an array of morphometric, functional and diffusion imaging at various field strengths, including on the SIGNA™ Premier 3.0T. Each year, the team performs between 800 and 1,000 scanning hours on research subjects. These high volumes are possible thanks to the close proximity to and collaboration with Saint-Luc University Hospital.
The team at UCLouvain also collaborates on research with Ron Kupers, PhD, Professor Department of Neuroscience and Coordinator BRAINlab at the University of Copenhagen. Prof. Kupers notes that UCLouvain also has a lot of expertise scanning children in an MRI without the use of anesthesia, which is beneficial in many of the studies they are conducting together.
fMRI, including rs-fMRI, is an integral part of the research being conducted at UCLouvain. In functional imaging, researchers of NIMA perform classical BOLD contrast imaging, task-based fMRI and brain connectivity studies. For research into neurodegenerative diseases, rs-fMRI acquisitions in patients with (mild) cognitive impairment are being used to identify connectivity changes as the patient progresses through the stages of Alzheimer’s disease.1
“The fMRI data is then fused with PET data for multi-modal analyses to better understand the evolution of the integrity of functional networks during the course of the disease,” Dr. Dricot explains. The imaging data is then linked with the patient’s clinical follow-up with a neurologist (Figure 1).
Figure 1.
Same patient as featured on front cover. 4 chamber acquisition with Sonic DL™ Cardiac Cine, 1.4 x 1.4 x 8 mm, 7 sec. per slice, 60 cardiac phases with a 23 ms temporal resolution per phase. Images courtesy of Stanford University.
Task-based fMRI that employs a simple computer game (bringing the apple back to the basket) is also performed to better understand the impact of aging and pre-clinical Alzheimer’s disease on the patient’s ability to perform tasks of simple spatial cognition.
GE HealthCare has developed an MR sequence for UCLouvain for rs-fMRI with seed-based analysis of the dentate nucleus to investigate essential tremors in connection with Parkinson’s disease. This research also includes DTI of the cerebellar microstructure. The goal is to establish any links between the cerebellum’s connectivity and behavioral control tasks and tremor severity and amplitude.
Within the area of multiple sclerosis research, UCLouvain has created an imaging processing pipeline to interrogate diffusion and FLAIR imaging data for detecting the paramagnetic rim lesions (PRL) and central vein signs (CVS) imaging biomarkers.
“One of the reasons we wanted to purchase the SIGNA™ Premier is because the higher gradient coil technology allows us to do more advanced diffusion imaging in a reasonable time for the patient,” Dr. Dricot adds.
In epilepsy patients, the Magnetization Transfer - TFL sequence on SIGNA™ Premier helps assess the integrity of the locus coeruleus in vagus nerve stimulation-implanted patients with drug-resistant epilepsy.
“We would like to understand why the stimulation will work for some patients and not for others,” Dr. Dricot adds.
Tied to this epilepsy research, the team is using fMRI in a pre-clinical sheep study to test a novel, MRI-compatible neurostimulator to better understand the mechanisms of vagus nerve simulation and develop new strategies for the titration of the stimulation parameters. For this study, Dr. Dricot and her team are using the AIR™ Anterior Array (AA) Coil wrapped around the anesthetized sheep’s head to capture the BOLD signals when the stimulation cycles begin and end.
“We did a test with resting-state fMRI and the AIR™ Coil and the results were very successful,” Dr. Dricot says.
Two important areas of research for Prof. Kupers on the SIGNA™ Premier involve blindness and deafness. He is interested in cross-modal brain plasticity, where the loss of one sensory modality leads to enhanced sensory performance in other modalities.
“If you ask a congenital blind person to smell something or listen to words, there is an activation in the visual or occipital cortex, which is rather surprising because the occipital cortex is supposed to process visual, and not olfactory or auditory, information,” Prof. Kupers explains. “My hypothesis is that this hyperexcitability of the occipital cortex might be related to a reduction in the levels of GABA due to the congenital absence of visual input.”
To further test this hypothesis, Prof. Kupers would like to use MR spectroscopy to measure the levels of gamma-aminobutyric acid (GABA) and he hopes to collaborate with other researchers using GE HealthCare MR who have experience with it.
Prof. Kupers and his colleagues at the University of Copenhagen are also working with the Danish Technical University to examine spatial navigation in congenital blind persons. Both centers have a SIGNA™ Premier, so they can run their studies in parallel.
Research on the plasticity of the brain also encompasses deaf persons and, in particular, patients with cochlear implants, which are expensive devices. Currently, scientists and clinicians don’t know why cochlear implants work in some patients and not in others. Prof. Kupers mentions that the success of cochlear implant therapy can be predicted by FDG-PET uptake in the auditory cortex pre-surgery, with those having the highest FDG uptake showing the least favorable results. His plan is to also measure GABA levels in these patients to see if it can predict those who will have a successful response to cochlear implant therapy.
Finally, in the realm of plasticity of the brain, Prof. Kupers and his colleagues are working with the polytechnic department at the UC Louvain to develop an fMRI-compatible and thermo-controllable gustometer to test the brain’s response to gustatory (taste) stimuli. Once the device is complete, they intend to use it to perform basic physiological studies on the perception of sweetness, saltiness and temperature, particularly in patients with bulimia and anorexia.
Figure 2.
NIMA researchers are examining multi-fixel microstructures in the brain using DTI tractography on the SIGNA™ Premier. In this study, metrics maps using angular weight recover the properties along the direction of the tract. Shown are microstructure maps of the (A, B)arcuate fasciculus and the (C, D) frontal aslant tract. Direction color-coded maps (RGB) of the direction of the fixel obtained with (A) DIAMOND (DMD) and (C) Microstructure Fingerprinting (MF) are compared to maps obtained with DTI. Microstructural maps of the (B) FA and (D) FVF are also compared to the FA obtained with DTI.2 Images courtesy of NIMA/UCLouvain.
Clinical advancements that also impact research
In GE HealthCare’s latest software, MR 30 for SIGNA™, the deep-learning-based reconstruction solution AIR™ Recon DL is now compatible with 3D and PROPELLER sequences, as well as DTI and distortion correction. Also in MR 30 for SIGNA™, 3D ASL now has a longer label duration capability, which translates to higher SNR in perfusion-weighted images, resulting in better cerebral blood flow (CBF) map estimations. The combination of longer labeling and long post-labeling delay is ideal for studying the older population, for example in Alzheimer’s disease.
Dr. Banerjee adds, “3D susceptibility weighted images, or SWAN, are also much faster thanks to highly optimized protocols and compatibility with compressed sensing in the new MR 30 for SIGNA™ software.”
There is also the ability to now output real and imaginary images from SWAN that can be used to compute quantitative susceptibility maps (QSM). Soon, GE HealthCare’s MAGiC sequence will be compatible with AIR™ Recon DL for faster, thin-slice imaging with excellent SNR and diagnostic quality.‡
3D isotropic imaging is an essential component of neuro research that provides structural information, including the volume of different brain regions, that is used for various neurological disorder diagnoses. This is where the 48-channel Head Coil really shines. It is designed for high SNR, optimal parallel imaging and HyperBand acceleration performance, as well as high patient population compatibility.
“Because of the technology used in the design of the 48-channel Head Coil, there is more signal in the deep brain,” Dr. Banerjee explains. “The coil’s inner dimension adjustments for larger heads also provides room for peripherals, such as an EEG cap, in fMRI studies.”
When used with GE HealthCare’s AIR™ Recon DL, it is now possible to acquire a motion robust (PROMO) 3D T1 scan that is 1 mm isotropic in under 4 minutes. Dr. Banerjee adds, “This is something that was not possible before, and of course we are not stopping there. We are continuing to develop AI-driven acceleration methods for even shorter scan times.”
“We have a large, global community of neuroscience researchers. Gauging their needs, we launched the GE HealthCare MR Connectome community that meets virtually four times a year,” Dr. Banerjee adds. “There is a lot of engagement and interaction in the community, including the sharing of prototypes and fostering multi-site studies and grant publications. GE HealthCare is very grateful for the collaboration among these bright minds who are coming together and making stellar use of our best-in-class solutions.”
