The Promise and Potential of DTI in Neurology
New research continues to advance the powerful potential of diffusion-tensor imaging (DTI) in brain research and brain mapping, ensuring the technology’s place on the path to precision medicine
“The role of neuroimaging in determining prognosis in concussion patients remains an area of huge interest and growth,” said Michael L. Lipton, MD, PhD, associate director of the Gruss Magnetic Resonance Research Center and director of radiology research and MRI at Albert Einstein College of Medicine and Montefiore Medical Center in the Bronx, New York.
“Our approach to individualized analysis of DTI and its enhancement of outcome prediction should be seen as a significant step toward realization of precision imaging (that is, precision medicine application of quantitative radiology methods to make patient-centered diagnostic inferences),” Dr. Lipton added.
Unlike standard imaging techniques, DTI can uncover the underlying pathology for traumatic brain injury (TBI) and mild traumatic brain injury (MTBI). Between 15 percent and 30 percent of people suffering MTBI - or concussion - will have continued problems resulting from such an injury, a group often referred to as the “miserable minority,” Dr. Lipton said.
“The biggest conundrum in TBI research and clinical care is who is going to recover and who is part of that miserable minority,” Dr. Lipton said. “We'd like to know who they are up front rather than waiting it out for the effects to present.”
DTI Could Aid Mild Traumatic Brain Injury Prognosis
Two recent studies presented by Dr. Lipton and colleagues at RSNA 2015 show the potential role DTI could play in helping people most at risk for persistent, long-term problems that result from head injuries.
DTI abnormalities around the time of injury are significantly related to long-term outcomes, said Sara B. Rosenbaum, MD, a second-year radiology resident at Albert Einstein College of Medicine and Montefiore Medical Center who presented one of the studies at RSNA 2015.
“Prospective identification of those at risk may allow for improved patient management and inform treatment trials,” Dr. Rosenbaum said.
The researchers recruited 31 MTBI patients from a local emergency center as well as 40 healthy volunteers. DTI at 3 Tesla (3T) was performed within two weeks of injury and cognition was tested at one year post-injury.
Subjects were classified based on the presence or absence of abnormally high radial diffusivity (RD) within two weeks of injury in brain regions commonly affected by TBI (left frontal, right frontal, left temporal, right temporal and corpus callosum). T-tests compared cognitive outcomes between subjects with or without abnormally high RD in each region.
The results showed subjects with abnormally high RD in the left temporal and right temporal lobes performed worse on cognitive tasks at one year post-injury.
“These results suggest that individualized quantitative analysis of DTI in the setting of MTBI might ultimately aid in MTBI prognostication,” Dr. Lipton said. “DTI could thus, if further study confirms its prognostic value, be used as a noninvasive biomarker in the acute setting to identify those who will have poor long-term outcome.”
Sex Plays Role in Negative Long-Term Effects of Sports-Related Head Injury
In a related study done at Einstein, researchers used DTI to determine that sex is a potential risk modifier for the negative long-term effects of head injury, specifically that women have a higher risk than men.
The researchers studied 41 females and 41 age- and education-matched males (ages 18-52) drawn from an ongoing longitudinal study of repetitive head impacts on amateur soccer players. The research included a questionnaire to help estimate the number of headers performed over the prior 12 months.
Analysis following 3T DTI imaging and neurocognitive testing revealed that women appear to have a greater response to repetitive head impacts for the same amount of heading. The researchers found more evidence of white matter microstructural damage and worse cognitive performance in women compared to men.
“The overall goal is to generate guidelines for safe heading exposure,” said Eva Catenaccio, MD, of Einstein, who presented the research. “These results demonstrate that these guidelines need to be sex-specific.”
DTI Plays Role in Brain Mapping
DTI also plays an essential role in preoperative brain mapping, which is creating a major shift in the neurosurgical care of brain tumor patients.
The mapping depicts individual white matter tracts, which aid surgeons in safely resecting and removing brain tumors, according to John. L. Ulmer, MD, chief of neuroradiology and director of neuroradiology research at the Medical College of Wisconsin in Milwaukee.
“Using standard imaging alone is insufficient in determining the relationship of the brain tumor to any of the given white matter networks around it,” Dr. Ulmer said.
Because white matter is difficult to identify anatomically during surgery, Dr. Ulmer said surgeons often cannot tell which white matter tract controls critical functional areas such as motor skills, language, vision and memory. DTI creates a color-coded image of the brain that establishes functional network resection boundaries around the tumor.
“Preoperative DTI helps the surgeon avoid injuring eloquent brain networks when taking tumors out. By doing that, we’re showing we can improve function and reduce post-operative deficits,” he said.
In research presented at RSNA 2015, Dr. Ulmer demonstrated that preoperative DTI leads to improved neurological outcomes. In one retrospective study, he measured outcomes in 33 left (dominant) posterior frontal lobe resected tumors. In 18 patients without DTI, seven (39 percent) experienced permanent neurologic deficits. Of the 15 patients where DTI was utilized, only one (7 percent) experienced permanent neurologic deficits.
In collaboration with the Department of Neurosurgery, a separate and ongoing retrospective pilot study also found improved postoperative neurological outcomes with preoperative mapping. There was no difference in the 30-month survival rates between groups with or without preoperative DTI and functional MRI (fMRI). The same study showed a non-significant trend in improved survival in the pre-mapped group during the first 15 months after surgery.
Dr. Ulmer said a next step in preoperative neurosurgery is adapting 3-D functional brain printing. This would provide neurosurgeons with a 3-D perspective of the critical functional white matter network relationships as well as an educational tool during consultations with brain tumor patients. The model would also provide patients with a take-home, customized model for greater understanding and consultation with family and loved ones.