What’s on the Horizon with MRI for Neuroradiology

When it comes to neuroradiology, there has been a significant amount of trailblazing technology developed in recent years, and now many of these tools are coming into clinical practice.

During this year’s Radiological Society of North America (RSNA) annual meeting, sub-specialty experts laid out some of the more interesting and effective technologies within the modality that are in the neuroradiology pipeline.

MRI-Guided Focused Ultrasound (MRgFUS)

Approved by the U.S. Food & Drug Administration in 2016, MRgFUS, which uses a water bath around the head to facilitate signal transmission, is showing great promise with several applications, said Levi Chasen, M.D., associate professor of radiology at Weill Cornell Medicine.

Essential Tremor: This condition affects more than 5 million Americans, and in recent history, it has been treated with stereotactic radiosurgery, gamma knife, and deep brain stimulation. But, MRgFUS is growing in popularity as a way to target the tremor more precisely via ventral intermediate nucleus thalamotomy. It can be used to intricately perform ablative techniques without damaging surrounding tissue.

Intraoperative Imaging: Because there is currently no head coil for the 3T MRI system, MRgFUS is being used to provide a better peak inside the skull during surgical procedures. Although further advancements are needed to refine this use, images of diagnostic quality are possible, Chasen said.

“We’ve been able to come up with some very nice images of diagnostic quality,” he said. “We can see, while the patient is still on the table with the water bath in place, the kind of lesion we’re creating.”

Blood-brain barrier: It is possible, he said, to use a lower-frequency helmet to deliver cavitations. To do so, patients are injected with micro-bubbles that can target different areas of the brain to induce cavitations and transiently open the blood-brain barriers, which subsequently re-seals. Being able to do this successfully opens the door for drug delivery applications, he said.

7T MRI

Although 7T MRI received FDA approval for clinical use in 2017, there have been several obstacles to its use, including the need for a larger scanner room and a lack of a body coil. But, the technology also presents several advantages, said Kirk Welker, M.D., associate professor of radiology at the Mayo Clinic. And, with those advantages have come several successes, he said.

Epilepsy: 7T does a better job of other MRI strengths in detecting focal central dysplasia, mesial temporal sclerosis, cavernous malformations, and cerebellar hemorrhage. For example, in recent research with focal central dysplasia, 7T MRI was able to change treatment for 19 percent of patients for whom these findings were occult on 3T and 1.5T MRI scans.

Pituitary Imaging: 7T MRI also performs better in detecting ACTH secreting microadenoma, Welker said. According to recent clinical findings he presented during the session, 7T MRI detected 90 percent of these findings that were present in patients who had other previous negative MRI scans.

Multiple sclerosis: This magnet strength is effective in identifying the central veins in the multiple sclerosis white matter lesions, he said, but its capabilities on follow-up are limited because no spine RF coil exists to image the spinal cord.

But, 7T MRI is not without its challenges, Welker explained. It still faces some stumbling blocks to wider use. Overall, six things stand in its way to getting more patients into the system:

• There are few metallic devices that are approved by the manufacturers to be used in 7T systems.
• Due to SAR limitations, 7T is not approved for use in children under 30 kg in weight.
• SAR limitations also make already long scans longer.
• The magnetic field can cause dizziness in patients.
• The long narrow bore can create claustrophobia in some patients.
• The small head coil might be not able to accommodate larger patients.

Overall, Welker said, it is important to remember that a 7T MRI does have unique factors.

“7T is not just 3T ‘on steroids,’” Welker explained.

Consequently, further comparative effectiveness research is necessary to address whether its benefits warrant the additional cost attached to the extra field strength, he said.

For additional RSNA coverage, click here.