Brain Gain: New Applications for MR-guided Focused Ultrasound

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 - Braingain

MR-guided focused ultrasound (MRgFUS) has spent 20 years upending the way certain conditions are treated. The noninvasive thermal ablation method can replace a number of surgical procedures for treating bone metastases and uterine fibroids. Now, researchers are pushing the technique into new realms, with very encouraging results. What does the literature say about where MRgFUS is headed next?

Taming Tremors

With prevalence estimates of up to 5 percent, essential tremor is the most common movement disorder in adults. It can cause embarrassment, early retirement and generally affect quality of life.

Medications can be beneficial for some, but when they are not effective, surgical therapies such as lesioning and deep brain stimulation in the thalamus become an option. With deep brain stimulation, electrodes are implanted into the thalamus or subthalamic region, and lesioning can be done with thalamotomy—both of which have risks. Intracerebral hemorrhage and neurological deficits are a concern.

Enter focused ultrasound, which researchers in Toronto have used in a pilot study to treat essential tremor. And based on the results, it has the potential to totally change the way patients with essential tremor are treated.

As the name suggests, the technique uses stereotactically guided MRI instead of diagnostic ultrasound to obtain accurate target definition, and delivers focused ultrasound to noninvasively produce ablative lesions. MR thermography also can monitor temperatures to better control energy delivery.

Nir Lipsman, MD, of the division of neurosurgery in the Krembil Neuroscience Centre at Toronto Western Hospital, and colleagues conducted the study between May 2012 and January 2013, publishing the findings in Lancet Neurology. While the study was small—four patients with chronic, medication-resistant essential tremor were treated with MRgFUS—the researchers were very encouraged by the findings.

“On the basis of the clinical benefits we observed with this non-invasive procedure, we believe that MR-guided focused ultrasound could represent a substantial advance for the management of disabling tremor,” they wrote.

Patients underwent tremor evaluation at baseline, and then were treated with MRgFUS to ablate tremor-mediating areas of the thalamus. They were reevaluated one and three months after surgery.

Lipsman and colleagues reported that patients showed immediate and sustained improvements in tremor in the dominant hand. Tremor scores were reduced an average of 89.4 percent at one month and 81.3 percent at three months. Results were clearly visible in improved ability to write and perform other motor tasks.

In addition to being effective, the procedure was also safe with an acceptable profile of adverse effects. One patient experienced paraesthesias—sensations of tingling or burning—which persisted at three months. This is not an uncommon side effect of other treatments for essential tremor—nearly four out of five patients treated with deep brain stimulation experience paraesthesias at three months, according to Lipsman and colleagues. Another patient developed a deep vein thrombosis, which the authors suspected was due to the length of the procedure.

“With technological advances in imaging software allowing easier positioning and target localization and with more experience of the treatment team, the procedure time will decrease substantially and the occurrence of adverse effects could decrease,” they wrote.

Lipsman and colleagues noted that the exact mechanism by which sonications alleviate tremor is not known, though it is likely related to the thermal ablation mediating the thalamocortical relay neurons, or “tremor cells.” There is much more to learn, but even at this early stage the authors celebrated the potential of MRgFUS for tremor.

“Our sample size is small, but the results show a large effect on tremor reduction that is remarkably robust and similar between patients,” they wrote.

Opening the Door to Alzheimer’s Relief

Alzheimer’s disease is one of the highest profile neurodegenerative diseases, with societal costs set to soar in the coming decades. More than 14 million Alzheimer’s patients in the U.S. will need treatment by 2050, at a price tag of more than $1.2 trillion.

Fortunately, preliminary research has shown that MRgFUS can play a role in Alzheimer’s treatment by opening the blood-brain barrier and improving drug delivery.

The work was done by Alison Burgess, PhD, of the Sunnybrook Research Institute