Polarized light imaging enhances accuracy of deep brain stimulation

Deep brain stimulation (DBS) is a widely used surgical treatment for neurological disorders such as Parkinson’s disease, essential tremor, and obsessive-compulsive disorder. The procedure involves implanting electrodes into specific brain regions to regulate abnormal activity. Success depends heavily on placing these electrodes with millimeter-level accuracy. However, current imaging tools like magnetic resonance imaging (MRI) often fall short in clearly identifying small, deep brain structures, making precise targeting difficult. A recent study published in Neurophotonics explores a promising solution: catheter-based polarization-sensitive optical coherence tomography (PS-OCT).

PS-OCT is an optical imaging technique that uses polarized light to detect subtle structural differences in tissue. Unlike MRI, which provides millimeter-scale resolution, PS-OCT can visualize brain structures at the micrometer level. This allows it to detect fine details in white matter fiber tracts—bundles of nerve fibers that are crucial landmarks for DBS targeting. The study, conducted by researchers from Laval University (Canada) and Harvard Medical School (USA), tested PS-OCT in a postmortem animal model, comparing its performance with MRI in visualizing three common DBS targets.

To simulate a DBS procedure, researchers inserted a PS-OCT probe into the brain along planned trajectories. The probe collected data as it was pulled back through the tissue, capturing high-resolution images of the brain’s internal structure. These images were then matched with MRI scans and anatomical references to assess accuracy. The PS-OCT system used a rotating catheter with a tiny lens and prism to direct light into the tissue, measuring how the light’s polarization changed as it passed through different structures. This change, known as birefringence, reflects the alignment and density of fibers in white matter.

The results showed that PS-OCT could distinguish between white and gray matter more clearly than MRI. It also revealed fine fiber structures that MRI missed, such as the internal capsule—a dense bundle of fibers important for DBS planning. In one case, PS-OCT identified highly organized fiber tracts near the GPe that were invisible in MRI scans. These findings suggest that PS-OCT could provide surgeons with intraoperative feedback during DBS procedures, improving accuracy and reducing the risk of misplacement.

To compare the two imaging methods, the team used a simplified segmentation approach. They averaged data along the probe path and applied clustering to separate tissue types. This allowed them to create “tissue barcodes” showing transitions between white and gray matter. PS-OCT produced sharper and more consistent barcodes than MRI, highlighting its potential for guiding electrode placement.

While PS-OCT offers clear advantages, it currently measures fiber orientation only in two dimensions. Future improvements could enable full 3D mapping, further enhancing its usefulness. The researchers also noted that the PS-OCT probe used in the study was slightly larger than standard DBS electrodes, but smaller probes are already available and could be adapted for clinical use.

Corresponding author Shadi Masoumi of Laval University remarked, “Catheter-based PS-OCT shows strong promise as a tool complementary to MRI in DBS neurosurgery. By providing high-resolution structural information and visualizing critical fiber pathways, it could help surgeons target brain regions more precisely.”

Next steps include live testing, integration into surgical workflows, and direct comparisons with diffusion MRI, another technique used to map brain fibers. If successful, PS-OCT could become a valuable addition to the neurosurgical toolkit, improving outcomes for patients undergoing DBS.

For details, see the original Gold Open Access article by S. Masoumi, “Catheter-based polarimetric imaging to complement MRI for deep brain stimulation neurosurgery,” Neurophotonics 12(3), 035001 (2025), doi: 10.1117/1.NPh.12.3.035001.