High-Resolution Laser Doppler Measurements of Microcirculation in the Deep Brain Structures: A Method for Potential Vessel Tracking

Abstract

Background: Laser Doppler flowmetry (LDF) can be used to measure cerebral microcirculation in relation to stereotactic deep brain stimulation (DBS) implantations. Objective: To investigate the microcirculation and total light intensity (TLI) corresponding to tissue grayness in DBS target regions with high-resolution LDF recordings, and to define a resolution which enables detection of small vessels. Methods: Stereotactic LDF measurements were made prior to DBS implantation with 0.5-mm steps in the vicinity to 4 deep brain targets (STN, GPi, Vim, Zi) along 20 trajectories. The Mann-Whitney U test was used to compare the microcirculation and TLI between targets, and the measurement resolution (0.5 vs. 1 mm). The numbers of high blood flow spots along the trajectories were calculated. Results: There was a significant difference (p < 0.05) in microcirculation between the targets. High blood flow spots were present at 15 out of 510 positions, 7 along Vim and GPi trajectories, respectively. There was no statistical difference between resolutions even though both local blood flow and TLI peaks could appear at 0.5-mm steps. Conclusions: LDF can be used for online tracking of critical regions presenting blood flow and TLI peaks, possibly relating to vessel structures and thin laminas along stereotactic trajectories.

5-ALA fluorescence and laser Doppler flowmetry for guidance in a stereotactic brain tumor biopsy

“…The blood perfusion did not show any significant difference (p > 0.05) in the tumor that could indicate a considerably higher perfusion in the tumor. It is previously investigated that blood flow measured with LDF is directly related with the vessel size, type and orientation [30,38] and the 0.5 mm insertion step is assumed to suffice for the look-ahead distance of the forward-looking probe [27,39]. Other methods of vessel detection are based on re-emission spectroscopy [19] which is an easy to implement module but might not be able to distinguish vessels (blood flow) from minor bleeding during the in vivo measurements.…”

“…Measurement at each position took around 20 s and thus the added time to the routine procedure was around 15 min. The step size of the mechanical device can be decreased to 0.5 mm [27], however, this will also increase the measurement time for a 50 mm long trajectory. In the routine application, a much quicker procedure is desired where the probe can be proceeded continuously.…”

“…In this setting the measurement probe was forward-looking and acted as a guide for the DBS lead to record the blood flow and tissue grayness. The LDF technique has a great potential to act as a 'vessel tracking' tool, and has so far been evaluated in over 120 stereotactic DBS lead implantations [26][27][28].…”

Optical Monitoring Techniques for Navigation during Stereotactic Neurosurgery

“…Within a few seconds from the movement, the laser Doppler signal is stable and the captured signals allow calculation of, for instance, mean perfusion, heart rate and peakto-peak of the microcirculation as well as the TLI at a specific position in the brain tissue. The microcirculation signal can also be used to track larger vessels along the trajectory, (46) and the TLI signals have been used to determine "bar-codes" towards two of the most common DBS targets; the STN and the Vim. (44) Figure 6 shows perfusion and TLI signals post-processed to "bar-codes" following insertion with the mechanical device at 1 mm steps towards the STN.…”

“…A recent study on patients implanted with DBS electrodes using optical guidance has shown that both TLI, i.e., grey-white tissue differences, and microvascular changes can be recorded with 0.5 mm resolution, and thus local blood flow and TLI peaks can be identified with this resolution. (46) An optical resolution of about 0.5-1 mm can therefore be considered reasonable in stereotactic and functional neurosurgery, especially as the DBS leads and RF electrodes are about 1.3 mm and 1.5-2 mm in diameter, respectively. These diameters are, on the other hand, rather large compared to the nuclei, which measure a few millimeters up to about 1 cm.…”