How can neuronavigation systems improve accuracy?

Neuronavigation systems, such as the Brainsight Neuronavigation system, allow real-time tracking of the position of transcranial ultrasound stimulation (TUS) transducers while providing live visual feedback to the researcher. By utilising a neuronavigation system, the position of TUS transducers can be tracked relative to a specified target within the system or with respect to a specific anatomical area of interest.

The Brainsight Neuronavigation system not only tracks the position of the transducers but also analyses the orientation of the transducer handle in relation to the area where the ultrasound field is most intense. The orientation of the transducer handle plays a crucial role in determining the neurons recruited by the TUS pulse. Consequently, any changes in the orientation of the transducer handle can impact the cortical response to TUS. Once a target location with optimal stimulation is identified, the orientation of the transducer handle during that specific location can be recorded, ensuring consistency in both the transducer orientation and target position throughout the experimental session. Targets can be defined in two ways within a neuronavigation system. One common approach is to identify a hotspot, such as a site that is most likely to evoke a specific response, such as a motor evoked potential (MEP) or a phosphene and set this hotspot as the target. This ensures consistent stimulation of the location most likely to elicit the desired response during the experiment. An alternative method is to utilise standardised coordinates, such as those based on the Montreal Neurological Institute (MNI) space, as the target. This approach is commonly used when participant-specific targets are derived from BOLD contrasts obtained from fMRI scans for each individual.

Neuronavigation systems can also be employed to transform a subject's MRI scan from its native space to a standardised coordinate space. This transformation enables identification of the MNI coordinates within a participant's MRI scan, facilitating the use of participant specific MNI coordinates.

How can Brainsight Neuronavigation improve the accuracy of a Transcranial Ultrasound Stimulation (TUS) study?

Researchers across multiple studies have highlighted the crucial role of the Brainsight Neuronavigation system in their respective studies on transcranial ultrasound stimulation (TUS) and transcranial focused ultrasound (FUS).

Yaakub et al. (2023) utilised Brainsight to accurately target deep cortical regions during their investigation of theta-burst TUS. The precise targeting facilitated the observation of selective reductions in GABA levels and increased functional connectivity in the posterior cingulate, along with state-dependent effects.

In Murphy (2023)’s study, Brainsight played a pivotal role in the development and implementation of the PhoCUS system, which enabled simultaneous monitoring of neural activity in subcortical cell types during FUS application. Brainsight's precision allowed the researchers to effectively target regions such as the hippocampus, resulting in the identification of parameter sets that selectively modulated specific cell types and suppressed epileptiform activity.

N'Djin (2023) leveraged Brainsight to explore the spatiotemporal dynamics of neural responses to low-energy FUS neurostimulation. Brainsight's assistance facilitated the investigation of FUS-induced electrophysiological effects across various in-vivo and ex-vivo models, providing valuable insights into the transient induction of action potentials, local field potentials, and calcium fluxes. 

Guinjoan et al. (2022) and Guinjoan (2023) highlight the use of Brainsight neuronavigation in studies on depression and repetitive negative thinking (RNT). By employing low-intensity transcranial focused ultrasound (LIFU), specific neural circuits associated with RNT can be targeted – with an aim to establish a causal relationship between these circuits and RNT symptoms. Brainsight's precise targeting is advantageous in the exploration of LIFU neuromodulation for depression and RNT.

Blackmore et al. (2023) acknowledged the instrumental role of Brainsight neuronavigation in optimising the application of FUS in their TUS study. By discussing different FUS modalities and their potential for short- and long-term improvements in brain disorders, they emphasised the importance of understanding optimal parameters and signalling cascades. Brainsight's guidance allowed for precise targeting, enhancing the efficacy of their FUS application.

Overall, Brainsight neuronavigation has consistently played a vital role in these studies, enabling researchers to accurately target specific brain regions, explore neurostimulation effects, investigate neural responses, and optimise the application of FUS for therapeutic purposes.