Speech
fiber-
tracking

Applications: Brain tumour surgery, epilepsy surgery, cerebrovascular surgery, radiation therapy

Unlock neural networks of higher order function

 

Several tools have been developed to facilitate preoperative planning in order to reduce the duration of awake direct cortical stimulation testing, including high-resolution MRI, fMRI, DTI, and more recently also nrTMS. An appealing special application of the latter modality in the noninvasive exploration of language networks is the possibility to generate truly functional seed points to be used in DTI FT. 

 

Given the “pinpoint” approach of nrTMS, it is no surprise that the use of these language-positive stimulation points as seed points in DTI tractography enables the visualization not merely of macroscopical white matter tracts but rather of fiber bundles and even fascicles. In this respect, nTMS/nrTMS appears to be very similar to DES in being mostly unaffected by a tumour mass or surrounding oedema (vs. possible signal loss in fMRI).

 

The focused language-positive stimulation points generated by nrTMS reflect a direct cortical inhibition and are therefore truly functional. The use of these as seed points in DTI FT comes as a clear advantage in the exploration of highly functional and complex organized networks as are the language pathways. 

How?

  • Following the completion of nrTMS speech mapping, the individual DTI, FLAIR, and gradient echo sequences of each pre-op MRI are uploaded to the server, which is then followed by fusion and alignment of positive nTMS data sets.

  • When the nTMS DICOM data is imported and merged with the pre-op FLAIR, DTI and contrast-enhanced 3D gradient echo sequences, all positive data sets are enlarged by a rim of 5mm and considered 'regions of interest' 

  • A deterministic tractography algorithm implemented into a surgical navigation server such as Brainlab's iPlan follows the fiber assignment by continuous tracking (FACT) method. Tractography of the arcuate fasciculus or other closes language-related tracts (i.e., SLF, ILF, UC, FoF) is performed with language-positive nTMS points.

  • From here, the lesion-to-tract distance can be calculated as a measure of risk stratification.

Hospital purchase of Nexstim NBS system with NexSpeech

In-house:

Referral for patient MRI

Outsourced:

Patient books appointment with Neuroclast

En-TMS conducted by Neuroclast

Data sent to consultant surgeon for analysis

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5d.png
5e.png
5f.png

Composite sagittal images showing the result of DTI FT using three different types of seed points: anatomical in green, fMRI-based in emerald, and nrTMS-based in yellow and beige (colours are randomly chosen without directional colour-coding). The red 3D objects represent the fMRI activation clusters and the blue spheres the language-positive nrTMS stimulation points. (a) Arcuate fascicle reconstructed using anatomical ROIs, (b) fibers generated by using fMRI-based seed points, (c) nrTMS stimulation point number 5 and resulting fiber bundle, (d) nrTMS stimulation point number 8 and resulting fiber bundle, (e) combined fiber bundles from c and d (language-positive nrTMS stimulation points 5 and 8), and (f) composite image of all fiber bundles obtained by using functional ROIs (fMRI and nrTMS).

von Campe & Jehna (2017).

En-TMS conducted by Neuroclast may be included in multiple multi-centre trials throughout Australia. Consent will be sought prior to any data capture, and acquired from the patient, consultant and hospital.

Recommended Reading

  • Chapter 9. Nikolenko, O. & Picht, T. (2017). Navigated TMS in Neurosurgery. 87-97.

  • Haddad et al. (2021). Preoperative applications of navigated transcranial magnetic stimulation. Frontiers in Neurology, 11, 1-11.

For patients:

Surgical procedures of any description pose risk. This is a safe and non-invasive measure to distinguish how close or far the areas of the brain are with respect to your procedure. Just because you're here reading this does not mean that you're in immediate danger whatsoever, in fact, this is a proactive and preventative measure to ensure that all possible data is acquired to contribute to a safe procedure.

When you schedule an appointment with Neuroclast, you'll be greeted and given an overview of the technology and what's in store. Here's a brief summary to get you ahead:

  • You'll enter our clinic, and see a big fancy piece of equipment

  • You'll sit in a comfortable chair and engage in banter with our clinical specialists

  • We'll load up your MRI scan, and find the 'target' areas necessary for mapping

  • If it puts you at ease, we'll show you how it works first!

  • You will hear occasional semi-loud clicks, and at times you may feel a twitch - all is perfectly normal

  • For this particular test, we're targeting the parts of your brain that enable you to talk. When we target these areas you may experience a momentary disruption of speech - again this is perfectly normal.

  • The test takes between 30-60 minutes, and then you're good to go!

  • We'll forward your data to your surgeon