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New sources of data for neurosurgical planning


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New sources of data for neurosurgical planning

  1. 1. New sources of data for neurosurgical planning Parts of the human cerebral cortex are critical for everyday activities, such as movement, speech and understanding. When a tumour or epileptic focus is located near these regions, they need to be mapped by function before surgery. Functionally important cerebral regions can be mapped in many ways, such as using MRI (Magnetic Resonance Imaging) or PET (Positron Emission Tomography). Speech regions can also be located by using the Wada test, where alternate hemispheres of the brain are anaesthetized by injecting a barbiturate into one of the carotid arteries. Tests can then determine which hemisphere is crucial for speech. The BioMag Laboratory at Helsinki University Central Hospital has developed a method for transcranial magnetic stimulation (nTMS), which can be used clinically to map functionally important area when planning neurosurgery, particularly epilepsy patients. The cerebral cortex is stimulated by delivering magnetic pulse through the cranium. TMS has a long history, and equipment has already been commercialised. Development work has been continued in SalWe’s Mind and Body Programme. Basic research began at Helsinki’s BioMag Laboratory in 1994 under Professor Risto Ilmoniemi, and a spin-off company, Nexstim Oy, was established in 2000. In 2009 the equipment that it has commercialised for nTMS was approved in the USA for mapping motor cortex. SalWe - Strategic Centre for Science, Technology and Innovation in Health and Well-being
  2. 2. “Extra individual information about the precise location of functional cerebral regions is valuable,” says Jyrki Mäkelä, head of the BioMag Laboratory. “If the neurosurgeon has this information before surgery, the patient can be told about the treatment options available. To leave part of a tumour intact is risky but to excise the whole growth sometimes has its own risks, for example to the patient’s ability to speak.” Strength through cooperation The BioMag Laboratory has developed speech mapping together with international partners. The correspondence between video nTMS and speech region mapping performed during surgery was analysed in collaboration with researchers from the Charité University Hospital of Berlin and the neurosurgical unit of Munich Technical University. BioMag development started with mapping motor cortex, which Mäkelä says is slightly easier than finding speech regions. Motor regions are mapped by subjecting the cortex to a rapidly fluctuating magnetic field, targeted according to a three-dimensional brain scan of the patient. The magnetic field induces Nexstim has been involved in the project to map speech regions. It has commercialised a speech module for nTMS that received the FDA approval in 2012. The method is already in clinical use in 17 hospitals in the USA, Germany, Italy, Sweden, Finland, among others. a weak electric current in the targeted region of the cortex. “The results of TMS are combined and compared with patient data obtained by other mapping methods. The comparison takes time and requires close cooperation between attending physicians.” Challenges of speech mapping “Mapping the parts of the cortex used in speech is hard, because their anatomy is poorly understood. There are individual variations in speech and they aren’t arranged as systematically as they are in motor cortex,” Mäkelä points out. “Speech is hard to disrupt with TMS, so we have developed a system at BioMag where we deliver pulses to a variety of cerebral regions. We video the stimulation, its target in a three-dimensional map of the brain and the patient’s performance as speech tests are given. The results are compiled afterwards by studying the videos.” BioMag development began with finance from Helsinki University Central Hospital but SalWe has facilitated its continuation. SalWe has created closer cooperation with Nexstim and also promoted Nexstim’s commercialisation of the speech application. BioMag nTMS screenshots and mapping have been integrated in Helsinki University Central Hospital’s picture archiving and communication system PACS since spring 2013. The results can therefore be transferred via the hospital’s imaging network to the clinics that need them and to a neuronavigator that guides the work of a neurosurgeon in the operating room. More information Jyrki Mäkelä associate professor BioMag Laboratory, HUS Medical Imaging +358 50 427 9051 SalWe - Strategic Centre for Science, Technology and Innovation in Health and Well-being