1. New sources of data for
neurosurgical planning
www.salwe.fi
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. “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
jyrki.makela@hus.fi
+358 50 427 9051
SalWe - Strategic Centre for Science, Technology and Innovation in Health and Well-being