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Technical facilities

Magnetic resonance scanner Siemens MAGNETOM 7T

In summer 2007, a third magnetic resonance scanner was installed at the Institute. Its magnet with an open bore of 60-centimeter inner diameter produces a field of 7 tesla — which is 140,000 times stronger than the magnetic field of planet earth. With covers, it is roughly 3.6 meters long and weighs more than 34 metric tons. The cryostat holds approximately 1,750 liters of liquid helium to cool the superconducting coil of niobium-titanium alloy permanently to 4,2 kelvins. For shielding, the magnet is installed within an iron box of 10 × 5.7 × 5.7 meters weighing 362 tons. Outside this iron shield, the stray field is efficiently reduced, and the 0.5 millitesla contour is well-contained within the elliptical building housing the scanner.

Two gradient systems are available for spatial encoding—a whole-body system producing up to 45 milliteslas per meter with a minimal ramp time of 225 microseconds or, alternatively, a head-gradient set capable of generating gradients of 80 millitesla per meter within 200 microseconds. The resonance frequency for hydrogen imaging is 300 megahertz. Thirty-two radiofrequency channels are available for receiving magnetic resonance signals. A special feature is the installation of an array of 8 independent transmit channels, which are sufficiently broad banded for magnetic resonance with most biologically relevant nuclei other than hydrogen.

Magnetic resonance scanner Siemens MAGNETOM Trio

This scanner, which was installed in 2003, has also a cryomagnet generating a static field of almost 3 teslas. The magnet is 2 meters long, weighs roughly 12 metric tons, and has an open bore diameter of 60 centimeters. The magnetic field is again produced by a coil from niobium-titanium alloy cooled by liquid helium (up to 2,160 liters) to 4.2 kelvins. The coil carries a current of roughly 480 amperes flowing through more than 100 kilometers of superconducting wire as thin as a human hair. This magnet is actively shielded, hence, within less than 6 meters its stray field decays to 0.5 milliteslas.

Spatial information is encoded by a whole-body gradient system producing gradients of up to 40 milliteslas per meter along each of the three Cartesian axes within a minimal ramp time of 200 microseconds. The resonance frequency in imaging experiments with hydrogen is 123.2 megahertz. The scanner was equipped as the first of its kind with a whole-body coil. In addition, various head coils are used to investigate the human brain. In pulsed mode, the amplifiers generate up to 35 and 8 kilowatts for the body coil and the transmit head coils, respectively. For receive, eight parallel channels are available with an analog bandwidth of 1 megahertz. A broad-banded second radiofrequency channel is available for magnetic resonance experiments with nuclei other than hydrogen.

Magnetic resonance scanner BRUKER MedSpec 30/100

The scanner was installed in 1996 as one of the first of its kind. Its central component is a magnet producing a field of 3 teslas—this is roughly 60,000 times stronger than the earth’s magnetic field. The field is generated by a superconducting coil of niobium-titanium alloy carrying an electric current of about 250 amperes without resistance and, hence, without losses. As the coil must be cooled permanently to 4.2 degrees above absolute zero (i.e., –269 degrees Celsius), it is contained in a thermally isolated vessel made of stainless steel and filled with up to 1,200 liters of liquid helium. On the outside, this helium cryostat is surrounded by another tank storing 600 liters of liquid nitrogen to reduce helium losses due to evaporation. The inner diameter of the distinctive hollow tube of the magnet is 55 centimeters.

To locate the recorded magnetic resonance signals to well-defined positions inside the human body a so-called gradient field is superimposed on the static main magnetic field. The built-in whole-body gradient system generates gradients of a maximal strength of 45 milliteslas per meter within a minimal switching time of 250 microseconds along any of the three Cartesian axes. The resonance frequency for imaging with hydrogen nuclei (mostly contained in the tissue water) is 125.3 megahertz. Either a circularly polarized radiofrequency headcoil or custom-built designated coils are used in such experiments. The amplifier can produce radiofrequency pulse with up to 5 kilowatts. The scanner is equipped with additional radiofrequency cannels for detection of magnetic resonance signals of other nuclei (e.g., carbon-13, oxygen-17, phosphorus-31) besides hydrogen.

Magnetoencephalograph Vektorview

The MEG system was installed in November/December 2006 by Elekta Neuromag Oy, Helsinki, Finnland. It is a whole head system hosting 306 magnetic channels in total. The system is also equipped with an integrated 128 channel electroencephalography system and devices for auditory, visual and somatosensory stimulation.

Currently, the maximum sampling rate is 5000 Hz for all channels. At this rate the device produces about 500 MByte of data per minute. This raw data usually passes extensive postprocessing before it allows conclusions about it's origin - the underlying brain activity.

The magnetic sensors are operational only at a very low temperature below 10 K(elvin). The is achieved by placing them in a bath of liquid helium. While the liquid helium boils it stays at the temperature of the phase transition at 4.2 K. The liquid helium reservoir is much smaller compared to the one of MR scanners. It holds about 100 litres of liquid helium. It has to be refilled once per week.

Magstim Rapid2 TMS

Transcranial magnetic stimulation (TMS) is a method that relies on a short-lived magnetic field which is induced by a high current (approx. 5000 Amp) running through a well insulated cable wound into a coil. This field lasts for about half a millisecond and reaches peak amplitudes of 3 Tesla, which is comparable to the field strength used in MRI scanning. Neurons react to these extreme magnetic fluctuations (rising from 0 to 3 Tesla and back to 0 within less than a millisecond) by producing signaling impulses themselves. If the coil, being relatively small and lightweight, is placed to the head of the subject, the nerve cells just underneath the focus of the coil send impulses synchronous to the TMS pulse (normally up to once a second). Since this simultaneous firing of complete neural populations is without any functional content, information processing in this part of the brain is disturbed for fractions of a second. This allows us to induce "virtual lesions", i.e. simulate the failure of the brain region in question without jeopardizing the subject. By deliberately integrating TMS in a well elaborated experiment, one can prove the importance of the brain part in a given cognitive function because performance deficits can be expected. To optimize targeting during TMS experiments, previously obtained (functional) MR imaging data can be utilized for the so called neuro-navigation. A computer compares the brain scan with the subject's head and thus enables a very precise positioning of the coil on the head, just over the brain region of interest.

Magnetic field strength:

0,5 - 3,5 Tesla

Maximum repetition rate:

50 Hz bei 30% max. stimulator output
30 Hz bei 50%
18 Hz bei 80%
15 Hz bei 100%

In our experiments, we normally use stimulation frequencies of 1Hz, and sometimes short pulse series of 10Hz. Duration of a single impluse: 400µs.

Further technical facilities at the Institute:

EEG Laboratories with 64 bzw. 96 channels

3-D Digitalisers for three-dimensional registration of scalp position of electrodes

Laboratories for reaction-time experiments, including one psychophysics and one pharmalogical lab

Psycho-acoustical lab with sound-isolated chamber
Language lab for the editing of language stimulus material for experimental-psychological tests

Analysis labs with three SGI-O2-Workstations

Parallel computer

Ethernet-LAN with GB-Ethernet-Backbone with components by Extreme Networks (Summit 48, Black Diamond)

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Last update: Apr 1, 2010 2.23.32 pm

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