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Biomedical Magnetic Resonance

Department 8.1

Laboratory for RF technology and coil development

Tasks

  • Development of transmit/receive coils for high-field and ultra-high-field MR systems
  • Performance tests and characterization measurements on MR coils, in particular on multi-channel transmit coils
  • Development and characterization of specific RF components (pre-amplifiers, matching networks)
  • Measurement of dielectric properties of phantom liquids

MR-TEM cell


 

 

MR-TEM cell for in-situ calibration of fiber optic E and H field probes in the MR scanner:

In the lower compartment, a small sphere filled with water is located in a polystyrene block. A flip angle measurement allows the transversal E and H field components in the upper compartment of the TEM cell to be traced back to the gyromagnetic ratio of water protons. The MR-TEM cell is a broadband device (up to 500MHz) and, thus, suited for all MR field strengths which are currently relevant.

See also:

T. Klepsch, T. D. Lindel, W. Hoffmann, H. Botterweck, B. Ittermann, F. Seifert
Calibration of fiber optic RF E/H-field probes using a magnetic resonance (MR) compatible TEM cell and dedicated MR measurement techniques
Opens external link in new windowBiomed Tech 57, 119-22 (2012).

Measurement of S-parameters in-situ


 

Measurement setup for the determination of S-parameters of multi-channel MR transmit/receive coils in situ:

Left: 8 x nonmagnetic directional couplers at the 'Coil Feeder Panel' of the 8-channel transmit system (3T, 7T)
Centre: Broadband electromechanical RF switching matrix for sequential measurements of the directional coupler signals
Right:     Switching matrix controller (top) as well as broadband measurement data acquisition system


See also:

G. Weidemann, F. Seifert, W. Hoffmann, H. Pfeiffer, R. Seemann, B. Ittermann
Measurements of RF power reflected and radiated by multichannel transmit MR coils at 7T
Opens external link in new windowMagn Reson Mater Phy DOI 10.1007/s10334-016-0551-6 (2016).

Butler matrix (3T, 7T)


16 x 16 Butler matrix for 3 tesla (left) or 7 tesla (right)

A Butler matrix serves to feed a multi-channel transmit coil with different phase increments of the input RF voltage. If fewer transmit channels than coil channels are available, a Butler matrix would allow, however, more diverse input voltage configurations to be realized at the full number of channels.

Broadband CW transmit system

Number of channels     2
2-channel synthesizer PTS D310; 1−310 MHz
RF amplifier I 2 x Ophir 5052; 0,15−230 MHz, 200 W
RF amplifier II 2 x in-house manufacture; 100−500 MHz, 200 W
Commissioning/Upgrade        2001/2005
Applications RF-induced temperature increase in phantoms for the characterization of MR coils (B0 = 0−11.7 T) to determine SAR distributions (specific absorption rate: measure of a possible patient hazard by absorbed radio-frequency power)