Entwicklung eines 6-Kanal Phased-Arrays für Mäuse

Translated title of the contribution: Development of a 6-channel Phased-Array for mice

Andreas Ambrusch

Research output: ThesisMaster's Thesis


This thesis deals with the construction of a 6-channel Phased-Array for mice. The requirements for the array are a SNR comparable to that of a birdcage-resonator but with a larger field of view (FOV).

When putting the body into the static B_0- field of the MR- tomograph the macroscopic magnetization gets aligned parallel and antiparallel to that field. A RF- Pulse, which is orthogonal to the direction of the static B_0- field can flip the spins. While returning to their thermodynamic equilibrium, the spins are generating a magnetic field of high frequency which induces the MR- Signal in the receiving coils. To ensure that the coils of the array are receiving the signal independently from each other, the coils have to be inductively decoupled as well as possible. This is achieved by overlapping the coils by a defined amount. Further coupling of the coils is prevented by the preamplifier which terminates the receiving coil with a high impedance via a λ/4- line. To receive the highest possible signal it is necessary to exactly adjust each component (receiving coil, active decoupling, λ/4-line, Pi-section, preamplifier) in the receiving chain. Because the signal is very low, it is also necessary to eliminate (as well as possible) the different mechanisms of losses which are constituting sources of noise. To eliminate them different methods like a symmetrical construction of the whole array, the usage of low- loss components and a capacitive division of the receiving coil (to minimize the antenna effect) were applied.

At first the results were not satisfying. In an overlap region a decrease of intensity resulted probably because of an inductive decoupling less than ideal. This decrease became minimized by pre- normalization during the acquisition. Indeed the array achieved a FOV of 11 cm but an insufficient homogeneity and SNR. The decrease of intensity could be eliminated by increasing the overlap in that region. But by doing this the SNR decreased heavily which yielded an impractical solution. Another approach to solve the problem was rotating of both 3-channel-arrays with respect to each other which yielded the desired result. With this configuration a SNR enhancement of 11% and a FOV- enhancement of 65% compared to that of the birdcage- resonator were reached. Thus all objectives were achieved.
Translated title of the contribution Development of a 6-channel Phased-Array for mice
Original languageGerman
QualificationMaster of Science
Awarding Institution
  • Graz University of Technology (90000)
  • Scharfetter, Hermann, Supervisor
Publication statusPublished - 2013
Externally publishedYes


  • Phased- Array
  • inductive decoupling
  • preamplifier decoupling
  • pre-normalization
  • decrease of intensity


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