Towards robust in vivo quantification of oscillating biomagnetic fields using Rotary Excitation based MRI.

Spin-lock based functional magnetic resonance imaging (fMRI) has the potential for direct spatially-resolved detection of neuronal activity and thus may represent an important step for basic research in neuroscience. In this work, the corresponding fundamental effect of Rotary EXcitation (REX) is investigated both in simulations as well as in phantom and in vivo experiments. An empirical law for predicting optimal spin-lock pulse durations for maximum magnetic field sensitivity was found. Experimental conditions were established that allow robust detection of ultra-weak magnetic field oscillations with simultaneous compensation of static field inhomogeneities. Furthermore, this work presents a novel concept for the emulation of brain activity utilizing the built-in MRI gradient system, which allows REX sequences to be validated in vivo under controlled and reproducible conditions. Via transmission of Rotary EXcitation (tREX), we successfully detected magnetic field oscillations in the lower nano-Tesla range in brain tissue. Moreover, tREX paves the way for the quantification of biomagnetic fields.

[Feasibilities and limitations of high field parallel MRI]. / Möglichkeiten und Grenzen der parallelen MRT im Hochfeld.

In medical magnetic resonance imaging (MRI) it is standard to use MR scanners with a field strength of 1.5 Tesla. Recently, an ongoing development to higher field strength can be observed and a new clinical standard at 3.0 Tesla seems to be established. High field MRI with its intrinsic higher signal to noise ratio (SNR) can enable new applications of MRI in medical diagnosis, or can serve to improve existing methods. It is important to note, that the use of high field MRI is not without its limitations. Besides the SNR, other unwanted effects increase with a higher field strength. Without correction, these high field problems cause a serious loss in image quality. An elegant way to address these problems is the use of parallel imaging. In many clinical applications, parallel MRI (pMRI) is part of the standard protocol, because pMRI can enhance virtually every MRI application, without necessarily affecting the contrast behavior of the underlying imaging sequence. In high field MRI, besides the speed advantage of pMRI, the positive influence on high field specific problems and therefore on the image quality will be of major importance.