TrueBOLD: Detection of brain activity with TrueFISP

DFG Reinhart Koselleck Project

Figure 1. left: functional map acquired with bSSFP at 1 mm isotropic resolution at 9.4T (from (4)). Right: functional activation of the retina acquired with bSSFP plus false activation near the stop band

TrueBOLD addresses the detection of neuronal activity in humans with magnetic resonance imaging based on the TrueFISP or balanced SSFP acquisition scheme at very high fields. Traditionally, blood oxygenation changes are detected with T2*-weighted echo planar sequences (EPI) that are sensitive to the static dephasing around small and larger vessels filled with deoxygenated blood. EPI is not specific to a certain type of vessel architecture or size, it sometimes shows blurring and blooming around larger vessels, it shows significant spatial distortions and thus severe challenges in precise co-registration to submillimeter anatomical scans. The proposed detection of BOLD changes with pass-band balanced SSFP, TrueBOLD, in combination with localized and dynamic shim arrays and strategies to minimize physiological signal fluctuations has the potential to overcome these limitations. The somewhat counterintuitive application of bSSFP at very high fields of 9.4T will boost the reduced sensitivity of this technique nearly into the range of EPI, but with significantly increased spatial specificity and absence of any spatial displacements. We will address a number of challenges and research questions that are linked to the fast and reliable implementation of bSSFP at 9.4T, as well as application of this technique in visual processing experiments to determine its spatial and neuronal point-spread-function. The ultimate goal is to advance TrueBOLD to the future standard for functional brain imaging at high fields.

We thus have recently implemented (and modified) rapid pass-band bSSFP at 9.4T, and we were able to produce highly reproducible activation maps, as shown in Figure 1.

The stability or temporal SNR is superior to that of EPI, however, observed functional signal changes are still about 2-3 times less. Preliminary comparisons of bSSFP to GE-EPI and SE-EPI suggest a mainly T2-related signal behavior (and diffusion effects) with an emphasis to the small vessel diffusion narrowing regime, and with reduced sensitivity to larger draining veins (5). Based on these findings we aim to push this technology by combining high field technology with advanced bSSFP imaging. We aim to address the following research question and challenges:

  • Boost the acquisition efficiency of bSSFP
  • Confine the local frequency distribution within the brain to the pass band of bSSFP by means of novel local shim coil arrays integrated into the RF transmit and receive helmet
  • Detection and minimization of physiological noise with real-time feedback
  • Detection and minimization of motion based on local receive coil navigators What do we see? Analysis the spatial and temporal specificity of TrueBOLD

DFG Reinhart Koselleck Project SCHE 658/12
TrueBOLD: Detection of brain activity with TrueFISP
PI: K. Scheffler
Funding: EUR 1.220.000 for 5 years

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