Nina Theysohn MD, Presenter: Nothing to Disclose

Shaozheng Qin, Abstract Co-Author: Nothing to Disclose

Stefan Maderwald, Abstract Co-Author: Nothing to Disclose

Mark E. Ladd PhD, Abstract Co-Author: Nothing to Disclose

Jens Matthias Theysohn MD, Abstract Co-Author: Nothing to Disclose

Elke Ruth Gizewski, Abstract Co-Author: Nothing to Disclose

Guillen Fernandez PhD, Abstract Co-Author: Nothing to Disclose

Indira Tendolkar MD, Abstract Co-Author: Nothing to Disclose

High field strength functional MRI has developed rapidly due to its advantages such as increasing SNR and BOLD contrast. Nevertheless, it suffers from i. e. signal dropouts in brain regions close to tissue air boundaries such as the medial temporal lobe, leading to an aggravated depiction of valuable activation. These deficits have challenged functional imaging of the hippocampus. An optimized sequence was set out at a 7T MRI scanner to visualize the medial temporal lobe (MTL) activity during an associative memory encoding task.

28 healthy volunteers were examined while performing a blocked-design face-professional name associative memory encoding task and a visual-motor judgment as control condition at 7T (n=14) or 3T (n=14; Magnetom 7T or Trio, Siemens Healthcare, Germany). Whole brain EPI images were acquired with Siemens’ integrated parallel acquisition technique (iPAT, GRAPPA R=2). 7T:50 slices, TE 25 ms, TR 2050 ms, resolution 2.5 x 2.5 x 2 mm³, 3T: 37 slices, TE 25 ms, TR 2180 ms, resolution 3 x 3 x 3 mm³). 3T and 7T data were compared and analyzed with SPM 5.

As expected, EPI images at 7T were of high quality due to a good visual white/grey matter contrast. Signal dropouts and artifacts at the lower MTL were acceptable at 7T. Assessing the memory-related neural activity in both groups the results revealed robust functional activations in the bilateral MTL especially the bilateral hippocampus, and associated brain areas at both field strengths (cluster level p < 0.05 corrected). To characterize the intensity of hippocampal activity, we performed a region of interest analysis for the hippocampus. Beta values of parameter estimation were extracted and compared. The results revealed significantly higher intensity of the hippocampal activity at 7T (0.72 ± 0.06) than 3T (0.33 ± 0.04) (t(23) = 5.63; p < 0.001).

The associative memory encoding task resulted in similar robust activations in the MTL. Hippocampal structures were detected consistently and reliably in all volunteers using whole-brain fMRI at 7T with higher BOLD signal changes as compared to data from 3T. Artifacts in the MTL were acceptable at 7T and not limiting the quality of EPI-imaging.

These preliminary results will be used for further high resolution region of interest (ROI) analysis concentrating on the hippocampal substructures, its role in memory encoding and in MTL disorders.

Theysohn, N, Qin, S, Maderwald, S, Ladd, M, Theysohn, J, Gizewski, E, Fernandez, G, Tendolkar, I, Visualizing Hippocampal Activity During Associative Memory Encoding in Humans at 3 and 7 Tesla.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034541.html