@article{LohrTerekhovWengetal.2019,
  author    = {Lohr, David and Terekhov, Maxim and Weng, Andreas Max and Schroeder, Anja and Walles, Heike and Schreiber, Laura Maria},
  title     = {Spin echo based cardiac diffusion imaging at 7T: An ex vivo study of the porcine heart at 7T and 3T},
  series = {PLoS ONE},
  volume    = {14},
  journal   = {PLoS ONE},
  number    = {3},
  doi       = {10.1371/journal.pone.0213994},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-201376},
  pages     = {e0213994},
  year      = {2019},
  abstract  = {Purpose of this work was to assess feasibility of cardiac diffusion tensor imaging (cDTI) at 7 T in a set of healthy, unfixed, porcine hearts using various parallel imaging acceleration factors and to compare SNR and derived cDTI metrics to a reference measured at 3 T. Magnetic resonance imaging was performed on 7T and 3T whole body systems using a spin echo diffusion encoding sequence with echo planar imaging readout. Five reference (b = 0 s/mm\(^2\)) images and 30 diffusion directions (b = 700 s/mm\(^2\)) were acquired at both 7 T and 3 T using a GRAPPA acceleration factor R = 1. Scans at 7 T were repeated using R = 2, R = 3, and R = 4. SNR evaluation was based on 30 reference (b = 0 s/mm\(^2\)) images of 30 slices of the left ventricle and cardiac DTI metrics were compared within AHA segmentation. The number of hearts scanned at 7 T and 3 T was n = 11. No statistically significant differences were found for evaluated helix angle, secondary eigenvector angle, fractional anisotropy and apparent diffusion coefficient at the different field strengths, given sufficiently high SNR and geometrically undistorted images. R≥3 was needed to reduce susceptibility induced geometric distortions to an acceptable amount. On average SNR in myocardium of the left ventricle was increased from 29±3 to 44±6 in the reference image (b = 0 s/mm\(^2\)) when switching from 3 T to 7 T. Our study demonstrates that high resolution, ex vivo cDTI is feasible at 7 T using commercial hardware.},
  language  = {en}
}
@article{LohrTerekhovVeitetal.2020,
  author    = {Lohr, David and Terekhov, Maxim and Veit, Franziska and Schreiber, Laura Maria},
  title     = {Longitudinal assessment of tissue properties and cardiac diffusion metrics of the ex vivo porcine heart at 7 T: Impact of continuous tissue fixation using formalin},
  series = {NMR in Biomedicine},
  volume    = {33},
  journal   = {NMR in Biomedicine},
  number    = {7},
  doi       = {10.1002/nbm.4298},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-215536},
  year      = {2020},
  abstract  = {In this study we aimed to assess the effects of continuous formalin fixation on diffusion and relaxation metrics of the ex vivo porcine heart at 7 T. Magnetic resonance imaging was performed on eight piglet hearts using a 7 T whole body system. Hearts were measured fresh within 3 hours of cardiac arrest followed by immersion in 10\% neutral buffered formalin. T\(_{2}\)* and T\(_{2}\) were assessed using a gradient multi-echo and multi-echo spin echo sequence, respectively. A spin echo and a custom stimulated echo sequence were employed to assess diffusion time-dependent changes in metrics of cardiac diffusion tensor imaging. SNR was determined for b = 0 images. Scans were performed for 5 mm thick apical, midcavity and basal slices (in-plane resolution: 1 mm) and repeated 7, 15, 50, 100 and 200 days postfixation. Eigenvalues of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) decreased significantly (P < 0.05) following fixation. Relative to fresh hearts, FA values 7 and 200 days postfixation were 90\% and 80\%, while respective relative ADC values at those fixation stages were 78\% and 92\%. Statistical helix and sheetlet angle distributions as well as respective mean and median values showed no systematic influence of continuous formalin fixation. Similar to changes in the ADC, values for T\(_{2}\), T\(_{2}\)* and SNR dropped initially postfixation. Respective relative values compared with fresh hearts at day 7 were 64\%, 79\% and 68\%, whereas continuous fixation restored T\(_{2}\), T\(_{2}\)* and SNR leading to relative values of 74\%, 100\%, and 81\% at day 200, respectively. Relaxation parameters and diffusion metrics are significantly altered by continuous formalin fixation. The preservation of microstructure metrics following prolonged fixation is a key finding that may enable future studies of ventricular remodeling in cardiac pathologies.},
  language  = {en}
}