title: Susceptibility-weighted MR imaging of radiation therapy-induced cerebral microbleeds in patients with glioma: a comparison between 3T and 7T.
abstract: BACKGROUND
  Cerebral microbleeds have been observed in normal-appearing brain tissue of patients with glioma years after receiving radiation therapy. The contrast of these paramagnetic lesions varies with field strength due to differences in the effects of susceptibility. The purpose of this study was to compare 3T and 7T MRI as platforms for detecting cerebral microbleeds in patients treated with radiotherapy using susceptibility-weighted imaging (SWI).
  
  
  METHODS
  SWI was performed with both 3T and 7T MR scanners on ten patients with glioma who had received prior radiotherapy. Imaging sequences were optimized to obtain data within a clinically acceptable scan time. Both T2*-weighted magnitude images and SWI data were reconstructed, minimum intensity projection was implemented, and microbleeds were manually identified. The number of microbleeds was counted and compared among datasets.
  
  
  RESULTS
  Significantly more microbleeds were identified on SWI than magnitude images at both 7T (p = 0.002) and 3T (p = 0.023). Seven-tesla SWI detected significantly more microbleeds than 3T SWI for seven out of ten patients who had tumors located remote from deep brain regions (p = 0.016), but when the additional three patients with more inferior tumors were included, the difference was not significant.
  
  
  CONCLUSIONS
  SWI is more sensitive for detecting microbleeds than magnitude images at both 3T and 7T. For areas without heightened susceptibility artifacts, 7T SWI is more sensitive to detecting radiation therapy-induced microbleeds than 3T SWI. Tumor location should be considered in conjunction with field strength when selecting the most appropriate strategy for imaging microbleeds.
authors.affiliation: The UC Berkeley & UCSF Graduate Program in Bioengineering, University of California San Francisco, San Francisco, CA, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Bian
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Hess
authors.forename: Susan M
authors.initials: SM
authors.lastname: Chang
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Nelson
authors.forename: Janine M
authors.initials: JM
authors.lastname: Lupo
mesh_terms: D001932:Brain Neoplasms / Q000150:complications / Q000473:pathology* / Q000532:radiotherapy*; D002543:Cerebral Hemorrhage / Q000209:etiology / Q000473:pathology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005910:Glioma / Q000150:complications / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D011832:Radiation Injuries / Q000209:etiology / Q000473:pathology*; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome