title: Accurate field mapping in the presence of B0 inhomogeneities, applied to MR thermometry.
abstract: OBJECTIVE
  To describe how B0 inhomogeneities can cause errors in proton resonance frequency (PRF) shift thermometry, and to correct for these errors.
  
  
  METHODS
  With PRF thermometry, measured phase shifts are converted into temperature measurements through the use of a scaling factor proportional to the echo time, TE. However, B0 inhomogeneities can deform, spread, and translate MR echoes, potentially making the "true" echo time vary spatially within the imaged object and take on values that differ from the prescribed TE value. Acquisition and reconstruction methods able to avoid or correct for such errors are presented.
  
  
  RESULTS
  Tests were performed in a gel phantom during sonication, and temperature measurements were made with proper shimming as well as with intentionally introduced B0 inhomogeneities. Errors caused by B0 inhomogeneities were observed, described, and corrected by the proposed methods. No statistical difference was found between the corrected results and the reference results obtained with proper shimming, while errors by more than 10% in temperature elevation were corrected for. The approach was also applied to an abdominal in vivo dataset.
  
  
  CONCLUSIONS
  Field variations induce errors in measured field values, which can be detected and corrected. The approach was validated for a PRF thermometry application.
authors: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.|Department of Physics, Soochow University, Taipei, Taiwan, Republic of China.
authors: Chang-Sheng
authors: CS
authors: Mei
authors: Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors: Renxin
authors: R
authors: Chu
authors: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors: W Scott
authors: WS
authors: Hoge
authors: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors: Lawrence P
authors: LP
authors: Panych
authors: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors: Bruno
authors: B
authors: Madore
mesh_terms: D000005:Abdomen / Q000033:anatomy & histology; D064368:Healthy Volunteers; D006801:Humans; D006979:Hyperthermia, Induced; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D011522:Protons; D013817:Thermography / Q000379:methods*; D014464:Ultrasonic Therapy
chemical_list: D011522:Protons
keywords: MR thermometry; PRF method; artifact correction; field mapping; multiecho sequence; quantitative imaging