title: T2 and T2* quantification using optimal B1 image reconstruction for multicoil arrays.
abstract: OBJECTIVE
  To investigate the accuracy of low signal-to-noise ratio (SNR) T(2) and T(2)* measurements using array coils and optimal B(1) image reconstruction (OBR) compared to the standard root sum of squares (RSS) reconstruction.
  
  
  METHODS
  Calibrated gels were used for the in vitro study of T(2). T(2) and T(2)* measurements were obtained from a volunteer's knee and liver, respectively. T(2) and T(2)* measurements were performed using multiecho spin echo and multiecho gradient echo sequences, respectively. SNR was deliberately kept low. The same raw data were used for both reconstructions. For the in vivo studies the effect of signal averaging was also investigated.
  
  
  RESULTS
  The optimal reconstructions demonstrated a lower mean background noise level than RSS. In vitro, the T(2) measurements made with OBR images agreed better with a reference high SNR measurement than measurements made from RSS images; the RSS image results overestimated the T(2.) In vivo, increasing the signal averages decreased the difference between the measurements obtained using the OBR and RSS methods, with RSS resulting in longer relaxation times.
  
  
  CONCLUSIONS
  This work demonstrates improvements to the accuracy of T(2) and T(2)* measurements obtained when OBR is used compared to RSS, particularly in the case of low SNR.
authors.affiliation: Department of Radiology, Cambridge University Hospitals NHS Foundation Trust, Addenbrooke's Hospital, Hills Road, Cambridge, UK. mjg40@radiol.cam.uk
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Graves
authors.forename: Daniel
authors.initials: D
authors.lastname: Emmens
authors.forename: Hubert
authors.initials: H
authors.lastname: Lejay
authors.forename: Hari
authors.initials: H
authors.lastname: Hariharan
authors.forename: Jason
authors.initials: J
authors.lastname: Polzin
authors.forename: David J
authors.initials: DJ
authors.lastname: Lomas
mesh_terms: D005782:Gels; D006801:Humans; D007717:Knee; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
chemical_list: D005782:Gels