PURPOSE: 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. MATERIALS AND 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. CONCLUSION: 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. (c) 2008 Wiley-Liss, Inc.
PURPOSE: 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. MATERIALS AND 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. CONCLUSION: 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. (c) 2008 Wiley-Liss, Inc.
Authors: Akshay S Chaudhari; Bragi Sveinsson; Catherine J Moran; Emily J McWalter; Ethan M Johnson; Tao Zhang; Garry E Gold; Brian A Hargreaves Journal: Magn Reson Med Date: 2017-01-11 Impact factor: 4.668