Estimating the apparent transverse relaxation time (R2*) from images with different contrasts (ESTATICS) reduces motion artifacts

Abstract

Relaxation rates provide important information about tissue microstructure. Multi-parameter mapping (MPM) estimates multiple relaxation parameters from multi-echo FLASH acquisitions with different basic contrasts, i.e., proton density (PD), T1 or magnetization transfer (MT) weighting. Motion can particularly affect maps of the apparent transverse relaxation rate R2*, which are derived from the signal of PD-weighted images acquired at different echo times. To address the motion artifacts, we introduce ESTATICS, which robustly estimates R2* from images even when acquired with different basic contrasts. ESTATICS extends the fitted signal model to account for inherent contrast differences in the PDw, T1w and MTw images. The fit was implemented as a conventional ordinary least squares optimization and as a robust fit with a small or large confidence interval. These three different implementations of ESTATICS were tested on data affected by severe motion artifacts and data with no prominent motion artifacts as determined by visual assessment or fast optical motion tracking. ESTATICS improved the quality of the R2* maps and reduced the coefficient of variation for both types of data—with average reductions of 30% when severe motion artifacts were present. ESTATICS can be applied to any protocol comprised of multiple 2D/3D multi-echo FLASH acquisitions as used in the general research and clinical setting.

Four in vivo g‐ratio‐weighted imaging methods: Comparability and repeatability at the group level

“…All data were coregistered to address inter‐scan motion. Maps of R2* and the PD‐, T1‐, and MT‐weighted maps at TE = 0 were estimated from the gradient echoes from all contrasts using the ordinary least squares ESTATICS approach [Weiskopf et al, ]. In addition, the image data for each acquired weighting (PDw, T1w, MTw) were averaged over the first six echoes to obtain a second set of PD‐, T1‐, and MT‐weighted maps with increased SNR [Helms and Dechent, ].…”

Brain functional impairment in beta‐thalassaemia: the cognitive profile in Italian neurologically asymptomatic adult patients in comparison to the reported literature

“…Brain tissue iron was quantified according to the analysis protocol described by Weiskopf et al (). Briefly, quantitative whole brain R2* maps were estimated using SPM12 (http://www.fil.ion.…”

SNR efficiency of combined bipolar gradient echoes: Comparison of three-dimensional FLASH, MPRAGE, and multiparameter mapping with VFA-FLASH and MP2RAGE

“…b) of the 9‐echo and 12‐echo VFA‐FLASH protocols are slightly more broadened than those of the 6‐echo protocol, which confirms the challenge of recovering pure PD from heavily ‐weighted MERGE images. A further explanation is that later echoes are more motion‐sensitive than early ones . The PD histogram from both the VFA‐FLASH1 and MP2R1 protocols is also broader, despite excellent WM/GM peak separation.…”

“…If motion is not negligible, an advanced combination procedure for the maps has been proposed recently to minimize the resulting artifacts . A summary of the postprocessing steps involved in the calculation of T 1 , PD , and is given in Figure a.…”