Diffusion MRI - Science@NICHD · diffusion MRI. Here we review the most common manifesta-tions of...
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303 18 Artifacts in Diffusion MRI CARLO PIERPAOLI Summary Box This chapter focuses on artifacts that are relevant for diffusion • imaging studies of the brain in a clinical research setting. For typical clinical studies, the most relevant sources of “physi- • ological noise” artifacts are subject motion and cardiac pulsation, and the most common sources of “system-related artifacts” are eddy current distortions. Artifacts not only increase the variability of diffusion MRI mea- • sures but also, most importantly, introduce bias, resulting in poten- tially false-positive findings. Physiological noise artifacts affect the statistical properties of • diffusion-derived measures in a regionally heterogeneous manner. Some anatomical regions are severely affected, while others are almost immune. For diffusion tensor imaging (DTI), there are several data-processing • approaches that can successfully remove effects of artifacts and improve the quality of the computed diffusion metrics. Identification and removal of artifactual data points in high • b-value /HARDI applications is still a largely unmet challenge. As technology improves and scanning is performed at higher • magnetic fields, the relative importance of thermal noise in deter- mining the quality of diffusion MRI measurements is decreasing, while that of physiological noise is increasing. Contrary to what is commonly assumed, if correctly implemented, • cardiac gating can be performed in a time-efficient way with no or very little increase in total scan time. Practical suggestions for designing optimal acquisition protocols • aimed at minimizing the effects of artifacts are provided in this chapter. 18-Jones-Chap-18.indd 303 18-Jones-Chap-18.indd 303 8/4/2010 2:45:13 PM 8/4/2010 2:45:13 PM
