title: A framework for accurate determination of the T₂ distribution from multiple echo magnitude MRI images.
abstract: Measurement of the T2 distribution in tissues provides biologically relevant information about normal and abnormal microstructure and organization. Typically, the T2 distribution is obtained by fitting the magnitude MR images acquired by a multi-echo MRI pulse sequence using an inverse Laplace transform (ILT) algorithm. It is well known that the ideal magnitude MR signal follows a Rician distribution. Unfortunately, studies attempting to establish the validity and efficacy of the ILT algorithm assume that these input signals are Gaussian distributed. Violation of the normality (or Gaussian) assumption introduces unexpected artifacts, including spurious cerebrospinal fluid (CSF)-like long T2 components; bias of the true geometric mean T2 values and in the relative fractions of various components; and blurring of nearby T2 peaks in the T2 distribution. Here we apply and extend our previously proposed magnitude signal transformation framework to map noisy Rician-distributed magnitude multi-echo MRI signals into Gaussian-distributed signals with high accuracy and precision. We then perform an ILT on the transformed data to obtain an accurate T2 distribution. Additionally, we demonstrate, by simulations and experiments, that this approach corrects the aforementioned artifacts in magnitude multi-echo MR images over a large range of signal-to-noise ratios.
authors.affiliation: Section on Tissue Biophysics and Biomimetics, PPITS, NICHD, National Institutes of Health, Bethesda, MD 20892, USA; Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20740, USA. Electronic address: ruiliang.bai@nih.gov.
authors.forename: Ruiliang
authors.initials: R
authors.lastname: Bai
authors.affiliation: Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705, USA.
authors.forename: Cheng Guan
authors.initials: CG
authors.lastname: Koay
authors.affiliation: Section on Tissue Biophysics and Biomimetics, PPITS, NICHD, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Hutchinson
authors.affiliation: Section on Tissue Biophysics and Biomimetics, PPITS, NICHD, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Basser
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D015233:Models, Statistical; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Gaussian; MRI; Magnitude; Multi-echo; Probability integral transform; Rician; Signal; T(2) distribution