Abstract
PurposeTo demonstrate three‐dimensional (3D) multiple b‐value diffusion‐weighted (DW) MRI of hyperpolarized 3He gas for whole lung morphometry with compressed sensing (CS).MethodsA fully‐sampled, two b‐value, 3D hyperpolarized 3He DW‐MRI dataset was acquired from the lungs of a healthy volunteer and retrospectively undersampled in the k y and k z phase‐encoding directions for CS simulations. Optimal k‐space undersampling patterns were determined by minimizing the mean absolute error between reconstructed and fully‐sampled 3He apparent diffusion coefficient (ADC) maps. Prospective three‐fold, undersampled, 3D multiple b‐value 3He DW‐MRI datasets were acquired from five healthy volunteers and one chronic obstructive pulmonary disease (COPD) patient, and the mean values of maps of ADC and mean alveolar dimension (Lm D) were validated against two‐dimensional (2D) and 3D fully‐sampled 3He DW‐MRI experiments.ResultsReconstructed undersampled datasets showed no visual artifacts and good preservation of the main image features and quantitative information. A good agreement between fully‐sampled and prospective undersampled datasets was found, with a mean difference of +3.4% and +5.1% observed in mean global ADC and Lm D values, respectively. These differences were within the standard deviation range and consistent with values reported from healthy and COPD lungs.ConclusionsAccelerated CS acquisition has facilitated 3D multiple b‐value 3He DW‐MRI scans in a single breath‐hold, enabling whole lung morphometry mapping. Magn Reson Med 77:1916–1925, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Highlights
Diffusion-weighted MRI (DW-MRI) with hyperpolarized (HP) noble gases is sensitive to changes in lung microstructure through the measurement of the apparent diffusion coefficient (ADC) of the gas in the alveoli [1,2,3]
MAEADC exhibited a similar trend to magnitude image (MAEMAG), ie, increasing undersampling resulted in larger error values
The opposite trend was observed with the full width at half maximum (FWHM) of the histogram, which decreased at higher acceleration factors (AF): FWHM 1⁄4 0.141 cm2/s at AF 1⁄4 1 and 0.118 cm2/s at AF 1⁄4 5
Summary
Diffusion-weighted MRI (DW-MRI) with hyperpolarized (HP) noble gases is sensitive to changes in lung microstructure through the measurement of the apparent diffusion coefficient (ADC) of the gas in the alveoli [1,2,3]. The measured ADC value can be influenced by nonGaussian phase behavior of the DW signal of the gas in the lungs, causing non-mono-exponential signal attenuation with increasing b-value. This behavior is determined by the specific diffusion regime, which is influenced by several factors including the DW measurement parameters, gas diffusivity, and the complex alveolar structure [4]. Various models of gas diffusion in the lungs have been proposed to address this non-Gaussian signal behavior, and provide estimates of lung alveolar length scales from the HP gas signal These include cylindrical geometrical models [5,6], q-space transforms [7], and more recently, stretched exponential models [8]. Multiple b-value acquisition in a single breath-hold requires long scan times, and multi-slice two-dimensional (2D) sequences have been used to date, which do not provide whole lung volumetric coverage for lung morphometry
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