Background: Imaging of the lung by MRI is challenging due to the intrinsic low proton density and rapid T 2 * relaxation. MRI methods providing lung parenchyma and function are in demand. Purpose: To investigate the feasibility of two-dimensional ultrashort echo-time (2D UTE) imaging for lung function assessment. Study Type: Prospective. Population: Eleven healthy volunteers. Field Strength/Sequence: 3T, 2D tiny golden angle UTE (2D-tyUTE). Assessment: The applicability of breath-hold (BH) and self-gated (SG) 2D-tyUTE for quantification of the lung parenchyma signal-to-noise ratio (SNR), proton fraction (f P), fractional ventilation (FV), and perfusion (f) was investigated. Dependencies on repetition time (BH S/I1/I2) and respiratory phase (expiration [EX], inspiration [IN]) were investigated and compared between smokers and nonsmokers.
Imaging the lung parenchyma with MRI is particularly difficult in small animals due to the high respiratory and heart rates, and ultrashort T2* at high magnetic field strength caused by the high susceptibilities induced by the air-tissue interfaces. In this study, a 2D ultrashort echo-time (UTE) technique was combined with tiny golden angle (tyGA) ordering. Data were acquired continuously at 11.7 T and retrospective center-of-k-space gating was applied to reconstruct respiratory multistage images.Lung (proton) density (f P ), T2*, signal-to-noise ratio (SNR), fractional ventilation (FV) and perfusion (f ) were quantified, and the application to dynamic contrast agent (CA)-enhanced (DCE) qualitative perfusion assessment tested. The interobserver and intraobserver and interstudy reproducibility of the quantitative parameters were investigated. High-quality images of the lung parenchyma could be acquired in all animals. Over all lung regions a mean T2* of 0.20 ± 0.05 ms was observed. FV resulted as 0.31 ± 0.13, and a trend towards lower SNR values during inspiration
Background: Imaging the lung parenchyma with magnetic resonance imaging (MRI) is challenging due to cardiac and respiratory motion, the low proton density and short T 2 * relaxation time, and therefore not well established in the clinical routine. As a further step in facilitating lung MRI for longitudinal monitoring, this study aimed to assess the reproducibility of 2D ultrashort echo time (UTE)-derived lung function parameters in healthy subjects.Methods: In this study, a 2D UTE technique was combined with tiny golden angle (tyGA) ordering. Data were acquired either during breath-holds (BH) or continuously during free-breathing (FB) at a field strength of 3T. Retrospective self-gating (image-and k-space-based) was used to reconstruct respiratory and cardiac multistage images from the FB acquisitions. The reproducibility of functional lung parameters derived from BH and FB acquisitions was assessed for three independent examinations (M1-3). M1 and M2 were acquired within 2h, whereas M3 was acquired at least 14d after M1/2. Different respiratory and cardiac phases were reconstructed for three coronal slices. Quantitative analysis including proton fraction (f P ), apparent signal-tonoise ratio (apparent SNR), fractional ventilation (FV), and perfusion (f) was performed by two independent observers, and inter-measurement and inter-observer repeatability were assessed.Results: All scans could be performed successfully in all volunteers. Intraclass correlation coefficients (ICC) of inter-measurement and inter-observer variability, and Bland-Altman analysis showed good to very good reproducibility. Larger breathing amplitudes were observed in the BH acquisitions, which also showed lower reproducibility when compared with the FB acquisitions. For the FB approach, the ICC ranged between 0.70 and 0.98 for all measurements, and ranged between 0.86 and 0.97 for the two observers. No bias or significant differences were observed between the three measurements or the two observers in healthy volunteers. Conclusions:The study proves the feasibility of FB 2D tyGA UTE for lung imaging. Functional parameters derived from FB acquisitions are reproducible in healthy volunteers, allowing for further investigation of this technique in patients with various underlying diseases.
MRI lung imaging is challenging due to cardiac and respiratory motion and the short T2*. In this study the reproducibility of lung function parameters derived from data acquired either from a breath-hold or free-breathing tiny golden angle UTE (2D tyGA UTE) technique have been assessed. Inter-observer and inter-measurement reproducibility was assessed for different lung parameters including lung density and qualitative and quantitative ventilation and perfusion. In general, a very good inter-observer reproducibility and superior reproducibility of the lung function parameters was observed for the free-breathing approach.
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