¹H‐guided reconstruction of ¹⁹F gas MRI in COPD patients

Abstract

Purpose:To reduce acquisition time and improve image quality and robustness of ventilation assessment in a single breath-hold using 1 H-guided reconstruction of fluorinated gas ( 19 F) MRI. Methods: Reconstructions constraining total variation in the image domain, L1 norm in the wavelet domain, and directional total variation between 19 F and 1 H images were compared in order to accelerate 19 F ventilation imaging using retrospectively undersampled data from a healthy volunteer. Using the optimal constrained reconstruction in 8 patients with chronic obstructive pulmonary disease (16-seconds breath-hold), ventilation maps of various acceleration factors (2-fold to 13-fold) were compared with maps of the full data set using the Dice coefficient, difference in volume defect percentage and overlap percentage, as well as hyperpolarized 129 Xe gas MRI. Results: The reconstruction constraining total variation and directional total variation simultaneously performed best in the healthy volunteer (RMS error = 0.07, structural similarity index = 0.77) for a measurement time of 2 seconds. Using the same reconstruction in the patients with chronic obstructive pulmonary disease, the Dice coefficient of defect volumes was 0.86 ± 0.05, the mean difference in volume defect percentage was −1.0 ± 1.7 percentage points, and the overlap percentage was 87% ± 2% for a measurement time of 6 seconds. Between volume defect percentage of 19 F and 129 Xe, a linear correlation (r = 0.75; P = .03) was found, with 19 F volume defect percentage being significantly higher (mean difference = 11%; P = .04). Conclusion: 1 H-guided reconstruction of pulmonary 19 F gas MRI enables reduction of acquisition time while maintaining image quality and robustness of functional parameters.

Flow Volume Loop and Regional Ventilation Assessment Using Phase‐Resolved Functional Lung (PREFUL) MRI: Comparison With 129Xenon Ventilation MRI and Lung Function Testing

“…It has been shown that the extent of VDP (and the reproducibility of measurements as well) with hyperpolarized gas depends on the chosen gas, the inflation state (ie, chosen breathing maneuver and applied gas volume 36 ) and the latency between inhalation and scan allowing gas uptake in delayed‐filling lung regions; for example, via collateral ventilation 37 . Kirby et al observed visually and quantitatively higher VDP obtained with 129 Xe MR imaging in comparison to 3 He MR imaging in patients with COPD but not in healthy subjects, 38 and Obert et al measured higher VDP using 19 F in comparison to 129 Xe 39 . These differences are likely attributed to differences in gas density and viscosity—the use of a gas/ gas mixture with a lower density and viscosity results in a higher VDP.…”

Novel imaging techniques for cystic fibrosis lung disease

“… 124‐126 The gas wash‐out time constant has been shown to distinguish between healthy volunteers and patients with CF who have normal spirometry (FEV 1 > 80%), pointing toward its potential utility for early/mild disease 124 . Recent work has focused on optimization of the imaging technique, for example by employing steady‐state 127 and accelerated imaging using compressed sensing, 128 and utilizing anatomical proton MRI during reconstruction to improve the quality of 19 F MR images 129 . It should be stressed that ventilation defects identified by HP 3 He or 129 Xe are not identical to those identified by PFP; for example, a slow filling area might be identified as a ventilation defect on 129 Xe imaging but not 19 F MRI imaging.…”

Evaluation of fluorine‐19 magnetic resonance imaging of the lungs using octafluorocyclobutane in a rat model

“…This attribute results from the natural Boltzmann distribution of the spins in the Zeeman energy states for fluorinated gases, as opposed to hyperpolarized gases. Multiple studies have researched ways of improving the quality of ventilation images acquired with fluorinated gases 2,12,14‐16 . The main factors that affect SNR are the number of equivalent 19 F atoms and the relaxation time of the fluorinated gas.…”