Optimization of steady‐state free precession MRI for lung ventilation imaging with 19 F C 3 F 8 at 1.5T and 3T

Purpose To assess alveolar perfusion by applying dynamic susceptibility contrast MRI to 19F‐MRI of inhaled perfluoropropane (PFP). We hypothesized that passage of gadolinium‐based contrast agent (GBCA) through the pulmonary microvasculature would reduce magnetic susceptibility differences between water and gas components of the lung, elevating the T2∗ of PFP. Methods Lung‐representative phantoms were constructed of aqueous PFP‐filled foams to characterize the impact of aqueous/gas phase magnetic susceptibility differences on PFP T2∗. Aqueous phase magnetic susceptibility was modulated by addition of different concentrations of GBCA. In vivo studies were performed to measure the impact of intravenously administered GBCA on the T2∗ of inhaled PFP in mice (7.0 Tesla) and in healthy volunteers (3.0 Tesla). Results Perfluoropropane T2∗ was sensitive to modulation of magnetic susceptibility difference between gas and water components of the lung, both in phantom models and in vivo. Negation of aqueous/gas phase magnetic susceptibility difference was achieved in lung‐representative phantoms and in mice, resulting in a ~2 to 3× elevation in PFP T2∗ (3.7 to 8.5 ms and 0.7 to 2.6 ms, respectively). Human studies demonstrated a transient elevation of inhaled PFP T2∗ (1.50 to 1.64 ms) during passage of GBCA bolus through the lung circulation, demonstrating sensitivity to lung perfusion. Conclusion We demonstrate indirect detection of a GBCA in the pulmonary microvasculature via changes to the T2∗ of gas phase PFP within directly adjacent alveoli. This approach holds potential for assessing alveolar perfusion by dynamic susceptibility contrast 19F‐MRI of inhaled PFP, with concurrent assessment of lung ventilation properties, relevant to lung physiology and disease.

Section: Discussionmentioning

confidence: 99%

Dynamic susceptibility contrast ¹⁹F‐MRI of inhaled perfluoropropane: a novel approach to combined pulmonary ventilation and perfusion imaging

Neal

Pippard

Simpson

et al. 2019

“…To calculate the theoretical signal for the steady‐state condition, the following equation can be used 2 :

S = S_{0} \frac{(1 ‐ e^{‐ TR / {normalT}_{1}}) e^{‐ TE / {normalT}_{2}^{*}}}{()(, 1 ‐ \cos ()(, α) e^{‐ TR false/ T_{1}})} \sin (α),

where α is the flip angle (FA). Because the T 1 time of the OFCB–O 2 mixture is approximately 70% longer compared with PFP–O 2 (Table 1), to make a proper estimation of their SNR performance, the number of signal averages (NSA) of OFCB–O 2 scans should be 70% less compared with PFP–O 2 NSA (to keep scan time the same for both measurements).…”

Section: Theorymentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Shepelytskyi

Grynko

et al. 2020

Purpose To test octafluorocyclobutane (OFCB) as an inhalation contrast agent for fluorine‐19 MRI of the lung, and to compare the image quality of OFCB scans with perfluoropropane (PFP) scans Theory and Methods After normalizing for the number of signal averages, a theoretical comparison between the OFCB signal‐to‐noise ratio (SNR) and PFP SNR predicted the average SNR advantage of 90% using OFCB during gradient echo imaging. The OFCB relaxometry was conducted using single‐voxel spectroscopy and spin‐echo imaging. A comparison of OFCB and PFP SNRs was performed in vitro and in vivo. Five healthy Sprague‐Dawley rats were imaged during single breath‐hold and continuous breathing using a Philips Achieva 3.0T MRI scanner (Philips, Andover, MA). The scan time was constant for both gases. Statistical comparison between PFP and OFCB scans was conducted using a paired t test and by calculating the Bayes factor. Results Spin‐lattice (T1) and effective spin‐spin (T2∗) relaxation time constants of the pure OFCB gas were determined as 28.5 ± 1.2 ms and 10.5 ± 1.8 ms, respectively. Mixing with 21% of oxygen decreased T1 by 30% and T2∗ by 20%. The OFCB in vivo images showed 73% higher normalized SNR on average compared with images acquired using PFP. The statistical significance was shown by both paired t test and calculated Bayes factors. The experimental results agree with theoretical calculations within the error of the relaxation parameter measurements. Conclusion The quality of the lung images acquired using OFCB was significantly better compared with PFP scans. The OFCB images had higher a SNR and were artifact‐free.

“…So far, 19 F gas MRI has been optimized for SNR regarding the sequence parameters of both spoiled gradient-echo and balanced SSFP imaging. 27 In a study of healthy volunteers, compressed sensing allowed a reduction of the acquisition time by a factor of approximately 1.8 without a significant loss of image quality. 28 Furthermore, deep learning approaches were developed to reconstruct highly undersampled data obtained using hyperpolarized gas MRI.…”

Section: Introductionmentioning

confidence: 99%

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

Obert

Gutberlet

Kern

et al. 2020

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.