Visualization of inert gas wash‐out during high‐frequency oscillatory ventilation using fluorine‐19 MRI

Abstract

High-frequency oscillatory ventilation is looked upon as a lung-protective ventilation strategy. For a further clarification of the physical processes promoting gas transport, a visualization of gas flow and the distribution of ventilation are of considerable interest. Therefore, fluorine-19 magnetic resonance imaging of the imaging gas octafluorocyclobutane (C 4 F 8 ) during high-frequency oscillatory ventilation was performed in five healthy pigs. For that, a mutually compatible ventilation-imaging system was set up and transverse images were acquired every 5 sec using FLASH sequences on a 1.5 T scanner. Despite a drop in signal-to-noise ratio after the onset of high-frequency oscillatory ventilation, for each pig, the four experiments could be analyzed. A mean wash-out time (t) at 5 Hz of 52.7 6 18 sec and 125.9 6 39 sec at 10 Hz, respectively, were found for regions of interest including the whole lung. This is in agreement with the clinical findings, in that washout of respiratory gases is significantly prolonged for increased high-frequency oscillatory ventilation frequencies. Our study could be a good starting-point for a further optimization of high-frequency oscillatory ventilation. Magn Reson Med 64:1479-1483,

Inert fluorinated gas MRI: a new pulmonary imaging modality

“…Naturally, this raises possibilities of using 19 F MRI to obtain information that is similar to pulmonary function tests, while using the imaging component to provide regional information that is complementary to the dynamic lung volume measurements. A number of animal studies have used dynamic 19 F MRI to investigate the kinetics of pulmonary ventilation by measuring the wash-in and/or wash-out of inert fluorinated gases (50)(51)(52). For example, one study in pigs measured both the wash-in and wash-out kinetics of SF 6 using a breathing scheme as follows: the animal was first ventilated with pure O 2 for 10 min (baseline), the animal was then ventilated with ten breaths of pure SF 6 (wash-in phase), and then the animal was ventilated with seven breaths of pure O 2 (wash-out phase).…”

“…A number of animal studies have used dynamic 19 F MRI to investigate the kinetics of pulmonary ventilation by measuring the wash‐in and/or wash‐out of inert fluorinated gases . For example, one study in pigs measured both the wash‐in and wash‐out kinetics of SF 6 using a breathing scheme as follows: the animal was first ventilated with pure O 2 for 10 min (baseline), the animal was then ventilated with ten breaths of pure SF 6 (wash‐in phase), and then the animal was ventilated with seven breaths of pure O 2 (wash‐out phase).…”

In vivo regional ventilation mapping using fluorinated gas MRI with an x‐centric FGRE method

“…Note that efficient hyperpolarized gas dynamic lung imaging requires very special imaging methods such as FAVOR to account for signal decay due to the transmission of RF pulses and presence of oxygen, whereas dynamic lung imaging with inert fluorinated gases is more straightforward due to the very short longitudinal relaxation times and benefits from the presence of oxygen. Although numerous preclinical studies have explored ventilation‐perfusion ratios and dynamic imaging using inert fluorinated gas MRI in animals , to our knowledge, regional fractional ventilation has not been measured in rat lungs using any inert fluorinated gas. The possibility of dynamic imaging using inert fluorinated gas MRI in humans has been demonstrated recently ; however, regional fractional ventilation maps were not produced from the obtained wash‐in/washout data.…”

19F MRI of the Lungs Using Inert Fluorinated Gases: Challenges and New Developments

“…On the other hand, inert fluorinated gas 19 F signal recovers quickly, and freebreathing can be performed with normoxic gas mixtures. A number of preclinical 47,48,57 and clinical 58,59 studies have used 19 F MRI to study inert gas washin/washout kinetics. One clinical study performed time-resolved imaging in patients with COPD, and the washin/washout curves were highly variable, reflecting ventilation heterogeneity.…”