Quantification of regional fractional ventilation in human subjects by measurement of hyperpolarized³He washout with 2D and 3D MRI

Abstract

Multiple-breath washout hyperpolarized (3)He MRI was used to calculate regional parametric images of fractional ventilation (r) as the ratio of fresh gas entering a volume unit to the total end inspiratory volume of the unit. Using a single dose of inhaled hyperpolarized gas and a total acquisition time of under 1 min, gas washout was measured by dynamic acquisitions during successive breaths with a fixed delay. A two-dimensional (2D) imaging protocol was investigated in four healthy subjects in the supine position, and in a second protocol the capability of extending the washout imaging to a three-dimensional (3D) acquisition covering the whole lungs was tested. During both protocols, subjects were breathing comfortably, only restricted by synchronization of breathing to the sequence timings. The 3D protocol was also successfully tested on one patient with cystic fibrosis. Mean r values from each volunteer were compared with global gas volume turnover, as calculated from flow measurement at the mouth divided by total lung volume (from MRI images), and a significant correlation (r = 0.74, P < 0.05) was found. The effects of gravity on R were investigated, and an average decrease in r of 5.5%/cm (Δr = 0.016 ± 0.006 cm(-1)) from posterior to anterior was found in the right lung. Intersubject reproducibility of r imaging with the 2D and 3D protocol was tested, and a significant correlation between repeated experiments was found in a pixel-by-pixel comparison. The proposed methods can be used to measure r on a regional basis.

Regional Fractional Ventilation by Using Multibreath Wash-in3He MR Imaging

“…Emami et al (10) reduced the use of gas and the duration of the protocol by implementing a wash-in ventilation sequence in pigs whereby an image was obtained after each breath over the multibreath sequence. Recently, Horn et al (11) performed multibreath 3 He ventilation imaging in human subjects by using a washout technique. However, as washout of the polarized gas proceeded, the signal-tonoise ratio often decreased such that only the images obtained after the first two or three breaths of the protocol were usable.…”

“…Without this adjustment of Pao 2 values, fractional ventilation would have been overestimated by approximately 10%. This approach thus builds on that of Horn et al (11), whose washout technique did not provide enough signal to directly produce a high-spatialresolution regional Pao 2 map.…”

Evaluation of high resolution computed tomography findings of cystic fibrosis

“…Following this, hyperpolarized helium-3 MRI (HP 3 He MRI) has been examined in multiple settings and has shown high sensitivity for the detection of ventilation impairments [34][35][36][37][38][39][40][41][42][43][44]. This typically requires production of hyperpolarized gas on site which is then mixed with nitrogen and administered to patients with a one litre Tedlar Bag.…”

“…Nevertheless, the method requires further testing and adjustments and only one CF patient was tested to check the tolerability of the protocol (Fig. 1) [44]. Hyperpolarized xenon-129 MRI 3 He is difficult and expensive to obtain due to the increasing demand for the helium-3 isotope in non-MRI applications and it is typically only sourced from the tritium decay in nuclear warheads [45] making the development of an alternative HP MRI noble gas highly desirable.…”

Clinical highlights from the 2013 ERS Congress in Barcelona

“…Recently published data of YSERBYT et al [60] on pulmonary confocal laser endomicroscopy of distal airways confirmed that this is a promising new technique for the in vivo evaluation of the respiratory tract and the three-dimensional characteristics of the pulmonary acinus. HORN et al [61] used hyperpolarised 3 He gas ventilation magnetic resonance imaging (MRI) to map bronchodilator treatment response in COPD. This concept is able to regionally resolve changes in lung ventilation in response to therapy in COPD [62].…”