A single‐breath‐hold protocol for hyperpolarized 129Xe ventilation and gas exchange imaging

Abstract

Hyperpolarized 129Xe MRI (Xe‐MRI) is increasingly used to image the structure and function of the lungs. Because 129Xe imaging can provide multiple contrasts (ventilation, alveolar airspace size, and gas exchange), imaging often occurs over several breath‐holds, which increases the time, expense, and patient burden of scans. We propose an imaging sequence that can be used to acquire Xe‐MRI gas exchange and high‐quality ventilation images within a single, approximately 10 s, breath‐hold. This method uses a radial one‐point Dixon approach to sample dissolved 129Xe signal, which is interleaved with a 3D spiral (“FLORET”) encoding pattern for gaseous 129Xe. Thus, ventilation images are obtained at higher nominal spatial resolution (4.2 × 4.2 × 4.2 mm3) compared with gas‐exchange images (6.25 × 6.25 × 6.25 mm3), both competitive with current standards within the Xe‐MRI field. Moreover, the short 10 s Xe‐MRI acquisition time allows for 1H “anatomic” images used for thoracic cavity masking to be acquired within the same breath‐hold for a total scan time of about 14 s. Images were acquired using this single‐breath method in 11 volunteers (N = 4 healthy, N = 7 post‐acute COVID). For 11 of these participants, a separate breath‐hold was used to acquire a “dedicated” ventilation scan and five had an additional “dedicated” gas exchange scan. The images acquired using the single‐breath protocol were compared with those from dedicated scans using Bland–Altman analysis, intraclass correlation (ICC), structural similarity, peak signal‐to‐noise ratio, Dice coefficients, and average distance. Imaging markers from the single‐breath protocol showed high correlation with dedicated scans (ventilation defect percent, ICC = 0.77, p = 0.01; membrane/gas, ICC = 0.97, p = 0.001; red blood cell/gas, ICC = 0.99, p < 0.001). Images showed good qualitative and quantitative regional agreement. This single‐breath protocol enables the collection of essential Xe‐MRI information within one breath‐hold, simplifying scanning sessions and reducing costs associated with Xe‐MRI.