B 1 and magnetization decay correction for hyperpolarized 129 Xe lung imaging using sequential 2D spiral acquisitions

• Published in: Magnetic resonance in medicine Vol. 90; no. 2; pp. 473 - 482
• Main Authors: Bdaiwi, Abdullah S, Costa, Mariah L, Plummer, Joseph W, Willmering, Matthew M, Walkup, Laura L, Cleveland, Zackary I
• Format: Journal Article
• Language: English
• Published: United States 01.08.2023
• Subjects: Breath Holding; Humans; Lung - diagnostic imaging; Lung - physiology; Magnetic Resonance Imaging - methods; Phantoms, Imaging; Respiration; Xenon Isotopes; bias field correction; spiral; lung ventilation images; hyperpolarized 129Xe; B1 inhomogeneity; flip-angle maps
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.29655

To mitigate signal variations caused by inhomogeneous RF and magnetization decay in hyperpolarized Xe ventilation images using flip-angle maps generated from sequential 2D spiral ventilation images acquired in a breath-hold. Images and correction maps were compared with those obtained using conventional, 2D gradient-recalled echo. Analytical expressions to predict signal intensity and uncertainty in flip-angle measurements were derived from the Bloch equations and validated by simulations and phantom experiments. Imaging in Xe phantoms and human subjects (1 healthy, 1 cystic fibrosis) was performed using 2D gradient-recalled echo and spiral. For both sequences, consecutive images were acquired with the same slice position during a breath-hold (Cartesian scan time = 15 s; spiral scan time = 5 s). The ratio of these images was used to calculate flip-angle maps and correct intensity inhomogeneities in ventilation images. Mean measured flip angle showed excellent agreement with the applied flip angle in simulations (R  = 0.99) for both sequences. Mean measured flip angle agreed well with the globally applied flip angle (∼15% difference) in Xe phantoms and in vivo imaging using both sequences. Corrected images displayed reduced coil-dependent signal nonuniformity relative to uncorrected images. Flip-angle maps were obtained using sequentially acquired, 2D spiral, Xe ventilation images. Signal intensity variations caused by RF-coil inhomogeneity can be corrected by acquiring sequential single-breath ventilation images in less than 5-s scan time. Thus, this method can be used to remove undesirable heterogeneity while preserving physiological effects on the signal distribution.