Hyperpolarized 129Xe diffusion-weighted MRI of the lung with 3D golden-angle radial sampling and keyhole reconstruction.

Abstract

Background: Hyperpolarized (HP) ¹²⁹Xe multiple b-values diffusion-weighted imaging (DWI) facilitates the assessment of pulmonary morphology. However, conventional DWI method, such as 2D GRE DWI, is limited in its application due to the long acquisition time and relatively thick slice.

Purpose: To develop a method combining 3D golden-angle radial sampling with keyhole reconstruction (GRSK) for accelerating ¹²⁹Xe multiple b-values DWI and obtaining thinner slice.

Methods: For 3D GRSK DWI, 3D kooshball golden-angle radial sampling was used for image acquisition, with each spoke assigned to 1 of 4 b-values, and keyhole method was applied for reconstructing DW images under different b-values. 2D fully sampled GRE DWI and 3D GRSK DWI were obtained in five healthy young volunteers (HYV; 25 [24-26] years). Lung morphological parameter maps, including mean linear intercept (L_m) and surface-to-volume ratio (SVR), were generated using a cylinder model (CM) from the four b-values DW images, and apparent diffusion coefficient (ADC) maps were derived through mono-exponential fitting. Spearman correlation and Bland-Altman analysis were performed to compare L_m, SVR and ADC from 2D GRE and 3D GRSK DWI. In addition, 3D GRSK DWI was applied in five emphysema patients (66 [60-69] years) and five age-matched healthy controls (AMC; 59 [54-68] years), and L_m, SVR and ADC maps were also derived. Wilcoxon rank-sum test was utilized to contrast L_m, SVR and ADC from patients with those from AMC.

Results: DW images with an isotropic resolution (5 mm) were obtained with 3D GRSK DWI within 11.4 s. In comparison, 2D GRE DWI acquired four slices with 30 mm thickness in 15.9 s. For L_m, SVR and ADC from 2D GRE and 3D GRSK DWI, the Spearman correlation coefficients were 0.975, 0.900, and 1.000, with corresponding p-values of 0.005, 0.037, and < 0.001, and the Bland-Altman analysis had biases of -3.19%, 1.44%, and -3.71%, respectively. Furthermore, L_m and ADC in patients were significantly higher (p = 0.008 and p = 0.008) than those in AMC, while SVR was notably reduced (p = 0.008).

Conclusion: The proposed method could obtain isotropic resolution DW images with four b-values within an 11.4 s breath-hold duration, mitigating the problems of long scan time and large slice thickness in conventional DWI.