T₁, T₁ contrast, and Ernst‐angle images of four rat‐lung pathologies

Abstract

Purpose To initiate the archive of relaxation‐weighted images that may help discriminate between pulmonary pathologies relevant to acute respiratory distress syndrome. MRI has the ability to distinguish pathologies by providing a variety of different contrast mechanisms. Lungs have historically been difficult to image with MRI but image quality is sufficient to begin cataloging the appearance of pathologies in T1‐ and T2‐weighted images. This study documents T1 and the use of T1 contrast with four experimental rat lung pathologies. Methods Inversion‐recovery and spoiled steady state images were made at 1.89 T to measure T1 and document contrast in rats with atelectasis, lipopolysaccharide‐induced inflammation, ventilator‐induced lung injury (VILI), and injury from saline lavage. Higher‐resolution Ernst‐angle images were made to see patterns of lung infiltrations. Results T1‐weighted images showed minimal contrast between pathologies, similar to T1‐weighted images of other soft tissues. Images taken shortly after magnetization inversion and displayed with inverted contrast highlight lung pathologies. Ernst‐angle images distinguish the effects of T1 relaxation and spin density and display distinctive patterns. T1 for pathologies were: atelectasis, 1.25 ± 0.046 s; inflammation from instillation of lipopolysaccharide, 1.24 ± 0.015 s; VILI, 1.55 ± 0.064 s (p = 0.0022 vs. normal lung); and injury from saline lavage, 1.90±0.080 s (p = 0.0022 vs. normal lung; p = 0.0079 vs. VILI). T1 of normal lung and erector spinae muscle were 1.25 ± 0.028 s and 1.02 ± 0.027 s, respectively (p = 0.0022). Conclusions Traditional T1‐weighting is subtle. However, images made with inverted magnetization and inverted contrast highlight the pathologies and Ernst‐angle images aid in distinguishing pathologies.

Validation of MRI for Volumetric Quantification of Atelectasis in the Perioperative Period: An Experimental Study in Swine

“…Quantitative assessment of lung aeration based on MRI has been very limited, mainly because of technical challenges of MR imaging (Ball et al, 2017b), for example, the prolonged time required for image acquisition, and the low proton density within the lung parenchyma. However, recent experimental data, ex vivo (Ball et al, 2018) and in-vivo (Kuethe et al, 2018) have suggested that lung MRI may be feasible and produce clinically valuable information (Ozcan et al, 2017), including functional imaging (Mendes Pereira et al, 2018). Ball et al observed in ex-vivo pig lungs that lung density was a linear function of MRI T2 signal intensity normalized to muscle intensity.…”

“…Indeed, ionizing radiation exposure during CT is up to 300 times the dose of a standard chest X-ray (Ludes et al, 2016). Magnetic resonance imaging (MRI), a radiation-free technique, is potential alternative to CT for atelectasis measurement (Ball et al, 2018; Kuethe et al, 2018). However, it has never been validated for the volumetric quantification of pulmonary aeration impairment (Duggan and Kavanagh, 2005).…”