In Vivo Measurements of T2 Relaxation Time of Mouse Lungs during Inspiration and Expiration

Abstract

PurposeThe interest in measurements of magnetic resonance imaging relaxation times, T1, T2, T2*, with intention to characterize healthy and diseased lungs has increased recently. Animal studies play an important role in this context providing models for understanding and linking the measured relaxation time changes to the underlying physiology or disease. The aim of this work was to study how the measured transversal relaxation time (T2) in healthy lungs is affected by normal respiration in mouse.MethodT2 of lung was measured in anaesthetized freely breathing mice. Image acquisition was performed on a 4.7 T, Bruker BioSpec with a multi spin-echo sequence (Car-Purcell-Meiboom-Gill) in both end-expiration and end-inspiration. The echo trains consisted of ten echoes of inter echo time 3.5 ms or 4.0 ms. The proton density, T2 and noise floor were fitted to the measured signals of the lung parenchyma with a Levenberg-Marquardt least-squares three-parameter fit.ResultsT2 in the lungs was longer (p<0.01) at end-expiration (9.7±0.7 ms) than at end-inspiration (9.0±0.8 ms) measured with inter-echo time 3.5 ms. The corresponding relative proton density (lung/muscle tissue) was higher (p<0.001) during end-expiration, (0.61±0.06) than during end-inspiration (0.48±0.05). The ratio of relative proton density at end-inspiration to that at end-expiration was 0.78±0.09. Similar results were found for inter-echo time 4.0 ms and there was no significant difference between the T2 values or proton densities acquired with different interecho times. The T2 value increased linearly (p< 0.001) with proton density.ConclusionThe measured T2 in-vivo is affected by diffusion across internal magnetic susceptibility gradients. In the lungs these gradients are modulated by respiration, as verified by calculations. In conclusion the measured T2 was found to be dependent on the size of the alveoli.

Lung T2* mapping using 3D ultrashort TE with tight intervals δTE

“…UTE images with high temporal TE resolution were previously collected ex vivo for various specimens and cadaveric tissues in tendon and knee 17 as well as in rodent lungs under anesthesia. 10,18 The current study shows the feasibility of T * 2 mapping using UTE imaging with high temporal TE resolution 𝛿TE on in vivo human lungs in 3D. The T * 2 values obtained in this study with the mono-exponential model are in good agreement with earlier findings obtained through single-slice UTE 8 and 3D UTE obtained in four separate acquisitions.…”

Characterization of and tissue density in the human lung: Application to neonatal imaging in the intensive care unit

“…In adult humans, has been shown to be affected by inflation state and gravitationally dependent position, and compares favorably to quantitative CT densitometry for clinical stage classification of chronic obstructive pulmonary disease (COPD) and pulmonary function in smokers . Notably, these works establish a consistent relationship between lung tissue density and and this relationship mirrors other works investigating within the lung . Because neonates with various pulmonary diagnoses, such as BPD or congenital diaphragmatic hernia (CDH), can have heterogeneous parenchymal abnormalities including emphysema, inflammation/fibrosis, and ventilation impairment, measurements of regional and density in this population may yield useful information on structural physiology and lung function in both normal and diseased neonatal lungs.…”

Tiny golden angle ultrashort echo‐time lung imaging in mice

“…A general limitation of using signal intensities for quantifying changes over the respiratory and/or cardiac cycle results from likely different T2* values between inspiration and expiration, as shown by Olsson and Hockings for T2 56 . Even although the intensity changes are still due to changes in the air/tissue fraction, a strictly linear relation cannot be expected due to the nonlinear contribution of the T2* contribution and needs further investigation.…”