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"Lung perfusion" in the context of imaging conventionally refers to the delivery of blood to the pulmonary capillary bed through the pulmonary arteries originating from the right ventricle required for oxygenation. The most important physiological mechanism in the context of imaging is the so‐called hypoxic pulmonary vasoconstriction (HPV, also known as "Euler‐Liljestrand‐Reflex"), which couples lung perfusion to lung ventilation. In obstructive airway diseases such as asthma, chronic‐obstructive pulmonary disease (COPD), cystic fibrosis (CF), and asthma, HPV downregulates pulmonary perfusion in order to redistribute blood flow to functional lung areas in order to conserve optimal oxygenation. Imaging of lung perfusion can be seen as a reflection of lung ventilation in obstructive airway diseases. Other conditions that primarily affect lung perfusion are pulmonary vascular diseases, pulmonary hypertension, or (chronic) pulmonary embolism, which also lead to inhomogeneity in pulmonary capillary blood distribution. Several magnetic resonance imaging (MRI) techniques either dependent on exogenous contrast materials, exploiting periodical lung signal variations with cardiac action, or relying on intrinsic lung voxel attributes have been demonstrated to visualize lung perfusion. Additional post‐processing may add temporal information and provide quantitative information related to blood flow. The most widely used and robust technique, dynamic‐contrast enhanced MRI, is available in clinical routine assessment of COPD, CF, and pulmonary vascular disease. Non‐contrast techniques are important research tools currently requiring clinical validation and cross‐correlation in the absence of a viable standard of reference. First data on many of these techniques in the context of observational studies assessing therapy effects have just become available. Level of Evidence: 5 Technical Efficacy: Stage 5 [ABSTRACT FROM AUTHOR]

Background: Noninvasive monitoring of early abnormalities and therapeutic intervention in cystic fibrosis (CF) lung disease using MRI is important. Lung T1 mapping has shown potential for local functional imaging without contrast material. Recently, it was discovered that observed lung T1 depends on the measurement echo time (TE). Purpose: To examine TE‐dependence of observed T1 in patients with CF and its correlation with clinical metrics. Study Type: Prospective. Population: In all, 75 pediatric patients with CF (8.6 ± 6.1 years, range 0.1–23 years), with 32 reexamined after 1 year. Field Strength/Sequence: Patients were examined at 1.5T using an established MRI protocol and a multiecho inversion recovery 2D ultrashort echo time (UTE) sequence for T1(TE) mapping at five TEs including TE1 = 70 μs. Assessment: Morphological and perfusion MRI were assessed by a radiologist (M.W.) with 11 years of experience using an established CF‐MRI scoring system. T1(TE) was quantified automatically. Clinical data including spirometry (FEV1pred%) and lung clearance index (LCI) were collected. Statistical Tests: T1(TE) was correlated with the CF‐MRI score, clinical data, and LCI. Results: T1(TE) showed a different curvature in CF than in healthy adults: T1 at TE1 was shorter in CF (1157 ms ± 73 ms vs. 1047 ms ± 70 ms, P < 0.001), but longer at TE3 (1214 ms ± 72 ms vs. 1314 ms ± 68 ms, P < 0.001) and later TEs. The correlations of T1(TE) with patient age (ρTE1‐TE5 = −0.55, −0.44, −0.24, −0.30, −0.22), and LCI (ρTE1‐TE5 = −0.43, −0.42, −0.33, 0.27, −0.22) were moderate at ultra‐short to short TE (P < 0.001) but decreased for longer TE. Moderate but similar correlations at all TE were found with MRI perfusion score (ρTE1‐TE5 = −0.43, −0.51, −0.47, −0.46, −0.44) and FEV1pred% (ρTE1‐TE5 = +0.44, +0.44, +0.43, +0.40, +0.39) (P < 0.05). Data Conclusion: TE should be considered when measuring lung T1, since observed differences between CF and healthy subjects strongly depend on TE. The different variation of correlation coefficients with TE for structural vs. functional metrics implies that TE‐dependence holds additional information which may help to discern effects of tissue structural abnormalities and abnormal perfusion. Level of Evidence: 2 Technical Efficacy Stage: 1 J. MAGN. RESON. IMAGING 2020;52:1645–1654. [ABSTRACT FROM AUTHOR]

Background This work is intended to demonstrate that T1 measured in the lungs depends on the echo time ( TE) used. Measuring lung T1 can be used to gain quantitative morphological and functional information. It is also shown that this dependence is particularly visible when using an ultra-short TE (UTE) sequence with TE well below 1 ms for T1 quantification in lung tissue, rather than techniques with TE on the order of 1-2 ms. Methods The lungs of 12 healthy volunteers (aged 22 to 33 years) were examined at 1.5 Tesla. A segmented inversion recovery Look-Locker multi-echo sequence based on two-dimensional UTE was used for independent T1 quantification at five TEs between TE1 = 70 μs and TE5 = 2.3 ms. Results The measured T1 was found to increase gradually with TE from 1060 ± 40 ms at TE1 to 1389 ± 53 ms at TE5 ( P < 0.001). Conclusion Measuring T1 at ultra-short echo times reveals a significant dependence of observed T1 on the echo time. Thus, any comparison of T1 values should also consider the TEs used. However, this dependence on TE could also be exploited to gain additional diagnostic information on the tissue compartments in the lung. J. Magn. Reson. Imaging 2015;42:610-616. [ABSTRACT FROM AUTHOR]

Purpose To provide a robust method for the simultaneous quantification of T1 and T2* in the human lung during free breathing. Breathing pure oxygen accelerates T1 and T2* relaxation in the lung. While T1 shortening reflects an increased amount of dissolved molecular oxygen in lung tissue, T2* shortening shows an increased concentration of oxygen in the alveolar gas. Therefore, both parameters reflect different aspects of the oxygen uptake and provide complementary lung functional information. Materials and Methods A segmented inversion recovery Look-Locker multiecho sequence based on a multiecho 2D ultrashort TE (UTE) was employed for simultaneous T1 and T2* quantification. The radial projections follow a modified golden angle ordering, allowing for respiratory self-gating and thus the reconstruction of a series of differently T1 and T2*-weighted images in arbitrary breathing states. The method was evaluated in nine healthy volunteers while breathing room air and pure oxygen, with two volunteers examined at five oxygen concentrations. Results Relative differences of Δ T1 between 7.9% and 12.7% and of Δ T2* between 13.2% and 6.0% were found. Conclusion The proposed method provides inherently coregistered, quantitative T1 and T2* maps in both expiration and inspiration from a single measurement acquired during free breathing and is thus well suited for clinical application. J. Magn. Reson. Imaging 2015;41:1708-1714. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]