In patients with COPD, the VDP obtained with hyperpolarized 29Xe MR imaging was significantly greater than that with 3He MR imaging, suggesting incomplete or delayed filling of lung regions that may be related to the different properties of 129Xe gas and physiologic and/or anatomic abnormalities in COPD.

ADC values for emphysematous lungs were significantly increased compared with healthy lungs in age-matched subjects, and all values were comparable to those reported previously at 1.5 Tesla. Ventilation defect score and ventilation defect volume results were also comparable to results previously reported in COPD subjects Reproducibility of ADC for same-day scan-rescan and 7-day rescan was high and similar to previously reported results.

Diffusion-weighted hyperpolarized (129) Xe MRI is a promising technique for mapping changes in human lung morphology and may be useful for early detection of emphysema associated with COPD.

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Purpose: We generated lung morphometry measurements using single-breath diffusion-weighted MRI and three different acinar duct models in healthy participants and patients with emphysema stemming from chronic obstructive lung disease (COPD) and alpha-1 antitrypsin deficiency (AATD). Methods: Single-breath-inhaled 3 He MRI with five diffusion sensitizations (b-value ¼ 0, 1.6, 3.2, 4.8, and 6.4 s/cm 2 ) was used, and signal intensities were fit using a cylindrical and single-compartment acinar-duct model to estimate MRIderived mean linear intercept (L m ) and surface-to-volume ratio (S/V). A stretched exponential model was also developed to estimate the mean airway length and L m . Results: We evaluated 42 participants, including 15 elderly never-smokers (69 6 5 years), 12 ex-smokers without COPD (67 6 11 years), 9 COPD ex-smokers (80 6 6 years), and 6 AATD patients (59 6 6 years). In the never-and ex-smokers, the diffusing capacity of the lung for carbon monoxide (DL CO ) and computed tomography relative area of less than 2950 Hounsfield units (RA 950 ) were normal, but these were abnormal in the COPD and AATD patients, which is reflective of emphysema. Although cylindrical and stretched-exponential-model estimates of L m and S/V were not significantly different, the single-compartment-model estimates were significantly different (P < 0.05) for the never-and ex-smoker subgroups. All models estimated significantly worse L m and S/V in the AATD and COPD subgroups compared with the never-and exsmokers without emphysema. Conclusions: Differences in airspace enlargement may be estimated using L m and S/V, generated using MRI and a stretchedexponential or cylindrical model of the acinar ducts. Magn Reson Med 79:439-448,

These results suggest that fluorinated gases can be reliably used in vivo in dynamic lung studies as an alternative to 3He/129Xe.

A novel imaging method is presented, Flip Angle Variation for Offset of RF and Relaxation (FAVOR), for rapid and efficient measurement of rat lung ventilation using hyperpolarized helium-3 ( 3 He) gas. The FAVOR technique utilizes variable flip angles to remove the cumulative effect of RF pulses and T 1 relaxation on the hyperpolarized gas signal and thereby eliminates the need for intervening air wash-out breaths and multiple cycles of 3 He wash-in breaths before each image. The former allows an improvement in speed (by a factor of Ϸ30) while the latter reduces the cost of each measurement (by a factor of Ϸ5). MR imaging with hyperpolarized 3 He gas has been proposed for measurement of regional ventilation in the rodent lung (1) and has been recently validated with xenon-enhanced CT imaging (2). It is anticipated that 3 He MR will provide a favorable approach for measurement of ventilation in animal cohorts to track lung disease over time without the complications associated with accumulated x-ray dose (3). This method measures the dynamic change in lung 3 He signal as a function of breath number and extracts the relative refreshment of gas in a given lung voxel per breath. However, the conventional 3 He ventilation measurement requires knowledge of the longitudinal relaxation time, T 1 , of the 3 He gas in the ventilator system and in the lung, the latter requiring knowledge of the alveolar oxygen partial pressure (p A O 2 ).Furthermore, without accurate knowledge of the RF pulse history the method requires multiple 3 He breathing cycles (i.e., 3 He wash-in breaths) with air wash-out breaths between cycles in order to completely clear the lung of 3 He gas, which is time-consuming (i.e., several minutes), an inefficient use of hyperpolarized 3 He gas (i.e., costly), and can lead to imprecision due to variations in tidal volume from the ventilator.Perhaps most important, the conventional technique involving multiple 3 He and air breathing cycles requires several minutes (Ϸ10 min) for a single ventilation map, which is likely too slow to capture rapid changes in ventilation associated with short-duration bronchoconstriction such as a methacholine (MCh) challenge (Ͻ1 min), similar to asthma (4,5). Previous work has been limited to measurement of pre-and postsensitization effects or postlong-term challenge in part due to the time required to measure ventilation using the conventional method. The ability to detect changes in ventilation over time scales of less than 1 min may provide improved sensitivity to shortterm challenge and insight into disease which more closely resembles asthma (6 -9). As well, rapid measurement of ventilation may prove critical for evaluation of fast-acting drug therapies for asthma (10,11).We propose a novel approach, Flip Angle Variation for Offset of RF and Relaxation (FAVOR), for obtaining regional ventilation in a single set of breathing cycles (i.e., only one set of 3 He wash-in breaths and no air wash-out breaths). This approach utilizes variable flip angle (VFA) RF pulses that comp...