Purpose:To determine the reproducibility of several parameters of the ADC measurement by calculating the scanto-scan intrasubject variability. Materials and Methods:Measurements were performed using a gradient-echo sequence with a bipolar gradient for diffusion weighting (b ϭ 3.89 sec/cm 2 ). Five patients with pulmonary emphysema, and six healthy-lung volunteers were included in the study. Images were acquired after inspiration of 3 He during a single inspiratory breath-hold. To assess the reproducibility, the measurement was performed twice (time between measurements ϭ 20 minutes) without repositioning the subjects. Analysis was performed on the basis of region-of-interest (ROI) analysis and global lung ADC histograms. Results:The mean ADC of a ROI varied by 5.1% between two measurements for volunteers and by 6.1% for patients. In the global evaluation, the 75th percentile demonstrated the best reproducibility (2%), while other parameters showed variations up to 12%. Only the variation of the standard deviation (SD) and the measure of homogeneity of the ADC map showed a significant difference between patients and volunteers.Conclusion: Diffusion-weighted imaging (DWI) is a well-reproducible method for assessing the lung microstructure.

The aim of the present study was to apply hyperpolarised (HP) 3 He magnetic resonance imaging (MRI) to identify patients with chronic obstructive pulmonary disease (COPD) and a 1 -antitrypsin deficiency (a 1 -ATD) from healthy volunteers and compare HP 3 He MRI findings with high-resolution computed tomography (HRCT) in a multicentre study. Quantitative measurements of HP 3He MRI (apparent diffusion coefficient (ADC)) and HRCT (mean lung density (MLD)) were correlated with pulmonary function tests.A prospective three centre study enrolled 122 subjects with COPD (either acquired or genetic) and age-matched never-smokers. All diagnostic studies were completed in 94 subjects (52 with COPD; 13 with a 1 -ATD; 29 healthy subjects; 63 males; and 31 females; median age 62 yrs). The consensus assessment of radiologists, blinded for other test results, estimated nonventilated lung volume (HP Using lung function tests as a reference, regional analysis of HP 3 He MRI and HRCT correctly categorised normal volunteers in 100% and 97%, COPD in 42% and 69% and a 1 -ATD in 69% and 85% of cases, respectively. Direct comparison of HP 3 He MRI and CT revealed 23% of subjects with moderate/severe structural abnormalities had only mild ventilation defects. In comparison with lung function tests, ADC was more effective in separating COPD patients from healthy subjects than MLD (p,0.001 versus 0.038). ADC measurements showed better correlation with DL,CO than MLD (r50.59 versus 0.29). Hyperpolarised 3 He MRI correctly categorised patients with COPD and normal volunteers. It offers additional functional information, without the use of ionising radiation whereas HRCT gives better morphological information. We showed the feasibility of a multicentre study using different magnetic resonance systems.

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In this initial study, He-MRI yield good correlations with HRCT and agrees better than HRCT with the functional characterization of emphysema regarding hyperinflation, large and small airway disease as provided by LFT.

Purpose:To study the influence of admixing inert buffer gases to laser-polarized 3 He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution. Materials and Methods:The diffusion coefficient of 3 He was altered by admixing buffer gases of various molecular weights ( 4 He, N 2 , and SF 6 ). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laserpolarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments.Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures. Conclusion:A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion. IN PHYSIOLOGICAL APPLICATIONS of imaging techniques, the fundamental quest is for improved resolution and contrast. MRI has undergone a tremendous development in this direction, and lung imaging using hyperpolarized gases is one of the recent highlights (1).The latter application became possible because hyperpolarization is most successful in gases ( 3 He and 129 Xe) using optical techniques for spin polarization. The increase in polarization by up to five orders of magnitude was also believed to significantly boost the principal resolution in MRI. One drawback of this approach is that only gases can be hyperpolarized, resulting in a loss of three orders of magnitude in sensitivity due to their lower density. In addition, the diffusion constants of gases are typically five orders of magnitude larger than that of liquids.The typical strategy to reduce the influence of diffusion, by applying a burst of 180°-pulses (2) in a CarrPurcell-Meiboom-Gill (CPMG)-type sequence, is problematic in the nonequilibrium state of polarization. First, imperfections in the radiofrequency (RF) homogeneity might cause a additional depolarization. Second, the application of such a sequence is debatable, due to the very strict limits of RF irradiation at high fields in clinical practice. Therefore, rapid data acquisition with gradient echoes is the common approach to minimize the influence of diffusion on the MRI signal. Of course, the timing of sequences is constrained by technical and safety limit...