Diffusion‐weighted MRI of the lung with hyperpolarized helium‐3: A study of reproducibility

Abstract

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.

Functional lung imaging using hyperpolarized gas MRI

“…Specifically, the sensitivity of the mean ADC for detecting microstructural changes in the lungs of patients with emphysema (31,91), asymptomatic smokers (69,102), and aging never-smokers (95) has been shown in various studies. The ADC measures have been shown to be highly reproducible (103,104) and to be potentially more sensitive than HR CT using the RA950 index (relative area of lung voxels below -950 Hounsfield units (Hu) (105)) for early detection of emphysematous changes in asymptomatic smokers (69,102). Several groups have shown that ADC measures are reproducible within better than 5% on consecutive scans and for studies on consecutive days (91,103).…”

“…Several groups have shown that ADC measures are reproducible within better than 5% on consecutive scans and for studies on consecutive days (91,103). Moreover, in subjects lying in the supine position, ADC values have been shown to increase from the anterior to posterior regions of the lungs due to expected gravitydependent changes in alveolar volume (103,104). This sensitivity of regional ADC maps to processes known to affect alveolar volume makes DW He-3 MRI a potential tool for planning surgical therapies for lung volume reduction (106), and for monitoring individual regional disease progression in response to drug therapies.…”

Design and evaluation of a 32‐channel phased‐array coil for lung imaging with hyperpolarized 3‐helium

“…Key words: MRI; parallel imaging; helium; lung; phased array coil Lung imaging using hyperpolarized 3 He has received increased attention in the last several years for studying lung diseases (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). So far, functional imaging, e.g., the apparent diffusion coefficient (ADC) or methods to observe the microstructure of the lung (12,13), requires long breath holds (up to 30 sec), which are the main barrier to applying this technology to patients with severe lung disease. Improvements in array coil methodology are a promising approach for increasing signal-to-noise ratio (SNR) and allowing significant acceleration of the image-encoding process.…”

Functional Imaging: CT and MRI

“…The ratio of these polarization changes allow the spatial mapping of ADC, with higher values allocated to larger air spaces (such as trachea and large bronchi). (190) ADC is homogeneously distributed in normal subjects, and becomes progressively more heterogeneous with normal smokers to emphysema (191)(192)(193)(194). ADC has been shown to increase under the influence of aging (195,196), emphysema (194,197,198) and due to gravity dependent compression of the lung (199); Figure 11).…”