Hyperpolarized ³He apparent diffusion coefficient MRI of the lung: Reproducibility and volume dependency in healthy volunteers and patients with emphysema

Abstract

Purpose:To measure the apparent diffusion coefficient (ADC) of hyperpolarized (HP) 3 He gas using diffusion weighted MRI in healthy volunteers and patients with emphysema and examine the reproducibility and volume dependency. Materials and Methods:A total of eight healthy volunteers and 16 patients with emphysema were examined after inhalation of HP 3 He gas mixed with nitrogen (N 2 ) during breathhold starting from functional residual capacity (FRC) in supine position. Coronal diffusion-sensitized MR images were acquired. Each subject was imaged on three separate days over a seven-day period and received two different volumes (6% and 15% of total lung capacity [TLC]) of HP 3 He each day. ADC maps and histograms were calculated. The mean and standard deviation (SD) of the ADC at different days and volumes were compared. Results:The reproducibility of the mean ADC and SD over several days was good in both healthy volunteers and patients (SD range of 0.003-0.013 cm 2 /second and 0.001-0.009 cm 2 /second at 6% and 15% of TLC for healthy volunteers, and a SD range of 0.001-0.041 cm 2 /second and 0.001-0.011 cm 2 /second, respectively, for patients). A minor but significant increase in mean ADC with increased inhaled gas volume was observed in both groups. Conclusion:Mean ADC and SD of HP 3 He MRI is reproducible and discriminates well between healthy controls and patients with emphysema at the higher gas volume. This method is robust and may be useful to gain new insights into the pathophysiology and course of emphysema. THE HABIT OF SMOKING is increasing worldwide and so is one of its direct consequences, i.e., the chronic obstructive pulmonary disease (COPD). By the year 2020, COPD is expected to rank third as a cause of mortality and fifth of morbidity (1). A validated imaging technique that is sensitive to very early structural changes in the lungs could be helpful in the design of therapy and management of emphysema.MRI using hyperpolarized (HP) gases as helium ( 3 He) have emerged as a promising technique for studies of the structure and function of the lungs. Inhalation of HP 3 He can be used not only to derive information related to regional ventilation but also to the size of the alveoli. This is accomplished by measurement of the apparent diffusion coefficient (ADC) of inhaled HP 3 He. When HP 3 He is inhaled, diffusion of the gas is restricted by the boundaries of the alveoli and if restricted diffusion measurement conditions are met, the measured ADC will reflect the size of the peripheral airway spaces (2-4). It could thereby allow quantification of the structural changes (of the lungs) in emphysema. The ADC has been shown to increase in animals with elastase-induced emphysema (5). Studies have also been performed in small numbers of healthy adult subjects and subjects with lung disease (6 -12). In these studies, the ADC values in emphysematous lungs were increased relative to ADC values obtained in subjects with healthy lungs.

Effect of Lung Inflation Level on Hyperpolarized3He Apparent Diffusion Coefficient Measurements in Never-Smokers

“…The findings by Diaz et al (20) demonstrated the sensitivity of ADC to small (6%-8%) changes in lung volume. The work presented herein builds on that of Diaz et al (20) by evaluating the dependence of ADC measurements on lung inflation levels at carefully controlled lung volumes between 20% and 100% of vital capacity (VC). We performed this study to evaluate effects encounters.…”

Novel imaging approaches in adult asthma and their clinical potential

“…The FDA have deemed 3 He a safe contrast agent. Various studies have assessed safely of 3 He in a range of patients with a variety of conditions [131, [168][169][170][171][172][173] with no major side effects reported. Minor symptoms such as lightheadedness, cough and transient desaturation can occur, and it does mean monitoring and careful choice of subjects is important.…”

Progression of Emphysema in a 12-month Hyperpolarized 3He-MRI Study

“…The fall will be less rapid if the distribution is more inhomogeneous. This is apparent in Figure 1, which shows lacunarity as a function of box size from data obtained in an earlier reproducibility study (20). The difference between the subjects with COPD with and without AAT deficiency is addressed in the ''Discussion'' section.…”