Mapping Alveolar Oxygen Partial Pressure in COPD Using Hyperpolarized Helium-3: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

Abstract

Chronic obstructive pulmonary disease (COPD) and emphysema are characterized by functional and structural damage which increases the spaces for gaseous diffusion and impairs oxygen exchange. Here we explore the potential for hyperpolarized (HP) 3He MRI to characterize lung structure and function in a large-scale population-based study. Participants (n = 54) from the Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study, a nested case-control study of COPD among participants with 10+ packyears underwent HP 3He MRI measuring pAO2, apparent diffusion coefficient (ADC), and ventilation. HP MRI measures were compared to full-lung CT and pulmonary function testing. High ADC values (>0.4 cm2/s) correlated with emphysema and heterogeneity in pAO2 measurements. Strong correlations were found between the heterogeneity of global pAO2 as summarized by its standard deviation (SD) (p < 0.0002) and non-physiologic pAO2 values (p < 0.0001) with percent emphysema on CT. A regional study revealed a strong association between pAO2 SD and visual emphysema severity (p < 0.003) and an association with the paraseptal emphysema subtype (p < 0.04) after adjustment for demographics and smoking status. HP noble gas pAO2 heterogeneity and the fraction of non-physiological pAO2 results increase in mild to moderate COPD. Measurements of pAO2 are sensitive to regional emphysematous damage detected by CT and may be used to probe pulmonary emphysema subtypes. HP noble gas lung MRI provides non-invasive information about COPD severity and lung function without ionizing radiation.

Keywords: COPD; average diffusion coefficient; hyper polarized gas MRI; partial pressure of oxygen; quantitative MRI.

Figure 1

Workflow for the lung MRI co-registration between different breath stages.

Figure 2

Color maps of three subjects with different levels of disease severity. Left column: subject with no COPD, center column: mild COPD, right column: severe COPD; from top to bottom: p_AO₂ color map, ADC color map, ventilation scan. On the ventilation scans blue corresponds to non-ventilated regions, green hypo-ventilated and yellow normal.

Figure 3

p_AO₂ mean vs. ADC mean (top), p_AO₂ SD vs. ADC mean (center) Percent negative p_AO₂ vs. ADC mean (bottom). Each measurement corresponds to an individual participant imaged with polarized ³He from the MESA COPD Study.

Figure 4

Average percent negative p_AO₂ per subject in normal, hypo-, and non-ventilated for a single subject.