Hyperpolarized ³He and ¹²⁹Xe MRI: Differences in asthma before bronchodilation

Abstract

In asthma, hyperpolarized (129) Xe MRI may help reveal ventilation abnormalities before bronchodilation that are not observed using hyperpolarized (3) He MRI.

Modelling resistance and reactance with heterogeneous airway narrowing in mild to severe asthma

“…One of the interesting findings from our study is that the percentage of airway narrowing that accounted for the in-vivo E rs in asthmatic subjects was much larger than would be required to produce the ventilation defects observed in recent imaging studies (Svenningsen et al 2013;Thomen et al 2015). Ventilation defects are regions with negligible or very poor inhalation of observable gas, presumably due to closure of the airways supplying these regions.…”

“…Modeling studies suggest that ventilation defects are largely caused by the heterogeneous pattern of constriction of small airways, which includes randomly distributed closures or near closures (Lutchen and Gillis 1997;Tgavalekos et al 2005). A number of methods have been applied to assess small airways, which include nitrogen gas washout (Verbanck et al 1997;King et al 2005), frequency dependence of dynamic compliance (Woolcock et al 1969), and imaging techniques such as magnetic resonance imaging using hyperpolarized helium and xenon (Altes et al 2001;Svenningsen et al 2013), and high resolution computed tomography (King et al 2004). While these methods provide insight to our understanding of the pathophysiology of asthma, at present they are largely limited to research applications.…”

Chronic Obstructive Pulmonary Disease: Lobar Analysis with Hyperpolarized 129Xe MR Imaging

“…High-spatial-resolution imaging of pulmonary ventilation is also possible with hyperpolarized 129 Xe MR imaging (4,5,7). With wider availability and lower cost than 3 He, 129 Xe MR imaging is a more clinically viable alternative and studies have compared ventilation image quality for the two gases (9). Hyperpolarized 129 Xe diffusion-weighted MR imaging has also shown utility in the assessment of lung microstructure (7,10), with elevated whole-lung mean apparent diffusion coefficient (ADC) values present in patients with COPD corresponding to emphysematous tissue destruction.…”

What are ventilation defects in asthma?

“…Although relatively simple and inexpensive, spirometry measurements provide a global estimate of the morphological changes in the small and medium-sized airways that are believed to be related to luminal inflammation, airway remodelling and constriction. We now realise using multiple breath nitrogen washout studies3 4 and pulmonary imaging methods, that functional abnormalities in asthma are in fact regionally heterogeneous,5–7 temporally persistent8–10 and that these abnormalities regionally respond to bronchoprovocation7 11 12 and to bronchodilator therapy 11 13. Thoracic X-ray CT has been used for over a decade as a non-invasive method to investigate structure-function relationships of asthmatic airways and has shown strong relationships between CT-derived airway measurements with inflammation,14 15 spirometry14–21 and disease severity 14 16 20 22.…”

“…In addition, 3 He MRI also provides a way to perform intensive serial measurements due in part to its excellent safety profile,30 and the speed with which imaging can be performed. More specifically, 3 He MRI ventilation defects have been shown to increase from baseline following methacholine7 11 12 and exercise12 challenge, and decrease from baseline following salbutamol administration 13. In asthma, the relationship between ventilation defects and patient outcomes such as exacerbation frequency and severity has not yet been evaluated; however this has been evaluated in chronic obstructive pulmonary disease 31.…”