Probing Changes in Lung Physiology in COPD Using CT, Perfusion MRI, and Hyperpolarized Xenon-129 MRI

Abstract

Xe129 MRI has high potential to uniquely identify multiple changes in lung physiology in COPD using a single breath-hold acquisition.

Characterisation of gas exchange in COPD with dissolved-phase hyperpolarised xenon-129 MRI

“…Multivariable correlation matrix analysis was performed to probe relationships between conventional diagnostics (PFT, per cent of %DLCO and quantitative MDCT) and HXeMRI indices, which included ventilation defect percentage (VDP, percent areas of the lung with no ventilation), xenon diffusion into interstitial tissues normalised to xenon in alveoli (tissue/Gas), and xenon diffusion into capillary red blood cells (RBCs) normalised to xenon in alveoli (RBC/Gas) ( figure 1 ). 6 8 Relevant PFT metrics correlating with HXeMRI indices were: per cent predicted value of forced expiratory volume in 1 s (%FEV 1 ) with VDP (Spearman r=−0.70, p<0.0001), per cent of the lung with Low Attenuation Area Hounsfield unit less than −950 (%LAA -950 ) with tissue/gas (Spearman r=−0.82, p<0.0001) and %DLCO with RBC/gas (Spearman r=0.72, p<0.0001) ( figure 2A–C ). Apparent diffusion coefficient (ADC, a marker of terminal airspace dilation) was performed in a subset of subjects (n=36) and was significantly correlated with %DLCO (Spearman r=−0.74, p<0.0001), tissue/gas (Spearman r=−0.78, p<0.0001), and RBC/gas (Spearman r=−0.73, p<0.0001 ( online supplemental figure 1 ).…”

“…Specifically, tissue/gas may be reduced with emphysema or non-ventilating lung regions and RBC/gas may reflect the amalgam of alveolar integrity and capillary perfusion in series. 6 By considering ventilation, tissue/gas, and RBC/gas signals as a gradient reflecting xenon movement from alveoli to RBCs, more resolved identification of aberrant regional physiology becomes feasible. 7 With this approach, we report considerable intersubject and intrasubject heterogeneity among ME-DCL subjects.…”

“… 6 In contrast, tissue/gas and RBC/gas defects in series reflect parenchymal destruction (subclinical emphysema). 6 …”

Investigating biases in the measurement of apparent alveolar septal wall thickness with hyperpolarized 129Xe MRI

“…3,9,[23][24][25][26][27][28][29][30] Both approaches have already been shown to be sensitive to various forms of lung disease. [31][32][33][34][35][36][37][38][39][40][41][42] More recently, efforts have been made to combine these methods by adding 2D or 3D spatial information to dynamic gas uptake measurements at the expense of lengthened scan times. 43,44 Nevertheless, although xenon uptake MR techniques for quantifying lung function have been in use for over 20 years, little attention has been paid to the impact of the acquisition parameters on the metrics extracted.…”

“…The DP imaging techniques currently in use can be divided into two general types: (1) static measurements of the regional xenon distribution within the lung parenchyma as dictated by the structure and physiology of the lung, 9‐19 and the MR acquisition parameters, in particular the flip angle and the TR 20‐22 ; and (2) dynamic measurements that capture the xenon gas uptake by the lung tissue and transport by the pulmonary circulation as a function of time 3,9,23‐30 . Both approaches have already been shown to be sensitive to various forms of lung disease 31‐42 . More recently, efforts have been made to combine these methods by adding 2D or 3D spatial information to dynamic gas uptake measurements at the expense of lengthened scan times 43,44 .…”