Lung MRI with hyperpolarised gases: current & future clinical perspectives.

Neil J Stewart,Smitha Rajaram,Jim M Wild,Gill Klafkowski,Ian Sabroe,Rod Lawson,Kelechi Ugonna,Ho-Fung Chan,James A Eaden,Helen Marshall,Christopher S Johns,Laurie J Smith,Nicholas D Weatherley,Guilhem J Collier,Stephen M Bianchi,Alberto Biancardi,David Hughes,Noreen West,Andrew J Swift

doi:10.1259/bjr.20210207

Abstract

The use of pulmonary MRI in a clinical setting has historically been limited. Whilst CT remains the gold-standard for structural lung imaging in many clinical indications, technical developments in ultrashort and zero echo time MRI techniques are beginning to help realise non-ionising structural imaging in certain lung disorders. In this invited review, we discuss a complementary technique – hyperpolarised (HP) gas MRI with inhaled 3He and 129Xe – a method for functional and microstructural imaging of the lung that has great potential as a clinical tool for early detection and improved understanding of pathophysiology in many lung diseases. HP gas MRI now has the potential to make an impact on clinical management by enabling safe, sensitive monitoring of disease progression and response to therapy. With reference to the significant evidence base gathered over the last two decades, we review HP gas MRI studies in patients with a range of pulmonary disorders, including COPD/emphysema, asthma, cystic fibrosis, and interstitial lung disease. We provide several examples of our experience in Sheffield of using these techniques in a diagnostic clinical setting in challenging adult and paediatric lung diseases.

Highlights

Pulmonary MRI has historically had limited clinical impact due to the poor image signal-to-noise and short T2* caused by magnetic susceptibility differences between air and lung parenchyma
Whilst CT remains the gold-standard for structural lung imaging in many clinical indications, the advent of ultrashort and zero echo time (UTE/ZTE) acquisition techniques has enabled 1H pulmonary MRI to advance to a point such that it is recommended clinically for certain disorders.[1]
Focusing on the substantial evidence base gathered to date, we review HP gas MRI studies in patients with a range of pulmonary disorders, including emphysema, asthma, cystic fibrosis, and interstitial lung disease

Summary

INTRODUCTION

Pulmonary MRI has historically had limited clinical impact due to the poor image signal-to-noise and short T2* caused by magnetic susceptibility differences between air and lung parenchyma. The HP gas protocol is usually combined with a 1H pulmonary MRI protocol, which can take an additional 10—30 min to complete and may include some or all of the following: anatomical scans including spoiled gradient echo-, turbo spin echo or steadystate free precession-based sequences; ultrashort echo time scans for high-resolution structural imaging; non-contrast and/ or contrast-enhanced perfusion scans; dynamic 1H MRI and possibly oxygen-enhanced imaging In our experience, these methods can be performed well on both 1.5 T and 3 T scanner platforms that are typical for the bulk of clinical practice, with the former generally more forgiving for thoracic applications.[22,23,24,25] As the HP gas portion of the scan is most time critical (due to the dose timing of the hyperpolarisation process) and costly to repeat, it is conventional to perform this prior to the 1H portion and certainly before any paramagnetic intravenous contrast agents have been administered. Ratios of 129Xe signal in RBC vs tissue plasma vs gas phase (alveoli) of the lungs: RBC/TP: metric of gas exchange function and parenchymal tissue thickening; RBC/Gas: metric of gas exchange and perfusion; TP/Gas: metric of tissue thickening

Healthy reference balues

Findings

Alveolar microstructure