Non-Uniform Self-Gating in 2D Lung Imaging

Patrick Metze,Hanna Frantz,Volker Rasche,Kilian Stumpf,Wolfgang Rottbauer,Tobias Speidel,Meinrad Beer,Fabian Straubmüller

doi:10.3389/fphy.2022.836178

Abstract

Purpose: To adapt the non-uniform Self-Gating (nuSG) method and compare it to established self-gating approaches for lung imaging in uniform and highly irregular respiratory patterns.Methods: Six healthy volunteers underwent free breathing lung MRI using a radial tiny golden angle ultrashort echo-time sequence. Acquisitions were performed with the volunteer breathing as uniformly as possible and with a deliberately non-uniform respiratory pattern. The acquired data was reconstructed with the nuSG method, previously introduced for cardiac imaging and imaging of the temporomandibular joint (TMJ) and compared to established k-space based and image-based self-gating approaches. Residual motion blur, SNR and functional values were assessed and compared to reference breath-hold acquisitions.Results: nuSG is capable of reconstructing high-quality images for uniform and non-uniform breathing patterns and is furthermore capable of resolving motion in cases where additional motion is superimposed or no clear motion surrogate exists. Derived functional values do not differ significantly from other image-based gated reconstructions - and in the case of non-uniform respiratory patterns replicate the reference BH values.Conclusion: Image based approaches are computationally more demanding but yield better results in all aspects. In scenarios with a direct surrogate for respiratory motion (i.e. the lung-liver interface) the extraction of a one-dimensional navigator is sufficient. When there is no direct surrogate for the motion of the target structure available (e.g., considerable through-plane motion or a different source of motion), the two-dimensional correlation-based measure used in nuSG is able to track the motion more accurately.

Highlights

Over the last decade, magnetic resonance imaging (MRI) has emerged as a promising alternative to high resolution computed tomography in lung imaging [1, 2]
The short transverse relaxation times have been addressed by ultrashort echo time (UTE) [6] and zero echo time (ZTE) [7] sequences, which have been optimized for lung imaging [8–12]
Where cardiac motion is neglected in most cases, in healthy and cooperative volunteers, breath-holds (BH) in combination with rapid data acquisition have proven feasible for high-quality lung imaging [13–15]

Summary

Introduction

Magnetic resonance imaging (MRI) has emerged as a promising alternative to high resolution computed tomography in lung imaging [1, 2]. Its capabilities in the visualization and assessment of functional and morphological information without ionizing radiation makes lung MRI attractive in paediatrics [1, 3], in the early detection of diseases [4], as well as in longitudinal imaging studies [5]. Its clinical use is still limited due to very short T2* relaxation times and low proton densities leading to intrinsically low signal to noise ratios (SNR) and respiratory and cardiac nuSG 2D Lung Imaging motion. Where cardiac motion is neglected in most cases, in healthy and cooperative volunteers, breath-holds (BH) in combination with rapid data acquisition have proven feasible for high-quality lung imaging [13–15]. Patients with lung diseases often exhibit limited breath-hold capabilities, leading to the necessity of acquisitions during free breathing in combination with motion compensation strategies

Methods

Results

Discussion

Conclusion