Free breathing lung T1 mapping using image registration in patients with idiopathic pulmonary fibrosis.

Laura C Saunders,Andrew J Swift,Jim M Wild,James A Eaden,Stephen M Bianchi

doi:10.1002/mrm.28342

Laura C Saunders, Andrew J Swift + Show 3 more

Open Access

https://doi.org/10.1002/mrm.28342

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Abstract

To assess the use of image registration for correcting respiratory motion in free breathing lung T1 mapping acquisition in patients with idiopathic pulmonary fibrosis (IPF). The method presented used image registration to synthetic images during postprocessing to remove respiratory motion. Synthetic images were generated from a model of the inversion recovery signal of the acquired images that incorporated a periodic lung motion model. Ten healthy volunteers and 19 patients with IPF underwent 2D Look-Locker T1 mapping acquisition at 1.5T during inspiratory breath-hold and free breathing. Eight healthy volunteers and seven patients with IPF underwent T1 mapping acquisition during expiratory breath-hold. Fourteen patients had follow-up scanning at 6 months. Dice similarity coefficient (DSC) was used to evaluate registration efficacy. Image registration increased image DSC (P < .001) in the free breathing inversion recovery images. Lung T1 measured during a free breathing acquisition was lower in patients with IPF when compared with healthy controls (inspiration: P = .238; expiration: P = .261; free breathing: P = .021). Measured lung T1 was higher in expiration breath-hold than inspiration breath-hold in healthy volunteers (P < .001) but not in patients with IPF (P = .645). There were no other significant differences between lung T1 values within subject groups. The registration technique significantly reduced motion in the Look-Locker images acquired during free breathing and may improve the robustness of lung T1 mapping in patients who struggle to hold their breath. Lung T1 measured during a free breathing acquisition was significantly lower in patients with IPF when compared with healthy controls.

Highlights

Parametric lung T1 mapping has the potential to characterize pathophysiological changes in the tissue of the lung.[1]
Lung T1 measured during a free breathing acquisition was lower in patients with Idiopathic pulmonary fibrosis (IPF) when compared with healthy controls
Lung T1 measured during a free breathing acquisition was significantly lower in patients with IPF when compared with healthy controls

Summary

| INTRODUCTION

Parametric lung T1 (longitudinal relaxation time) mapping has the potential to characterize pathophysiological changes in the tissue of the lung.[1]. A synthetic image based registration method for motion correction is presented to allow free breathing lung T1 mapping using a conventional 2D Look-Locker acquisition sequence. The approach implemented in our work does not require a segmentation and uses a single parameter model (see Equation 2) where the third image input into the model (St3 which is determined using the CRIR model, see Figure 1 “Data-driven image selection”) is used as a surrogate for a fully recovered image This provides a more robust initial fit and removes the necessity of time-costly iterations and manual segmentation. Three spatially aligned images (alignment assessed on diaphragmatic position) are input into the synthetic image model (Equation 2) and a non-rigid pair-wise image registration between the synthetic images and the corresponding acquired images is performed For this method to be applicable for free breathing acquisitions, an algorithm automatically selects images with a similar respiratory state from the free breathing acquisition by fitting the image data to the CRIR model.

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| RESULTS

Findings

| DISCUSSION

| CONCLUSIONS