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

Purpose: 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).

Theory and methods: 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.

Results: 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.

Conclusions: 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.