Performance of spiral UTE-MRI of the lung in post-COVID patients

Abstract

Patients recovered from COVID-19 may develop long-COVID symptoms in the lung. For this patient population (post-COVID patients), they may benefit from longitudinal, radiation-free lung MRI exams for monitoring lung lesion development and progression. The purpose of this study was to investigate the performance of a spiral ultrashort echo time MRI sequence (Spiral-VIBE-UTE) in a cohort of post-COVID patients in comparison with CT and to compare image quality obtained using different spiral MRI acquisition protocols. Lung MRI was performed in 36 post-COVID patients with different acquisition protocols, including different spiral sampling reordering schemes (line in partition or partition in line) and different breath-hold positions (inspiration or expiration). Three experienced chest radiologists independently scored all the MR images for different pulmonary structures. Lung MR images from spiral acquisition protocol that received the highest image quality scores were also compared against corresponding CT images in 27 patients for evaluating diagnostic image quality and lesion identification. Spiral-VIBE-UTE MRI acquired with the line in partition reordering scheme in an inspiratory breath-holding position achieved the highest image quality scores (score range = 2.17-3.69) compared to others (score range = 1.7-3.29). Compared to corresponding chest CT images, three readers found that 81.5% (22 out of 27), 81.5% (22 out of 27) and 37% (10 out of 27) of the MR images were useful, respectively. Meanwhile, they all agreed that MRI could identify significant lesions in the lungs. The Spiral-VIBE-UTE sequence allows for fast imaging of the lung in a single breath hold. It could be a valuable tool for lung imaging without radiation and could provide great value for managing different lung diseases including assessment of post-COVID lesions.

Keywords: COVID-19; Lung imaging; MRI; Post-COVID; Spiral sampling; Stack-of-spirals; Ultrashort echo time.

Fig. 1

The stack-of-spirals are acquired in the kx-ky plane and every slice maintains the same number of spiral interleaves rotating by a pre-defined angle. The ultra-short echo time (TE) is achieved by shortening the duration of the RF pulse, varying TE for different image slices (with minimum TE at kz = 0) and center-out spiral sampling during data acquisition.

Fig. 2

Different reordering schemes can be implemented in stack-of-spirals acquisition including line in partition (Lin-in-Par) reordering and partition in line (Par-in-Lin) scheme. For Lin-in-Par reordering, all spiral interleaves are acquired for one slice before moving to the next slice, while for Par-in-Line reordering, a spiral interleaf with the same rotation angle in all slices are acquired before moving to the next stack. The order of acquisition is labelled from 1 to 10 for acquiring the total 10 spiral interleaves.

Fig. 3

Comparisons of lung MR images acquired with different spiral protocols in the healthy volunteer. For the breath-hold spiral images, the Lin-in-Par reordering yielded better image quality than the Par-in-Lin reordering. Corresponding breath-hold Cartesian image also produced clear ghosting artifacts due to cardiac motion. For free-breathing acquisitions, all images show strong motion artifacts from both respiratory and cardiac motion.

Fig. 4

Comparison of different spiral lung MR acquisition protocols in the first representative post-COVID patient.

Fig. 5

Comparison of different spiral lung MR acquisition protocols in the second representative post-COVID patient.

Fig. 6

Comparison of different spiral lung MR acquisition protocols in the third representative post-COVID patient.

Fig. 7

Comparison of chest CT and lung MR images in two representative post-COVID patients without COVID-related lesions.

Fig. 8

Comparison between CT and MR images in a post-COVID patient with COVID-related lesions. According to the expert chest radiologist, the MR images have a similar diagnostic quality compared to CT for this case. The ground glass opacities (red arrows) can be clearly observed both in CT and MRI. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 9

Diagnostic quality comparison between CT and MRI for two post-COVID patients with COVID related lesions in the lungs. (a) For the first patient (Patient A), acceptable diagnostic quality according to the expert chest radiologist. Subacute ground glass opacities (red arrows) observed in the left lung in CT can also be identified in MRI. (b) For the second patient (Patient B), MR images are not useful according to the expert chest radiologist. Ground glass opacities (red arrows) observed in the left lung in CT are not identifiable in the MR images. The big gap in time between the CT and MRI exams (∼1 year) may explain why the lesions were not observable on the MRI. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)