Three-dimensional magnetic resonance imaging ultrashort echo-time cones for assessing lung density in pediatric patients

Abstract

Background MRI of lung parenchyma is challenging because of the rapid decay of signal by susceptibility effects of aerated lung on routine fast spin-echo sequences. Objective To assess lung signal intensity in children on ultrashort echo-time sequences in comparison to a fast spin-echo technique. Materials and methods We conducted a retrospective study of lung MRI obtained in 30 patients (median age 5 years, range 2 months to 18 years) including 15 with normal lungs and 15 with cystic fibrosis. On a fast spin-echo sequence with radial readout and an ultrashort echo-time sequence, both lungs were segmented and signal intensities were extracted. We compared lung-to-background signal ratios and histogram analysis between the two patient cohorts using non-parametric tests and correlation analysis. Results On ultrashort echo-time the lung-to-background ratio was age-dependent, ranging from 3.15 to 1.33 with high negative correlation (R s = −0.86). Signal in posterior dependent portions of the lung was 18% and 11% higher than that of the anterior lung for age groups 0-2 and 2-18 years, respectively. The fast spin-echo sequence showed no variation of signal ratios by age or location, with a median of 0.99 (0.98-1.02). Histograms of ultrashort echo-time slices between controls and children with aggravated cystic fibrosis with mucus plugging and wall thickening exhibited significant discrepancies that differentiated between normal and pathological lungs. Conclusion Signal intensity of lung on ultrashort echo-time is higher than that on fast spin-echo sequences, is age-dependent and shows a gravity-dependent anterior to posterior gradient. This signal variation appears similar to lung density described on CT.

Pediatric MR lung imaging with 3D ultrashort‐TE in free breathing: Are we past the conventional T2 sequence?

“…10 The superiority of the UTE over the T2-TSE sequence for the determination of lung density is in line with the findings of Zeimpekis et al 17 Here, in an age cohort similar to this study, an improved representation of lung density was obtained in UTE compared with T2-TSE. 17 The lung density as measured in the UTE also corresponds to the severity of lung involvement in cystic fibrosis, for example, and can be automatically quantified volumetrically, and thus fairly objectively. 18 The merits of this study, which involves a mixed pediatric collective, are highlighted in the review of the literature: Studies with a 3D UTE in free breathing are focused, to our knowledge, exclusively on the visualization of micronodules, nodules, masses, as well as F I G U R E 7 Pleural effusion in an 11-year-old girl after metastasectomy for alveolar rhabdomyosarcoma (A) UTE shows the effusion compared with (B) T2-TSE with low signal intensity (white arrow).…”

“…Furthermore, these studies are also centered on adults. The few studies that have systematically evaluated the benefit of UTE sequences in neonates and children were limited to more technical aspects like measuring signal intensity 17,19 or respiratory compensation 20 …”

Clinical application of ultrashort echo-time MRI for lung pathologies in children

“…3D Cones is able to quantify age-and gravity-dependent lung intensity in children comparable to lung density described in CT studies. 25 This review illustrates various clinical applications of UTE lung MRI in the paediatric population. We demonstrate the potential and spectrum of the 3D Cones sequence for depicting lung pathologies in congenital and acquired pulmonary diseases in comparison to conventional lung MRI sequences.…”

Practical protocol for lung magnetic resonance imaging and common clinical indications

“…However, 3-D radial imaging comes at the cost of slower scanning, and more recently sequences have used more complicated trajectories that are spiral interleaves on a conical surface, yielding faster scan times [ 27 , 28 ]. An example is shown in Fig.…”