Quantitative Assessment of Regional Dynamic Airway Collapse in Neonates via Retrospectively Respiratory‐Gated ¹H Ultrashort Echo Time MRI

Abstract

Background Neonatal dynamic tracheal collapse (tracheomalacia, TM) is a common and serious comorbidity in infants, particularly those with chronic lung disease of prematurity (bronchopulmonary dysplasia, BPD) or congenital airway or lung‐related conditions such as congenital diaphragmatic hernia (CDH), but the underlying pathology, impact on clinical outcomes, and response to therapy are not well understood. There is a pressing clinical need for an accurate, objective, and safe assessment of neonatal TM. Purpose To use retrospectively respiratory‐gated ultrashort echo‐time (UTE) MRI to noninvasively analyze moving tracheal anatomy for regional, quantitative evaluation of dynamic airway collapse in quiet‐breathing, nonsedated neonates. Study Type Prospective. Population/Subjects Twenty‐seven neonatal subjects with varying respiratory morbidities (control, BPD, CDH, abnormal polysomnogram). Field Strength/Sequence High‐resolution 3D radial UTE MRI (0.7 mm isotropic) on 1.5T scanner sited in the neonatal intensive care unit. Assessment Images were retrospectively respiratory‐gated using the motion‐modulated time‐course of the k‐space center. Tracheal surfaces were generated from segmentations of end‐expiration/inspiration images and analyzed geometrically along the tracheal length to calculate percent‐change in luminal cross‐sectional area (A %) and ratio of minor‐to‐major diameters at end‐expiration (r D,exp). Geometric results were compared to clinically available bronchoscopic findings (n = 14). Statistical Tests Two‐sample t‐test. Results Maximum A % significantly identified subjects with/without a bronchoscopic TM diagnosis (with: 46.9 ± 10.0%; without: 27.0 ± 5.8%; P < 0.001), as did minimum r D,exp (with: 0.346 ± 0.146; without: 0.671 ± 0.218; P = 0.008). Subjects with severe BPD exhibited a far larger range of minimum r D,exp than subjects with mild/moderate BPD or controls (0.631 ± 0.222, 0.782 ± 0.075, and 0.776 ± 0.030, respectively), while minimum r D,exp was reduced in CDH subjects (0.331 ± 0.171) compared with controls (P < 0.001). Data Conclusion Respiratory‐gated UTE MRI can quantitatively and safely evaluate neonatal dynamic tracheal collapse, as validated with the clinical standard of bronchoscopy, without requiring invasive procedures, anesthesia, or ionizing radiation. Level of Evidence: 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;49:659–667.

Validation of a new predictive model to improve risk stratification in bronchopulmonary dysplasia

“…A limitation of our study is that our cohorts did not include premature infants on mechanical support beyond NICU discharge; however, these babies would likely be included in this new category given that this group was characterized by prolonged mechanical ventilatory support (mean 59 days). Given their exceedingly high risk for severe complications, we believe these vulnerable infants with "very severe BPD" (new level IV) may require a detailed assessment of their upper and large airways 28 , lung parenchyma structure [12][13][14][15][16] , pulmonary vasculature 29 , and ventilatory responses 30,31 , as well as intense surveillance by a specialized multi-disciplinary team during and after NICU discharge 32 . We feel that babies with ≥120 days of O2 requirements should be considered in a different severity category because we found they have a much greater risk of respiratory complications (see Table 3) and may require new strategies to improve their outcomes.…”

Subglottic Stenosis Position Affects Work of Breathing

“…To determine the alignment of the lumen through the glottis and the stenosis, another axial plane was specified at the level of the glottis using a method described previously. 24 The normal vector of the plane (parallel to the longitudinal axis) was projected from the centroid of the glottis onto the plane of the stenosis. The anteroposterior distance between the point projected from the glottis plane and the centroid of the stenotic plane was then measured as shown in Figure 2.…”

“…Though this may effectively be true for the stenotic tissue, the trachea is highly dynamic during tidal breathing and patient movement. 24,29 Neonates with SGS may have concomitant laryngomalacia and tracheomalacia, which significantly impact airflow dynamics. These are not captured by the simulations used in this study.…”

Characterization of and tissue density in the human lung: Application to neonatal imaging in the intensive care unit

“…Given that exposure to ionizing radiation associated with CT carries significant risk to the safety of these patients, particularly for repeated exposure, researchers have begun developing MRI techniques suitable for imaging of neonatal pulmonary structure . The original 3D ultrashort echo time (UTE) technique, applied by our group in the NICU setting, has been further developed to allow self‐navigated retrospective respiratory gating to reduce motion‐related blurring and reconstruction of images at multiple respiratory phases. Furthermore, it has been demonstrated to provide quantitative parenchymal lung density measures that correlate well with CT, quantify lung volumes and hyperinflation, and predict short‐term clinical outcomes in NICU patients with bronchopulmonary dysplasia (BPD) .…”