TITLE: Spirometer controlled cine-magnetic resonance imaging to diagnose tracheobronchomalacia in pediatric patients

Background Tracheobronchomalacia (TBM) is defined as an excessive collapse of the intrathoracic trachea. Bronchoscopy is the gold standard to diagnose TBM, but bronchoscopy has major disadvantages, such as general anesthesia. Cine-CT is a non-invasive alternative to diagnose TBM, but its use in children is restricted by ionizing radiation. Our aim was to evaluate the feasibility of spirometercontrolled cine-MRI as alternative to cine-CT in a retrospective study. Material and Methods 12 children (mean 12 years, range 7-17), suspected to have TBM, underwent cine-MRI. Static scans were acquired at end-inspiration and expiration covering the thorax using a 3D SPGR sequence. 3D-Dynamic-scans were performed covering only the central airways. TBM was defined as a decrease of the trachea or bronchi diameter greater than 50% at end-expiration in the static and dynamic scans. Results The success rate of the cine-MRI protocol was 92%. Cine-MRI was compared with bronchoscopy or chest-CT in 7 subjects. TBM was diagnosed by cine-MRI in 7 out of 12 children (58%) and was confirmed by bronchoscopy or CT. In 4 patients, cine-MRI demonstrated tracheal narrowing that was not present in the static scans. Conclusions Spirometer-controlled cine–MRI is a promising technique to assess TBM in children and has the potential to replace bronchoscopy. (197 words) Introduction Tracheobronchomalacia (TBM) is defined as an excessive collapse of the intrathoracic part of the trachea and/or main bronchi during expiration[1]. When TBM is suspected, a diagnostic bronchoscopy, which is the current gold standard, is used to confirm the diagnosis[1,2]. In pediatric populations, bronchoscopy has the disadvantage that it is invasive and requires general anesthesia, while the child maintains spontaneous breathing [1]. In addition, relevant daily life breathing maneuvers, such as forced expiration and coughing, cannot be routinely performed during the procedure[3-4]. Bronchoscopy using conscious sedation, which preserves spontaneous ventilation for the evaluation of TBM, is used in adults. [4]. However, in children this technique is in general not feasible due to lack of cooperation[4]. Finally, bronchoscopy does not provide exact measurements of airway dimensions as imaging techniques can supply[3,4,5]. For these reasons, as alternative to bronchoscopy, cine-computed tomography (cine-CT) has been used to assess TBM[6]. An advantage of this technique is that the collapsibility of trachea and main stem bronchi can be evaluated during static and dynamic conditions[7,8,9]. However cine-CT to detect TBM exposes the patient to ionizing radiation[1], which is a more significant problem for children than adults because they are more susceptible to the harmful effects of ionizing radiation[10-14]. Cine-Magnetic Resonance Imaging (Cine-MRI) might be an attractive, radiation-free alternative to cine-CT to diagnose TBM [15-19]. Recent improvements in MR technology (ultrafast imaging) allow dynamic evaluations of the central airway dimensions (cine-MRI)[15]. Ideally, breathing maneuvers during cine-MRI should be standardized using cine-MRI spirometry. A MRI compatible spirometer was recently developed and tested[20]. To our knowledge, spirometer controlled cine-MRI has not been applied before in TBM assessment[16, 18]. We have previously demonstrated feasibility of the spirometer-controlled cine-MRI protocol in healthy adult volunteers [21]. The aim of this study was to retrospectively evaluate the diagnostic feasibility of this protocol in a group of children, who needed a chest MRI for various indications and in whom the treating clinician requested assessment of TBM to be included in the evaluation. In this paper we describe our methodology and the results of a retrospective image analysis of static and dynamic changes in central airway dimensions in 12 patients.