Assessment of mean transit time in the engrafted lung with ¹³³Xe lung ventilation scintigraphy improves diagnosis of bronchiolitis obliterans syndrome in living-donor lobar lung transplant recipients

Objective: Staging of bronchiolitis obliterans syndrome (BOS) following lung transplantation is based on declines in forced expiratory volume in 1 s (FEV₁). The aim of this study was to evaluate the usefulness of ¹³³Xe ventilation scintigraphy in the early detection of BOS following living-donor lobar lung transplantation (LDLLT), to compare ¹³³Xe washout imaging with computed tomography (CT) findings for early detection of BOS following LDLLT, and to evaluate ¹³³Xe washout imaging by quantitative analyses. Methods: Subjects comprised 30 double-lung recipients and 1 single-lung recipient, who had undergone LDLLT at our institution and survived more than 1 year. Clinically diagnosed BOS developed in six recipients. Declines in graft function were evaluated using a combination of three methods, namely, dynamic spirometry, high-resolution CT (HRCT), and ¹³³Xe ventilation scintigraphy. Findings for all transplanted lungs were compared between CT and ¹³³Xe washout imaging. ¹³³Xe washout imaging was assessed using mean transit time (MTT) of bi-and unilateral lungs. Correlations between MTT of bilateral lungs and FEV₁% were evaluated. Differences in MTT between BOS and non-BOS lungs, and between non-BOS and donor lungs were also evaluated on unilateral lungs. Appropriate cut-off values of MTT of unilateral lungs were set for the diagnosis of BOS. Results: In all six BOS cases, prolonged-washout images of engrafted lungs revealed early-phase BOS with declines from baseline FEV₁, whereas only one BOS case could be detected using early CT findings of BO (bronchodilatation, decrease in number and size of pulmonary vessels, thickening of septal lines, and volume reduction). A significant correlation was identified between MTT and FEV₁% (r = -0.346, P < 0.0001). MTT of unilateral lungs was significantly longer in BOS lungs than in non-BOS lungs (P < 0.0001). The cut-off MTT of unilateral lungs for the diagnosis of BOS was set at 64.77 s. Conclusions: Our data show that ¹³³Xe washout imaging offers excellent potential for early detection of BOS compared with early CT findings. Using ¹³³Xe washout imaging and MTT with radioactive tracer offers a noninvasive indication of selective ventilatory function in engrafted lungs following LDLLT. MTT appears useful for identifying BOS following LDLLT and allows quantitative evaluation of graft function in unilateral lungs.