Application Of Dual Source CT In Airway Imaging Of Infants And Children

Objectives:To assess the feasibility of low-dose prospective ECG-gated dual-source CT (DSCT) in detecting airway anomalies in pediatric patients with cardiovascular anomalies compared with flexible tracheobronchoscopy (FTB).Materials and Methods:The study was approved by local ethics board with written informed consent obtained from all patients’guardian. Infants and children who had undergone transthoracic echocardiography which revealed the presence of cardiovascular anomalies and who had undergone FTB for possible tracheobronchial narrowing and/or anomaly were enrolled in the study and underwent DSCT for detection of cardiovascular abnormalities between2010and2012. The mean interval between CT examination and flexible bronchoscopy was2.5days (ranging from0to7days). A total of33patients (16/17male/female) with a history of persistent airway obstruction (abnormal breathing sounds, persisting or recurrent pulmonary infections), and/or presented stridor with related symptoms (cyanosis, fever, hemoptysis or dyspnea at feeding) were enrolled in this study, with ages ranging from1month to93months (meanl5.2±22.8months) and weight from3.0kg to19.0kg (mean6.9±4.0kg kg).All DSCT examinations were performed by weight-adjusted low-dose protocol while patients were freely breathing. Body weight-based adjustments of tube voltage and tube current were performed:<6kg, tube voltage80kV, tube current40±59mAs;6-10kg, tube voltage80kV, tube current60-79mAs;>10kg, tube voltage80kV, tube current80-120mAs.Two radiologists independently performed CT image analysis. The FTB reports were reviewed by an experienced pulmonologist. To provide a reference standard, an experienced pulmonologist reviewed the flexible bronchoscopy reports without knowledge of the CT findings and clinical histories (derived from written bronchoscopy reports). The airways were classified into six locations as follows: location I, upper third of the trachea; location II, middle third of the trachea; location III, lower third of the trachea; location IV, right main bronchus; location V, left main bronchus; location VI, lobe bronchus. We classified all the CT findings as tracheobronchial narrowing and abnormality, using5-score scale to evaluate the airway at each location as follows:score0(absence of tracheobronchial narrowing and abnormality), score1(0<luminal narrowing<one third), score2(luminal narrowing≥one third but<two thirds), and score3(luminal narrowing≥two thirds), score4(airway abnormality). For any disagreement in data analysis between the two observers, consensus agreement was achieved.FTB results were taken as the reference standard. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of CT were calculated from2X2contingency tables, with calculation of the95%confidence intervals being calculated.Spearman’s rank order correlation (r) was calculated to measure the strength of correlation between the results of CT and flexible bronchoscopy for grading of tracheobronchial stenosis. A p value of less than0.05was considered significant.Interobserver agreement for evaluation of tracheobronchial narrowing and abnormality was assessed by kappa, test, and κ-values of0.80-1.00were considered to indicate good agreement.The parameters for volume CT dose index (CTDIvol) and dose-length product (DLP) were obtained from the patient protocol and effective radiation dose was calculated.Results:1. FTB and CT findingsIn30(91%) of33patients, tracheobronchial narrowing and/or abnormality was present at FTB, while3patients had normal FTB results.Twenty-eight cases were diagnosed with tracheobronchial narrowing and/or abnormality in33patients by CT.27patients were confirmed by FTB, while1patient with diagnosis of tracheobronchial narrowing on CT was diagnosed with mucus by FTB. In the5patients with negative CT results,2patients were also negative at FTB, while3patients were diagnosed with tracheobronchial narrowing due to tracheobronchomalacia by FTB.For all27patients with airway anomalies detected by both DSCT and FTB,26sites of tracheobronchial stenoses were detected. The described location was consistent with each other, including:location I (4sites), location Ⅱ(1sites), location Ⅲ(5sites), location Ⅳ(4sites), location V(10sites), location VI(2sites). In26stenoses, grading degree of23stenoses detected by both CT and FTB was consistent with each other, including:grade1(5stenoses), grade2(11stenoses), grade3(7stenoses). Based on CT,1stenosis was overestimated by1grade, and2stenoses were underestimated by1grade.All patients with proven airway abnormalities without narrowing (n=10) had correctly identified findings at CT, including bridge bronchus (n=3), tracheal bronchus (n=4) and segmental bronchial agenesis (n=3).Vascular abnormalities that caused airway narrowing were confirmed in9(45%) of20patients with airway stenosis demonstrated by FTB. Pulmonary artery sling (PAS) was the most common finding (n=5), while PAS was associated with bridge bronchus in3cases. The other vascular abnormalities that caused airway narrowing included right aortic arch (n=2), aberrant left subclavian artery (n=1) and double aortic arch (n=1). Nonvascular airway stenosis was detected in11(55%) of20patients. CT revealed a7-month old infant to have tracheobronchial stenosis due to widespread ossification of tracheobronchial cartilage while the fiberscope could not pass the lesion.3patients presented trachea stenosis due to anonymous soft tissue compression. FTB demonstrated4cases with tracheobronchial narrowing due to bronchial wall fibrosis.3cases with airway stenosis due to tracheomalacia were confirmed at FTB.2. Statistical ParametersSensitivity and specificity of CT were calculated as90.0%(95%CI:72.3%,97.4%) and66.7%(95%CI:12.5%,98.2%) respectively, while PPV and NPV were96.4%(95%CI:79.8%,99.8%) and40.0%(95%CI:7.3%,83.0%) respectively. Overall accuracy was87.9%(95%CI:74.5%,97.6%). The correlation between the findings of CT and FTB for grading of tracheobronchial stenosis was excellent (r=0.89).There was good agreement (κ=0.81) for evaluation of tracheobronchial narrowing and abnormality between the two reviewers.3. Radiation DoseThe mean volume CT dose index was0.87±0.34mGy (range:0.61-1.98).The mean dose-length product was10.15±5.39mGy·cm (range:5-34) resulting in an estimated mean effective radiation dose of0.60±0.20mSv (range:0.33-1.41).Conclusion:In children with congenital heart disease and a high suspicion of airway involvement the probability of fixed airway involvement seems high. In pediatric patients, ECG-triggered CT to evaluate congenital cardiovascular anomalies can also be used to diagnose and characterize fixed airway involvement in relation to the vascular structures. If no fixed airway abnormalities are seen, a dynamic CT or bronchoscopy may identify dynamic airway narrowing. Objective:To evaluate the application of high-pitch spiral computed tomography in airway imaging of infants and children and compared with conventional scan techniques.Materials and Methods:Sixty children with clinically suspected airway disease who underwent CT examination were included in the study. All patients were randomly divided into group A and B. There were19males and11females in group A who were examined with a dual source CT (DSCT) system in an high pitch mode(HPM)(pitch=3.0), with mean age16.0±13.4months (age range0.5month to48months), mean body weight10.1±4.0kg (range from3.5kg to17.0kg). None of the children was sedated for the CT examination and no breathing instructions were given. There were17males and13females in group B who were examined under sedation on the same CT systems in conventional pitch mode (CPM)(pitch=1.4), with mean age16.0±15.3months (range,0.5-72month), mean body weight9.9±4.1kg (range from4.0kg to22.0kg). Sedation was achieved with oral administration of chloral hydrate.All CT examinations were performed by weight-adjusted low-dose protocol while patients were freely breathing. Body weight-based adjustments of tube voltage and tube current were performed:<5kg, tube voltage80kV, tube current40-59mAs;5-10kg, tube voltage80kV, tube current60-79mAs;>10kg, tube voltage80kV, tube current80-120mAs.Subjective image quality was independently assessed by2radiologists with several years of experience. Overall image quality was assessed using a4-point grading scale:0, excellent, no artifacts present;1, good, mild artifacts, not relevant for diagnosis;2, moderate, marked artifacts, not relevant for diagnosis;3, poor, severe artifacts. Image attenuation, noise and signal-to-noise-ratio (SNR) in the trachea above the level of carina were calculated.The effective mAs, CTDIvol, DLP and scan time were recorded in every cases. The differences of radiation dose and scan time between two scan modes were analyzed using independent samples t test. Inter-observer agreement in subjective image quality grading was assessed by Cohen’s k-test.Results:There was statistical difference of subjective image quality between the two groups (Z=-6.803, P=0.00).Subjective image quality was superior with HPM, as compared to CPM. There was no difference of noise and SNR between the two groups. There was significant difference of mean scan time between the two groups (P<0.05). Dose values were within the same range in the two groups (group A:CTDIvol (1.25±0.26mGy),ED (1.65±0.38mSv); group B:CTDIvol (1.29±0.29mGy),ED (1.67±0.31mSv), P>0.05). There was good agreement for overall image quality scoring between the two reviewers (κ-value of0.870and0.828, respectively, P<0.05)Conclusion:We showed that excellent image quality can be achieved in infants and children using HPM-DSCT with fast table speed without sedation at a very low radiation exposure.