Three-Section Expiratory CT: Insufficient for Trapped Air Assessment in Patients with Cystic Fibrosis?
Abstract
This pilot study suggests that expiratory three-section protocols result in underestimation of trapped air in patients with cystic fibrosis when using the Brody II system.
Purpose
To estimate the effect of the number of computed tomography (CT) sections on trapped air (TA) assessment in patients with cystic fibrosis (CF) by using an established scoring system and a new quantitative scoring system and to compare CT and pulmonary function test (PFT) estimates of TA in a cross-sectional and longitudinal study.
Materials and Methods
In this institutional review board–approved pilot study, 20 subjects aged 6–20 years (12 female and eight male; median age, 12.6 years) contributed two expiratory CT studies (three-section baseline CT, volumetric follow-up CT) and two PFT studies over 2 years after parental informed consent was obtained. From follow-up CT studies, seven sets were composed: Set 1 was volumetric. Sets 2, 3, 4, and 5, had spacing of 2.4, 4.8, 9.6, and 20.4 mm, respectively, between sections. Sets 6 and 7 contained five and three sections, respectively. Longitudinal follow-up was performed with three sections. All images were deidentified and randomized, and TA was scored with the Brody II system and a new quantitative system. Statistical analysis included the Wilcoxon signed rank test, calculation of Spearman and intraclass correlation coefficients, and use of three-section and linear mixed models.
Results
For the Brody II system, the intraclass correlation coefficient for set 1 versus those for sets 2 through 7 was 0.75 versus 0.87; however, mean scores from sets 6 and 7 were significantly lower than the mean score from set 1 (P = .01 and P < .001, respectively). For the quantitative system, the number of sections did not affect TA assessment (intraclass correlation coefficient range, 0.82–0.88; P > .13 for all). CT and PFT estimates were not correlated (rs = 20.19 to 0.09, P = .43–.93). No change in TA over time was found for CT or PFT (P > .16 for all).
Conclusion
The number of sections affected Brody II estimates, suggesting that three-section protocols lead to underestimation of TA assessment in patients with CF when using the Brody II system; CT and PFT estimates of TA showed no correlation and no significant change over time.
© RSNA, 2012
References
- 1 . High-resolution computed tomography of the lung in children with cystic fibrosis: technical factors. Proc Am Thorac Soc 2007;4(4):306–309.
- 2 . Detection of air trapping on inspiratory and expiratory phase images obtained by 0.3-second cine CT in the lungs of free-breathing young children. AJR Am J Roentgenol 2006;187(4):1019–1023.
- 3 . High-resolution computed tomography imaging of airway disease in infants with cystic fibrosis. Am J Respir Crit Care Med 2005;172(9):1133–1138.
- 4 . Gas trapping in normal infants and in infants with cystic fibrosis. Pediatr Pulmonol 2004;37(5):461–469.
- 5 . Lung disease at diagnosis in infants with cystic fibrosis detected by newborn screening. Am J Respir Crit Care Med 2009;180(2):146–152.
- 6 . The spectrum of structural abnormalities on CT scans from patients with CF with severe advanced lung disease. Thorax 2009;64(10):876–882.
- 7 . Bronchiectasis in infants and preschool children diagnosed with cystic fibrosis after newborn screening. J Pediatr 2009;155(5):623–628.e1.
- 8 . Cystic fibrosis lung disease starts in the small airways: can we treat it more effectively? Pediatr Pulmonol 2010;45(2):107–117.
- 9 . An automated approach to quantitative air trapping measurements in mild cystic fibrosis. Chest 2003;123(5):1655–1663.
- 10 . Evaluation of air trapping at CT: comparison of continuous- versus suspended-expiration CT techniques. Radiology 2000;216(3):768–772.
- 11 . Expiratory high-resolution CT scan. Radiol Clin North Am 1998;36(1):189–209.
- 12 . Quantitative air-trapping analysis in children with mild cystic fibrosis lung disease. Pediatr Pulmonol 2004;38(5):396–405.
- 13 . High-resolution computed tomography of the lungs: the borderlands of normality. Eur Radiol 2006;16(4):771–780.
- 14 . Expiratory high-resolution CT: diagnostic value in diffuse lung diseases. AJR Am J Roentgenol 2000;175(6):1537–1543.
- 15 . Pulmonary disease assessment in cystic fibrosis: comparison of CT scoring systems and value of bronchial and arterial dimension measurements. Radiology 2004;231(2):434–439.
- 16 . Progression of pulmonary hyperinflation and trapped gas associated with genetic and environmental factors in children with cystic fibrosis. Respir Res 2006;7:138.
- 17 . Progression of lung disease on computed tomography and pulmonary function tests in children and adults with cystic fibrosis. Thorax 2006;61(1):80–85.
- 18 . Progressive damage on high resolution computed tomography despite stable lung function in cystic fibrosis. Eur Respir J 2004;23(1):93–97.
- 19 . Computed tomography correlates with pulmonary exacerbations in children with cystic fibrosis. Am J Respir Crit Care Med 2005;172(9):1128–1132.
- 20 . Pulmonary abnormalities on high-resolution CT demonstrate more rapid decline than FEV1 in adults with cystic fibrosis. Chest 2006;130(5):1424–1432.
- 21 . High-resolution computed tomography in young patients with cystic fibrosis: distribution of abnormalities and correlation with pulmonary function tests. J Pediatr 2004;145(1):32–38.
- 22 . Computed tomography reflects lower airway inflammation and tracks changes in early cystic fibrosis. Am J Respir Crit Care Med 2007;175(9):943–950.
- 23 . Air trapping on computed tomography images of healthy individuals: effects of respiration and body mass index. Clin Radiol 2006;61(10):883–887.
- 24 . Air trapping on expiratory high-resolution CT scans in the absence of inspiratory scan abnormalities: correlation with pulmonary function tests and differential diagnosis. AJR Am J Roentgenol 1998;170(5):1349–1353.
- 25 . Sampling density for the quantitative evaluation of air trapping. Pediatr Radiol 2009;39(3):221–225.
- 26 . Regional heterogeneity of air trapping at expiratory thin-section CT of patients with bronchiolitis: potential implications for dose reduction and CT protocol planning. Radiology 2008;247(3):862–870.
- 27 . Survey of CT practice in the UK: normalised organ doses for x-ray computed tomography using Monte Carlo techniques. Harwell, England: National Radiological Protection Board, 1991.
- 28 . Influence of patient age on normalized effective doses calculated for CT examinations. Br J Radiol 2002;75(898):819–830.
- 29 . Vessel-guided airway tree segmentation: a voxel classification approach. Med Image Anal 2010;14(4):527–538.
- 30 . Medical image processing, analysis and visualization in clinical research. In: Proceedings of the 14th IEEE Symposium on Computer-Based Medical Systems (CBMS 2001). Piscataway, NJ: Institute of Electrical and Electronics Engineers, 2001; 381–386.
- 31 Standardized lung function testing: official statement of the European Respiratory Society. Eur Respir J Suppl 1993;16:1–100.
- 32 . Lung function in children and adolescents: methods, reference values. Basel, Switzerland: Karger, 1987.
- 33 . Dornase alfa reduces air trapping in children with mild cystic fibrosis lung disease: a quantitative analysis. Chest 2005;128(4):2327–2335.
- 34 . Air trapping in mild and moderate asthma: effect of inhaled corticosteroids. J Allergy Clin Immunol 2007;119(3):583–590.
- 35 . Thoracic gas volume measurement: increased variability in patients with obstructive ventilatory defects. Chest 1984;85(2):272–275.
- 36 . Assessment of lung volumes in children and adolescents: comparison of two plethysmographic techniques. Clin Physiol Funct Imaging 2005;25(1):62–68.
- 37 . Multiple-breath inert gas washout and spirometry versus structural lung disease in cystic fibrosis. Thorax 2008;63(2):129–134.
- 38 . Method for assessment of volume of trapped gas in infants during multiple-breath inert gas washout. Pediatr Pulmonol 2003;35(1):42–49.
Article History
Received May 11, 2011; revision requested July 23; revision received August 26; accepted September 10; final version accepted October 17.Published online: Mar 2012
Published in print: Mar 2012