Cystic fibrosis: are volumetric ultra-low-dose expiratory CT scans sufficient for monitoring related lung disease?

Static end-expiratory and dynamic forced expiratory tracheal collapse in COPD

AIM

To determine the range of tracheal collapse at end-expiration among chronic obstructive pulmonary disease (COPD) patients and to compare the extent of tracheal collapse between static end-expiratory and dynamic forced-expiratory multidetector-row computed tomography (MDCT).

MATERIALS AND METHODS

After institutional review board approval and obtaining informed consent, 67 patients meeting the National Heart, Lung, and Blood Institute (NHLBI)/World Health Organization (WHO) Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria for COPD were sequentially imaged using a 64-detector-row CT machine at end-inspiration, during forced expiration, and at end-expiration. Standardized respiratory coaching and spirometric monitoring were employed. Mean percentage tracheal collapse at end-expiration and forced expiration were compared using correlation analysis, and the power of end-expiratory cross-sectional area to predict excessive forced-expiratory tracheal collapse was computed following construction of receiver operating characteristic (ROC) curves.

RESULTS

Mean percentage expiratory collapse among COPD patients was 17 ± 18% at end-expiration compared to 62 ± 16% during forced expiration. Over the observed range of end-expiratory tracheal collapse (approximately 10-50%), the positive predictive value of end-expiratory collapse to predict excessive (≥80%) forced expiratory tracheal collapse was <0.3.

CONCLUSION

COPD patients demonstrate a wide range of end-expiratory tracheal collapse. The magnitude of static end-expiratory tracheal collapse does not predict excessive dynamic expiratory tracheal collapse.

Conversion factors for estimation of effective dose in paediatric chest tomosynthesis

For chest tomosynthesis in adults, a conversion factor of 0.26 mSv/Gy cm² has been reported for calculating the effective dose from the registered dose-area-product. The aim of this study was to determine conversion factors for chest tomosynthesis in children. Using the Monte Carlo-based computer software PCXMC 2.0, simulations were performed on modified phantoms for males and females aged 8-19 y, in the posteroanterior and anteroposterior projection, with energies 80-140 kV and copper filtration 0.1-0.3 mm. Resulting conversion factors ranged between 0.23 and 1.09 mSv/Gy cm², decreased with patient age, were significantly higher in the anteroposterior projection and increased with increased energy or copper filtration. To avoid an underestimation of effective dose in children, it is recommended to use age-dependent conversion factors. As a simplified approach, three conversion factors might be used for posteroanterior chest tomosynthesis and radiography in children, namely 0.6 (8-10 y), 0.4 (11-14 y) and 0.3 mSv/Gy cm² (15-19 y).

Radiography, tomosynthesis, CT and MRI in the evaluation of pulmonary cystic fibrosis: an untangling review of the multitude of scoring systems

Objective

The first radiographic scoring system for pulmonary cystic fibrosis was presented in 1958. Since then a multitude of scoring systems for radiography and computed tomography (CT) have been presented, recently also for tomosynthesis and magnetic resonance imaging (MRI). The aim of the current review was to analyse and compare the plethora of scoring systems for cystic fibrosis, especially regarding which scoring components are considered most important.

Methods

Four scoring systems for chest radiography, one for tomosynthesis, eight for CT and one for MRI were compared regarding components evaluated and their terminology; the areas scored; scoring levels; the weighting of each component in percentage of the total score; and the calculations for the final score.

Results

In most radiological scoring systems the lungs are evaluated for increased volume, bronchial wall thickening, bronchiectasis, mucus plugging, atelectasis and consolidation. In addition, for instance abscesses, bullae, septal thickening, mosaic perfusion, ground glass opacities and air trapping are evaluated in some CT scoring systems. Pleural affection and perfusion defects are scored on MRI.

Conclusions

Bronchiectasis alone, or in combination with mucus plugging, is given the highest weighting in most scoring systems and is thus commonly considered to be the most significant finding when evaluating cystic fibrosis lung disease.

Teaching points

Scoring of examinations is used for comparison of outcome in studies.

Scoring of examinations can also be used for monitoring disease progression.

Cystic fibrosis can be scored on radiography, tomosynthesis, CT or MRI.

The typical imaging findings of cystic fibrosis depend on the imaging modality used.

Bronchiectasis is commonly considered the most significant finding when scoring cystic fibrosis.

Radiation dose optimization and thoracic computed tomography

In the past 3 decades, radiation dose from computed tomography (CT) has contributed to an increase in overall radiation exposure to the population. This increase has caused concerns over harmful effects of radiation dose associated with CT in scientific publications as well as in the lay press. To address these concerns, and reduce radiation dose, several strategies to optimize radiation dose have been developed and assessed, including manual or automatic adjustment of scan parameters. This article describes conventional and contemporary techniques to reduce radiation dose associated with chest CT.

Distribution of early structural lung changes due to cystic fibrosis detected with chest computed tomography

OBJECTIVE

To examine the distribution of early structural lung changes in clinically stable infants and young children with cystic fibrosis using chest computed tomography (CT).

STUDY DESIGN

This cross-sectional study included 62 children aged 1-6 years with volume-controlled volumetric chest CT scans performed under general anesthesia as part of an early surveillance program. Each lobe was scored for presence and extent of bronchiectasis, mucus plugging, and air trapping using a semiquantitative score. The topographic distribution of structural abnormalities was evaluated by comparing the presence and extent of abnormalities in different lung regions and examining relationships between components.

RESULTS

Although bronchiectasis was most common in the right upper lobe, overall changes in lung structure were not more common or more extensive in the upper lobes. Rather, bronchiectasis was more common in the right lung (right lung 0.95, left lung 0.68, P = .003), and mucus plugging (upper 0.41, middle 0.41, lower 0.72, P = .028) and air trapping (upper 0.79, middle 0.48, lower 0.96, P < .001) were more common in the lower lobes. The extents of bronchiectasis (P < .001) and air trapping (P = .011) were greater in the right lung. Scans with bronchiectasis were also more likely to have coexisting mucus plugging (P = .008) and air trapping (P < .001).

CONCLUSION

Early structural lung disease is heterogeneously distributed in the lung. Quantitative scoring tools for studies using chest CT as an end point, and mechanistic studies that seek to better understand the pathogenesis of early cystic fibrosis lung disease, should take account of this differential topographic expression of disease early in life.

Bronchiectasis in chronic pulmonary aspiration: risk factors and clinical implications

INTRODUCTION

Bronchiectasis is a well-known sequela of chronic pulmonary aspiration (CPA) that can result in significant respiratory morbidity and death. However, its true prevalence is unknown because diagnosis requires high resolution computed tomography which is not routinely utilized in this population. This study describes the prevalence, time course for development, and risk factors for bronchiectasis in children with CPA.

MATERIALS AND METHODS

Using a cross-sectional design, medical records were reviewed for all patients with swallow study or airway endoscopy-confirmed aspiration in our airway center over a 21 month period. All patients underwent rigid and flexible bronchoscopy, and high resolution chest computed tomography. Prevalence, distribution, and risk factors for bronchiectasis were identified.

RESULTS

One hundred subjects age 6 months to 19 years were identified. Overall, 66% had bronchiectasis, including 51% of those less than 2 years old. The youngest was 8 months old. Severe neurological impairment (OR 9.45, P<0.004) and history of gastroesophageal reflux (OR 3.36, P=0.036) were identified as risk factors. Clinical history, exam, and other co-morbidities did not predict bronchiectasis. Sixteen subjects with bronchiectasis had repeat chest computed tomography with 44% demonstrating improvement or resolution.

DISCUSSION

Bronchiectasis is highly prevalent in children with CPA and its presence in young children demonstrates that it can develop rapidly. Early identification of bronchiectasis, along with interventions aimed at preventing further airway damage, may minimize morbidity and mortality in patients with CPA.

Paediatric multi-detector row chest CT: what you really need to know

Background

The emergence of multi-detector row CT (MDCT) has established and extended the role of CT especially in paediatric chest imaging. This has altered the way in which data is acquired and is perceived as the 'gold standard' in the detection of certain chest pathologies. The range of available post-processing tools provide alternative ways in which CT images can be manipulated for review and interpretation in order to enhance diagnostic accuracy.

Methodology

Paediatric imaging technique/protocol together with radiation dose reduction is discussed in detail. The use of different post-processing tools to best demonstrate the wide range of important congenital anomalies and thoracic pathologies is outlined and presented pictorially.

Conclusion

MDCT with its isotropic resolution and fast imaging acquisition times reduces the need for invasive diagnostic investigations. However, users must be vigilant in their imaging techniques to minimise radiation burden, whilst maintaining good image quality.

Main Messages

• CT examinations should be clinically justified by the referring clinician and radiologist.

• MDCT is invaluable for evaluating the central airway, mediastinal structures and lung parenchyma.

• MDCT is more sensitive than plain radiographs in detection of structural changes within the lungs.

Lung morphology assessment with balanced steady-state free precession MR imaging compared with CT

PURPOSE

To evaluate the utility of 1.5-T noncontrast magnetic resonance (MR) imaging of the lung parenchyma and to compare it with computed tomography (CT) in the assessment of interstitial lung disease and other morphologic lung abnormalities.

MATERIALS AND METHODS

Institutional review board approval was obtained for retrospective image analysis. A total of 236 patients who underwent MR imaging and CT as part of their assessment for suspected pulmonary hypertension were included in this study. Lung MR imaging was performed with a 1.5-T system as a stack of axial two-dimensional balanced steady-state free precession (bSSFP) acquisitions. Two radiologists independently evaluated CT and MR images for various morphologic abnormalities, such as pulmonary fibrosis, pleural and mediastinal disease, solid lesions, bronchial disease, and emphysema. Κ statistics were used to measure interobserver agreement.

RESULTS

Sensitivity and specificity of MR imaging in the identification of pulmonary fibrosis (n = 46) were 89% (95% confidence interval: 77%, 96%) and 91% (95% confidence interval: 76%, 98%), respectively, when compared with CT. In comparison to CT, MR imaging depicted 75% of ground-glass opacities. Nine of the 12 noncalcified nodules were identified on MR images. Lung nodules (75%, κ = 0.71) and effusions (100%, κ = 0.89) were also well visualized on MR images. MR imaging was however less effective in depicting emphysema (16%, κ = 0.60) and minor fibrosis (67%, κ = 0.79).

CONCLUSION

This study shows bSSFP MR imaging is inferior to CT in imaging parenchymal lung disease; however, this study does demonstrate for the first time a potential role for the bSSFP sequence as an alternative radiation-free noncontrast imaging modality for use in patients with pulmonary fibrosis.

Lung MRI as a possible alternative to CT scan for patients with primary immune deficiencies and increased radiosensitivity

BACKGROUND

Patients with common variable immunodeficiency (CVID) suffer from respiratory infections leading over time to permanent lung damage. Increased radiosensitivity has been described, and clinicians should consider a risk-benefit assessment when ordering a CT scan, in that the exact level of "safe" radiation exposure is unknown.

METHODS

Twenty-one patients with CVID were evaluated with chest CT scan, MRI, and pulmonary function tests on the same day. MRI protocol included a T2-weighted rotating blade-like k-space covering sequence (time repetition, 2,000; echo train = 27; field of view, 400 mm; flip angle, 150; slice thickness, 5 mm) on axial and coronal planes. The bronchial and parenchymal abnormalities were compared with those identified by CT scan applying a modified Bhalla scoring system to assess bronchiectasis, bronchial wall thickening, number of bronchial generations involved, mucous plugging, consolidations, emphysema, bullae, and nodules.

RESULTS

CT scan and MRI findings were comparable for moderate to severe degrees of bronchial and parenchymal alterations. A low concordance was found between MRI and CT scan for lower scores of bronchial abnormalities. CT scan allowed a better identification of peripheral airways abnormalities.

CONCLUSIONS

Lung alterations in patients with higher radiation sensitivity, such as patients with CVID, might be evaluated by MRI, a radiation-free technique alternative to CT scan.

Computed tomography and magnetic resonance imaging in cystic fibrosis lung disease

Computed tomography (CT) is the current "gold standard" for assessment of lung morphology and is so far the most reliable imaging modality for monitoring cystic fibrosis (CF) lung disease. CT has a much higher radiation exposure than chest x-ray. The cumulative radiation dose for life-long repeated CT scans has limited its use for CF patients as their life expectancy increases. Clearly, no dose would be preferable over low dose when the same or more relevant information can be obtained. Magnetic resonance imaging (MRI) is comparable to CT with regard to the detection of most morphological changes in the CF lung. It is thought to be less sensitive to detect small airway disease. At the same time, MRI is superior to CT when it comes to the assessment of functional changes such as altered pulmonary perfusion. The recommendation is to further reduce radiation dose related to the use of CT and to use MRI in the follow-up of morphological changes where possible.

Adaptive statistical iterative reconstruction technique for radiation dose reduction in chest CT: a pilot study

PURPOSE

To compare lesion detection and image quality of chest computed tomographic (CT) images acquired at various tube current-time products (40-150 mAs) and reconstructed with adaptive statistical iterative reconstruction (ASIR) or filtered back projection (FBP).

MATERIALS AND METHODS

In this Institutional Review Board-approved HIPAA-compliant study, CT data from 23 patients (mean age, 63 years ± 7.3 [standard deviation]; 10 men, 13 women) were acquired at varying tube current-time products (40, 75, 110, and 150 mAs) on a 64-row multidetector CT scanner with 10-cm scan length. All patients gave informed consent. Data sets were reconstructed at 30%, 50%, and 70% ASIR-FBP blending. Two thoracic radiologists assessed image noise, visibility of small structures, lesion conspicuity, and diagnostic confidence. Objective noise and CT number were measured in the thoracic aorta. CT dose index volume, dose-length product, weight, and transverse diameter were recorded. Data were analyzed by using analysis of variance and the Wilcoxon signed rank test.

RESULTS

FBP had unacceptable noise at 40 and 75 mAs in 17 and five patients, respectively, whereas ASIR had acceptable noise at 40-150 mAs. Objective noise with 30%, 50%, and 70% ASIR blending (11.8 ± 3.8, 9.6 ± 3.1, and 7.5 ± 2.6, respectively) was lower than that with FBP (15.8 ± 4.8) (P < .0001). No lesions were missed on FBP or ASIR images. Lesion conspicuity was graded as well seen on both FBP and ASIR images (P < .05). Mild pixilated blotchy texture was noticed with 70% blended ASIR images.

CONCLUSION

Acceptable image quality can be obtained for chest CT images acquired at 40 mAs by using ASIR without any substantial artifacts affecting diagnostic confidence.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101450/-/DC1.

Validation of computational fluid dynamics in CT-based airway models with SPECT/CT

PURPOSE

To compare the results obtained by using numerical flow simulations with the results of combined single photon emission computed tomography (SPECT) and computed tomography (CT) and to demonstrate the importance of correct boundary conditions for the numerical methods to account for the large amount of interpatient variability in airway geometry.

MATERIALS AND METHODS

This study was approved by all relevant institutional review boards. All patients gave their signed informed consent. In this study, six patients with mild asthma (three men; three women; overall mean age, 46 years ± 17 [standard deviation]) underwent CT at functional residual capacity and total lung capacity, as well as SPECT/CT. CT data were used for segmentation and computational fluid dynamics (CFD) simulations. A comparison was made between airflow distribution, as derived with (a) SPECT/CT through tracer concentration analysis, (b) CT through lobar expansion measurement, and (c) CFD through flow computer simulation. Also, the heterogeneity of the ventilation was examined.

RESULTS

Good agreement was found between SPECT/CT, CT, and CFD in terms of airflow distribution and hot spot detection. The average difference for the internal airflow distribution was less than 3% for CFD and CT versus SPECT/CT. Heterogeneity in ventilation patterns could be detected with SPECT/CT and CFD.

CONCLUSION

This results of this study show that patient-specific computer simulations with appropriate boundary conditions yield information that is similar to that obtained with functional imaging tools, such as SPECT/CT.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100322/-/DC1.

Bronchiectasis and pulmonary exacerbations in children and young adults with cystic fibrosis

OBJECTIVE

Respiratory tract exacerbation rate (RTE-R) is a key clinical efficacy end point in cystic fibrosis (CF) trials. Chest CT scanning holds great potential as a surrogate end point. Evidence supporting the ability of CT scan scores to predict RTE-R is an important step in validating CT scanning as a surrogate end point. The objective of this study was to investigate the association between CT scan scores and RTE-R in a cohort of pediatric patients with CF.

METHODS

A retrospective review of data from pediatric patients with CF included chest CT scans, spirometry, and 2 years follow-up. RTE-R was defined as the number of IV antibiotics courses per year. CT scans were scored with the Brody-II system, assessing bronchiectasis, airway wall thickening, mucus, and opacities.

RESULTS

One hundred fifteen patients contributed 170 CT scans. Median age and FEV(1) at first CT scan were 12 years (range, 5-20 years) and 90% predicted (range, 23% predicted-132% predicted), respectively. Analyzing exacerbation counts using Poisson regression models, bronchiectasis score and FEV(1) both were found to be strong independent predictors of RTE-R in the subsequent 2 years. For the bronchiectasis score categorized in quartiles, RTE-R increased by factors of 1.8 (95% CI, 0.6-6.1; P = .31), 5.5 (95% CI, 1.9-15.4; P = .001), and 10.6 (95% CI, 3.8-29.4; P < .001), respectively, for each quartile compared with the quartile with the best (ie, lowest) scores. Similarly, time to first respiratory tract exacerbation was significantly associated with quartiles of both bronchiectasis score and FEV(1).

CONCLUSIONS

The CT scan bronchiectasis score is strongly associated with RTE-R in pediatric patients with CF, providing an important piece of evidence in the validation of CT scans as an end point for CF clinical trials.

Development of low-dose protocols for thin-section CT assessment of cystic fibrosis in pediatric patients

PURPOSE

To develop low-dose thin-section computed tomographic (CT) protocols for assessment of cystic fibrosis (CF) in pediatric patients and determine the clinical usefulness thereof compared with chest radiography.

MATERIALS AND METHODS

After institutional review board approval and informed consent from patients or guardians were obtained, 14 patients with CF and 11 patients without CF (16 male, nine female; mean age, 12.6 years ± 5.4 [standard deviation]; range, 3.5-25 years) who underwent imaging for clinical reasons underwent low-dose thin-section CT. Sections 1 mm thick (protocol A) were used in 10 patients, and sections 0.5 mm thick (protocol B) were used in 15 patients at six levels at 120 kVp and 30-50 mA. Image quality and diagnostic acceptability were scored qualitatively and quantitatively by two radiologists who also quantified disease severity at thin-section CT and chest radiography. Effective doses were calculated by using a CT dosimetry calculator.

RESULTS

Low-dose thin-section CT was performed with mean effective doses of 0.19 mSv ± 0.03 for protocol A and 0.14 mSv ± 0.04 for protocol B (P < .005). Diagnostic acceptability and depiction of bronchovascular structures at lung window settings were graded as almost excellent for both protocols, but protocol B was inferior to protocol A for mediastinal assessment (P < .02). Patients with CF had moderate lung disease with a mean Bhalla score of 9.2 ± 5.3 (range, 0-19), compared with that of patients without CF (1.1 ± 1.4; P < .001). There was excellent correlation between thin-section CT and chest radiography (r = 0.88-0.92; P < .001).

CONCLUSION

Low-dose thin-section CT can be performed at lower effective doses than can standard CT, approaching those of chest radiography. Low-dose thin-section CT could be appropriate for evaluating bronchiectasis in pediatric patients, yielding appropriate information about lung parenchyma and bronchovascular structures.