Xenon-Enhanced Dual-Energy CT of Patients With Asthma: Dynamic Ventilation Changes After Methacholine and Salbutamol Inhalation
Department of Radiology, Seoul National University Hospital and Institute of Radiation Medicine, Seoul National University Medical Research Center, 101 Daehangno Jongno-gu, Seoul 110-744, Korea. American Journal of Roentgenology
(Impact Factor: 2.73).
11/2012; 199(5):975-81. DOI: 10.2214/AJR.11.7624
The purpose of this study was to evaluate the use of xenon-enhanced dual-energy CT of the chest to assess ventilation changes after methacholine and salbutamol inhalation in subjects with asthma and healthy subjects.
Twenty-five subjects with asthma and 10 healthy subjects underwent three-phase (basal, after methacholine inhalation, after salbutamol inhalation) xenon-enhanced chest CT. Each phase was composed of wash-in and washout scans. For visual analysis, two radiologists evaluated ventilation defects and gas trapping lobe by lobe on a 10-point scale. Total ventilation defect and gas trapping scores were calculated by adding ventilation defect and gas trapping scores. Xenon and total lung volume were quantified automatically. Total xenon concentration index was calculated as total xenon concentration divided by lung volume. Repeated measures analysis of variance and Student t test were used for comparisons of total ventilation defect score, total gas trapping score, and total xenon concentration index between the two groups. The Friedman test was used for within-group analysis.
In the basal state, subjects with asthma had a higher total ventilation defect score (p = 0.004) and higher total gas trapping score (p = 0.05) than did healthy subjects. On washout images, total ventilation defect score, total gas trapping score, and total xenon concentration index after methacholine and salbutamol inhalation were statistically different between the two groups (p < 0.05). However, total xenon concentration index on wash-in images was not significantly different between the two groups. In within-group analysis, total ventilation defect score and total gas trapping score in subjects with asthma and total ventilation defect score in healthy subjects increased significantly after methacholine inhalation and decreased significantly after salbutamol inhalation (p < 0.05).
Xenon-enhanced chest CT may be a useful technique for visualizing dynamic changes in airflow in response to methacholine and salbutamol inhalation in patients with asthma. Optimization of the protocol for radiation exposure is warranted.
Available from: Francis C K Thien
- "Xenon ventilation CT using dual source and dual energy is a new technique for functional lung imaging which visualises lung ventilation and allows quantification of regional ventilation defects as well as gas trapping behind obstructed airways [21, 22]. Using this technique, abnormalities of regional ventilation were found to be highly associated with measures of asthma control, airway hyperreactivity (as assessed by methacholine-induced bronchoconstriction) and subsequent bronchodilator response to salbutamol, but not with baseline FEV1 in a group of asthmatic subjects . "
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ABSTRACT: Asthma is a chronic inflammatory disorder of the airways causing typical symptoms, and the diagnosis is supported by evidence of airflow obstruction which is variable, reversible or inducible. However, standard assessment of lung function with spirometry does not measure dysfunction in small airways which are < 2 mm in diameter towards the periphery of the lung. These airways make only a small contribution to airway resistance under normal circumstances. Nevertheless, there is mounting evidence that pathology and dysfunction in these small airways are implicated in the pathogenesis and natural history of asthma. Using forced oscillation and the multibreath nitrogen washout techniques, uneven ventilation (ventilation heterogeneity) due to small airways dysfunction has been shown to be an important marker of asthma disease activity, even in the absence of abnormalities in standard spirometric measurements. Recent advances in imaging research, particularly with hyperpolarised gas magnetic resonance imaging, have also given insights into the significance and dynamic nature of ventilation heterogeneity in asthma. The challenge is to integrate these new physiological and imaging insights to further our understanding of asthma and facilitate potential new treatments.
Available from: Hye-Ryun Kang
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ABSTRACT: Image analyses include computed tomography (CT), magnetic resonance imaging, and xenon ventilation CT, which is new modality to evaluate pulmonary functional imaging.
To examine the usefulness of dual-energy xenon ventilation CT in asthmatic patients.
A total of 43 patients 18 years or older who were nonsmokers were included in the study. Xenon CT images in wash-in and wash-out phases were obtained at baseline and after inhalation of methacholine and salbutamol. The degrees of ventilation defects and xenon trappings were evaluated through visual analysis.
Ventilation defects and xenon trapping were significantly increased and decreased after methacholine challenge and salbutamol inhalation, respectively (P < .005). The ventilation abnormalities were not significantly related to the percentage of forced expiratory volume in 1 second (FEV1) or the ratio of FEV1 to forced vital capacity. Xenon trappings after salbutamol inhalation were negatively related to the scores of the asthma control test, wheezing, or night symptoms, with statistical significance (P < .05), whereas, FEV1 showed no significant correlation with symptom scores. Baseline FEV1 was significantly lower and dyspnea and wheezing were more severe in the non-full reversal group than in the full reversal group after salbutamol inhalation in xenon CT (P < .05). The degree of ventilation defects were positively correlated with FEV1 improvement after 3 months of treatment (P = .02).
The results of this study suggest that xenon ventilation CT can be used as a new method to assess ventilation abnormalities in asthma, and these ventilation abnormalities can be used as novel parameters that reflect the status of asthma control and symptom severity.
Available from: Del Leary
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To compare hyperpolarized helium-3 ((3) He) and xenon-129 ((129) Xe) MRI in asthmatics before and after salbutamol inhalation.
Materials and methods:
Seven asthmatics provided written informed consent and underwent spirometry, plethysmography, and MRI before and after salbutamol inhalation. (3) He and (129) Xe ventilation defect percent (VDP) and ventilation coefficient of variation (COV) were measured. To characterize the airways spatially related to ventilation defects, wall area percent (WA%) and lumen area (LA) were evaluated for two subjects who had thoracic x-ray computed tomography (CT) acquired 1 year before MRI.
Before salbutamol inhalation, (129) Xe VDP (8 ± 5%) was significantly greater than (3) He VDP (6 ± 5%, P = 0.003). Post-salbutamol, there was a significant improvement in both (129) Xe (5 ± 4%, P < 0.0001) and (3) He (4 ± 3%, P = 0.001) VDP, and the improvement in (129) Xe VDP was significantly greater (P = 0.008). (129) Xe MRI COV (Pre: 0.309 ± 0.028, Post: 0.296 ± 0.036) was significantly greater than (3) He MRI COV (Pre: 0.282 ± 0.018, Post: 0.269 ± 0.024), pre- (P < 0.0001) and post-salbutamol (P < 0.0001) and the decrease in COV post-salbutamol was significant ((129) Xe, P = 0.002; (3) He, P < 0.0001). For a single asthmatic, a sub-segmental (129) Xe MRI ventilation defect that was visible only before salbutamol inhalation but not visible using (3) He MRI was spatially related to a remodeled fourth generation sub-segmental airway (WA% = 78%, LA = 2.9 mm(2) ).
In asthma, hyperpolarized (129) Xe MRI may help reveal ventilation abnormalities before bronchodilation that are not observed using hyperpolarized (3) He MRI.
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