Objective: The purport of this study was to prospectively view if quantitative computed tomography (QCT) could separate asthmatic patients from normal command subjects.

Objective: The purport of this study was to prospectively view if quantitative computed tomography (QCT) could separate asthmatic patients from normal command subjects. The QCT results were also correlated with the pulmonary function experiments (PFT) that were done onward both the asthmatic patients and hinder subjects.

Subjects and methods: Eighteen adult nonsmoking asthmatics and 22 adult have charge of subjects were entered into the application of mind Quantitative CT was performed at the even of the transverse aorta and just above the diaphragm at the pair end inspiration and end expiration in all patients and repress subjects: 10-mm and 1.5-mm collimation using a high spatial oftenness algorithm was used to obtain the QCT examinations. The percent of pixels below -900 Hounsfeld units, pixel index, in each of the QCT axial images of the lung was calculated for each asthmatic and have the direction of subject in the study. Pulmonary function testing was performed in succession both the asthmatics and superintend subjects and included determination of [FEVsub1] FVC FRC RV and TLC Unpaired Student's t proof analysis of the QCT data was done to statistically compare the asthmatics with the have the direction of subjects. Linear regression analysis was done to compare the QCT be deriveds with PFT data on the asthmatics and mastery subjects.

Results: When scans were performed at expiration expiration, at a level immediately superior to the diaphragm, the mean pixel index was significantly higher in asthmatic subdues compared with normal individuals onward both CT (mean for normal bring under rules 0.16 vs 4.45 for asthmatics, p<0004) and high-resolution CT (HRCT) images (mean for normal controls 1.04 vs 10.03 in asthmatics, p<00001) indicating more areas of depressed attenuation in asthmatics. The CT and HRCT images from the lower lung surface bounded by parallel circles s that were performed at [i]finale[/i] expiration provided the best separation between the clusters The pixel index on expiration correlated with the step of air trapping and airflow limitation in the asthmatic assign places to based on [FEV.sub.1], FRC, RV and to a less extent, FVC.

Conclusion: Expiratory QCT is a useful way to assess air trapping in asthmatic patients. The percent of abnormal lung in asthmatics as determined by way of QCT has a significant correlation with the PFT that bring reproach air trapping in asthmatic patients. Quantitative CT may be helpful in assessing steps of air trapping present in other diseases affecting the airways.

(Chest 1994; 106: 105-09)

HRCT = high-resolution CT;

HU = Hounsfeld unit;

RV = residual volume

Comput tomography (CT) and high-resolution CT (HRCT) are useful in diagnosing airways diseases similar as emphysema,(1)(2)(3)(4)(5)(6)(7)(8) bronchiectasis,(9)(10)(11) bronchiolitis,(12) and bronchiolitis obliterans.(13)(14)(15)(16) However, these tools have a long more limited role in the assessment of asthma and chronic bronchitis, in part because bronchial wall thickening and air trapping have been difficult to quantify from CT.

Lung density can be quantitatively assessed in the pair normal and diseased patients from using CT attenuation values. Each pixel (picture element) of a CT image has a CT attenuation value that is declareed in Hounsfeld units (HU), which range from 3095 HU for condensed cortical bone, to --1,000 HU for the CT density of air. The normal CT density of the lung is --700 to --800 in succession inspiration. Pixels that have reasonable attenuation values can be highlighted by the agency of the use of "density mask" software. This technique has been described in several prior publications as a arrangement to quantitate the amount of emphysema not past nor future in the lungs.(6)(7)(8) We have observ focal areas of decreased attenuation that are principally evident on expiratory CT images of the lung in asthmatic patients who have no evidence of lung disease similar as emphysema, leading us to speculate that CT might experience applicable to the assessment of asthma.

This application of mind was designed to answer sum of two units questions: (1) can quantitative CT and HRCT scanning, using an index of decreased attenuation, discriminate asthmatics from normal direct subjects, and (2) does this index of decreased attenuation consider physiologically significant hyperaeration and airflow limitation?

METHODS

application of mind Population

We studied 18 adult asthmatic patients of whom 8 were men and 10 were women none of whom eternally smoked. Their ages ranged from 24 to 76 years (average age, 535 years). We defined asthma as (1) the air of intermittent symptoms of wheezing, coughing, or chest tightness, plus (2) significant bronchial hyperresponsiveness. Bronchial hyperresponsiveness was considered significant if the patient's forced expiratory body in 1 s ([FEV.sub.1]) rose at least 20 percent following the administration of a bronchodilator or malicious by at least 20 percent in rejoinder to a methacholine bronchial challenge of 8 [micro]g/ml or les All patients were well at the time of evaluation without evidence of asthma exacerbation or respiratory tract infection.

We also studied 22 adult normal superintend subjects (12 men and 10 women) none of whom evermore smoked or had any history of lung disease as determined on the American Thoracic Society respiratory symptom questionnaire. Their ages ranged from 25 to 49 years (average age, 322 years). These make subordinates were younger than the asthmatic subdues (p<0.001).

...