Reproducibility of spirometrically controlled CT lung densitometry in a clinical setting

Abstract

aaDensitometry of the lung is extensively used in pulmonary research. It has the potential to become an important addition to standard lung function tests in diagnosing and following the extent of pulmonary emphysema and interstitial lung disease. For recent reviews of this extensive work we refer to the literature [1,2]. The value of the technique is clearly proven in pulmonary emphysema. During inspiration, computed tomography (CT) correlates well with the pathologic score of emphysema [3]. Expiratory CT reflects airway obstruction and air-trapping more than it does emphysema [4,5]. Densitometric data may contribute to improved patient selection and to better evaluation of the response to volume reduction surgery [6,7]. Densitometry may provide an additional measure in selecting the side of greatest severity for unilateral lung reduction surgery [7].The methodologogy of CT densitometry has been established as well as factors affecting parameters derived from a histogram of Hounsfield units (HU). The accuracy and conformity of modern CT scanners have proved to be adequate after correction for poor air calibration [8,9]. CT number histograms of the lung are strongly dependent on section thickness and reconstruction filter [10][11][12]. To optimize CT evaluation procedures, semi-automatic algorithms isolating lung parenchyma by fast contour tracking have been developed, as well as automatic evaluation algorithms calculating various densitometric parameters automatically. Usually, mean lung density is determined as an average over a relatively large area. Unfortunately, it can be spuriously misleading especially at localized disease onset [13]. Mean lung density, however, is not the only densitometric parameter which can be extracted from the CT data. Pixel index analysis [3,4,14] and the lowest 10th percentile of the frequency distribution of densities [15] have shown promising results in the assessment of emphysema.If densitometry of the lung is used for diagnosis and follow-up of pulmonary emphysema or interstitial lung disease, the overall precision of the procedure has to be established. Reproducibility errors due to instrumental and technical factors have generally been considered to be smaller than patient-related factors. The CT density of the lung is considerably influenced by the level of inspiration at which the CT images are obtained. Control and monitoring this level of inspiration during scanning is of major importance to obtain reproducible CT lung density measurements. A spirometrically controlled CT technique has been developed, offering the opportunity to obtain CT scans at defined levels of inspiration [16].The purpose of this study was to assess the reproducibility of a number of histogram-related parameters of single CT slices through the upper and the lower zones of the lungs at 90 and 10% of the vital capacity (VC) in a hospitalized patient population. Reproducibility of spirometrically controlled CT lung desitometry in a clinical setting. R.J.S. Lamers, G.J. Kemerink, M. Drent, J.M.A. van E...

Lung densitometry: why, how and when

“…Notably, lung volume at end inspiration is most reproducible as compared to volumes attained in expiration, either at forced respiratory capacity (FRC) or at residual volume (RV), corresponding to end expiration and forced expiration, respectively (14,82).…”

Outcomes for COPD pharmacological trials: from lung function to biomarkers

“…Consistent measurements are most likely to be achieved at maximum inspiration [353] because variation in CT lung density is lowest at full inspiration [356]; in cooperative patients, breath-holding at maximum inspiration is most reproducible [357]. A study aimed at investigating the relationship between HRCT lung attenuation measurements (employing spirometric lung volume control), pulmonary dysfunction and dyspnoea severity in patients with COPD [358], has shown that pulmonary dysfunction in COPD cannot be assessed by a single modality of lung attenuation measurements.…”

“…This approach of volume correction has been shown to improve reproducibility [351,352], but its use in long-term studies may mask some of the lung density loss secondary to emphysema-related hyperinflation. The routine use of these volume-control methods in densitometric studies remains contentious [350][351][352][353][354][355].…”

A Comparative Study of HRCT Image Metrics and PFT Values for Characterization of ILD and COPD

“…As a result, various CT image metrics have been proposed towards a more consistent and facilitated assessment. Early investigations into CT lung analysis employed relatively simple metrics, such as the mean attenuation value and other such first-order statistical measurements obtainable from the attenuation histogram [1][2][3]. More sophisticated metrics relying on texture descriptions of the parenchyma have shown promise in recent studies [4].…”