Monitoring of Smoking-induced Emphysema with CT in a Lung Cancer Screening Setting: Detection of Real Increase in Extent of Emphysema

Impact of low-dose computed tomography (LDCT) screening on lung cancer-related mortality

BACKGROUND

Lung cancer is the most common cause of cancer-related death in the world, however lung cancer screening has not been implemented in most countries at a population level. A previous Cochrane Review found limited evidence for the effectiveness of lung cancer screening with chest radiography (CXR) or sputum cytology in reducing lung cancer-related mortality, however there has been increasing evidence supporting screening with low-dose computed tomography (LDCT).  OBJECTIVES: To determine whether screening for lung cancer using LDCT of the chest reduces lung cancer-related mortality and to evaluate the possible harms of LDCT screening.

SEARCH METHODS

We performed the search in collaboration with the Information Specialist of the Cochrane Lung Cancer Group and included the Cochrane Lung Cancer Group Trial Register, Cochrane Central Register of Controlled Trials (CENTRAL, the Cochrane Library, current issue), MEDLINE (accessed via PubMed) and Embase in our search. We also searched the clinical trial registries to identify unpublished and ongoing trials. We did not impose any restriction on language of publication. The search was performed up to 31 July 2021.  SELECTION CRITERIA: Randomised controlled trials (RCTs) of lung cancer screening using LDCT and reporting mortality or harm outcomes.  DATA COLLECTION AND ANALYSIS: Two review authors were involved in independently assessing trials for eligibility, extraction of trial data and characteristics, and assessing risk of bias of the included trials using the Cochrane RoB 1 tool. We assessed the certainty of evidence using GRADE. Primary outcomes were lung cancer-related mortality and harms of screening. We performed a meta-analysis, where appropriate, for all outcomes using a random-effects model. We only included trials in the analysis of mortality outcomes if they had at least 5 years of follow-up. We reported risk ratios (RRs) and hazard ratios (HRs), with 95% confidence intervals (CIs) and used the I2 statistic to investigate heterogeneity.  MAIN RESULTS: We included 11 trials in this review with a total of 94,445 participants. Trials were conducted in Europe and the USA in people aged 40 years or older, with most trials having an entry requirement of ≥ 20 pack-year smoking history (e.g. 1 pack of cigarettes/day for 20 years or 2 packs/day for 10 years etc.). One trial included male participants only. Eight trials were phase three RCTs, with two feasibility RCTs and one pilot RCT. Seven of the included trials had no screening as a comparison, and four trials had CXR screening as a comparator. Screening frequency included annual, biennial and incrementing intervals. The duration of screening ranged from 1 year to 10 years. Mortality follow-up was from 5 years to approximately 12 years.  None of the included trials were at low risk of bias across all domains. The certainty of evidence was moderate to low across different outcomes, as assessed by GRADE. In the meta-analysis of trials assessing lung cancer-related mortality, we included eight trials (91,122 participants), and there was a reduction in mortality of 21% with LDCT screening compared to control groups of no screening or CXR screening (RR 0.79, 95% CI 0.72 to 0.87; 8 trials, 91,122 participants; moderate-certainty evidence). There were probably no differences in subgroups for analyses by control type, sex, geographical region, and nodule management algorithm. Females appeared to have a larger lung cancer-related mortality benefit compared to males with LDCT screening. There was also a reduction in all-cause mortality (including lung cancer-related) of 5% (RR 0.95, 95% CI 0.91 to 0.99; 8 trials, 91,107 participants; moderate-certainty evidence).  Invasive tests occurred more frequently in the LDCT group (RR 2.60, 95% CI 2.41 to 2.80; 3 trials, 60,003 participants; moderate-certainty evidence). However, analysis of 60-day postoperative mortality was not significant between groups (RR 0.68, 95% CI 0.24 to 1.94; 2 trials, 409 participants; moderate-certainty evidence).  False-positive results and recall rates were higher with LDCT screening compared to screening with CXR, however there was low-certainty evidence in the meta-analyses due to heterogeneity and risk of bias concerns. Estimated overdiagnosis with LDCT screening was 18%, however the 95% CI was 0 to 36% (risk difference (RD) 0.18, 95% CI -0.00 to 0.36; 5 trials, 28,656 participants; low-certainty evidence). Four trials compared different aspects of health-related quality of life (HRQoL) using various measures. Anxiety was pooled from three trials, with participants in LDCT screening reporting lower anxiety scores than in the control group (standardised mean difference (SMD) -0.43, 95% CI -0.59 to -0.27; 3 trials, 8153 participants; low-certainty evidence). There were insufficient data to comment on the impact of LDCT screening on smoking behaviour.  AUTHORS' CONCLUSIONS: The current evidence supports a reduction in lung cancer-related mortality with the use of LDCT for lung cancer screening in high-risk populations (those over the age of 40 with a significant smoking exposure). However, there are limited data on harms and further trials are required to determine participant selection and optimal frequency and duration of screening, with potential for significant overdiagnosis of lung cancer. Trials are ongoing for lung cancer screening in non-smokers.

Comparison of CT Lung Density Measurements between Standard Full-Dose and Reduced-Dose Protocols

Purpose

To evaluate the reproducibility and predicted clinical outcomes of CT-based quantitative lung density measurements using standard fixed-dose (FD) and reduced-dose (RD) scans.

Materials and Methods

In this retrospective analysis of prospectively acquired data, 1205 participants (mean age, 65 years ± 9 [standard deviation]; 618 men) enrolled in the COPDGene study who underwent FD and RD CT image acquisition protocols between November 2014 and July 2017 were included. Of these, the RD scans of 640 participants were also reconstructed using iterative reconstruction (IR). Median filtering was applied to the RD scans (RD-MF) to investigate an alternative noise reduction strategy. CT attenuation at the 15th percentile of the lung CT histogram (Perc15) was computed for all image types (FD, RD, RD-MF, and RD-IR). Reproducibility coefficients were calculated to quantify the measurement differences between FD and RD scans. The ability of Perc15 to predict chronic obstructive pulmonary disease (COPD) diagnosis and exacerbation frequency was investigated using receiver operating characteristic analysis.

Results

The Perc15 reproducibility coefficients with and without volume adjustment were as follows: RD, 29.43 HU ± 0.62 versus 32.81 HU ± 1.70; RD-MF, 7.42 HU ± 0.42 versus 19.40 HU ± 2.65; and RD-IR, 7.10 HU ± 0.52 versus 22.46 HU ± 3.91. Receiver operating characteristic curve analysis indicated that Perc15 on volume-adjusted FD and RD scans were both predictive for COPD diagnosis (area under the receiver operating characteristic curve [AUC]: FD, 0.724 ± 0.045; RD, 0.739 ± 0.045) and for having one or more exacerbation per year (AUCs: FD, 0.593 ± 0.068; RD, 0.589 ± 0.066). Similar trends were observed when volume adjustment was not applied.

Conclusion

A combination of volume adjustment and noise reduction filtering improved the reproducibility of lung density measurements computed using serial FD and RD CT scans.Supplemental material is available for this article.© RSNA, 2021.

Ultra-low-dose CT combined with noise reduction techniques for quantification of emphysema in COPD patients: An intra-individual comparison study with standard-dose CT

PURPOSE

Phantom studies in CT emphysema quantification show that iterative reconstruction and deep learning-based noise reduction (DLNR) allow lower radiation dose. We compared emphysema quantification on ultra-low-dose CT (ULDCT) with and without noise reduction, to standard-dose CT (SDCT) in chronic obstructive pulmonary disease (COPD).

METHOD

Forty-nine COPD patients underwent ULDCT (third generation dual-source CT; 70ref-mAs, Sn-filter 100kVp; median CTDIvol 0.38 mGy) and SDCT (64-multidetector CT; 40mAs, 120kVp; CTDIvol 3.04 mGy). Scans were reconstructed with filtered backprojection (FBP) and soft kernel. For ULDCT, we also applied advanced modelled iterative reconstruction (ADMIRE), levels 1/3/5, and DLNR, levels 1/3/5/9. Emphysema was quantified as Low Attenuation Value percentage (LAV%, ≤-950HU). ULDCT measures were compared to SDCT as reference standard.

RESULTS

For ULDCT, the median radiation dose was 84 % lower than for SDCT. Median extent of emphysema was 18.6 % for ULD-FBP and 15.4 % for SDCT (inter-quartile range: 11.8-28.4 % and 9.2 %-28.7 %, p = 0.002). Compared to SDCT, the range in limits of agreement of emphysema quantification as measure of variability was 14.4 for ULD-FBP, 11.0-13.1 for ULD-ADMIRE levels and 10.1-13.9 for ULD-DLNR levels. Optimal settings were ADMIRE 3 and DLNR 3, reducing variability of emphysema quantification by 24 % and 27 %, at slight underestimation of emphysema extent (-1.5 % and -2.9 %, respectively).

CONCLUSIONS

Ultra-low-dose CT in COPD patients allows dose reduction by 84 %. State-of-the-art noise reduction methods in ULDCT resulted in slight underestimation of emphysema compared to SDCT. Noise reduction methods (especially ADMIRE 3 and DLNR 3) reduced variability of emphysema quantification in ULDCT by up to 27 % compared to FBP.

Emphysema quantification using low-dose computed tomography with deep learning-based kernel conversion comparison

OBJECTIVE

This study determined the effect of dose reduction and kernel selection on quantifying emphysema using low-dose computed tomography (LDCT) and evaluated the efficiency of a deep learning-based kernel conversion technique in normalizing kernels for emphysema quantification.

METHODS

A sample of 131 participants underwent LDCT and standard-dose computed tomography (SDCT) at 1- to 2-year intervals. LDCT images were reconstructed with B31f and B50f kernels, and SDCT images were reconstructed with B30f kernels. A deep learning model was used to convert the LDCT image from a B50f kernel to a B31f kernel. Emphysema indices (EIs), lung attenuation at 15th percentile (perc15), and mean lung density (MLD) were calculated. Comparisons among the different kernel types for both LDCT and SDCT were performed using Friedman's test and Bland-Altman plots.

RESULTS

All values of LDCT B50f were significantly different compared with the values of LDCT B31f and SDCT B30f (p < 0.05). Although there was a statistical difference, the variation of the values of LDCT B50f significantly decreased after kernel normalization. The 95% limits of agreement between the SDCT and LDCT kernels (B31f and converted B50f) ranged from - 2.9 to 4.3% and from - 3.2 to 4.4%, respectively. However, there were no significant differences in EIs and perc15 between SDCT and LDCT converted B50f in the non-chronic obstructive pulmonary disease (COPD) participants (p > 0.05).

CONCLUSION

The deep learning-based CT kernel conversion of sharp kernel in LDCT significantly reduced variation in emphysema quantification, and could be used for emphysema quantification.

KEY POINTS

• Low-dose computed tomography with smooth kernel showed adequate performance in quantifying emphysema compared with standard-dose CT. • Emphysema quantification is affected by kernel selection and the application of a sharp kernel resulted in a significant overestimation of emphysema. • Deep learning-based kernel normalization of sharp kernel significantly reduced variation in emphysema quantification.

The Emerging Role of Radiomics in COPD and Lung Cancer

Medical imaging plays a key role in evaluating and monitoring lung diseases such as chronic obstructive pulmonary disease (COPD) and lung cancer. The application of artificial intelligence in medical imaging has transformed medical images into mineable data, by extracting and correlating quantitative imaging features with patients' outcomes and tumor phenotype - a process termed radiomics. While this process has already been widely researched in lung oncology, the evaluation of COPD in this fashion remains in its infancy. Here we outline the main applications of radiomics in lung cancer and briefly review the workflow from image acquisition to the evaluation of model performance. Finally, we discuss the current assessments of COPD and the potential application of radiomics in COPD.

Implementation planning for lung cancer screening in China

Lung cancer is the leading cause of cancer-related deaths in China, with over 690 000 lung cancer deaths estimated in 2018. The mortality has increased about five-fold from the mid-1970s to the 2000s. Lung cancer low-dose computerized tomography (LDCT) screening in smokers was shown to improve survival in the US National Lung Screening Trial, and more recently in the European NELSON trial. However, although the predominant risk factor, smoking contributes to a lower fraction of lung cancers in China than in the UK and USA. Therefore, it is necessary to establish Chinese-specific screening strategies. There have been 23 associated programmes completed or still ongoing in China since the 1980s, mainly after 2000; and one has recently been planned. Generally, their entry criteria are not smoking-stringent. Most of the Chinese programmes have reported preliminary results only, which demonstrated a different high-risk subpopulation of lung cancer in China. Evidence concerning LDCT screening implementation is based on results of randomized controlled trials outside China. LDCT screening programmes combining tobacco control would produce more benefits. Population recruitment (e.g. risk-based selection), screening protocol, nodule management and cost-effectiveness are discussed in detail. In China, the high-risk subpopulation eligible for lung cancer screening has not as yet been confirmed, as all the risk parameters have not as yet been determined. Although evidence on best practice for implementation of lung cancer screening has been accumulating in other countries, further research in China is urgently required, as China is now facing a lung cancer epidemic.

Longitudinal airway remodeling in active and past smokers in a lung cancer screening population

OBJECTIVES

To longitudinally investigate smoking cessation-related changes of quantitative computed tomography (QCT)-based airway metrics in a group of heavy smokers.

METHODS

CT scans were acquired in a lung cancer screening population over 4 years at 12-month intervals in 284 long-term ex-smokers (ES), 405 continuously active smokers (CS), and 31 subjects who quitted smoking within 2 years after baseline CT (recent quitters, RQ). Total diameter (TD), lumen area (LA), and wall percentage (WP) of 1st-8th generation airways were computed using airway analysis software. Inter-group comparison was performed using Mann-Whitney U test or Student's t test (two groups), and ANOVA or ANOVA on ranks with Dunn's multiple comparison test (more than two groups), while Fisher's exact test or chi-squared test was used for categorical data. Multiple linear regression was used for multivariable analysis.

RESULTS

At any time, TD and LA were significantly higher in ES than CS, for example, in 5th-8th generation airways at baseline with 6.24 mm vs. 5.93 mm (p < 0.001) and 15.23 mm² vs. 13.51 mm² (p < 0.001), respectively. RQ showed higher TD (6.15 mm vs. 5.93 mm, n.s.) and significantly higher LA (14.77 mm² vs. 13.51 mm², p < 0.001) than CS after 3 years, and after 4 years. In multivariate analyses, smoking status independently predicted TD, LA, and WP at baseline, at 3 years and 4 years (p < 0.01-0.001), with stronger impact than pack years.

CONCLUSIONS

Bronchial dimensions depend on the smoking status. Smoking-induced airway remodeling can be partially reversible after smoking cessation even in long-term heavy smokers. Therefore, QCT-based airway metrics in clinical trials should consider the current smoking status besides pack years.

KEY POINTS

• Airway lumen and diameter are decreased in active smokers compared to ex-smokers, and there is a trend towards increased airway wall thickness in active smokers. • Smoking-related airway changes improve within 2 years after smoking cessation. • Smoking status is an independent predictor of airway dimensions.

On the Potential Role of MRI Biomarkers of COPD to Guide Bronchoscopic Lung Volume Reduction

RATIONALE AND OBJECTIVES

In patients with severe emphysema and poor quality of life, bronchoscopic lung volume reduction (BLVR) may be considered and guided based on lobar emphysema severity. In particular, x-ray computed tomography (CT) emphysema measurements are used to identify the most diseased and the second-most diseased lobes as BLVR targets. Inhaled gas magnetic resonance imaging (MRI) also provides chronic obstructive pulmonary disease (COPD) biomarkers of lobar emphysema and ventilation abnormalities. Our objective was to retrospectively evaluate CT and MRI biomarkers of lobar emphysema and ventilation in patients with COPD eligible for BLVR. We hypothesized that MRI would provide complementary biomarkers of emphysema and ventilation that help determine the most appropriate lung lobar targets for BLVR in patients with COPD.

MATERIALS AND METHODS

We retrospectively evaluated 22 BLVR-eligible patients from the Thoracic Imaging Network of Canada cohort (diffusing capacity of the lung for carbon monoxide = 37 ± 12%_predicted, forced expiratory volume in 1 second = 34 ± 7%_predicted, total lung capacity = 131 ± 17%_predicted, and residual volume = 216 ± 36%_predicted). Lobar CT emphysema, measured using a relative area of <-950 Hounsfield units (RA₉₅₀) and MRI ventilation defect percent, was independently used to rank lung lobe disease severity.

RESULTS

In 7 of 22 patients, there were different CT and MRI predictions of the most diseased lobe. In some patients, there were large ventilation defects in lobes not targeted by CT, indicative of a poorly ventilated lung. CT and MRI classification of the most diseased and the second-most diseased lobes showed a fair-to-moderate intermethod reliability (Cohen κ = 0.40-0.59).

CONCLUSIONS

In this proof-of-concept retrospective analysis, quantitative MRI ventilation and CT emphysema measurements provided different BLVR targets in over 30% of the patients. The presence of large MRI ventilation defects in lobes next to CT-targeted lobes might also change the decision to proceed or to guide BLVR to a different lobar target.

Standardizing CT lung density measure across scanner manufacturers

PURPOSE

Computed Tomography (CT) imaging of the lung, reported in Hounsfield Units (HU), can be parameterized as a quantitative image biomarker for the diagnosis and monitoring of lung density changes due to emphysema, a type of chronic obstructive pulmonary disease (COPD). CT lung density metrics are global measurements based on lung CT number histograms, and are typically a quantity specifying either the percentage of voxels with CT numbers below a threshold, or a single CT number below which a fixed relative lung volume, nth percentile, falls. To reduce variability in the density metrics specified by CT attenuation, the Quantitative Imaging Biomarkers Alliance (QIBA) Lung Density Committee has organized efforts to conduct phantom studies in a variety of scanner models to establish a baseline for assessing the variations in patient studies that can be attributed to scanner calibration and measurement uncertainty.

METHODS

Data were obtained from a phantom study on CT scanners from four manufacturers with several protocols at various tube potential voltage (kVp) and exposure settings. Free from biological variation, these phantom studies provide an assessment of the accuracy and precision of the density metrics across platforms solely due to machine calibration and uncertainty of the reference materials. The phantom used in this study has three foam density references in the lung density region, which, after calibration against a suite of Standard Reference Materials (SRM) foams with certified physical density, establishes a HU-electron density relationship for each machine-protocol. We devised a 5-step calibration procedure combined with a simplified physical model that enabled the standardization of the CT numbers reported across a total of 22 scanner-protocol settings to a single energy (chosen at 80 keV). A standard deviation was calculated for overall CT numbers for each density, as well as by scanner and other variables, as a measure of the variability, before and after the standardization. In addition, a linear mixed-effects model was used to assess the heterogeneity across scanners, and the 95% confidence interval of the mean CT number was evaluated before and after the standardization.

RESULTS

We show that after applying the standardization procedures to the phantom data, the instrumental reproducibility of the CT density measurement of the reference foams improved by more than 65%, as measured by the standard deviation of the overall mean CT number. Using the lung foam that did not participate in the calibration as a test case, a mixed effects model analysis shows that the 95% confidence intervals are [-862.0 HU, -851.3 HU] before standardization, and [-859.0 HU, -853.7 HU] after standardization to 80 keV. This is in general agreement with the expected CT number value at 80 keV of -855.9 HU with 95% CI of [-857.4 HU, -854.5 HU] based on the calibration and the uncertainty in the SRM certified density.

CONCLUSIONS

This study provides a quantitative assessment of the variations expected in CT lung density measures attributed to non-biological sources such as scanner calibration and scanner x-ray spectrum and filtration. By removing scanner-protocol dependence from the measured CT numbers, higher accuracy and reproducibility of quantitative CT measures were attainable. The standardization procedures developed in study may be explored for possible application in CT lung density clinical data.

Segmental bronchi collapsibility: computed tomography-based quantification in patients with chronic obstructive pulmonary disease and correlation with emphysema phenotype, corresponding lung volume changes and clinical parameters

BACKGROUND

Global pulmonary function tests lack region specific differentiation that might influence therapy in severe chronic obstructive pulmonary disease (COPD) patients. Therefore, the aim of this work was to assess the degree of expiratory 3^rd generation bronchial lumen collapsibility in patients with severe COPD using chest-computed tomography (CT), to evaluate emphysema-phenotype, lobar volumes and correlate results with pulmonary function tests.

METHODS

Thin-slice chest-CTs acquired at end-inspiration & end-expiration in 42 COPD GOLD IV patients (19 females, median-age: 65.9 y) from November 2011 to July 2014 were re-evaluated. The cross-sectional area of all segmental bronchi was measured 5 mm below the bronchial origin in both examinations. Lung lobes were semi-automatically segmented, volumes calculated at end-inspiratory and end-expiratory phase and visually defined emphysema-phenotypes defined. Results of CT densitometry were compared with lung functional tests including forced expiratory volume at 1 s (FEV₁), total lung capacity (TLC), vital capacity (VC), residual volume (RV), diffusion capacity parameters and the maximal expiratory flow rates (MEFs).

RESULTS

Mean expiratory bronchial collapse was 31%, stronger in lobes with homogenous (38.5%) vs. heterogeneous emphysema-phenotype (27.8%, P=0.014). The mean lobar expiratory volume reduction was comparable in both emphysema-phenotypes (volume reduction 18.6%±8.3% in homogenous vs. 17.6%±16.5% in heterogeneous phenotype). The degree of bronchial lumen collapsibility, did not correlate with expiratory volume reduction. MEF₂₅ correlated weakly with 3^rd generation airway collapsibility (r=0.339, P=0.03). All patients showed a concentric expiratory reduction of bronchial cross-sectional area.

CONCLUSIONS

Changes in collapsibility of 3^rd generation bronchi in COPD grade IV patients is significantly lower than that in the trachea and the main bronchi. Collapsibility did not correlate with the reduction in lung volume but was significantly higher in lobes with homogeneous vs. heterogeneous emphysema phenotype. Changes in the 3^rd generation bronchial calibres between inspiration and expiration are not predictive for the degree of small airway collapsibility and related airflow limitation.

Variation of densitometry on computed tomography in COPD--influence of different software tools

Objectives

Quantitative multidetector computed tomography (MDCT) as a potential biomarker is increasingly used for severity assessment of emphysema in chronic obstructive pulmonary disease (COPD). Aim of this study was to evaluate the user-independent measurement variability between five different fully-automatic densitometry software tools.

Material and Methods

MDCT and full-body plethysmography incl. forced expiratory volume in 1s and total lung capacity were available for 49 patients with advanced COPD (age = 64±9 years, forced expiratory volume in 1s = 31±6% predicted). Measurement variation regarding lung volume, emphysema volume, emphysema index, and mean lung density was evaluated for two scientific and three commercially available lung densitometry software tools designed to analyze MDCT from different scanner types.

Results

One scientific tool and one commercial tool failed to process most or all datasets, respectively, and were excluded. One scientific and another commercial tool analyzed 49, the remaining commercial tool 30 datasets. Lung volume, emphysema volume, emphysema index and mean lung density were significantly different amongst these three tools (p<0.001). Limits of agreement for lung volume were [−0.195, −0.052l], [−0.305, −0.131l], and [−0.123, −0.052l] with correlation coefficients of r = 1.00 each. Limits of agreement for emphysema index were [−6.2, 2.9%], [−27.0, 16.9%], and [−25.5, 18.8%], with r = 0.79 to 0.98. Correlation of lung volume with total lung capacity was good to excellent (r = 0.77 to 0.91, p<0.001), but segmented lung volume (6.7±1.3 – 6.8±1.3l) were significantly lower than total lung capacity (7.7±1.7l, p<0.001).

Conclusions

Technical incompatibilities hindered evaluation of two of five tools. The remaining three showed significant measurement variation for emphysema, hampering quantitative MDCT as a biomarker in COPD. Follow-up studies should currently use identical software, and standardization efforts should encompass software as well.

Progress in Imaging COPD, 2004 - 2014

Computed tomography (CT) has contributed substantially to our understanding of COPD over the past decade. Visual and quantitative assessments of CT in COPD are complementary. Visual assessment should provide assessment of centrilobular, panlobular and paraseptal emphysema, airway wall thickening, bronchiectasis, findings of respiratory bronchiolitis, and enlargement of the pulmonary artery. Quantitative CT permits evaluation of severity of emphysema, airway wall thickening, and expiratory air trapping, and is now being used for longitudinal evaluation of the progression of COPD. Innovative techniques are being developed to use CT to characterize the pattern of emphysema and smoking- related respiratory bronchiolitis. Magnetic resonance imaging (MRI) and positron emission tomography PET-CT are useful research tools in the evaluation of COPD.

Repeatability and Sample Size Assessment Associated with Computed Tomography-Based Lung Density Metrics

RATIONALE AND OBJECTIVES

Density-based metrics assess severity of lung disease but vary with lung inflation and method of scanning. The aim of this study was to evaluate the repeatability of single center, CT-based density metrics of the lung in a normal population and assess study sample sizes needed to detect meaningful changes in lung density metrics when scan parameters and volumes are tightly controlled.

MATERIALS AND METHODS

Thirty-seven subjects (normal smokers and non-smokers) gave consent to have randomly assigned repeated, breath-held scans at either inspiration (90% vital capacity: TLC) or expiration (20% vital capacity: FRC). Repeated scans were analyzed for: mean lung density (MLD), 15th percentile point of the density histogram (P15), low attenuation areas (LAA) and alpha (fractal measure of hole size distribution). Using inter-subject differences and previously reported bias, sample size was estimated from month or yearly change in density metrics obtained from published literature (i.e. meaningful change).

RESULTS

Inter-scan difference measurements were small for density metrics (ICC > 0.80) and average ICCs for whole lung alpha-910 and alpha-950 were 0.57 and 0.64, respectively. Power analyses demonstrated that, under the control conditions with minimal extrinsic variation, population sizes needed to detect meaningful changes in density measures for TLC or FRC repeated scans ranged from a few (20-40) to a few hundred subjects, respectively.

CONCLUSION

A meaningful sample size was predicted from this study using volume-controlled normal subjects in a controlled imaging environment. Under proper breath-hold conditions, high repeatability was obtained in cohorts of normal smokers and non-smokers.

Quantitative computed tomography in chronic obstructive pulmonary disease

Quantitative computed tomography is being increasingly used to quantify the features of chronic obstructive pulmonary disease, specifically emphysema, air trapping, and airway abnormality. For quantification of emphysema, the density mask technique is most widely used, with threshold on the order of-950 HU, but percentile cutoff may be less sensitive to volume changes. Sources of variation include depth of inspiration, scanner make and model, technical parameters, and cigarette smoking. On expiratory computed tomography (CT), air trapping may be quantified by evaluating the percentage of lung volume less than a given threshold (eg, -856 HU) by comparing lung volumes and attenuation on expiration and inspiration or, as done more recently, by coregistering inspiratory and expiratory CT scans. All of these indices correlate well with the severity of physiological airway obstruction. By constructing a 3-dimensional model of the airway from volumetric CT, it is possible to measure dimensions (external and internal diameters and airway wall thickness) of segmental and subsegmental airways orthogonal to their long axes. Measurement of airway parameters correlates with the severity of airflow obstruction and with the history of chronic obstructive pulmonary disease exacerbation.

Normal variance in emphysema index measurements in 64 multidetector-row computed tomography

The purpose of this study was to identify the normal variance of emphysema index (EI) measured in examinations acquired with 64 multidetector‐row computed tomography (64‐MDCT). A longitudinal, noninterventional study was performed retrieving all patients in our institution who are currently registered in our lung nodule protocol. All patients with clinical, functional, or significant radiological changes were excluded. We assumed that EI should remain unchanged within a short period of time. We reviewed 475 MDCTs in order to select 50 clinically stable patients who had two sequential chest MDCTs performed within a time interval of less than three months, and who presented at least one lung free of abnormalities but emphysema. CT densitovolumetry was used to calculate EI with thresholds set at −950 Hounsfield units (HUs) (EI‐950) and −970 HUs (EI‐970); on both studies from each patient. We observed the variation of total lung volume (TLV), mean lung density (MDL), and EI for measurements at the baseline and at follow‐up scans. Differences observed between baseline and follow‐up measurements were: TLVμ=149ml; IC=μ+1.96(133); EI−950=0.02%; p95=0.89%; EI−970μ=0.04%; p95=0.23% and MLDμ=15HU; IC=μ+1.96(18). The correlations obtained were the following: TLV r=0.96, EI−950r=0.79, EI−970r=0.85. Accepting that emphysema would remain unchanged within three months on stable patients, differences of less than 0.89% for EI‐950 and of less than 0.23% for EI‐970 are within the variance of the method.

PACS number: 87.50.ct

Genetic ancestry and the relationship of cigarette smoking to lung function and per cent emphysema in four race/ethnic groups: a cross-sectional study

BACKGROUND

Cigarette smoking is the major cause of chronic obstructive pulmonary disease and emphysema. Recent studies suggest that susceptibility to cigarette smoke may vary by race/ethnicity; however, they were generally small and relied on self-reported race/ethnicity.

OBJECTIVE

To test the hypothesis that relationships of smoking to lung function and per cent emphysema differ by genetic ancestry and self-reported race/ethnicity among Caucasians, African-Americans, Hispanics and Chinese-Americans.

DESIGN

Cross-sectional population-based study of adults age 45-84 years in the USA.

MEASUREMENTS

Principal components of genetic ancestry and continental ancestry estimated from one million genome-wide single nucleotide polymorphisms; pack-years of smoking; spirometry measured for 3344 participants; and per cent emphysema on computed tomography for 8224 participants.

RESULTS

The prevalence of ever-smoking was: Caucasians, 57.6%; African-Americans, 56.4%; Hispanics, 46.7%; and Chinese-Americans, 26.8%. Every 10 pack-years was associated with -0.73% (95% CI -0.90% to -0.56%) decrement in the forced expiratory volume in 1 s to forced vital capacity (FEV1 to FVC) and a 0.23% (95% CI 0.08% to 0.38%) increase in per cent emphysema. There was no evidence that relationships of pack-years to the FEV1 to FVC, airflow obstruction and per cent emphysema varied by genetic ancestry (all p>0.10), self-reported race/ethnicity (all p>0.10) or, among African-Americans, African ancestry. There were small differences in relationships of pack-years to the FEV1 among male Chinese-Americans and to the FEV1 to FVC ratio with African and Native American ancestry among male Hispanics only.

CONCLUSIONS

In this large cohort, there was little to no evidence that the associations of smoking to lung function and per cent emphysema differed by genetic ancestry or self-reported race/ethnicity.

Low-dose CT measurements of airway dimensions and emphysema associated with airflow limitation in heavy smokers: a cross sectional study

Background

Increased airway wall thickness (AWT) and parenchymal lung destruction both contribute to airflow limitation. Advances in computed tomography (CT) post-processing imaging allow to quantify these features. The aim of this Dutch population study is to assess the relationships between AWT, lung function, emphysema and respiratory symptoms.

Methods

AWT and emphysema were assessed by low-dose CT in 500 male heavy smokers, randomly selected from a lung cancer screening population. AWT was measured in each lung lobe in cross-sectionally reformatted images with an automated imaging program at locations with an internal diameter of 3.5 mm, and validated in smaller cohorts of patients. The 15^th percentile method (Perc15) was used to assess the severity of emphysema. Information about respiratory symptoms and smoking behavior was collected by questionnaires and lung function by spirometry.

Results

Median AWT in airways with an internal diameter of 3.5 mm (AWT_3.5) was 0.57 (0.44 - 0.74) mm. Median AWT in subjects without symptoms was 0.52 (0.41-0.66) and in those with dyspnea and/or wheezing 0.65 (0.52-0.81) mm (p<0.001). In the multivariate analysis only AWT_3.5 and emphysema independently explained 31.1%and 9.5%of the variance in FEV₁%predicted, respectively, after adjustment for smoking behavior.

Conclusions

Post processing standardization of airway wall measurements provides a reliable and useful method to assess airway wall thickness. Increased airway wall thickness contributes more to airflow limitation than emphysema in a smoking male population even after adjustment for smoking behavior.

Changes in volume-corrected whole-lung density in smokers and former smokers during the ITALUNG screening trial

PURPOSE

To evaluate with a volume-corrected whole-lung approach changes in lung density over 2 years consistent with progression of pulmonary emphysema in smokers and former smokers enrolled in the ITALUNG trial of lung cancer screening using low-dose computed tomography (LDCT).

MATERIALS AND METHODS

A total of 103 subjects (mean age 63±4 y with a pack-year history of at least 20) underwent 2 whole-lung LDCT examinations 2 years apart. Visual assessment was made independently by 2 experienced observers on the initial LDCT examination with a 0 to 4 grading system for each of 6 regions (right and left upper, mid, and lower lung). The whole-lung 15th percentile of attenuation coefficient and relative area (RA) at -910 HU, both corrected to the individual lung volume (Perc15v and RA910v), were measured on the 2 LDCT examinations. The intrasubject variability of Perc15v and RA910v was previously determined in 32 other subjects of the trial examined using the same scanner and technique twice over a 3-month interval for suspicious nodules.

RESULTS

The 2 operators agreed on the presence of mild to severe emphysema (visual score ≥1 in at least 1 region) at initial LDCT examination in 24 (23%) of the 103 subjects. Fifteen subjects (15%) showed a Perc15v change between the 2 examinations exceeding the lower 95% limit of agreement, indicating progression of emphysema with a mean difference in lung density of -14.7%±2.6%. Ten of the 15 were identified as showing emphysema progression by RA910v as well. No association was observed between progression of emphysema and visual evidence of emphysema at initial LDCT examination, smoking status, or pack-years at baseline, or intervening changes in smoking habits.

CONCLUSION

Once variations in inspiratory lung volumes are taken into account, changes in lung density over 2 years consistent with progression of pulmonary emphysema in elderly smokers and former smokers are uncommon.

Reference standard and statistical model for intersite and temporal comparisons of CT attenuation in a multicenter quantitative lung study

PURPOSE

The purpose of this study was to detect and analyze anomalies between a large number of computed tomography (CT) scanners, tracked over time, utilized to collect human pulmonary CT data for a national multicenter study: chronic obstructive pulmonary disease genetic epidemiology study (COPDGene).

METHODS

A custom designed CT reference standard "Test Object" has been developed to evaluate the relevant differences in CT attenuation between CT scanners in COPDGene. The materials used in the Test Object to assess CT scanner accuracy and precision included lung equivalent foam (-856 HU), internal air (-1000 HU), water (0 HU), and acrylic (120 HU). Nineteen examples of the Test Object were manufactured. Initially, all Test Objects were scanned on the same CT scanner before the Test Objects were sent to the 20 specific sites and 42 individual CT scanners that were used in the study. The Test Objects were scanned over 17 months while the COPDGene study continued to recruit subjects. A mixed linear effect statistical analysis of the CT scans on the 19 Test Objects was performed. The statistical model reflected influence of reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency on CT attenuation.

RESULTS

Depending on the Test Object material, there were significant differences between reconstruction kernels, tube current, individual Test Objects, CT scanner models, and temporal consistency. The two Test Object materials of most interest were lung equivalent foam and internal air. With lung equivalent foam, there were significant (p < 0.05) differences between the Siemens B31 (-856.6, ±0.82; mean ± SE) and the GE Standard (-856.6 ± 0.83) reconstruction kernel relative to the Siemens B35 reference standard (-852.5 ± 1.4). Comparing lung equivalent foam attenuation there were also significant differences between CT scanner models (p < 0.01), tube current (p < 0.005), and in temporal consistency (p < 0.005) at individual sites. However, there were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. For internal air, significant (p < 0.005) differences were found between all reconstruction kernels (Siemens B31, GE Standard, and Phillips B) compared to the reference standard. There were significant differences between CT models (p < 0.005), and tube current (p < 0.005). There were no significant effects measurable using different examples of the Test Objects at the various sites compared to the reference scans of the 19 Test Objects. Differences, across scanners, between external air and internal air measures in this simple (relative to the in vivo lung) test object varied by as much as 15 HU.

CONCLUSIONS

The authors conclude that the Test Object designed for this study was able to detect significant effects regarding individual CT scanners that altered the CT attenuation measurements relevant to the study that are used to determine lung density. Through an understanding of individual scanners, the Test Object analysis can be used to detect anomalies in an individual CT scanner and to statistically model out scanner differences and individual scanner changes over time in a large multicenter trial.

Variation in quantitative CT air trapping in heavy smokers on repeat CT examinations

Objectives

To determine the variation in quantitative computed tomography (CT) measures of air trapping in low-dose chest CTs of heavy smokers.

Methods

We analysed 45 subjects from a lung cancer screening trial, examined by CT twice within 3 months. Inspiratory and expiratory low-dose CT was obtained using breath hold instructions. CT air trapping was defined as the percentage of voxels in expiratory CT with an attenuation below −856 HU (EXP₋₈₅₆) and the expiratory to inspiratory ratio of mean lung density (E/I-ratio_MLD). Variation was determined using limits of agreement, defined as 1.96 times the standard deviation of the mean difference. The effect of both lung volume correction and breath hold reproducibility was determined.

Results

The limits of agreement for uncorrected CT air trapping measurements were −15.0 to 11.7 % (EXP₋₈₅₆) and −9.8 to 8.0 % (E/I-ratio_MLD). Good breath hold reproducibility significantly narrowed the limits for EXP₋₈₅₆ (−10.7 to 7.5 %, P = 0.002), but not for E/I-ratio_MLD (−9.2 to 7.9 %, P = 0.75). Statistical lung volume correction did not improve the limits for EXP₋₈₅₆ (−12.5 to 8.8 %, P = 0.12) and E/I-ratio_MLD (−7.5 to 5.8 %, P = 0.17).

Conclusions

Quantitative air trapping measures on low-dose CT of heavy smokers show considerable variation on repeat CT examinations, regardless of lung volume correction or reproducible breath holds.

Key Points

• Computed tomography quantitatively measures small airways disease in heavy smokers.

• Measurements of air trapping vary considerably on repeat CT examinations.

• Variation remains substantial even with reproducible breath holds and lung volume correction.

Improved correlation between CT emphysema quantification and pulmonary function test by density correction of volumetric CT data based on air and aortic density

OBJECTIVES

To determine the improvement of emphysema quantification with density correction and to determine the optimal site to use for air density correction on volumetric computed tomography (CT).

METHODS

Seventy-eight CT scans of COPD patients (GOLD II-IV, smoking history 39.2±25.3 pack-years) were obtained from several single-vendor 16-MDCT scanners. After density measurement of aorta, tracheal- and external air, volumetric CT density correction was conducted (two reference values: air, -1,000 HU/blood, +50 HU). Using in-house software, emphysema index (EI) and mean lung density (MLD) were calculated. Differences in air densities, MLD and EI prior to and after density correction were evaluated (paired t-test). Correlation between those parameters and FEV1 and FEV1/FVC were compared (age- and sex adjusted partial correlation analysis).

RESULTS

Measured densities (HU) of tracheal- and external air differed significantly (-990 ± 14, -1016 ± 9, P<0.001). MLD and EI on original CT data, after density correction using tracheal- and external air also differed significantly (MLD: -874.9 ± 27.6 vs. -882.3 ± 24.9 vs. -860.5 ± 26.6; EI: 16.8 ± 13.4 vs. 21.1 ± 14.5 vs. 9.7 ± 10.5, respectively, P<0.001). The correlation coefficients between CT quantification indices and FEV1, and FEV1/FVC increased after density correction. The tracheal air correction showed better results than the external air correction.

CONCLUSION

Density correction of volumetric CT data can improve correlations of emphysema quantification and PFT.

Computer-aided diagnosis: how to move from the laboratory to the clinic

Computer-aided diagnosis (CAD), encompassing computer-aided detection and quantification, is an established and rapidly growing field of research. In daily practice, however, most radiologists do not yet use CAD routinely. This article discusses how to move CAD from the laboratory to the clinic. The authors review the principles of CAD for lesion detection and for quantification and illustrate the state-of-the-art with various examples. The requirements that radiologists have for CAD are discussed: sufficient performance, no increase in reading time, seamless workflow integration, regulatory approval, and cost efficiency. Performance is still the major bottleneck for many CAD systems. Novel ways of using CAD, extending the traditional paradigm of displaying markers for a second look, may be the key to using the technology effectively. The most promising strategy to improve CAD is the creation of publicly available databases for training and validation. This can identify the most fruitful new research directions, and provide a platform to combine multiple approaches for a single task to create superior algorithms.

Robust, standardized quantification of pulmonary emphysema in low dose CT exams

RATIONALE AND OBJECTIVES

The aim of this study was to present and evaluate a fully automated system for emphysema quantification on low-dose computed tomographic images. The platform standardizes emphysema measurements against changes in the reconstruction algorithm and slice thickness.

MATERIALS AND METHODS

Emphysema was quantified in 149 patients using a fully automatic, in-house developed software (the Robust Automatic On-Line Pulmonary Helper). The accuracy of the system was evaluated against commercial software, and its reproducibility was assessed using pairs of volume-corrected images taken 1 year apart. Furthermore, to standardize quantifications, the effect of changing the reconstruction parameters was modeled using a nonlinear fit, and the inverse of the model function was then applied to the data. The association between quantifications and pulmonary function testing was also evaluated. The accuracy of the in-house software compared to that of commercial software was measured using Spearman's rank correlation coefficient, the mean difference, and the intrasubject variability. Agreement between the methods was studied using Bland-Altman plots. To assess the reproducibility of the method, intraclass correlation coefficients and Bland-Altman plots were used. The statistical significance of the differences between the standardized data and the reference data (soft-tissue reconstruction algorithm B40f; slice thickness, 1 mm) was assessed using a paired two-sample t test.

RESULTS

The accuracy of the method, measured as intrasubject variability, was 3.86 mL for pulmonary volume, 0.01% for emphysema index, and 0.39 Hounsfield units for mean lung density. Reproducibility, assessed using the intraclass correlation coefficient, was >0.95 for all measurements. The standardization method applied to compensate for variations in the reconstruction algorithm and slice thickness increased the intraclass correlation coefficients from 0.87 to 0.97 and from 0.99 to 1.00, respectively. The correlation of the standardized measurements with pulmonary function testing parameters was similar to that of the reference (for the emphysema index and the obstructive subgroup: forced expiratory volume in 1 second, -0.647% vs -0.615%; forced expiratory volume in 1 second/forced vital capacity, -0.672% vs -0.654%; and diffusing capacity for carbon monoxide adjusted for hemoglobin concentration, -0.438% vs -0.523%).

CONCLUSIONS

The new emphysema quantification method presented in this report is accurate and reproducible and, thanks to its standardization method, robust to changes in the reconstruction parameters.

Defining the intra-subject variability of whole-lung CT densitometry in two lung cancer screening trials

RATIONALE AND OBJECTIVES

To define a statistically based variation of individual whole-lung densitometry above which a real increase of pulmonary extent can be suspected in lung cancer screening trials.

MATERIALS AND METHODS

Baseline and 3-month follow-up low-dose computed tomography (LDCT) examinations of 131 smokers or former smokers recruited in the ITALUNG (32 subjects) and MILD (99 subjects) trials were compared using for each data set two different image processing tools for whole-lung densitometry. Both trials were approved by institutional review boards, and written informed consent was obtained from all participants. Assuming that no change of emphysema extent can occur in a 3-month interval, the Bland and Altman method was used to assess the agreement between baseline and follow-up LDCT examinations for lung volume, 15th percentile (Perc15) of lung density and Perc15 corrected for lung volume by application of a linear detrend on log-transformed data.

RESULTS

Similar results were obtained in each data set using two different image processing tools. In the ITALUNG cohort the 95% limits of agreement (LoA) interval of volume corrected Perc15 was -9.7 to 10.7% using image processing method 1 and -10.3 to 11.5% using image processing method 2. In the MILD cohort, the 95% LoA interval of volume corrected Perc15 was -14.7 to 17.3% with both image processing methods.

CONCLUSION

In the two considered lung cancer screening settings a range of 9.7-14.7% decrease of volume corrected Perc15 represents a statistically defined threshold to suspect a real increase of emphysema extent in serial LDCT examinations.

Multivariate compensation of quantitative pulmonary emphysema metric variation from low-dose, whole-lung CT scans

OBJECTIVE

Emphysema is a disease of the lung characterized by the destruction of the alveolar sac walls. Several quantitative densitometric measures of emphysema from wholelung CT have been proposed for evaluating disease severity and progression. However, a concern with these quantitative measures has been the large interscan variability observed during longitudinal studies of emphysema. To account for and reduce inherent measure variability, this work implements and evaluates the use of a multivariate random-effects model for correcting longitudinal variation in densitometric scores of emphysema due to inspiration.

MATERIALS AND METHODS

The method of multivariate compensation was validated on three of the most commonly reported densitometric measures of emphysema: the emphysema index, histogram percentile, and fractal dimension. Two short-interval, zero-change datasets, one for model development (n = 105) and one for validation (n = 106), were retrospectively identified and used to ensure that all variation was caused by inherent measure variability.

RESULTS

A statistically significant (F test, p < 0.001) reduction of 42.40% in measurement limits of agreement could be obtained after model application, with compensated emphysema metric differences showing 31-33% of the variance compared with uncompensated metric variance.

CONCLUSION

Compensation was still effective when the trained model was applied to the second validation dataset. Multivariate compensation was found to be useful in reducing interscan measurement variability and should be applied to future longitudinal studies of emphysema.

Reconstruction algorithms influence the follow-up variability in the longitudinal CT emphysema index measurements

OBJECTIVE

We wanted to compare the variability in the longitudinal emphysema index (EI) measurements that were computed with standard and high resolution (HR) reconstruction algorithms (RAs).

MATERIALS AND METHODS

We performed a retrospective review of 475 patients who underwent CT for surveillance of lung nodules. From this cohort, 50 patients (28 male) were included in the study. For these patients, the baseline and follow-up scans were acquired on the same multidetector CT scanner and using the same acquisition protocol. The CT scans were reconstructed with HR and standard RAs. We determined the difference in the EI between CT1 and CT2 for the HR and standard RAs, and we compared the variance of these differences.

RESULTS

The mean of the variation of the total lung volume was 0.14 L (standard deviation [SD] = 0.13 L) for the standard RA and 0.16 L (SD = 0.15 L) for the HR RA. These differences were not significant. For the standard RA, the mean variation was 0.13% (SD = 0.44%) for EI -970 and 0.4% (SD = 0.88%) for EI -950; for the HR RA, the mean variation was 1.9% (SD = 2.2%) for EI -970 and 3.6% (SD = 3.7%) for EI -950. These differences were significant.

CONCLUSION

Using an HR RA appears to increase the variability of the CT measurements of the EI.

Repeated low-dose computed tomography in current and former smokers for quantification of emphysema

OBJECTIVE

To quantify different emphysema evolution in current and former smokers.

METHODS

We retrospectively analyzed low-dose computed tomography scans from a lung cancer screening study of 59 current and 75 former smokers. The quantitative emphysema analysis was performed using a home-built software (YACTA version 0.9), yielding the parameters lung volume, emphysema volume (EV), emphysema index (EI), mean lung density, and 15th percentile.

RESULTS

The baseline EV and EI were significantly different (median EVformer =422 mL vs EVcurrent =249 mL, P = 0.0003; and median EIformer =7.6 % vs EIcurrent =4.1 %, P = 0.0001, respectively). On the annual repeat scan, the median EI and EV for former smokers had decreased significantly (ΔEIformer = -0.257%, P = 0.004; and ΔEVcurrent = -0.203 mL, P = 0.020), whereas there was no emphysema change in current smokers.

CONCLUSIONS

We were able to demonstrate different emphysema evolution in current versus former smokers; emphysema parameters decreased in the former smokers and remained stable in current smokers.

Early detection of emphysema progression

Emphysema is one of the most widespread diseases in subjects with smoking history. The gold standard method for estimating the severity of emphysema is a lung function test, such as forced expiratory volume in first second (FEV1). However, several clinical studies showed that chest CT scans offer more sensitive estimates of emphysema progression. The standard CT densitometric score of emphysema is the relative area of voxels below a threshold (RA). The RA score is a global measurement and reflects the overall emphysema progression. In this work, we propose a framework for estimation of local emphysema progression from longitudinal chest CT scans. First, images are registered to a common system of coordinates and then local image dissimilarities are computed in corresponding anatomical locations. Finally, the obtained dissimilarity representation is converted into a single emphysema progression score. We applied the proposed algorithm on 27 patients with severe emphysema with CT scans acquired five time points, at baseline, after 3, after 12, after 21 and after 24 or 30 months. The results showed consistent emphysema progression with time and the overall progression score correlates significantly with the increase in RA score.

Emphysema quantification in inflation-fixed lungs using low-dose computed tomography and 3He magnetic resonance imaging

OBJECTIVE

To evaluate the use of inflation-fixed lung tissue for emphysema quantification with computed tomography (CT) and He magnetic resonance (MR) diffusion imaging.

METHODS

Fourteen subjects representing a range of chronic obstructive pulmonary disease severity who underwent complete or lobar lung resection were studied. Computed tomographic measurements of lung attenuation and MR measurements of the hyperpolarized 3He apparent diffusion coefficient (ADC) in resected specimens fixed in inflation with heated formalin vapor were compared with measurements obtained before fixation.

RESULTS

The mean (SD) CT emphysema indices were 56% (17%) before and 58% (19%) after fixation (P = 0.77; R = 0.76). Index differences correlated with differences in lung volume (R = 0.47). The mean (SD) 3He ADCs were 0.40 (0.15) cm/s before and 0.39 (0.14) cm/s after fixation (P = 0.03, R = 0.98). The CT emphysema index and the 3He ADC were correlated before (R = 0.89) and after fixation (R = 0.79).

CONCLUSIONS

Concordance of CT and 3He MR imaging measurements in unfixed and inflation-fixed lungs supports the use of inflation-fixed lungs for quantitative imaging studies in emphysema.

Relationship between diseased lung tissues on computed tomography and motion of fiducial marker near lung cancer

PURPOSE

For lung cancer patients with poor pulmonary function because of emphysema or fibrosis, it is important to predict the amplitude of internal tumor motion to minimize the irradiation of the functioning lung tissue before undergoing stereotactic body radiotherapy.

METHODS AND MATERIALS

Two board-certified diagnostic radiologists independently assessed the degree of pulmonary emphysema and fibrosis on computed tomography scans in 71 patients with peripheral lung tumors before real-time tumor-tracking radiotherapy. The relationships between the computed tomography findings of the lung parenchyma and the motion of the fiducial marker near the lung tumor were investigated. Of the 71 patients, 30 had normal pulmonary function, and 29 had obstructive pulmonary dysfunction (forced expiratory volume in 1 s/forced vital capacity ratio of <70%), 6 patients had constrictive dysfunction (percentage of vital capacity <80%), and 16 had mixed dysfunction.

RESULTS

The upper region was associated with smaller tumor motion, as expected (p = .0004), and the presence of fibrosis (p = .088) and pleural tumor contact (p = .086) were weakly associated with tumor motion. The presence of fibrotic changes in the lung tissue was associated with smaller tumor motion in the upper region (p <.05) but not in the lower region. The findings of emphysema and pulmonary function tests were not associated with tumor motion.

CONCLUSION

Tumors in the upper lung region with fibrotic changes have smaller motion than those in the upper region of the lungs without fibrotic changes. The tumor motion in the lower lung region was not significantly different between patients with and without lung fibrosis. Emphysema was not associated with the amplitude of tumor motion.

Accuracy of emphysema quantification performed with reduced numbers of CT sections

OBJECTIVE

The purpose of this study was to assess the accuracy of emphysema measurements obtained from systematic samples of evenly spaced CT images compared with measurements obtained from the entire scan.

MATERIALS AND METHODS

Evenly spaced transverse sections from the CT studies of 136 heavy smokers who underwent screening for lung cancer in the National Lung Screening Trial and of 112 subjects who underwent imaging before lung volume reduction surgery were sampled retrospectively. The samples were acquired both by selection of specific numbers of evenly spaced images and by selection of images at specific distance intervals. The percentage of lung pixels with attenuation below specific thresholds was used as an emphysema index. The image sample error was determined as the difference in emphysema index between the image samples and the entire scan.

RESULTS

The largest absolute image sample errors in the National Lung Screening Trial cohort with image sample sizes of five, 10, and 20 were 2.2, 0.8, and 0.5 index percentage points, respectively, at 1-mm section thickness (-960 HU threshold), and 2.6, 1.1, and 0.5 index percentage points at 5-mm section thickness (-930 HU threshold). The largest errors in the lung volume reduction surgery cohort for image sample sizes of five and 10 were 5.6 and 2.3 index percentage points at 8- to 10-mm section thickness (-900 HU threshold). Image sample errors were equivalent for the two sampling methods.

CONCLUSION

Systematic sampling resulted in very small errors in emphysema quantification and may be useful for decreasing radiation exposure in clinical research studies of emphysema.

Evolution of emphysema in relation to smoking

PURPOSE

We have little knowledge about the evolution of emphysema, and relatively little is understood about its evolution in relation to smoking habits. This study aims to assess the evolution of emphysema in asymptomatic current and former smokers over 2 years and to investigate the association with subjects' characteristics. The study was approved by our Ethics Committee and all participants provided written informed consent.

MATERIALS AND METHODS

We measured emphysema by automatic low-dose computed tomography densitometry in 254 current and 282 former smokers enrolled in a lung-cancer screening. The measures were repeated after 2 years. The association between subjects' characteristics, smoking habits and emphysema were assessed by chi-squared and Wilcoxon tests. Univariate and multivariate odds ratios (OR) with 95% confidence intervals (CI) were calculated for the risk of emphysema worsening according to subjects' characteristics. We assessed the trend of increasing risk of emphysema progression by smoking habits using the Mantel-Haenszel chi-squared test.

RESULTS

The median percentage increase in emphysema over a 2-year period was significantly higher in current than in former smokers (OR 1.8; 95% CI 1.3-2.6; p < 0.0001). The risk of worsening emphysema (by 30% in 2 years) in current smokers increased with smoking duration (p for trend <0.02).

CONCLUSION

As emphysema is a known risk factor for lung cancer, its evaluation could be used as a potential factor for identification of a high-risk population. The evaluation of emphysema progression can be added to low-dose CT screening programmes to inform and incite participants to stop smoking.

Reproducibility and validity of lung density measures from cardiac CT Scans--The Multi-Ethnic Study of Atherosclerosis (MESA) Lung Study

RATIONALE AND OBJECTIVES

Cardiac computed tomographic (CT) scans for the assessment of coronary calcium scores include approximately 70% of the lung volume and may be useful for the quantitative assessment of emphysema. The reproducibility of lung density measures from cardiac computed tomography and their validity compared to lung density measures from full-lung scans is unknown.

MATERIALS AND METHODS

The Multi-Ethnic Study of Atherosclerosis (MESA) performed paired cardiac CT scans for 6814 participants at baseline and at follow-up. The MESA-Lung Study assessed lung density measures in the lung fields of these cardiac scans, counting voxels below -910 HU as moderate-to-severe emphysema-like lung regions. We evaluated: 1) the reproducibility of lung density measures among 120 randomly selected participants; 2) the comparability of measures acquired on electron beam CT (EBCT) and multidetector CT (MDCT) scanners among 10 participants; and 3) the validity of these measures compared to full-lung scans among 42 participants. Limits of agreement were determined using Bland-Altman approaches.

RESULTS

Percent emphysema measures from paired cardiac scans were highly correlated (r = 0.92-0.95) with mean difference of -0.05% (95% limits of agreement: -8.3, 8.4%). Measures from EBCT and MDCT scanners were comparable (mean difference -0.9%; 95% limits of agreement: -5.1, 3.3%). Percent emphysema measures from MDCT cardiac and MDCT full-lung scans were highly correlated (r = 0.93) and demonstrated reasonable agreement (mean difference 2.2%; 95% limits of agreement: -9.2, 13.8%).

CONCLUSIONS

Although full-lung imaging is preferred for the quantification of emphysema, the lung imaging from paired cardiac computed tomography provided a reproducible and valid quantitative assessment of emphysema in a population-based sample.

Natural history of emphysema

Chronic obstructive pulmonary disease (COPD) is a progressive disease with studies of disease progression generally focusing on measures of airflow and mortality. In nonsmokers, maximal lung function is attained around age 15 to 25 years, and after a variable plateau phase, subsequently declines at approximately 20 to 25 ml/year. Smoking may reduce the maximal FEV(1) achieved, shorten or eliminate the plateau phase, and may accelerate the rate of decline in lung function in a dose-dependent manner. Some smokers are predisposed to more rapid declines in lung function than others, and recent reports suggest that females may be at higher risk of lung damage related to smoke exposure than males. Progressive deterioration in dyspnea, functional status, and health-related quality of life (HRQL) in patients with COPD is well known, but the magnitude and rate of decline and its association with severity of airflow obstruction remains poorly defined. Many studies have identified pulmonary function, in particular the FEV(1), as the single best predictor of survival. An impaired diffusing capacity and overall impairment in functional status have also been associated with impaired survival in COPD. The National Emphysema Treatment Trial has provided additional insight into these features in a large, well-characterized group of patients with severe airflow obstruction and structural emphysema.