Computational Analysis of Thoracic Multidetector Row HRCT for Segmentation and Quantification of Small Airway Air Trapping and Emphysema in Obstructive Pulmonary Disease

Rationale and Objectives

Obstructive pulmonary disease phenotypes are related to variable combinations of emphysema and small-airway disease, the latter manifested as air trapping (AT) on imaging. The investigators propose a method to extract AT information quantitatively from thoracic multi–detector row high-resolution computed tomography (HRCT), validated by pulmonary function testing (PFT) correlation.

Materials and Methods

Seventeen patients with obstructive pulmonary disease who underwent HRCT and PFT within a 3-day interval were retrospectively identified. Thin-section volumetric HRCT in inspiration and expiration was registered and analyzed using custom-made software. Nonaerated regions of lung were segmented through exclusion of voxels > −50 Hounsfield units (HU); emphysematous areas were segmented as voxels < −950 HU on inspiratory images. Small-airway AT volume (ATV) was segmented as regions of lung voxels whose attenuation values increased by less than a specified change threshold (set from 5 to 300 HU in 25-HU increments) between inspiration and expiration. Inspiratory and expiratory total segmented lung volumes, emphysema volume (EV), and ATV for each threshold were subsequently calculated and correlated with PFT parameters.

Results

A strong positive correlation was obtained between total segmented lung volume in inspiration and total lung capacity ( r = 0.83). A strong negative correlation ( r = −0.80) was obtained between EV and the ratio between forced expiratory volume in 1 second and forced vital capacity. Stronger negative correlation with forced expiratory volume in 1 second/forced vital capacity ( r = −0.85) was demonstrated when ATV (threshold, 50 HU) was added to EV, indicating improved quantification of total AT to predict obstructive disease severity. A moderately strong positive correlation between ATV and residual volume was observed, with a maximum r value of 0.72 (threshold, 25 HU), greater than that between EV and residual volume ( r = 0.58). The benefit of ATV quantification was greater in a subgroup of patients with negligible emphysema compared to patients with moderate to severe emphysema.

Conclusions

Small-airway AT segmentation in conjunction with emphysema segmentation through computer-assisted methodologies may provide better correlations with key PFT parameters, suggesting that the quantification of emphysema-related and small airway–related components of AT from thoracic HRCT has great potential to elucidate phenotypic differences in patients with chronic obstructive pulmonary disease.

Obstructive pulmonary disease is most often due to chronic obstructive pulmonary disease (COPD), which is a major global public health problem. It is the fourth leading cause of chronic morbidity and mortality in the United States and is anticipated to rank fifth in 2020 in burden of disease caused worldwide . Moreover, among the four major causes of mortality, namely, cardiovascular disease, malignant neoplasm, cerebrovascular disease, and COPD, the last is the only one that has been steadily rising in prevalence .

COPD is defined as chronic, progressive airflow limitation that is not fully reversible, associated with a range of pathologic changes in the lungs with significant extrapulmonary effects, caused by chronic inflammation and structural changes . The chronic airflow limitation is caused by a mixture of small-airway disease (obstructive bronchiolitis) and parenchymal destruction (emphysema). The relative contributions of these two components vary substantially from patient to patient. The presence and extent of each component has the potential to affect clinical presentation, disease severity, prognosis, and therapeutic response .

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Materials and methods

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Patient Selection

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Image Acquisition and Reconstruction

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Image Analysis

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Statistical Analysis

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Results

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Table 1

Calculated Volumes and Sample Standard Deviations for All Patients ( n = 17), Subgroup with Negligible Emphysema ( n = 7), and Subgroup with Moderate or Severe Emphysema ( n = 10)

Group TSLVi (mL) TSLVe (mL) EV (mL) EV (%) ∗ TSLVi − TSLVe (%) † Volume SD Volume SD Volume SD Volume SD Volume SD All patients 5355.43 1315.38 4240.41 1496.48 824.07 762.14 14.10 12.45 22.35 10.77 Negligible EV 4492.36 706.90 3196.84 619.85 40.10 32.13 0.88 0.68 28.59 ‡ 10.06 Moderate or severe EV 5959.58 1325.86 4970.90 1511.68 1372.85 468.30 23.35 6.66 17.98 ‡ 9.35

EV, emphysema volume; SD, standard deviation; TSLVe, total segmented lung volume in expiration; TSLVi, total segmented lung volume in inspiration.

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Table 2

Pearson’s Linear Correlation Coefficients and Respective P Values Between Key PFT Parameters and Calculated EV and ATV

Volume FVC (%P) FEV 1 (%P) FEV 1 /FVC (%P) FEF 25%–75% (%P) ERV (%P) RV (%P) ∗ TLC (%P) ∗ r__P__r__P__r__P__r__P__r__P__r__P__r__P EV −0.037 .889 −0.550 .022 −0.802 <.001 −0.460 .063 0.582 .029 0.579 .030 0.631 .016 ATV 5 HU −0.140 .591 −0.528 .029 −0.709 .001 −0.423 .091 0.653 .011 0.725 .003 0.860 <.001 25 HU −0.027 .917 −0.548 .023 −0.770 <.001 −0.511 .036 0.771 .001 0.723 .003 0.933 <.001 50 HU 0.033 .901 −0.521 .032 −0.701 .002 −0.604 .010 0.675 .008 0.649 .012 0.881 <.001 75 HU 0.139 .595 −0.386 .126 −0.574 .016 −0.557 .020 0.574 .032 0.545 .044 0.791 .001 100 HU 0.271 .292 −0.193 .457 −0.422 .092 −0.395 .117 0.562 .036 0.418 .137 0.711 .004 125 HU 0.366 .149 −0.050 .848 −0.313 .221 −0.262 .309 0.568 .034 0.321 .262 0.656 .011 150 HU 0.433 .082 0.050 .848 −0.242 .349 −0.170 .515 0.575 .032 0.251 .386 0.623 .017 175 HU 0.474 .055 0.113 .666 −0.198 .446 −0.112 .668 0.577 .031 0.205 .481 0.602 .023 200 HU 0.500 .041 0.155 .553 −0.168 .520 −0.073 .781 0.578 .030 0.174 .553 0.586 .028 225 HU 0.518 .033 0.184 .479 −0.146 .575 −0.045 .864 0.578 .030 0.150 .608 0.575 .032 250 HU 0.530 .029 0.206 .428 −0.131 .617 −0.024 .926 0.577 .031 0.133 .651 0.566 .035 275 HU 0.539 .026 0.221 .393 −0.119 .649 −0.009 .973 0.577 .031 0.120 .683 0.559 .038 300 HU 0.546 .023 0.233 .368 −0.110 .674 0.003 .991 0.577 .031 0.110 .708 0.553 .040 EV + ATV 5 HU −0.061 .816 −0.565 .018 −0.810 <.001 −0.469 .058 0.631 .016 0.646 .013 0.722 .004 25 HU −0.034 .897 −0.593 .012 −0.848 <.001 −0.529 .029 0.749 .002 0.716 .004 0.876 <.001 50 HU 0.007 .979 −0.613 .009 −0.852 <.001 −0.632 .007 0.720 .004 0.700 .005 0.893 <.001 75 HU 0.085 .747 −0.561 .019 −0.826 <.001 −0.643 .005 0.682 .007 0.658 .011 0.871 <.001 100 HU 0.185 .476 −0.459 .064 −0.776 <.001 −0.561 .019 0.711 .004 0.595 .025 0.851 <.001 125 HU 0.262 .311 −0.376 .137 −0.734 .001 −0.485 .048 0.743 .002 0.544 .044 0.837 <.001 150 HU 0.318 .213 −0.313 .222 −0.705 .002 −0.429 .086 0.767 .001 0.504 .066 0.832 <.001 175 HU 0.355 .163 −0.271 .292 −0.685 .002 −0.392 .120 0.781 .001 0.477 .085 0.827 <.001 200 HU 0.379 .134 −0.242 .349 −0.671 .003 −0.366 .148 0.789 .001 0.457 .100 0.822 <.001 225 HU 0.396 .115 −0.221 .394 −0.659 .004 −0.347 .173 0.794 .001 0.442 .114 0.819 <.001 250 HU 0.409 .103 −0.205 .430 −0.651 .005 −0.332 .193 0.798 .001 0.430 .125 0.815 <.001 275 HU 0.418 .095 −0.193 .458 −0.644 .005 −0.321 .209 0.801 .001 0.422 .133 0.812 <.001 300 HU 0.425 .089 −0.183 .481 −0.638 .006 −0.312 .223 0.802 .001 0.415 .140 0.810 <.001

ATV, small-airway air-trapping volume; ERV, end-respiratory volume; EV, emphysema volume; FEF 25%–75%, forced expiratory volume between 25% and 75% of forced vital capacity; FEV 1 , forced expiratory volume in 1 second; FVC, forced vital capacity; HU, Hounsfield units; %P, percentage of predicted value; PFT, pulmonary function testing; RV, residual volume; TLC, total lung capacity.

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Discussion

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Conclusions

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References

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Computational Analysis of Thoracic Multidetector Row HRCT for Segmentation and Quantification of Small Airway Air Trapping and Emphysema in Obstructive Pulmonary Disease

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Patient Selection

Image Acquisition and Reconstruction

Image Analysis

Statistical Analysis

Results

Discussion

Conclusions

References

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