CT-Based Evaluation of the Shape of the Diaphragm Using 3D Slicer

The diaphragm is the main inspiratory muscle and separates the thorax and the abdomen. In COPD, the evaluation of the diaphragm shape is clinically important, especially in the case of hyperinflation. However, delineating the diaphragm remains a challenge as it cannot be seen entirely on CT scans. Therefore, the lungs, ribs, sternum, and lumbar vertebrae are used as surrogate landmarks to delineate the diaphragm. We herein describe a CT-based method for evaluating the shape of the diaphragm using 3D Slicer-a free software that allows delineation of the diaphragm landmarks-in ten COPD patients. Using the segmentation performed with 3D Slicer, the diaphragm shape was reconstructed with open-source Free Pascal Compiler. From this graduated model, the length of the muscle fibers, the radius of curvature, and the area of the diaphragm-the main determinants of its function-can be measured. Inter- and intra-user variabilities were evaluated with Bland and Altman plots and linear mixed models. Except for the coronal length (p = 0.049), there were not statistically significant inter- or intra-user differences (p values ranging from 0.326 to 0.910) suggesting that this method is reproducible and repeatable. In conclusion, 3D Slicer can be applied to CT scans for determining the shape of the diaphragm in COPD patients.

Automated evaluation of diaphragm configuration based on chest CT in COPD patients

BACKGROUND

Severe chronic obstructive pulmonary disease (COPD) often results in hyperinflation and flattening of the diaphragm. An automated computed tomography (CT)-based tool for quantifying diaphragm configuration, a biomarker for COPD, was developed in-house and tested in a large cohort of COPD patients.

METHODS

We used the LungQ platform to extract the lung-diaphragm intersection, as direct diaphragm segmentation is challenging. The tool computed the diaphragm index (surface area/projected surface area) as a measure of diaphragm configuration on inspiratory scans in a COPDGene subcohort. Visual inspection of 250 randomly selected segmentations served as a quality check. Associations between the diaphragm index, Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages, forced expiratory volume in 1 s (FEV1) % predicted, and CT-derived emphysema scores were explored using analysis of variance and Pearson correlation.

RESULTS

The tool yielded incomplete segmentation in 9.2% (2.4% major defect, 6.8% minor defect) of 250 randomly selected cases. In 8431 COPDGene subjects (4240 healthy; 4191 COPD), the diaphragm index was increasingly lower with higher GOLD stages (never-smoked 1.83 ± 0.16; GOLD-0 1.79 ± 0.18; GOLD-1 1.71 ± 0.15; GOLD-2: 1.67 ± 0.16; GOLD-3 1.58 ± 0.14; GOLD-4 1.54 ± 0.11) (p < 0.001). Associations were found between the diaphragm index and both FEV1% predicted (r = 0.44, p < 0.001) and emphysema score (r = -0.36, p < 0.001).

CONCLUSION

We developed an automated tool to quantify the diaphragm configuration in chest CT. The diaphragm index was associated with COPD severity, FEV1%predicted, and emphysema score.

RELEVANCE STATEMENT

Due to the hypothesized relationship between diaphragm dysfunction and diaphragm configuration in COPD patients, automatic quantification of diaphragm configuration may prove useful in evaluating treatment efficacy in terms of lung volume reduction.

KEY POINTS

Severe COPD changes diaphragm configuration to a flattened state, impeding function. An automated tool quantified diaphragm configuration on chest-CT providing a diaphragm index. The diaphragm index was correlated to COPD severity and may aid treatment assessment.

Inspiratory and expiratory CT analyses of the diaphragmatic crus in chronic obstructive pulmonary disease

PURPOSE

This study aimed to investigate the association between the results of pulmonary function tests (PFTs) in patients with chronic obstructive pulmonary disease (COPD) and the size of their diaphragmatic crus (DC) using inspiratory and expiratory CT.

MATERIALS AND METHODS

Thirty-three patients who underwent inspiratory and expiratory CT and PFTs between July and December 2019 were studied retrospectively. The short axis, long axis, and cross-sectional area (CSA) of the bilateral DC were measured, and the percentage change of the DC after expiration (% change of DC) in the size was calculated. The correlation between the results of the PFTs (forced expiratory volume in 1 s [FEV₁], FEV₁/forced vital capacity [FVC], and percent predicted FEV₁ [%FEV₁]) and the size and % change of DC was statistically analyzed.

RESULTS

Significant correlations were observed between the short axis of the right and left DC at expiration and PFTs (FEV₁, r = -0.35, -0.48, p = 0.04, .007; FEV₁/FVC, r = -0.52, -0.65, p = 0.002, < .001; %FEV₁, r = -0.56, -0.60, p < 0.001, < 0.001; respectively), between the CSA of the right DC at expiration and PFTs (FEV₁/FVC, r = -0.42, p = 0.01; %FEV₁, r = -0.41, p = 0.017; respectively), and between the % change of the short axis of the left DC and the CSA of the left DC and PFTs (FEV₁, r = 0.64, 0.56, p < 0.001, .001; %FEV₁, r = 0.52, 0.51, p = 0.004, 0.004; respectively). The smaller the short axis of the DC and CSA at expiration and the larger the % change in DC of the CSA, the lower the airflow limitation.

CONCLUSION

There were significant correlations between airflow limitation and the short axis of the bilateral DC at expiration, and the % change in the DC of the CSA. Certain CT measurements of the DC may reflect airflow limitation in patients with COPD.

Diaphragm Morphology Assessed by Computed Tomography in Chronic Obstructive Pulmonary Disease

Rationale: Chronic obstructive pulmonary disease (COPD) is associated with abnormal skeletal muscle morphology and function. Objectives: To test the hypothesis that in vivo diaphragm muscle morphology assessed by computed tomography (CT) imaging would be associated with COPD severity, exacerbations, health status, and exercise capacity. Methods: The COPD Morphometry Study is a cross-sectional study that enrolled a clinical sample of smokers with COPD. Spirometry was performed and COPD severity was defined according to guidelines. Three-dimensional left hemidiaphragm morphology was segmented from contiguous axial CT images acquired at maximal inspiration, yielding quantitative measures of diaphragm CT density in Hounsfield units, dome height, and muscle volume. Exacerbations prompting pharmacotherapy or hospitalization in the preceding 12 months and St. George's Respiratory Questionnaire for COPD were assessed. Incremental symptom-limited cycle ergometry quantified peak oxygen uptake ([Formula: see text]o_2Peak). Associations were adjusted for age, sex, body height, body mass index, and smoking status. Results: Among 65 smokers with COPD (75% male; [mean ± standard deviation (SD)] 56 ± 26 pack-years; forced expiratory volume in 1 second [FEV₁] percentage predicted 55 ± 23%), mean diaphragm CT density was 3.1 ± 10 Hounsfield units, dome height was 5.2 ± 1.3 cm, and muscle volume was 57 ± 24 cm³. A 1-SD decrement in the diaphragm CT density was associated with 8.3% lower FEV₁, 3.27-fold higher odds of exacerbation history, 9.7-point higher score on the St. George's Respiratory Questionnaire for COPD, and 2.5 ml/kg/min lower [Formula: see text]o_2Peak. A 1-SD decrement in dome height was associated with 11% lower FEV₁ and 1.3 ml/kg/min lower [Formula: see text]o_2Peak. There were no associations with diaphragm volume observed. Conclusions: CT-assessed diaphragm morphology was associated with COPD severity, exacerbations, impaired health status, and exercise intolerance. The mechanisms and functional impact of lower diaphragm CT density merit investigation.

Computed tomographic thoracic morphologic indices in normal subjects and patients with chronic obstructive pulmonary disease: Comparison with spiral CT densitometry and pulmonary function tests

OBJECTIVES

To determine what computed tomographic (CT) dimensions can predict obstructive lung disease on routine chest CT scans by comparing morphological and densitometric CT findings with pulmonary function test (PFT) in normal subjects and patients with chronic obstructive pulmonary disease (COPD).

MATERIALS AND METHODS

Consecutive patients (n = 646; 260 females and 386 males; mean age 54.9 years, ranged 20-90 years) who received chest CT scans with densitometry during a 3-month period were retrospectively analyzed in single center. PFT was undertaken in 235 patients (152 males, 83 females) at same times of CT scanning. The patients were grouped by age (<30 years, 31-45 years, 46-60 years, and >61 years). CT parameters including tracheal, azygoesophageal, thoracic vertical, anterior-posterior (AP), transverse diameters, transverse cardiac diameter, diameters of main, right, and left pulmonary arteries, and CT densitometric values including lung volume and density (-900 to -1000 Hounsfield Units, HU), low attenuation value cluster (default threshold: -950 HU) were compared with PFT values. Spearman correlation coefficients was used to evaluate the relationship between the CT indices and PFT.

RESULTS

Ninety of 235 patients with PFT were smokers (76 males, 14 females). Obstructive PFT was detected in 65 patients (27.7%: 46 males, 19 females). Male smokers with obstructive PFT displayed significantly larger thoracic anterior-posterior (mean: normal, 172.3 cm versus COPD, 185.9 cm, p = 0.0001) and smaller transverse diameters (mean: normal, 247.0 cm vs. COPD, 235.8 cm, p = 0.01), and increased right pulmonary artery diameter (mean: normal, 20.3 cm v s. COPD, 22.1 cm, p < 0.001), and increased left pulmonary artery diameter (mean: normal, 19.7 cm vs. COPD, 20.6 cm, p < 0.025). The lung parenchyma density (-1000 to -900 HU) and greater concentration of largest cluster on densitometry were significantly different between normal and obstructive PFT pattern in male smoker. Residual volume and total lung capacity are positively correlated with lung volume and lung density (-1000 to -800) of densitometry.

CONCLUSIONS

CT findings of the overexpansion of the lungs, such as increases in the vertical diameter of the lung and decreases in the transverse diameter of the heart, can be significant as indirect findings of early chronic obstructive diseases. However, despite the significant CT findings in male smokers, particularly those in their 40s, most lung function parameters were not decidedly abnormal.