Low-Normal Lung Volume Correlates With Pulmonary Hypertension in Fibrotic Idiopathic Interstitial Pneumonia: Computer-Aided 3D Quantitative Analysis of Chest CT

W166 AJR:203, August 2014

limitation—make it difficult to detect pulmo-nary hypertension in patients with IIP [8]. Right heart catheterization (RHC) is the most accurate diagnostic tool for pulmonary hyper-tension. However, because RHC is invasive and expensive, a reliable and noninvasive sur-rogate marker is desirable.

CT is an essential imaging modality and widely performed in patients with IIP [2, 9]. The overall extent of pulmonary fibrosis on CT (the combination of reticulation and hon-eycomb changes) correlates with disease se-verity, and the extent of honeycombing and reticulation on CT increases with disease progression [10, 11]. Recent studies have suggested that the biologic process underly-ing progressive fibrosis also contributes to vascular remodeling and pulmonary hyper-tension [3]. If fibrogenesis correlates directly with the biologic mechanism involved in the induction of pulmonary hypertension, the se-

Low-Normal Lung Volume Correlates With Pulmonary Hypertension in Fibrotic Idiopathic Interstitial Pneumonia: Computer-Aided 3D Quantitative Analysis of Chest CT

Tae Iwasawa1 Shingo Kato2 Takashi Ogura3 Yuka Kusakawa2 Shinichiro Iso1,4 Tomohisa Baba3 Kazuki Fukui2 Mari S. Oba5

Iwasawa T, Kato S, Ogura T, et al.

1 Department of Radiology, Kanagawa Cardiovascular and Respiratory Center, 6-16-1, Tomioka-higashi, Kanazawa-ku, Yokohama, Kanagawa 236-8651, Japan. Address correspondence to T. Iwasawa ([email protected]).

2Department of Cardiology, Kanagawa Cardiovascular and Respiratory Center, Kanagawa, Japan.

3Department of Respiratory Medicine, Kanagawa Cardiovascular and Respiratory Center, Kanagawa, Japan.

4Department of Radiology, Yokohama Rousai Hospital for Labour Welfare Corporation, Yokohama, Japan.

5Department of Biostatistics and Epidemiology, Yokohama City University School of Medicine, Yokohama, Japan.

Cardiopulmonar y Imaging • Or ig ina l Research

WEB This is a web exclusive article.

AJR 2014; 203:W166–W173

0361–803X/14/2032–W166

© American Roentgen Ray Society

Pulmonary arterial hypertension is an unfavorable complication in idiopathic interstitial pneumonia (IIP) [1]. Idiopathic pulmonary fi-

brosis (IPF) is the most common form of chronic fibrosing interstitial pneumonia in the American Thoracic Society/European Respi-ratory Society (ATS/ERS) classification of IIP [2]. The reported prevalence of pulmo-nary hypertension in patients with IPF ranges from 32% to 85% [3–7]. The development of pulmonary hypertension in IIP patients has important prognostic implications [4]. Lett-ieri et al. [4] reported that 1-year mortality rates of patients with IPF were higher in those with pulmonary hypertension compared with those without pulmonary hypertension (28.0% vs 5.5%, respectively; p = 0.002). Al-though early diagnosis of pulmonary hyper-tension is important, the overlapping main symptoms—shortness of breath and exercise

Keywords: computer-aided design, hypertension, idiopathic pulmonary fibrosis, interstitial, lung disease, MDCT, pulmonary

DOI:10.2214/AJR.13.11409

Received June 13, 2013; accepted after revision October 19, 2013.

Supported by the Kanagawa Cancer Research Fund.

OBJECTIVE. We investigated whether the lung volume determined on CT, especially the volume of the normal lung, is correlated with mean pulmonary artery pressure (PAP) in pa-tients with chronic fibrosing idiopathic interstitial pneumonia (IIP).

MATERIALS AND METHODS. The subjects were 40 patients with IIP who under-went right heart catheterization (RHC) and chest CT. Thirty-three patients (82.5%) were smokers or former smokers. Using a computer-aided system, the lungs in the 3D CT imag-es were automatically categorized pixel-by-pixel with gaussian histogram-normalized cor-relations, and the relative volume of each lesion to the CT lung volume was calculated as “normal(%),” “ground-glass opacities(%),” “consolidation(%),” “emphysema(%),” and “fi-brosis(%).” The relationship between each “volume(%)” and pulmonary hypertension was evaluated using logistic regression analysis. ROC curves were constructed to assess the pre-dictive value of these CT-based volumes in the identification of pulmonary hypertension.

RESULTS. Sixteen patients had pulmonary hypertension at rest (mean PAP > 25 mm Hg on RHC). Emphysema constituted more than 10% of the CT lung volume in 13 patients. On multivariate analysis of each volume(%), normal(%) was significant for detecting pulmonary hypertension (odds ratio, 0.92; 95% CI, 0.86–0.96; p = 0.02). On ROC analysis, the AUC of normal(%) was 0.849 (0.731–0.967).

CONCLUSION. The relative CT volume of any single lesion was of limited value in predicting pulmonary hypertension in patients with pulmonary fibrosis and emphysema. In these patients, normal(%), measured by a 3D computer-aided system, was correlated with pulmonary hypertension measured by RHC.

Iwasawa et al.CT in Pulmonary Hypertension

Cardiopulmonary ImagingOriginal Research

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AJR:203, August 2014 W167

CT in Pulmonary Hypertension

verity of lung fibrosis should correlate with the prevalence and extent of pulmonary hy-pertension. However, previous studies have concluded that the CT score, an index of fi-brosis using 25% steps, does not correlate with pulmonary hypertension [12, 13].

These somewhat disappointing results are likely due to emphysema. In smokers, some emphysema may be associated with intersti-tial pneumonia [2, 14]. Cottin et al. [15, 16] reported a high prevalence of pulmonary hy-pertension in patients with pulmonary fibro-sis combined with emphysema. Emphysema is also a well-known etiologic factor of pul-monary hypertension [17]. In patients with lung damage caused by both fibrosis and em-physema, it is difficult to isolate the main contributor to pulmonary hypertension. We hypothesized that normal lung volume cor-relates negatively with the severity of pul-monary hypertension. In many of the previ-ous studies on this topic, the main target of CT evaluation in IIP was the extent of fibro-sis; normal lung volume was not measured directly [14, 18]. In this study, we examined whether the CT-determined lesion volume data, especially normal lung, correlated with pulmonary hypertension in patients with IIP.

Materials and MethodsSubjects

This retrospective cross-sectional study using CT data was approved by the institutional review board, and informed consent was waived. To avoid selection bias, all patients with pulmonary fibrosis who underwent RHC between January 2011 and

April 2013 were candidates for this study. Seven-ty-eight patients with pulmonary fibrosis (or sus-pected pulmonary fibrosis) underwent RHC during this period. Patients with fibrotic IIP who under-went CT within 6 months of RHC were included. Patients with heart disease or pulmonary vascu-lar disease (heart valve insufficiency [n = 4], left heart disease [pulmonary arterial wedge pressure > 15 mm Hg, n = 4], and chronic pulmonary arterial thromboembolism [n = 3]) were excluded. Patients with lung cancer (including postoperative state, n = 8) and secondary pulmonary fibrosis (due to col-lagen disease or vasculitis, n = 14) as well as four patients who did not undergo CT within 6 months of RHC were also excluded. One patient with pneu-mothorax was excluded because the lesion vol-ume on CT could not be accurately estimated due to collapse of the lung. Thus, 40 consecutive pa-tients with chronic fibrosing interstitial pneumo-nia were included. Of these 40 patients, 33 (82.5%) were smokers or former smokers (mean smoking history, 36.8 pack-years; median, 35.8 pack-years; range, 0–94.5 pack-years and median interval be-tween stopping smoking and RHC, 10.5 years; range, 0–58 years).

All 40 patients had demonstrable interstitial ab-normalities suggestive of pulmonary fibrosis in the lower lung zones on CT images. Nineteen pa-tients (47.5%) had undergone surgical lung biop-sy and were diagnosed histopathologically with pulmonary fibrosis (usual interstitial pneumonia [UIP] pattern [n = 12], fibrosing nonspecific inter-stitial pneumonia [NSIP] pattern [n = 5], and non-classifiable fibrosis [n = 2]). According to the cri-teria developed by the ATS [2, 9, 19], five patients with pathologically fibrotic NSIP were diagnosed

as having idiopathic fibrosing NSIP, and 35 patients were clinically diagnosed as having IPF. RHC was performed in resting patients using a standard tech-nique. Pulmonary hypertension was defined as mean pulmonary artery pressure (PAP) > 25 mm Hg at rest in the setting of a normal pulmonary ar-terial wedge pressure of ≤ 15 mm Hg [1].

Pulmonary function tests (PFTs) were conduct-ed in only 32 of 40 patients within 6 months of RHC. The median interval between PFT and RHC was 42 days (range, 1–130 days). CHESTAC-8800, CHESTAC-33 (Chest MI), and Fudac-77 (Fukuda Denshi) were used to measure vital capacity (VC), forced expiratory volume in 1 second (FEV1), to-tal lung capacity (TLC), and diffusing capacity using standard measurement techniques [20]. The results are expressed as percentage of predicted performance using standard values [20].

CT and Analysis by RadiologistsThin-section CT images were obtained dur-

ing inspiration in the supine position using a 64-MDCT scanner (Aquilion-64, Toshiba). The me-dian interval between CT and RHC was 31 days (mean, 45 days; range, 0–149 days). All CT im-ages were obtained without contrast administra-tion. Slice thickness was 0.5 mm (n = 31) or 1 mm (n = 9). Images were reconstructed with stan-dard and high-resolution algorithms.

The diameters of the pulmonary artery and as-cending aorta were measured at the widest sec-tion as described by Wells et al. [21]. One author (a board-certified radiologist with more than 20 years of experience) measured the diameter of the main pulmonary artery at the level of its bifurca-tion and the diameter of the ascending aorta at its

A

Fig. 1—54-year-old man with idiopathic pulmonary fibrosis combined with emphysema. Nonclassifiable fibrosis was confirmed on surgical biopsy. Patient was former smoker (30 pack-years). Mean pulmonary artery pressure was 20 mm Hg measured by right heart catheterization. A, Three-dimensional CT image analysis shows emphysema volume (%LAA-950) 29.9%, fibrosis 11.6%, and normal 52.5%.B and C, Sagittal reformatted CT images show computer-aided segmentation result on sagittal images corresponding to A. Pink = normal, dark blue = emphysema, light green = ground-glass opacity, light blue and yellow = fibrosis, dark green = trachea and bronchi, orange = vessels.

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Iwasawa et al.

maximum dimension using a CT viewer and an electrical caliper (Synapse, Fujifilm). The extent of parenchymal abnormality was determined for each lung using a 5-point scale as described pre-viously with some modifications (0, no involve-ment; 1, 1–25% involvement; 2, 26–50% involve-ment; 3, 51–75% involvement, and 4, 76–100% involvement) [12, 13, 22]. Images were evaluated independently by two board-certified chest radi-ologists with 20 and 10 years of experience who were blinded to the clinical information. Each lung was scored in three zones (upper zone, lung apex to aortic arch; middle zone, aortic arch to a position inferior to the pulmonary veins; and lower zone, from the inferior pulmonary veins to the diaphragm). The mean score for each of the six zones was calculated for each parenchy-mal pattern. Fibrosis (reticulation, honeycomb-ing, and architectural distortion), emphysema (low-attenuation area without a thick wall), and ground-glass opacity (GGO) (hazy parenchy-mal opacity in the absence of reticular opacity or architectural distortion) were evaluated [12]. The sum of these scores was called the total CT score. Interobserver variation of these scores was analyzed with the kappa statistic. Interobserver agreement was classified as slight (κ = 0.00–0.20), fair (κ = 0.21–0.40), moderate (κ = 0.41–0.60), substantial (κ = 0.61–0.80), or almost per-fect (κ = 0.81–1.00). The kappa value was 0.65 for the emphysema score, 0.49 for the fibrosis score, 0.56 for the GGO score, and 0.52 for the total score. There was moderate to substantial agreement for each score. A final score was ob-tained by taking the average of the scores of the individual observers.

Volume Analysis on CTAll CT images were transferred to a PC (Build-

To-Order PC with Intel Core i7 CPU 950 at 3.07 GHz using Microsoft Windows 7 64 bit). Before the segmentation process, the CT values were correct-ed by the mean attenuation value in tracheal gas of −1000 HU [23]. The lung on thin-section CT was extracted using a semiautomated threshold tech-nique that selects all pixels between –200 and –1024 HU. The mathematic morphologic closing and open-ing techniques were then applied to include the ar-eas of subpleural consolidation or thick reticulation with more than –200 HU. In some cases, residual subpleural lesions needed to be included in the lung manually using a paint tool. After that, the bronchial trees and blood vessels were excluded using the fail-ure-recovery algorithm reported by Iwao et al. [24]. The algorithm consists of region growing, failure de-tection, history storage, and backtracking modules. It is possible to backtrack to a previous stable state using history storage and restart the processing from the state when a failure is detected. Consequently, tracking with high accuracy proceeds at a low com-putational cost.

After each lesion was extracted from the lung, it was segmented using two types of procedures: one was the simple threshold technique designed to measure emphysema volume as “%LAA-950” [25], and the other was a gaussian histogram-normalized correlation system for measuring the volume of each lesion [26, 27]. Briefly, this sys-tem divides lung pixels into five categories along predesigned samples using CT attenuation val-ues and their local histograms. The five catego-ries were as follows: normal, emphysema, GGO, consolidation, and fibrosis. The volume of each

lesion and total CT lung volume were computed automatically by the computer-aided diagnosis (CADx) system. CT lung volume was expressed as both an absolute value and relative to the predict-ed total lung capacity (“%predTLC”). The vol-ume of each lesion was expressed relative to CT lung volume (expressed as a percentage).

Statistical AnalysisThe subjects were divided into two groups

(with and without pulmonary hypertension). Dif-ferences in patients’ characteristics and CT re-sults were tested for significance using the Mann-Whitney U test. The relationship between mean PAP and CT findings was examined by Spear-man correlation analysis. Univariate and multi-variate regression analyses were also performed to assess the independent predictive values of CT measurements. ROC curves were used to com-pare the diagnostic capability of CT results. The cutoff value that yielded the highest sensitivity and specificity was identified. The highest nega-tive predictive values were also considered on the basis of the use of CT as a screening test in the diagnosis of pulmonary hypertension. This was followed by statistical comparisons of sensitivi-ty, specificity, and accuracy using the McNemar test. All statistical analyses were performed us-ing SPSS software, version 21. A p value less than 0.05 was considered significant.

ResultsHigh mean PAP (> 25 mm Hg) was identi-

fied on RHC in 16 of 40 patients (the pulmo-nary hypertension group). The mean PAP in the remaining 24 subjects was ≤ 25 mm Hg,

A

Fig. 2—69-year-old man with idiopathic pulmonary fibrosis combined with emphysema. Patient was former smoker (45 pack-years). Mean pulmonary artery pressure was 29 mm Hg measured by right heart catheterization.A, Image from computer-aided analysis shows emphysema volume (%LAA-950) 32.5%, fibrosis 16.0%, and normal 35.7%.B and C, Sagittal reformatted CT images show computer-aided segmentation results corresponding to A. Sagittal images show decreased normal lung compared with case shown in Figure 3. Pink = normal, dark blue = emphysema, light green = ground-glass opacity, light blue and yellow = fibrosis, dark green = trachea and bronchi, orange = vessels.

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and they were categorized as the nonpulmo-nary hypertension group [1]. Tables 1 and 2 compare the PFT and CT findings in the two groups. There were no significant dif-ferences between the two groups with regard to age, smoking habit, and time between CT and RHC. The median diffusing capacity was significantly worse in patients with pul-monary hypertension.

Table 2 and Figures 1 and 2 show the results of CT analysis. The median di-ameter of the pulmonary artery was larg-er in patients with pulmonary hyperten-sion (34.7 mm; range, 30.6–44.1 mm) than in those without pulmonary hyper-tension (30.4 mm; range, 23–40.8 mm) (p = 0.002). There was no significant dif-ference between the two groups in fibro-

sis and GGO scores. However, the medi-an total score was significantly greater in patients with pulmonary hypertension (4.1; range, 2.6–5.3) than in the nonpulmonary hypertension group (3.1; range, 1.5–4.7) (p = 0.001). Of the 40 patients, 13 had em-physema of more than 10% on %LAA-950 analyses, but only eight of these 13 patients had pulmonary hypertension.

TABLE 1: Comparison of Physiologic Data Between Patients With and Without Pulmonary Hypertension

Characteristic Total (n = 40)Without Pulmonary Hypertension

Mean PAP ≤ 25 mm Hg (n = 24)With Pulmonary Hypertension Mean PAP > 25 mm Hg (n = 16) p

Mean PAP (mm Hg) 21 (7–48) 16.5 (7–25) 31 (26–48) < 0.001

Age (y) 70.5 (53–82) 71.5 (54–81) 70 (53–82) 0.76

Sex (M/F) 29/11 16/8 13/3 0.47

Smoking (pack-years) 35.8 (0–94.5) 33.8 (0–94.5) 37.3 (0–78) 0.99

Never-smokers/former smokers 7/33 5/19 2/14 0.68

Surgical biopsy done (UIP/fibrosing NSIP/nonclassifiable)

19 14 5

12/5/2 9/3/2 3/2/0

No. of patients with PFT 33 23 10

Time between PFT and RHC (d) 42 (1–130) 43 (1–130) 40.5 (3–129) 0.58

Predicted vital capacity(%) 76.6 (33.5–119) 78.0 (33.5–119) 72.2 (40.2–113) 0.19

Predicted FEV1(%) 78.3 (36–120) 80.9 (38.7–120) 68.6 (36–120) 0.13

Predicted TLC(%) 73.8 (42–128) 73.8 (42–128) 58.9 (42–99.7) 0.25

Diffusion capacity of lung for carbon monoxide (%) 45.4 (10–95.5) 55.2 (10–95.5) 36.9 (23.2–51.3) 0.04

Note—Data in parentheses are range. PAP = pulmonary artery pressure, UIP = usual interstitial pneumonia, NSIP = nonspecific interstitial pneumonia, PFT = pulmonary function test, RHC = right heart catheterization, FEV1 = forced expiratory volume in 1 second, TLC = total lung capacity

TABLE 2: Comparison of CT Results Between Patients With and Without Pulmonary Hypertension

Characteristic Total (n = 40)Without Pulmonary Hypertension

Mean PAP ≤ 25 mm Hg (n = 24)With Pulmonary Hypertension Mean PAP > 25 mm Hg (n = 16) p

Time between CT and RHC (d) 31 (0–149) 48.5 (3–135) 24 (0–149) 0.32

Pulmonary artery diameter (mm) 32.6 (23–44.1) 30.4 (23–40.8) 34.7 (30.6–44.1) 0.002

Aorta diameter (mm) 34.9 (25.6–45.8) 34.9 (26.8–45.8) 34.9 (25.6–38.4) 0.57

Emphysema score 1.3 (0–3.7) 1.0 (0–2.5) 1.9 (0–3.7) 0.07

Fibrosis score 1.2 (0.4–2) 1.1 (0.4–2) 1.3 (0.4–2) 0.14

GGO score 0.8 (0–3.5) 0.9 (0.25–1.8) 0.7 (0–3.5) 0.92

Total score 3.5 (1.5–5.3) 3.1 (1.5–4.7) 4.1 (2.6–5.3) 0.001

Percentage emphysema volume (LAA-950) 6.8 (0–43.4) 4.7 (0–29.9) 9.8 (0–43.4) 0.09

Percentage LAA-950 > 10% 13 5 8 0.09

CT lung volume 3.6 (1.5–6.2) 3.9 (1.8–6.2) 3.2 (1.5–5.8) 0.46

CT lung volume (%predTLC) 70.3 (29.3–112.1) 70.6 (47.4–112.1) 66.6 (29.3–110.6) 0.41

Normal(%) 56.8 (8.9–88.8) 60.7 (32.9–88.8) 46.9 (8.8–68.9) < 0.001

Emphysema(%) 7.7 (0–57.3) 5.2 (0–31.6) 10.8 (0–57.3) 0.10

GGO(%) 10.2 (4–39.2) 9.4 (4.2–22.7) 12.8 (4–39.2) 0.05

Consolidation(%) 0.2 (0–2.7) 0.2 (0–2.7) 0.3 (0–2.6) 0.14

Fibrosis(%) 18.8 (3.6–48.6) 16.2 (3.6–42.2) 23.8 (9–48.6) 0.03

Note—Data in parentheses are range. PAP = pulmonary artery pressure, RHC = right heart catheterization, %predTLC = percentage to predicted total lung capacity, GGO = ground-glass opacity.

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On gaussian histogram-normalized cor-relation analysis, the median normal(%) was smaller in patients with pulmonary hyperten-sion than in those without pulmonary hyper-tension (46.9%; range, 8.8–68.9% vs 60.7%; range, 32.9–88.8%; p < 0.001). The median fibrosis(%) was larger in patients with pul-monary hypertension than in those without pulmonary hypertension (23.8%; range, 9.0–48.6% vs 16.2%; range, 3.6–42.2%; p = 0.03). The other gaussian histogram-normalized correlation results were not significantly dif-ferent between the two groups (Table 2).

Figure 3 shows the relationship between mean PAP and CT findings. Normal(%) (r = −0.708) was negatively correlated with mean PAP (p < 0.001). Fibrosis(%) (r = 0.401, p = 0.001) and emphysema(%) (r = 0.403, p = 0.01) were positively correlated with mean PAP, whereas CT lung volume and CT lung volume (“%predTLC”) were not correlated with mean PAP. The %LAA-950 (r = 0.410, p = 0.009) was positively correlated with mean PAP. Diffusing capacity (%pred) (r = −0.427, p = 0.015) was negatively correlated with mean PAP. The CT total score was correlated with mean PAP (r = 0.630, p < 0.001), and diameter of the pulmonary artery (r = 0.444, p = 0.004) was positively correlated with mean PAP.

Table 3 shows the results of the univar-iate and multivariate logistic regression analyses. Univariate analysis showed that diameter of the pulmonary artery, emphy-sema score, total score, normal(%), and fi-brosis(%) were significant variables for de-tecting pulmonary hypertension. Variables

were considered for multivariate models if their p values were less than 0.01. The di-ameter of the pulmonary artery and total score showed no significant correlation, whereas diameter of the pulmonary artery and normal(%) showed a significant weak correlation (r = −0.41, p = 0.008) on Spear-man correlation analysis. However, total score was highly significantly correlated with normal(%) (r = −0.84, p < 0.001). The number of patients in our study was not high enough to enable us to distinguish between total score and normal(%). The two vari-ables of diameter of the pulmonary artery and normal(%) were then investigated, and normal(%) was a significant variable for predicting pulmonary hypertension (odds ratio, 0.92; range, 0.87–0.96; p = 0.02).

Figure 4 shows the ROC curves for the pres-ence of pulmonary hypertension and CT vol-ume analysis and diameter of the pulmonary artery. The AUC was 0.849 (95% CI, 0.731–0.967) for normal(%), 0.827 (0.696–0.957) for total score, and 0.789 (0.651–0.927) for diam-

eter of the pulmonary artery. Table 4 lists the sensitivity, specificity, and accuracy for CT evaluation. When a cutoff value of 51% was used for normal(%), the accuracy was 77.5%. When a cutoff value of 3.4 was used for the CT total score, the accuracy was 70.0%.

DiscussionIn this study, normal lung volume, rep-

resented by normal(%) on 3D CT images, correlated negatively and significantly with pulmonary hypertension in patients with chronic fibrosing interstitial pneumonia. On logistic regression analysis, decreased nor-mal(%) accurately predicted pulmonary hypertension in our subjects. On the other hand, the results showed a weak correlation between mean PAP and fibrosis(%). Total lung volume measured on CT and expressed as CT lung volume (%predTLC) did not cor-relate with mean PAP. These results are ex-plainable by the coexistence of emphysema.

Cottin et al. [16] proposed pulmonary fi-brosis combined with emphysema as an im-

TABLE 3: Results of Univariate and Multivariate Logistic Analyses

Characteristic

Univariate Analysis Multivariate Analysis

Odds Ratio 95% CI p Odds Ratio 95% CI p

Predicted diffusing capacity (%) (n = 32) 0.06 0.92–1.00 0.06

Diameter of pulmonary artery 1.30 1.08–1.57 0.006 1.23 0.99–1.54 0.06

Emphysema score 2.11 1.02–4.35 0.04

Fibrosis score 3.43 0.67–17.70 0.14

GGO score 1.51 0.57–4.01 0.41

Total score 5.29 1.75–16.01 0.003

Percentage emphysema volume (LAA-950) 1.06 1.00–1.14 0.07

CT-based volume

Normal(%) 0.91 0.86–0.97 0.003 0.92 0.87–0.96 0.02

Emphysema(%) 1.05 0.99–1.10 0.09

GGO(%) 1.11 1.00–1.24 0.06

Consolidation(%) 2.02 0.78–5.25 0.15

Fibrosis(%) 1.08 1.00–1.16 0.04

Note—GGO = ground-glass opacity.

TABLE 4: Diagnostic Accuracy of CT Parameters for Predicting Pulmonary Hypertension

ParameterCutoff Value

Sensitivity (%)

Specificity (%)

Negative Predictive Value

(%)Accuracy

(%)

Normal(%) < 51 62.5 (10/16) 87.5 (21/24) 77.8 (21/27) 77.5 (31/40)

Total score > 3.4 81.3 (13/16) 62.5 (15/24) 83.3 (15/18) 70.0 (28/40)

Diameter of pulmonary artery (mm)

> 31 93.8 (15/16) 54.2 (13/24) 92.9 (13/14) 70.0 (28/40)

Note—Data in parentheses are number/total.

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portant phenotype of pulmonary fibrosis. Hyperinflation and high compliance of the emphysematous areas of the lungs probably compensate for the volume loss due to fibro-sis [28], whereas pulmonary emphysema and fibrosis may have additive or synergistic ef-fects on the capillary beds of the lung, result-ing in low diffusing capacity [16, 18]. In the

current study, 82.5% of subjects were smok-ers or former smokers. Thirteen patients had emphysema with %LAA-950 of more than 10% and met the criteria of pulmonary fi-brosis combined with emphysema defined by Ryerson et al. [18] and Mejía et al. [14]. These patients had large CT lung volume and low fibrosis(%) compared with patients with-

out emphysema (Fig. 1). The results indicate that the score of a single lesion (emphysema only or fibrosis only) in pulmonary fibrosis combined with emphysema patients is not sufficient for the expression of disease sever-ity. We hypothesized that normal lung vol-ume is an important index in these patients.

Previous studies on the relationship be-tween IIP and pulmonary hypertension did not investigate normal lung volume, al-though the volume of functional lung (i.e., lung volume minus emphysema volume, tumor volume, or atelectatic lung volume) has been applied to patients with lung can-cer and chronic obstructive pulmonary dis-ease [29, 30]. Recent studies have proposed several methods of segmenting 3D CT im-ages of the lungs in patients with IIP [24, 31–35], and some studies have measured normal lung volume in patients with pulmo-nary fibrosis using various computer-aided systems [27, 34]. In the current study, the sagittal color images (Figs. 1 and 2) clearly showed the craniocaudal extent of each le-

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Fig. 3—Correlation between mean pulmonary artery pressure (PAP) and CT findings.A–D, Graphs show that CT-based volume (normal(%)) (A) correlates negatively with mean PAP (r = −0.708, p < 0.001), fibrosis (fibrosis(%)) (B) correlates with mean PAP (r = 0.401, p = 0.001), emphysema volume (%LAA-950) (C) correlates with mean PAP (r = −0.410, p = 0.009), and CT lung volume (D) does not correlate with mean PAP. Solid circles represent patients with emphysema of more than 10% in %LAA and open circles, patients without or with small volume of emphysema.

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Fig. 4—Graph shows ROC curve analysis for data derived from thin-section CT to predict pulmonary hypertension. Thick line indicates normal lung volume on CT (normal(%)) (AUC, 0.849; 95% CI, 0.731–0.967). Dotted line indicates total score (AUC, 0.827; 0.696–0.957). Dashed line indicates diameter of pulmonary artery (AUC, 0.789; 0.651–0.927).

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Iwasawa et al.

sion, and the system used for analysis was helpful for the understanding of residual normal lung volume.

In previous studies, the fibrosis score on CT images did not correlate with pulmo-nary hypertension [12, 13]. Unfortunately, the study by Zisman et al. [12] did not in-clude emphysema. The study by Alhamad et al. [13] included only a small proportion of smokers, and they analyzed patients with various diseases, including collagen vascular diseases. In patients with collagen vascular diseases, increased pulmonary vascular re-sistance is probably multifactorial, includ-ing chronic pulmonary arterial thromboem-boli and pulmonary venoocclusive disease [36]. Although our study included only pa-tients with IIP and most subjects were former smokers, we believe that the results are con-sistent with these previous studies.

The results of the CADx system and radi-ologist scores in our study are highly corre-lated with each other [27, 37]. The fibrosis score correlated significantly with fibrosis(%) (r = 0.716, p < 0.001). Fibrosis(%) was signif-icant for predicting pulmonary hypertension on univariate analysis, although the p value was low. The fibrosis score was not a signif-icant variable. The small number of patients involved in the study may have affected the results. In binary analysis, any single data val-ue plays a key role in a small study.

This study has certain limitations. The study design was retrospective, and the study was based on a small number of pa-tients from a single institution. Patients were continuously enrolled during the study, but selection bias cannot be ruled out because not all patients with IIP in our hospital underwent RHC. Further studies of larger numbers of patients are needed to confirm the utility of 3D CT analysis in patients with IIP.

In conclusion, the results showed that normal lung volume measured on 3D CT, represented by normal(%), correlated with mean PAP measured by RHC. The nonin-vasive and accessible nature of CT makes it an attractive tool for predicting pulmonary hypertension. The pathobiology of pulmo-nary hypertension in pulmonary fibrosis is not completely understood [38]. However, our results suggest that quantitative mea-surement of normal lung volume can be useful for predicting pulmonary hyperten-sion in patients with chronic fibrosing in-terstitial pneumonia, especially those with coexisting emphysema.

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