Rationale and Objectives
Digital chest imaging has replaced film chest radiographs in many centers, but the International Labour Organization classification system, which is the most widely used system for recognition and classification of dust-related abnormalities, is predicated on film chest radiographs. The purpose of this study was to evaluate the equivalency of digital chest radiographs (including both hard copy and soft copy) with film radiographs for the recognition and quantification of abnormalities consistent with pneumoconiosis using the International Labour Organization classification system.
Materials and Methods
Digital chest images and film images, obtained from 107 subjects with a range of parenchymal and pleural abnormalities, were classified in random order by six B readers.
Results
Readings of film and soft copy images were equivalent for small opacity profusion; readings of hard copy images had significantly greater prevalence of small opacities compared to film and soft copy. The prevalence of large opacities differed significantly among all three image formats: hard copy greater than film greater than soft copy. However, film and soft copy readings for large opacities did not differ significantly when images demonstrating the coalescence of small opacities that had not yet become a large opacity were grouped with large opacities. The prevalence of pleural abnormalities differed significantly among all three image formats: film greater than hard copy greater than soft copy.
Conclusions
Film and soft copy images can be recommended for the recognition and classification of dust-related parenchymal abnormalities using International Labour Organization classifications. The role of digital radiography in reading for pleural abnormalities requires additional investigation.
Pneumoconioses are fibrotic or granulomatous lung diseases related to the inhalation of certain inorganic dusts . Workers in selected occupations have been at risk of pneumoconiosis since antiquity. Silica, asbestos, and coal have been the major dust hazards, though there are many other less commonly encountered materials that can present an inhalation hazard for pneumoconiosis.
In the 1930s, the International Labour Organization (ILO) based in Geneva, Switzerland, became involved in the development and evolution of a system for standardizing the classification of posteroanterior (PA) chest radiographs for pneumoconiosis . After multiple revisions, the ILO system remains the most widely used method for classifying chest radiographic abnormalities related to inhalation of pathogenic dusts .
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Materials and methods
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Recruitment of Subjects and Questionnaire
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Chest Radiographic Imaging Methods and Quality Control
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Standard ILO Radiographic Images
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Reading of Images
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Table 1
Reading Order of Image Formats by B Readers
Round 1 Round 2 Reader Cycle 1 Cycle 2 Cycle 3 Cycle 1 Cycle 2 Cycle 3 1 Hard ∗ Film † Soft ‡ Hard Soft Film 2 Soft Film Hard Film Soft Hard 3 Film Soft Hard Film Hard Soft 4 Hard Soft Film Soft Hard Film 5 Film Hard Soft Hard Film Soft 6 Soft Hard Film Soft Film Hard
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Statistical Analyses
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Results
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Table 2
Subject Characteristics
Frequency Percent Gender Male 86 80 Female 21 20 Body mass index (kg/m 2 ) <25 (normal) 28 26 ≥25 to <30 (overweight) 45 42 ≥30 (obese) 34 32 Ever smoked No 39 36 Yes 68 64 Current smoking No 97 91 Yes 10 9 History of dust exposure No 47 44 Yes 60 56 Dust exposure type ( n = 60) ∗ Silica 34 57 Asbestos 28 47 Other/unknown 12 20 Mean (S.D.) Median (range) Age (y) 64.7 (11.9) 65 (31–91) Body mass index (kg/m 2 ) 28.5 (5.2) 28.1 (19.5–48.8) Pack-years All subjects ( n = 107) 19.5 (24.1) 12 (0–96) Ever smoked ( n = 68) 30.7 (23.8) 23.5 (1–96)
SD, standard deviation.
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Table 3
Results of ILO Classifications Overall and by Image Format
Overall Film Hard Copy Soft Copy Outcome variable_n_ %n %n %n % X 2 ( P Value) 1. Image quality ( n = 3816 ∗ ) 1 1130 29% 398 31% 301 24% 431 34% 76.62 2 2282 60% 774 61% 778 61% 730 57% (<.0001) 3 382 10% 98 8% 175 14% 109 9% (6 df) 4 (unreadable) 22 1% 2 0% 18 1% 2 0% 2A. Any parenchymal abnormalities ( n = 3794 ∗ ) 11.97 No 1216 32% 443 35% 358 29% 415 33% (.0025) Yes 2578 68% 827 65% 896 71% 855 67% (2 df) 2Ba. Shape/size of primary small opacities ( n = 2578) 1.85 Round (p, q, r) 829 32% 281 34% 280 31% 268 31% (.3958) Irregular (s, t, u) 1749 68% 546 66% 616 69% 587 69% (2 df) 2Bc. Small opacity profusion 0 1529 40% 543 43% 455 36% 531 42% 16.55 1 1158 31% 385 30% 392 31% 381 30% (.0111) 2 852 22% 265 21% 306 25% 281 22% (6 df) 3 255 7% 77 6% 101 8% 77 6% 2C. Large opacities 0 3216 85% 1076 85% 1036 83% 1104 87% 14.12 A 228 6% 78 6% 79 6% 71 6% (.0284) B 271 7% 93 7% 101 8% 77 6% (6 df) C 79 2% 23 2% 38 3% 18 1% 2C. Large opacities 9.09 No (0) 3216 85% 1076 85% 1036 83% 1104 87% (.0106) Yes (A or B or C) 578 15% 194 15% 218 17% 166 13% (2 df) 2C. Large opacities or ax 7.87 No (0) 3026 80% 1020 80% 969 77% 1037 82% (.02) Yes (A or B or C or ax) 768 20% 250 20% 285 23% 233 18% (2 df) 3A. Pleural abnormalities 30.26 No 2585 68% 795 63% 868 69% 922 73% (<.0001) Yes 1209 32% 475 37% 386 31% 348 27% (2 df) 3C. Costophrenic angle obliteration 6.37 No 3546 93% 1169 92% 1183 94% 1194 94% (.0413) Yes (right and/or left) 248 7% 101 8% 71 6% 76 6% (2 df) 3D. Diffuse pleural thickening 4.52 No 3620 95% 1199 94% 1201 96% 1220 96% (.1043) Yes (right and/or left) 174 5% 71 6% 53 4% 50 4% (2 df)
df = degrees of freedom.
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Table 4
Pairwise Comparisons of Prevalence of Findings by Image Format (FSR, HC, and SC) based on Dichotomous Outcomes
Classification Comparison FSR vs. HC ∗ FSR vs. SC ∗ HC vs. SC ∗ 1A: Film quality (category 1 vs. 2, 3, 4) 0.67 (0.49–0.92) 1.11 (0.85–1.45) 1.66 (1.39–1.96) 1.A: Film quality (categories 1, 2 vs. 3, 4) 0.47 (0.31–0.73) 0.89 (0.56–1.41) 1.87 (1.53–2.30) 2.A: Parenchymal abnormalities (yes/no) 0.75 (0.65–0.86) 0.91 (0.80–1.04) 1.22 (1.09–1.35) 2.C: Large opacities (yes/no) 0.86 (0.75–0.98) 1.18 (1.03–1.36) 1.38 (1.20–1.58) 2.C: Large opacities with ax (yes/no) 0.83 (0.74–0.93) 1.07 (0.98–1.17) 1.29 (1.16–1.44) 3.A: Pleural abnormalities (yes/no) 1.30 (1.10–1.53) 1.53 (1.31–1.78) 1.18 (1.04–1.33) 3.C: Costophrenic angle obliteration (yes/no) 1.45 (0.99–2.11) 1.36 (0.93–1.99) 0.94 (0.79–1.12) 3.D: Diffuse pleural thickening (yes/no) 1.35 (0.94–1.95) 1.45 (0.99–2.12) 1.07 (0.84–1.37)
FSR, film-screen radiographs; HC, hard copy; SC, soft copy.
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Table 5
Pairwise Comparisons of Mean Scores by Image Format (FSR, HC, and SC) based on Ordinal Outcomes
Classification Comparison FSR vs. HC ∗ FSR vs. SC ∗ HC vs. SC ∗ 1.A: Film quality (4-point scale) −0.166 (.0002) 0.013 (.7366) 0.179 (<.0001) 2.B: Small opacities (12-point scale) −0.381 (<.0001) −0.028 (.6771) 0.353 (<.0001) 2.B: Small opacities (4-point scale) −0.136 (<.0001) −0.015 (.5596) 0.122 (<.0001) 2.C: Large opacities (4-point scale) −0.051 (.0142) 0.041 (.0098) 0.092 (<.0001)
FSR, film-screen radiographs; HC, hard copy; SC, soft copy.
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Table 6
Adjusted Pairwise Comparisons of Prevalence of Findings by Image Format (FSR, HC, and SC) based on Dichotomous Outcomes
Classification Comparison FSR vs. HC ∗ FSR vs. SC ∗ HC vs. SC ∗ 1.A: Film quality (Category 1 vs. 2, 3, 4) 0.65 (0.46–0.91) 1.12 (0.84–1.49) 1.72 (1.43–2.08) 1.A: Film quality (Categories 1, 2 vs. 3, 4) 0.42 (0.24–0.71) 0.87 (0.50–1.54) 2.10 (1.63–2.70) 2.A: Parenchymal abnormalities (yes/no) 0.72 (0.60–0.86) 0.90 (0.78–1.04) 1.26 (1.09–1.46) 2.C: Large opacities (yes/no) 0.83 (0.70–0.99) 1.23 (1.04–1.46) 1.48 (1.24–1.76) 2.C: Large opacities with ax (yes/no) 0.79 (0.66–0.94) 1.12 (0.99–1.27) 1.43 (1.22–1.67) 3.A: Pleural abnormalities (yes/no) 1.28 (1.08–1.53) 1.59 (1.35–1.88) 1.24 (1.08–1.42) 3.C: Costophrenic angle obliteration (yes/no) 1.41 (0.99–2.00) 1.39 (0.98–1.97) 0.98 (0.80–1.22) 3.D: Diffuse pleural thickening (yes/no) 1.32 (0.97–1.80) 1.43 (1.04–1.98) 1.08 (0.84–1.40)
FSR, film-screen radiographs; HC, hard copy; SC, soft copy.
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Table 7
Adjusted Pairwise Comparisons of Mean Scores by Image Format (FSR, HC, and SC) based on Ordinal Outcomes
FSR vs. HC ∗ FSR vs. SC ∗ HC vs. SC ∗ 1.A: Film quality (4-point scale) −0.166 (.0002) 0.013 (.7379) 0.179 (<.0001) 2.B: Small opacities (12-point scale) −0.420 (<.0001) −0.026 (.6871) 0.393 (<.0001) Adjusted for primary and secondary shape −0.404 (<.0001) −0.048 (.5652) 0.452 (<.0001) 2.B: Small opacities (4-point scale) −0.148 (<.0001) −0.014 (.5642) 0.134 (<.0001) Adjusted for primary and secondary shape −0.150 (<.0001) −0.007 (.8232) 0.157 (<.0001) 2.C: Large opacities (4-point scale) −0.058 (.0093) 0.041 (.0078) 0.099 (<.0001)
FSR, film-screen radiographs; HC, hard copy; SC, soft copy.
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Discussion
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Acknowledgment
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