Interstitial Lung Disease in Systemic Sclerosis
Interstitial Lung Disease in Systemic Sclerosis
A total of 205 consecutive patients with a diagnosis of SSc and annual follow-up in the Department of Rheumatology, University Hospital Zurich, were prospectively included in this study. All patients fulfilled either the American College of Rheumatology classification criteria or the Very Early Diagnosis Of Systemic Sclerosis (VEDOSS) criteria for SSc. Assessment of clinical parameters and image acquisition was done prospectively following international standards. All patients signed informed consent. The study was approved as part of the Zurich cohort of the European Scleroderma Trial and Research registry by the institutional review board.
All patients were examined between January 2012 and September 2013. CT scans were performed with a 64-slice multidetector CT (Somatom Definition AS, Siemens Healthcare, Erlangen, Germany) or a 128-slice multidetector CT (Definition Flash Dual Source, Siemens Healthcare, Germany). Patients were examined in prone position and at end inspiration. Standard HRCT of the entire chest was performed and considered the standard of reference (tube potential 120 kV, reference tube current–time product 40or 110 mAs, care dose on). Data were reconstructed with filtered back projection (FBP), a slice thickness of 1 mm, an increment of 0.8 mm, using a sharp (B60f) or very sharp convolution kernel (B70f).
Furthermore, a low-sampling HRCT of the chest with nine sequential slices, the so-called 'reduced HRCT', was obtained (tube potential 120 kV, reference tube current–time product 30 or 110 mAs, care dose on). The first three slices had an increment of 80 mm and were placed as follows: the first slice at the manubrium sterni, the second at the carina and the third at the lower lobe. For the following six basal slices, the increment was 15 mm (figure 1). Due to technical reasons, the CT scanner performed two slices per level. Data were reconstructed with FBP, a slice thickness of 1 mm and a very sharp (B70f) or ultrasharp convolution kernel (B80f).
(Enlarge Image)
Figure 1.
Topogram displaying the levels of high-resolution CT scans with a reduced number of slices. One image apical, one at the level of the carina and six images at the basal level with 1 mm slices, the upper three images with an increment of 80 mm, the basal six images with an increment of 15 mm.
The readout was performed on dedicated PACS-Viewer (Impax 6.4, AGFA, Dübendorf, Switzerland) and licensed reading screens. The readers were allowed to use all functions without multiplanar reformation, including changing window and level setting. All images were displayed on lung window.
On standard HRCT of the entire chest, presence of ILD (yes/no; for ILD definition, see online supplementary text http://ard.bmj.com/content/73/12/2069/suppl/DC1) was assessed by one reader experienced with chest CT (TF, 12 years of experience) as previously described. The extent of ILD was graded as no lung involvement, lung involvement less than 20% (i.e. limited disease), lung involvement more than 20% (i.e. extensive disease) or indeterminate (i.e. extent not readily classifiable) as described by Goh et al. In cases of uncertainty concerning the presence of ILD, the CT scans from previous annual follow-ups were taken into account. Degree of diagnostic confidence was recorded (score 1 to 4; 1=fully confident; 2=probably confident; 3=confident only under limited conditions; 4=not confident). Before the analysis of the reduced HRCT scans, all three readers underwent a training session including assessment and discussion of 10 non-study-related cases.
The reduced HRCT scans were evaluated in a blinded manner, without knowing the results of the standard HRCT, by two radiologists (AW, 4 years of experience; SB, 6 years of experience). Again, presence and extent of ILD and the related diagnostic confidence were assessed. Furthermore, the quality of the image acquisition of reduced HRCT scans was rated on a scale from 1 to 3 as follows: 1=excellent (all slices contain lung tissue, base of the lung covered, second slice less than 2 cm above or below the level of the carina); 2=acceptable (1–2 slices without capture of lung tissue and/or second slice more than 2 cm above or below the level of the carina); and 3=not acceptable (three or more slices without capture of lung tissue and/or second slice more than 3 cm above or below the level of the carina).
Radiation dose parameters of standard HRCT of the entire chest and reduced HRCT were assessed from the patient protocol. Effective radiation dose in millisievert was estimated by multiplying the dose length product (DLP) with the region-specific conversion coefficient (chest 0.014 mSv/mGycm).
Statistical analysis was performed using SPSS (SPSS, release V.21.0 for Windows; SPSS, Chicago, Illinois, USA). Continuous variables were reported as mean±SD, and categorical variables as frequencies or percentages. Cohen's κ statistics or Kendall's τ test was calculated for interobserver agreements as appropriate. Presence of ILD was compared with Cochrane's Q test and McNemar test. Sensitivity, specificity, accuracy and negative predictive value were calculated concerning the detection of ILD. The CI was 95%. Statistical significance was inferred at a p value below 0.05.
Methods
Patients' Population
A total of 205 consecutive patients with a diagnosis of SSc and annual follow-up in the Department of Rheumatology, University Hospital Zurich, were prospectively included in this study. All patients fulfilled either the American College of Rheumatology classification criteria or the Very Early Diagnosis Of Systemic Sclerosis (VEDOSS) criteria for SSc. Assessment of clinical parameters and image acquisition was done prospectively following international standards. All patients signed informed consent. The study was approved as part of the Zurich cohort of the European Scleroderma Trial and Research registry by the institutional review board.
Image Acquisition
All patients were examined between January 2012 and September 2013. CT scans were performed with a 64-slice multidetector CT (Somatom Definition AS, Siemens Healthcare, Erlangen, Germany) or a 128-slice multidetector CT (Definition Flash Dual Source, Siemens Healthcare, Germany). Patients were examined in prone position and at end inspiration. Standard HRCT of the entire chest was performed and considered the standard of reference (tube potential 120 kV, reference tube current–time product 40or 110 mAs, care dose on). Data were reconstructed with filtered back projection (FBP), a slice thickness of 1 mm, an increment of 0.8 mm, using a sharp (B60f) or very sharp convolution kernel (B70f).
Furthermore, a low-sampling HRCT of the chest with nine sequential slices, the so-called 'reduced HRCT', was obtained (tube potential 120 kV, reference tube current–time product 30 or 110 mAs, care dose on). The first three slices had an increment of 80 mm and were placed as follows: the first slice at the manubrium sterni, the second at the carina and the third at the lower lobe. For the following six basal slices, the increment was 15 mm (figure 1). Due to technical reasons, the CT scanner performed two slices per level. Data were reconstructed with FBP, a slice thickness of 1 mm and a very sharp (B70f) or ultrasharp convolution kernel (B80f).
(Enlarge Image)
Figure 1.
Topogram displaying the levels of high-resolution CT scans with a reduced number of slices. One image apical, one at the level of the carina and six images at the basal level with 1 mm slices, the upper three images with an increment of 80 mm, the basal six images with an increment of 15 mm.
Image Assessment
The readout was performed on dedicated PACS-Viewer (Impax 6.4, AGFA, Dübendorf, Switzerland) and licensed reading screens. The readers were allowed to use all functions without multiplanar reformation, including changing window and level setting. All images were displayed on lung window.
On standard HRCT of the entire chest, presence of ILD (yes/no; for ILD definition, see online supplementary text http://ard.bmj.com/content/73/12/2069/suppl/DC1) was assessed by one reader experienced with chest CT (TF, 12 years of experience) as previously described. The extent of ILD was graded as no lung involvement, lung involvement less than 20% (i.e. limited disease), lung involvement more than 20% (i.e. extensive disease) or indeterminate (i.e. extent not readily classifiable) as described by Goh et al. In cases of uncertainty concerning the presence of ILD, the CT scans from previous annual follow-ups were taken into account. Degree of diagnostic confidence was recorded (score 1 to 4; 1=fully confident; 2=probably confident; 3=confident only under limited conditions; 4=not confident). Before the analysis of the reduced HRCT scans, all three readers underwent a training session including assessment and discussion of 10 non-study-related cases.
The reduced HRCT scans were evaluated in a blinded manner, without knowing the results of the standard HRCT, by two radiologists (AW, 4 years of experience; SB, 6 years of experience). Again, presence and extent of ILD and the related diagnostic confidence were assessed. Furthermore, the quality of the image acquisition of reduced HRCT scans was rated on a scale from 1 to 3 as follows: 1=excellent (all slices contain lung tissue, base of the lung covered, second slice less than 2 cm above or below the level of the carina); 2=acceptable (1–2 slices without capture of lung tissue and/or second slice more than 2 cm above or below the level of the carina); and 3=not acceptable (three or more slices without capture of lung tissue and/or second slice more than 3 cm above or below the level of the carina).
Radiation Dose
Radiation dose parameters of standard HRCT of the entire chest and reduced HRCT were assessed from the patient protocol. Effective radiation dose in millisievert was estimated by multiplying the dose length product (DLP) with the region-specific conversion coefficient (chest 0.014 mSv/mGycm).
Statistical Analysis
Statistical analysis was performed using SPSS (SPSS, release V.21.0 for Windows; SPSS, Chicago, Illinois, USA). Continuous variables were reported as mean±SD, and categorical variables as frequencies or percentages. Cohen's κ statistics or Kendall's τ test was calculated for interobserver agreements as appropriate. Presence of ILD was compared with Cochrane's Q test and McNemar test. Sensitivity, specificity, accuracy and negative predictive value were calculated concerning the detection of ILD. The CI was 95%. Statistical significance was inferred at a p value below 0.05.
