The impact of slice-reduced computed tomography on histogram-based densitometry assessment of lung fibrosis in patients with systemic sclerosis

Validation of a semi-quantitative method to assess interstitial lung disease severity and progression in systemic sclerosis by standard and low-dose HRCT scans

BACKGROUND

While the presence of distinct imaging abnormalities by high-resolution CT (HRCT) defines interstitial lung disease (ILD), there is a relative lack of validated methods to quantify these abnormalities in clinical practice, limiting ILD severity and progression assessments. We aimed to validate a semi-quantitative method for lung fibrosis assessment in patients with systemic sclerosis associated ILD (SSc-ILD) by standard and low-dose HRCT, considering lung structure and function as integral components of ILD evaluation.

METHODS

SSc patients from Oslo and Zurich with HRCT images, pulmonary function tests, including forced vital capacity (FVC), diffusing capacity for carbon monoxide (DLCO) and the 6-minute walk test with oxygen (O2) desaturation were enrolled. We validated the semi-quantitative fibrosis extent method by HRCT using criteria for content and construct validity, discrimination, sensitivity to change and feasibility, as well as inter- and intra-rater variability.

RESULTS

65 SSc patients from Zurich and 90 from Oslo were included. Significant correlations were observed between the extent of fibrosis on HRCT and FVC (r=-0.517, p<0.001), DLCO (r=-0.400, p<0.001) and O2 desaturation (r=-0.500, p<0.001), indicating content, construct and criterion validity. Discrimination and sensitivity to change assessments showed moderate correlation with DLCO (r=-0.377, p=0.003) but not with FVC or O2 desaturation. Inter- and intra-rater variability demonstrated excellent reliability (κ=0.891 and κ=0.996, respectively), with HRCT quantification averaging 9-15 min, indicating high feasibility.

CONCLUSION

This study confirms that semi-quantitative fibrosis assessment of HRCT for SSc-ILD meets most validation criteria, supporting its use in clinical practice and showing additive value of structural to functional ILD assessment.

Histogram-Based Densitometry Index to Assess the Severity of Interstitial Lung Disease in Systemic Sclerosis in Standard and Low-Dose Computed Tomography

OBJECTIVE

Mean lung attenuation, skewness, and kurtosis are histogram-based densitometry variables that quantify systemic sclerosis-associated interstitial lung disease (SSc-ILD) and were recently merged into a computerized integrated index (CII). Our work tested the CII in low-dose 9-slice (reduced) and standard high-resolution computed tomography (CT) scans to evaluate extensive SSc-ILD and predict mortality.

METHODS

CT scans from patients with SSc-ILD were assessed using the software Horos to compute standard and reduced CIIs. Extensive ILD was determined following the Goh staging system. The association between CIIs and extensive ILD was analyzed with a generalized estimating equation regression model, the predictive ability of CIIs by the area under the receiver-operation characteristic curve (AUC), and the association between CIIs and death by Kaplan-Meier analysis.

RESULTS

Among 243 patients with standard and reduced CT scans available, 157 CT scans from 119 patients with SSc-ILD constituted the derivation cohort. The validation cohort included 116 standard and 175 reduced CT scans. Both CIIs from standard (odds ratio [OR] 0.53, 95% CI 0.37-0.75; AUC 0.77, 95% CI 0.68-0.87) and reduced CT scans (OR 0.54, 95% CI 0.35-0.82; AUC 0.78, 95% CI 0.70-0.87) were significantly associated with extensive ILD. A threshold of CII ≤ -0.96 for standard CT scans and CII ≤ -1.85 for reduced CT scans detected extensive ILD with high sensitivity in both derivation and validation cohorts. Extensive ILD according to Goh staging (OR 2.94, 95% CI 1.10-7.82) and standard CII ≤ -0.96 (OR 1.78, 95% CI 1.24-2.56) significantly predicted mortality; a marginal P value was observed for reduced CII ≤ -1.85 (OR 1.27, 95% CI 0.93-1.75).

CONCLUSION

Thresholds for both standard and reduced CII to identify extensive ILD were developed and validated, with an additional association with mortality. CIIs might help in clinical practice when radiology expertise is missing.

Sex influence on outcomes of patients with systemic sclerosis-associated interstitial lung disease: a EUSTAR database analysis

OBJECTIVE

Interstitial lung disease (ILD) is the leading cause of morbidity and mortality in systemic sclerosis (SSc) patients. We aimed to investigate the impact of sex on SSc-ILD.

METHODS

EUSTAR SSc patients with radiologically confirmed ILD and available percentage predicted forced vital capacity (%pFVC) were included. Demographics and disease features were recorded. A change in %pFVC over 12 months (s.d. 6) (cohort 1) was classified into stable (≤4%), mild (5-9%) and large progression (≥10%). In those with 2-year longitudinal %pFVC (cohort 2), the %pFVC change at each 12-month (s.d. 6) interval was calculated. Logistic regression analyses [odds ratio (OR) and 95% CI] and Cox proportional hazards models adjusted for age and %pFVC were applied.

RESULTS

A total of 1136 male and 5253 female SSc-ILD patients were identified. Males were significantly younger, had a shorter disease duration, had a higher prevalence of CRP elevation and frequently had diffuse cutaneous involvement. In cohort 1 (1655 females and 390 males), a higher percentage of males had stable ILD (74.4% vs 69.4%, P = 0.056). In multivariable analysis, disease duration and %pFVC [OR 0.99 (95% CI 0.98, 0.99) and OR 0.97 (95% CI 0.95, 0.99), respectively] in males and age, %pFVC and anti-centromere [OR 1.02 (95% CI 1.00, 1.04), OR 0.97 (95% CI 0.96, 0.98) and OR 0.39 (95% CI 0.245, 0.63), respectively] in females were associated with large progression. The 1-year mortality rate was higher in males (5.1% vs 2.5%, P = 0.013). In cohort 2 (849 females and 209 males), a higher percentage of females showed periods of large progression (11.7% vs 7.7%, P = 0.023), the percentage of patients with none, one or two periods of worsening was not different. The overall death rate was 30.9% for males and 20.4% in females (P < 0.001). In the survival analysis, male sex was a predictor of mortality [OR 1.95 (95% CI 1.66, 2.28)].

CONCLUSIONS

Male SSc-ILD patients have a poorer prognosis and sex-specific predictors exist in SSc-ILD.

Viewpoint: a multidisciplinary approach to the assessment of patients with systemic sclerosis-associated interstitial lung disease

Systemic sclerosis (SSc) is a rare and heterogeneous disease affecting the skin and internal organs. SSc-associated ILD (SSc-ILD) is a common and often early manifestation of SSc. This article discusses the rationale for a multidisciplinary approach (MDA) to the early identification and assessment of patients with SSc-ILD. Diagnosis of SSc-ILD is often challenging as patients with early disease can be asymptomatic, and SSc-ILD symptoms, such as exertional dyspnea and cough, are non-specific. High-resolution computed tomography (HRCT) of the lungs is the gold standard for diagnosis of SSc-ILD since pulmonary function tests lack sensitivity and specificity, especially in early disease. On HRCT, most patients with SSc-ILD have a non-specific interstitial pneumonia (NSIP) pattern. In addition, findings of pulmonary hypertension and esophageal dysmotility may be present. The multi-organ involvement of SSc and the diverse spectrum of symptoms support an MDA for the diagnosis and assessment of patients with SSc-ILD, with input from rheumatologists, pulmonologists, gastroenterologists, radiologists, and other specialists. Key Points • Interstitial lung disease (ILD) is a common manifestation of systemic sclerosis (SSc). • Early diagnosis is key to reducing the morbidity and mortality associated with SSc-ILD and other manifestations of SSc. • The multi-organ involvement of SSc supports a multidisciplinary approach to the diagnosis and assessment of patients with SSc-ILD, with input from rheumatologists, pulmonologists, gastroenterologists, radiologists, and other specialists.

Potential of Photon-Counting Detector CT for Radiation Dose Reduction for the Assessment of Interstitial Lung Disease in Patients With Systemic Sclerosis

OBJECTIVE

The aim of this study was to determine the potential of photon-counting detector computed tomography (PCD-CT) for radiation dose reduction compared with conventional energy-integrated detector CT (EID-CT) in the assessment of interstitial lung disease (ILD) in systemic sclerosis (SSc) patients.

METHODS

In this retrospective study, SSc patients receiving a follow-up noncontrast chest examination on a PCD-CT were included between May 2021 and December 2021. Baseline scans were generated on a dual-source EID-CT by selecting the tube current-time product for each of the 2 x-ray tubes to obtain a 100% (D 100 ), a 66% (D 66 ), and a 33% dose image (D 33 ) from the same data set. Slice thickness and kernel were adjusted between the 2 scans. Image noise was assessed by placing a fixed region of interest in the subcutaneous fat. Two independent readers rated subjective image quality (5-point Likert scale), presence, extent, diagnostic confidence, and accuracy of SSc-ILD. D 100 interpreted by a radiologist with 22 years of experience served as reference standard. Interobserver agreement was calculated with Cohen κ, and mean variables were compared by a paired t test.

RESULTS

Eighty patients (mean 56 ± 14; 64 women) were included. Although CTDI vol of PCD-CT was comparable to D 33 (0.72 vs 0.76 mGy, P = 0.091), mean image noise of PCD-CT was comparable to D 100 (131 ± 15 vs 113 ± 12, P > 0.05). Overall subjective image quality of PCD-CT was comparable to D 100 (4.72 vs 4.71; P = 0.874). Diagnostic accuracy was higher in PCD-CT compared with D 33 /D 66 (97.6% and 92.5%/96.3%, respectively) and comparable to D 100 (98.1%).

CONCLUSIONS

With PCD-CT, a radiation dose reduction of 66% compared with EID-CT is feasible, without penalty in image quality and diagnostic performance for the evaluation of ILD.

Diagnosis and monitoring of systemic sclerosis-associated interstitial lung disease using high-resolution computed tomography

Patients with systemic sclerosis are at high risk of developing systemic sclerosis-associated interstitial lung disease. Symptoms and outcomes of systemic sclerosis-associated interstitial lung disease range from subclinical lung involvement to respiratory failure and death. Early and accurate diagnosis of systemic sclerosis-associated interstitial lung disease is therefore important to enable appropriate intervention. The most sensitive and specific way to diagnose systemic sclerosis-associated interstitial lung disease is by high-resolution computed tomography, and experts recommend that high-resolution computed tomography should be performed in all patients with systemic sclerosis at the time of initial diagnosis. In addition to being an important screening and diagnostic tool, high-resolution computed tomography can be used to evaluate disease extent in systemic sclerosis-associated interstitial lung disease and may be helpful in assessing prognosis in some patients. Currently, there is no consensus with regards to frequency and scanning intervals in patients at risk of interstitial lung disease development and/or progression. However, expert guidance does suggest that frequency of screening using high-resolution computed tomography should be guided by risk of developing interstitial lung disease. Most experienced clinicians would not repeat high-resolution computed tomography more than once a year or every other year for the first few years unless symptoms arose. Several computed tomography techniques have been developed in recent years that are suitable for regular monitoring, including low-radiation protocols, which, together with other technologies, such as lung ultrasound and magnetic resonance imaging, may further assist in the evaluation and monitoring of patients with systemic sclerosis-associated interstitial lung disease. A video abstract to accompany this article is available at: https://www.globalmedcomms.com/respiratory/Khanna/HRCTinSScILD.

Paraclinical Aspects in Systemic Sclerosis

Systemic sclerosis (SSc) is a chronic inflammatory disease with an autoimmune substrate that affects the skin and a large number of internal organs. The chronic inflammatory process is sustained by a wide range of cytokines and chemokines, which are discharged by inflammatory cells, with fibrosis and nail bed vascular changes (disorganized vasculature architecture with microhemorrhages, megacapillaries and areas without capillaries). Confocal microscopy contributes to the understanding of the molecular mechanism involved in chronic inflammation and mainly targets the field of research. Coherent optical tomography, capillaroscopy, and skin biopsy are useful for the differential diagnosis of SSc with other sclerodermoid syndromes. The immunological profile is a classification criterion for SSc and directs the diagnosis to the two subsets of the disease. Multisystemic damage requires evaluation with the help of a set of investigations specific to each affected organ, such as: diffusing capacity for carbon monoxide, forced vital capacity, 6-minute walk test, high-resolution computed tomography standard and reduced sequential, cardiac ultrasound and right cardiac catheterization. The current possibilities of diagnosis, treatment and monitoring are permanently adapting to new medical discoveries.

High-Resolution Computed Tomography: Lights and Shadows in Improving Care for SSc-ILD Patients

The diagnosis and classification of systemic sclerosis-associated interstitial lung disease (SSc-ILD) is essential to improve the prognosis of systemic sclerosis (SSc) patients. The risk-stratification of disease severity and follow-up requires a multidisciplinary approach, integrating high-resolution computed tomography (HRTC) of the lung, pulmonary function tests (PFT), along with clinical and symptomatic evaluations. The use of HRCT in detecting SSc-ILD is not so much based on a definitive validation, but rather reflects the widespread clinician recognition of dissatisfaction with other modalities. However, due to the heterogeneity of SSc-ILD and the potential absence of symptoms in early or mild disease, it is prudent to consider as many parameters as possible in the assessment and monitoring of newly diagnosed patients. An early diagnosis meets the primary goal, i.e., the prevention of disease progression. The current first line treatment regimens are mainly centered on immunosuppressive therapy. This review assesses the role HRCT plays in optimizing care and improving clinical outcomes in SSc-ILD patients.

Applicability of radiomics in interstitial lung disease associated with systemic sclerosis: proof of concept

Objective

To retrospectively evaluate if texture-based radiomics features are able to detect interstitial lung disease (ILD) and to distinguish between the different disease stages in patients with systemic sclerosis (SSc) in comparison with mere visual analysis of high-resolution computed tomography (HRCT).

Methods

Sixty patients (46 females, median age 56 years) with SSc who underwent HRCT of the thorax were retrospectively analyzed. Visual analysis was performed by two radiologists for the presence of ILD features. Gender, age, and pulmonary function (GAP) stage was calculated from clinical data (gender, age, pulmonary function test). Data augmentation was performed and the balanced dataset was split into a training (70%) and a testing dataset (30%). For selecting variables that allow classification of the GAP stage, single and multiple logistic regression models were fitted and compared by using the Akaike information criterion (AIC). Diagnostic accuracy was evaluated from the area under the curve (AUC) from receiver operating characteristic (ROC) analyses, and diagnostic sensitivity and specificity were calculated.

Results

Values for some radiomics features were significantly lower (p < 0.05) and those of other radiomics features were significantly higher (p = 0.001) in patients with GAP2 compared with those in patients with GAP1. The combination of two specific radiomics features in a multivariable model resulted in the lowest AIC of 10.73 with an AUC of 0.96, 84% sensitivity, and 99% specificity. Visual assessment of fibrosis was inferior in predicting individual GAP stages (AUC 0.86; 83% sensitivity; 74% specificity).

Conclusion

The correlation of radiomics with GAP stage, but not with the visually defined features of ILD-HRCT, implies that radiomics might capture features indicating severity of SSc-ILD on HRCT, which are not recognized by visual analysis.

Key Points

• Radiomics features can predict GAP stage with a sensitivity of 84% and a specificity of almost 100%.

• Extent of fibrosis on HRCT and a combined model of different visual HRCT-ILD features perform worse in predicting GAP stage.

• The correlation of radiomics with GAP stage, but not with the visually defined features of ILD-HRCT, implies that radiomics might capture features on HRCT, which are not recognized by visual analysis.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-07293-8) contains supplementary material, which is available to authorized users.

Predictors of progression in systemic sclerosis patients with interstitial lung disease

Systemic sclerosis (SSc) is a systemic autoimmune disease affecting multiple organ systems, including the lungs. Interstitial lung disease (ILD) is the leading cause of death in SSc.

There are no valid biomarkers to predict the occurrence of SSc-ILD, although auto-antibodies against anti-topoisomerase I and several inflammatory markers are candidate biomarkers that need further evaluation. Chest auscultation, presence of shortness of breath and pulmonary function testing are important diagnostic tools, but lack sensitivity to detect early ILD. Baseline screening with high-resolution computed tomography (HRCT) is therefore necessary to confirm an SSc-ILD diagnosis. Once diagnosed with SSc-ILD, patients' clinical courses are variable and difficult to predict, although certain patient characteristics and biomarkers are associated with disease progression. It is important to monitor patients with SSc-ILD for signs of disease progression, although there is no consensus about which diagnostic tools to use or how often monitoring should occur. In this article, we review methods used to define and predict disease progression in SSc-ILD.

There is no valid definition of SSc-ILD disease progression, but we suggest that either a decline in forced vital capacity (FVC) from baseline of ≥10%, or a decline in FVC of 5–9% in association with a decline in diffusing capacity of the lung for carbon monoxide of ≥15% represents progression. An increase in the radiographic extent of ILD on HRCT imaging would also signify progression. A time period of 1–2 years is generally used for this definition, but a decline over a longer time period may also reflect clinically relevant disease progression.

Lung function tests and chest imaging help predict who has SSc-associated ILD and whether it will progress. In the absence of standardised methods for doctors, we recommend a strategy that combines both lung function tests and chest imaging.http://bit.ly/2uK9ZD2

Circulating biomarkers of systemic sclerosis - interstitial lung disease

Interstitial lung disease is a frequent organ manifestation in systemic sclerosis and is associated with high mortality. It is crucial to diagnose interstitial lung disease in systemic sclerosis and to assess severity and identify patients prone to progression at an early stage to ultimately decrease organ damage and improve outcome. Circulating anti-topoisomerase-I autoantibodies have long been associated with the presence and development of systemic sclerosis - interstitial lung disease, evidence on their potential to further predict the clinical course of systemic sclerosis is however conflicting. C-reactive protein is a marker of infection and systemic inflammation with widespread clinical application and is elevated in systemic sclerosis with a tendency towards higher abundancy in patients with early disease. The role of other circulating biomarkers is promising but hampered by the lack of standardized criteria and guidelines for sample/data collection, analyses, reporting and validation and has not reached prime time for clinical application. However, epithelial markers including Krebs von den Lungen-6 and surfactant protein D and several cytokines and chemokines including CCL2 and CCL18 for severity assessment of systemic sclerosis - interstitial lung disease patients at the time of interstitial lung disease diagnosis and to predict interstitial lung disease progression have been reported and seem to be promising candidate biomarkers in the future.

Interstitial Lung Disease in Systemic Sclerosis: Focus on Early Detection and Intervention

Systemic sclerosis (SSc) is a progressive and often devastating disease characterized by autoimmune dysfunction, vasculopathy, and fibrosis. Interstitial lung disease (ILD) is identified in the majority of patients with SSc and is the leading cause of SSc-related mortality. Although clinical manifestations and ILD severity vary among patients, lung function typically declines to the greatest extent during the first 3-4 years after disease onset. We aim to provide an overview of SSc-associated ILD (SSc-ILD) with a focus on current and emerging tools for early diagnosis of ILD and current and novel treatments under investigation. Early detection of ILD provides the opportunity for early therapeutic intervention, which could improve patient outcomes. Thoracic high-resolution computed tomography is the most effective method of identifying ILD in patients with SSc; it enables detection of mild lung abnormalities and plays an important role in monitoring disease progression. Cyclophosphamide and mycophenolate mofetil are the most commonly prescribed treatments for SSc-ILD. Recently, nintedanib (an antifibrotic) was approved by the Food and Drug Administration for patients with SSc-ILD; it is indicated for slowing the rate of decline in pulmonary function. However, there is a need for additional effective and well-tolerated disease-modifying therapy. Ongoing studies are evaluating other antifibrotics and novel agents. We envision that early detection of lung involvement, combined with the emergence and integration of novel therapies, will lead to improved outcomes in patients with SSc-ILD.

Quantitative CT texture analysis for diagnosing systemic sclerosis: Effect of iterative reconstructions and radiation doses

To test whether texture analysis (TA) can discriminate between Systemic Sclerosis (SSc) and non-SSc patients in computed tomography (CT) with different radiation doses and reconstruction algorithms.In this IRB-approved retrospective study, 85 CT scans at different radiation doses [49 standard dose CT (SDCT) with a volume CT dose index (CTDIvol) of 4.86 ± 2.1 mGy and 36 low-dose (LDCT) with a CTDIvol of 2.5 ± 1.5 mGy] were selected; 61 patients had Ssc ("cases"), and 24 patients had no SSc ("controls"). CT scans were reconstructed with filtered-back projection (FBP) and with sinogram-affirmed iterative reconstruction (SAFIRE) algorithms. 304 TA features were extracted from each manually drawn region-of-interest at 6 pre-defined levels: at the midpoint between lung apices and tracheal carina, at the level of the tracheal carina, and 4 between the carina and pleural recesses. Each TA feature was averaged between these 6 pre-defined levels and was used as input in the machine learning algorithm artificial neural network (ANN) with backpropagation (MultilayerPerceptron) for differentiating between SSc and non-SSc patients.Results were compared regarding correctly/incorrectly classified instances and ROC-AUCs.ANN correctly classified individuals in 93.8% (AUC = 0.981) of FBP-LDCT, in 78.5% (AUC = 0.859) of FBP-SDCT, in 91.1% (AUC = 0.922) of SAFIRE3-LDCT and 75.7% (AUC = 0.815) of SAFIRE3-SDCT, in 88.1% (AUC = 0.929) of SAFIRE5-LDCT and 74% (AUC = 0.815) of SAFIRE5-SDCT.Quantitative TA-based discrimination of CT of SSc patients is possible showing highest discriminatory power in FBP-LDCT images.

Novel Imaging Approaches in Systemic Sclerosis-Associated Interstitial Lung Disease

PURPOSE OF THE REVIEW

Novel imaging approaches, such as quantitative computed tomography (CT), magnetic resonance imaging (MRI), and molecular imaging, are being applied to interstitial lung diseases to provide prognostic, functional, and molecular information. Here, we review such imaging approaches and their applicability to systemic sclerosis-associated interstitial lung disease (SSc-ILD).

RECENT FINDINGS

Quantitative CT can be used to quantify the radiographic response to SSc-ILD therapy. Due to advances in MRI sequence development, MRI can detect the presence of SSc-ILD with high accuracy. MRI can also be utilized to provide functional information as to SSc-ILD and paired with molecular probes to provide non-invasive molecular information. MRI and ultrasound have promising test characteristics for diagnosing ILD in SSc without the use of ionizing radiation. Novel imaging approaches can detect SSc-ILD without the use of ionizing radiation, provide non-invasive functional and molecular information, and quantify treatment response in SSc-ILD. These techniques hold promise for translation into clinical care and clinical trials.