Abstract
PurposeTo assess whether grating-based X-ray dark-field imaging can increase the sensitivity of X-ray projection images in the diagnosis of pulmonary emphysema and allow for a more accurate assessment of emphysema distribution.Materials and MethodsLungs from three mice with pulmonary emphysema and three healthy mice were imaged ex vivo using a laser-driven compact synchrotron X-ray source. Median signal intensities of transmission (T), dark-field (V) and a combined parameter (normalized scatter) were compared between emphysema and control group. To determine the diagnostic value of each parameter in differentiating between healthy and emphysematous lung tissue, a receiver-operating-characteristic (ROC) curve analysis was performed both on a per-pixel and a per-individual basis. Parametric maps of emphysema distribution were generated using transmission, dark-field and normalized scatter signal and correlated with histopathology.ResultsTransmission values relative to water were higher for emphysematous lungs than for control lungs (1.11 vs. 1.06, p<0.001). There was no difference in median dark-field signal intensities between both groups (0.66 vs. 0.66). Median normalized scatter was significantly lower in the emphysematous lungs compared to controls (4.9 vs. 10.8, p<0.001), and was the best parameter for differentiation of healthy vs. emphysematous lung tissue. In a per-pixel analysis, the area under the ROC curve (AUC) for the normalized scatter value was significantly higher than for transmission (0.86 vs. 0.78, p<0.001) and dark-field value (0.86 vs. 0.52, p<0.001) alone. Normalized scatter showed very high sensitivity for a wide range of specificity values (94% sensitivity at 75% specificity). Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology.ConclusionIn a murine model, the complementary information provided by X-ray transmission and dark-field images adds incremental diagnostic value in detecting pulmonary emphysema and visualizing its regional distribution as compared to conventional X-ray projections.
Highlights
Chronic obstructive pulmonary disease (COPD) involves progressive airflow obstruction and airway inflammation [1] and represents one of the leading causes of morbidity and mortality throughout the world. [2] Emphysema is a common component of COPD and is characterized by irreversible destruction of alveolar architecture with enlargement of distal airspaces
Using the normalized scatter signal to display the regional distribution of emphysema provides color-coded parametric maps, which show the best correlation with histopathology
[6] Since emphysema is characterized on CT by abnormally low attenuating lung parenchyma, the presence and degree of pulmonary emphysema can be assessed visually or by densitometry. [8,9,10] the malignancy risk associated with the radiation exposure from a single CT examination of an adult is – if any – very low, the radiation exposure associated with CT limits its use for frequent follow-up examinations to monitor disease progression in emphysema
Summary
Chronic obstructive pulmonary disease (COPD) involves progressive airflow obstruction and airway inflammation [1] and represents one of the leading causes of morbidity and mortality throughout the world. [2] Emphysema is a common component of COPD and is characterized by irreversible destruction of alveolar architecture with enlargement of distal airspaces. Conventional chest radiography is commonly used to diagnose the presence of emphysema in patients with suspected COPD. [7] Imaging of pulmonary emphysema has been greatly improved with highresolution computed tomography, at the cost of exposing the patient to a higher radiation dose as compared to conventional chest radiography. [6] Since emphysema is characterized on CT by abnormally low attenuating lung parenchyma, the presence and degree of pulmonary emphysema can be assessed visually or by densitometry. In addition to an accurate diagnosis, assessing the regional distribution of pulmonary emphysema can be crucial for clinical decision-making, e.g., regarding lung volume reduction surgery and endobronchial procedures. [10,11,12] Conventional chest Xrays are of limited use in assessing the regional distribution of emphysema. In addition to an accurate diagnosis, assessing the regional distribution of pulmonary emphysema can be crucial for clinical decision-making, e.g., regarding lung volume reduction surgery and endobronchial procedures. [10,11,12] Conventional chest Xrays are of limited use in assessing the regional distribution of emphysema. [10] Using CT densitometry, parametric maps of emphysema distribution can be generated by identifying voxels in the lung parenchyma with a CT density below a relative (e.g. 15th percentile) or absolute (e.g. 2950 Hounsfield units) threshold. [13,14] This technique shows good reproducibility [15] and has been validated against pulmonary function tests in clinical trials of pulmonary emphysema. [16,17] Emphysema distribution can be assessed by ventilation/perfusion scintigraphy or SPECT, but this offers little additional value over CT scanning [10] and is unable to detect important comorbidities
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