Severe COVID-19 pneumonia: Perfusion analysis in correlation with pulmonary embolism and vessel enlargement using dual-energy CT data

Abstract

Background Gas exchange in COVID-19 pneumonia is impaired and vessel obstruction has been suspected to cause ventilation-perfusion mismatch. Dual-energy CT (DECT) can depict pulmonary perfusion by regional assessment of iodine uptake. Objective The purpose of this study was the analysis of pulmonary perfusion using dual-energy CT in a cohort of 27 consecutive patients with severe COVID-19 pneumonia. Method We retrospectively analyzed pulmonary perfusion with DECT in 27 consecutive patients (mean age 57 years, range 21–73; 19 men and 8 women) with severe COVID-19 pneumonia. Iodine uptake (IU) in regions-of-interest placed into normally aerated lung, ground-glass opacifications (GGO) and consolidations was measured using a dedicated postprocessing software. Vessel enlargement (VE) within opacifications and presence of pulmonary embolism (PE) was assessed by subjective analysis. Linear mixed models were used for statistical analyses. Results Compared to normally aerated lung 106/151 (70.2%) opacifications without upstream PE demonstrated an increased IU, 9/151 (6.0%) an equal IU and 36/151 (23.8%) a decreased IU. The estimated mean iodine uptake (EMIU) in opacifications without upstream PE (GGO 1.77 mg/mL; 95%-CI: 1.52–2.02; p = 0.011, consolidations 1.82 mg/mL; 95%-CI: 1.56–2.08, p = 0.006) was significantly higher compared to normal lung (1.22 mg/mL; 95%-CI: 0.95–1.49). In case of upstream PE, EMIU of opacifications (combined GGO and consolidations) was significantly decreased compared to normal lung (0.52 mg/mL; 95%-CI: -0.07–1.12; p = 0.043). The presence of VE in opacifications correlated significantly with iodine uptake (p<0.001). Conclusions DECT revealed the opacifications in a subset of patients with severe COVID-19 pneumonia to be perfused non-uniformly with some being hypo- and others being hyperperfused. Mean iodine uptake in opacifications (both ground-glass and consolidation) was higher compared to normally aerated lung except for areas with upstream pulmonary embolism. Vessel enlargement correlated with iodine uptake: In summary, in a cohort of 27 consecutive patients with severe COVID-19 pneumonia, dual-energy CT demonstrated a wide range of iodine uptake in pulmonary ground-glass opacifications and consolidations as a surrogate marker for hypo- and hyperperfusion compared to normally aerated lung. Applying DECT to determine which pathophysiology is predominant might help to tailor therapy to the individual patient´s needs.

Quantitative lung perfusion blood volume using dual energy CT–based effective atomic number (Zeff) imaging

“…In addition, as shown by the human subject results in this work, lung regions with consolidations and GGOs can generate a higher PBV iodine signal relative to the normally aerated lung regions.In fact,data published in multiple prior studies support the existence of this effect. [37][38][39] For example, in a fast kV switching DECT study of patients with COVID-19 pneumonia and suspected PE, two of the three showcases demonstrated higher iodine material image signal in the consolidation regions than the normally aerated parenchyma regions: one case shows a I value of 6.053 mg/ml in the consolidation, compared to 0.723 mg/ml in the normally aerated region. 37 In another dual-source DECT-based study of patients with GGOs, two of the three showcases demonstrated higher a I signals in the GGO regions than normally aerated regions.…”

“…7,[30][31][32][33][34][35] However, as shown by a recent survey conducted by the Society of Thoracic Radiology, 36 iodine material image-based pulmonary perfusion imaging remains underutilized in clinical practice due to several important limitations.The first important limitation of the iodine material image is that its signal does not necessarily reflect the magnitude of the pulmonary blood pool, as noniodine materials with Z eff different from that of the counterpart basis material (e.g., water) can also contribute to the iodine image signal. This is particularly a problem for pulmonary consolidation and ground-glass opacity (GGO) that may not only have different Z eff (relative to water), but also much higher densities than the normal lung tissue: as shown by the analysis in Section 2.2 and published literature, [37][38][39] those tissues can generate a relatively high signal in PBV iodine images which can mislead the evaluation of regional perfusion conditions. The second limitation lies in the fact that DECT-based iodine material images can only provide a relative measurement of PBV.…”

COVID-19-Related ARDS: Key Mechanistic Features and Treatments

“…Enlarged vessels suggestive of vasodilatation can be frequently observed within an area of ground glass or consolidation [ 91 ], contrary to the expected physiologic response to regional hypoxia (i.e., vasoconstriction). Perfusion imaging confirms that a considerable fraction of opacified lung parenchyma demonstrates increased uptake (indicating blood flow) in spite of diminished or even absent ventilation [ 92 ]. Perfusion abnormalities, on the other hand, are detected in areas of normal lung density [ 90 ], with one study of mechanically ventilated C-ARDS patients reporting that perfusion defects were not only present in every patient studied, but that the median extent of vascular abnormality approached 50% [ 93 ].…”

Quantitative Assessment of Lung Volumes and Enhancement in Patients with COVID-19: Role of Dual-Energy CT

“…Many studies have addressed the pathophysiology of the thrombotic events occurring in patients with COVID-19, unveiling that a prominent role is played by the cytokine cascade [ 9 , 10 , 11 , 12 ]. The latter seems to trigger micro-embolic phenomena that reduce pulmonary vascularization, inducing a ventilation–perfusion mismatch and, together with the purely inflammatory and infectious alterations, aggravate the respiratory picture [ 13 , 14 , 15 , 16 ].…”

“…Among CT findings observed, there was also an increased perfusion of the lungs in the proximal areas of lung opacity, decreased areas of peripheral perfusion and a dilatation of pulmonary vessels in areas of parenchymal abnormality [ 8 ]. Poschenrieder et al demonstrated that opacifications in patients with severe COVID-19 pneumonia can be both hypoperfused and hyperperfused [ 16 ].…”