Rationale and Objectives
The objective of this study was to investigate the correlation between the computed tomography (CT) cross-sectional area (CSA) of small pulmonary vessels and the CT obstruction index in patients with acute pulmonary embolism (PE) and the correlation between the changes in these measurements after anticoagulant therapy.
Materials and Methods
Fifty-two patients with acute PE were selected for this study. We measured the CSA less than 5 mm 2 on coronal reconstructed images to obtain the percentage of the CSA (%CSA < 5). CT angiographic index was obtained based on the Qanadli method for the evaluation of the degree of pulmonary arterial obstruction. Spearman rank correlation analysis was used to evaluate the relationship between the initial and the follow-up values and changes in the %CSA < 5 and the CT obstruction index.
Results
There was no significant correlation between the %CSA < 5 and CT obstruction index on both initial ( ρ = −0.03, P = 0.84) and follow-up ( ρ = −0.03, P = 0.82) assessments. In contrast, there was a significant negative correlation between the changes in %CSA < 5 and the CT obstruction index ( ρ = −0.59, P < 0.0001).
Conclusions
Although the absolute %CSA < 5 and CT obstruction index were not significantly correlated, the changes in the values of the two parameters had a significant correlation. Changes in %CSA < 5, which can be obtained easily, can be used as biomarker of therapeutic response in patients with acute PE.
Introduction
Computed tomography (CT) has been established as the first-line imaging study for the diagnosis of acute pulmonary embolism (PE). In addition to the role as a diagnostic tool, evaluation of the severity of PE may be performed by several methods on CT imaging. The CT obstruction index , dual-energy CT pulmonary perfusion , the ratio of the right ventricular diameter to the left ventricular diameter , and the heterogeneity in lung attenuation have been advocated as quantitative CT biomarkers of the severity of acute PE.
The CT obstruction index can be obtained by calculating the clot in the large pulmonary arteries . Some studies suggested that scoring of clot burden could predict short-term mortality in patients with acute PE . However, most CT obstruction indexes are calculated visually and are time-consuming. Although semiautomatic clot volume measurement had been demonstrated by recent studies to calculate clot burden precisely, it requires special imaging processing software. In addition, measurement of clot burden cannot provide information on pulmonary perfusion. The ratio of the right ventricular diameter to the left ventricular diameter could predict the clinical outcome of patients with PE , but the validity and reproducibility of this method have not been confirmed well enough. Alteration in pulmonary perfusion is the essential pathophysiology of PE. Dual-energy CT can provide information of pulmonary perfusion, but its use for objective quantitative analysis has not been established and it has not been used widely. Heterogeneity in lung attenuation is an alternative CT measurement to quantitatively assess the severity of acute PE. In fact, skewness and kurtosis correlate with arterial blood gas levels . However, quantitative evaluation of lung heterogeneity has not been widely recognized.
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Materials and Methods
Subjects
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CT Scanning
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CT Measurement of Small Pulmonary Vessels
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Quantitative Evaluation of Heterogeneity in Lung Attenuation
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CT Obstruction Index
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Statistical Analysis
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Results
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TABLE 1
Patients Characteristics, CT Obstruction Index, and CT Measurements
Age (y) 61 ± 15 Male/female 20/32 Initial CT obstruction index 12.7 ± 7.9 Follow-up CT obstruction index 5.0 ± 5.7 Initial %CSA (%) 0.88 ± 0.27 Follow-up %CSA (%) 0.96 ± 0.28 Initial skewness 1.79 ± 0.29 Follow-up skewness 3.50 ± 1.30 Initial kurtosis 1.81 ± 0.28 Follow-up kurtosis 3.62 ± 1.25
CSA, cross-sectional area; CT, computed tomography.
TABLE 2
Correlations Between %CSA and CT Obstruction Index, Skewness, and Kurtosis
CT obstruction index Skewness Kurtosis_ρ__P__ρ__P__ρ__P_ Initial %CSA −0.03 0.84 −0.68 <0.0001 −0.73 <0.0001 Follow-up %CSA −0.03 0.82 −0.80 <0.0001 −0.81 <0.0001
CSA, cross-sectional area; CT, computed tomography.
TABLE 3
Correlations Between CT Obstruction Index and Skewness, and Kurtosis
Skewness Kurtosis_ρ__P__ρ__P_ Initial CT obstruction index −0.06 0.69 −0.06 0.65 Follow-up CT obstruction index −0.06 0.67 −0.11 0.43
CT, computed tomography.
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Discussion
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