Abstract Body (Do not enter title and authors here): Introduction: On CT, small size pulmonary artery (PA) thrombus is sometimes difficult to detect and diagnostic accuracy depends on the physician’s skill.
Hypothesis: Using novel spectral CT, an effective atomic number (EAN) and iodine no water (INW) can be determined, which are new CT parameters to evaluate lung tissue and blood flow, respectively. The former can reveal the area of lung tissue degeneration such as occurs in infarction and the latter can reveal the area of decreased PA blood flow.
Methods: A total of 30 patients (13 male, 71±19 years old) who were suspected of having PA thrombus underwent enhanced spectral CT (7500, Philips).
Results: Eighteen had PA thrombus, with abnormal EANs in 17 of the 18 and abnormal INWs in 15 of the 17. Among 30 patients, 12 patients did not have any PA thrombi but 9 of these 12 had abnormal EANs and 7 of these 9 had abnormal INWs. From the location of abnormal EANs and INWs, we rechecked for the presence of PA thrombus and detected a small thrombus in all 7 patients with abnormal EANs and INWs. Both EANs and INWs were significantly lower in the lung with abnormal EANs and INWs than in normal lung (10.1±1.3 vs 7.3±1.1, 1.1±0.5 vs 0.1±0.2 mg/ml, both P<0.01).
Discussion: During this analysis, we noticed three patterns of PA thrombus detection. The first and seconds patterns were represented in Figure 1 and 2, respectively. The third pattern was undetectable thrombi in the PA, an area of decreased PA blood flow on the INW images or lung tissue degeneration on the EAN images or both, or diffusely formed multiple small-size PA thrombi possibly causing decreased PA blood flow or infarction. We speculate that the difference between the first pattern and second pattern might be due to the complexity of the pulmonary circulation. The population in this study were all acute onset cases. If collateral vessels were present among the several pulmonary arteries, or collateral vessels between pulmonary arteries and branchial arteries, enhanced CT that is usually acquired during the first pass of contrast medium through the right heart system (approximately 20 seconds after the contrast injection) would show absence of PA blood flow on the INW images (Figure 2). However, lung tissue degeneration is not due to collateral blood supply, and area of EAN abnormality is much smaller than the area of decreased PA blood flow in INW images.
Conclusion: This new spectral CT technique can improve the accuracy of PA thrombus diagnosis.