Lung tissue density measured by low-dose CT during pulmonary perfusion SPECT/CT as a tool for differentiation pulmonary embolism from chronic obstructive pulmonary disease – A pilot study

ObjectiveInterpretation of lung perfusion scintigraphy in patients with suspected pulmonary embolism (PE) is difficult, especially in the presence of chronic obstructive pulmonary disease (COPD) and most often has to be combined with pulmonary ventilation scintigraphy. We investigated the data from the CT portion of pulmonary perfusion SPECT/CT for possible resolution of this problem.MethodsWe assessed data from 12 patients (4 male, 8 female, mean age 68 y) with perfusion defects, 6 with PE, 6 with COPD. Final interpretation was based on ventilation/perfusion (V/Q) scintigraphy (mismatch or match). Lung tissue density was measured from the CT portion of pulmonary perfusion SPECT/CT. We analyzed 32 areas in mismatch defects (PE), 25 areas in match defects (COPD), and 17 areas without perfusion defects. Perfusion defects cause easily identifiable on X-ray (e.g. effusion) were excluded from the analysis. Data were compared with ANOVA test and Bonferroni post-hoc analysis, p<0.05 was considered statistically significant.ResultsThe mean lung tissue density in areas without perfusion defects was −758 HU, in V/Q mismatch defects (PE) −695 HU, and in V/Q match defects (COPD) −900 HU. The differences of lung tissue density was statistically significant (p=0.000).ConclusionLung tissue density measured by CT is significantly lower in perfusion defects caused by COPD than in those caused by PE. We believe this data could be used as an adjunct in interpretation of pulmonary perfusion studies and potentially help avoid the performance of ventilation scintigraphy in patients with suspected PE.