Distribution of Ventilation/Perfusion Ratios in Pulmonary Embolism: An Adjunct to the Interpretation of Ventilation/Perfusion Lung Scans
Emmanuel Itti, MD; Severine Nguyen, MD; Fabrice Robin, MD; Serge Desarnaud, MD; Jean Rosso, MD; ´ Alain Harf, MD, PhD; and Michel Meignan, MD, PhD
Department of Nuclear Medicine, Henri Mondor Hospital, Paris XII University, Creteil, France ´
Diagnosis of pulmonary embolism (PE) by visual interpretation of ventilation/perfusion (V/Q) scans is limited by the high percentages of patients classiﬁed in the intermediate- and low-probability categories. This study proposes a quantitative analysis of the distribution of V/Q ratios to better identify patients with PE. Methods: We studied 99 consecutive patients who underwent dual-isotope 81mKr/99mTc-macroaggregate V/Q scanning and arterial blood gas analysis within 48 h. The 8-view V/Q scans were visually analyzed by 2 observers according to the revised criteria of the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) (normal scan or low, intermediate, or high probability of PE). Quantitative analysis of the posterior-view distribution histogram of V/Q ratios was performed using dedicated software. Brieﬂy, regions of interest were drawn around the lungs on the matched V/Q images, smooth ﬁltering was applied, normalized regional V/Q ratios were calculated within each pixel, and a distribution histogram was built. Results: Patients with normal scans (n 16) had a predominance of V/Q ratios (63.3% 13.0%) between 0.8 and 1.2. They had only 9.8% 5.8% of ratios 1.2, and the remaining 26.9% 7.5% of ratios were 0.8. By contrast, patients with PE (n 34) were characterized by a signiﬁcant increase (15.5 10.0%, P 0.04) in high V/Q ratios ( 1.2) and a signiﬁcant increase (34.5% 8.2%, P 0.003) in low V/Q ratios ( 0.8). Interestingly, a similar pattern was found in patients with a high PIOPED probability of PE, 21.3% 11.0% and 37.5% 9.2%, respectively. Within the nondiagnostic group...