title: What radiologists need to know about the pulmonary-systemic flow ratio (Qp/Qs): what it is, how to calculate it, and what it is for.
abstract: Cardiac magnetic resonance imaging (cMRI) provides abundant morphological and functional information in the study of congenital heart disease. The functional information includes pulmonary output and systemic output; the ratio between these two (Qp/Qs) is the shunt fraction. After birth, in normal conditions the pulmonary output is practically identical to the systemic output, so Qp/Qs = 1. In patients with « shunts » between the systemic and pulmonary circulations, the ratio changes, and the interpretation of these findings varies in function of the location of the shunt (intracardiac or extracardiac) and of the associated structural or postsurgical changes. We review the concept of Qp/Qs; the methods to calculate it, with special emphasis on cMRI; and the meaning of the results obtained. We place special emphasis on the relevance of these findings depending on the underlying disease and the treatment the patient has undergone.
authors.affiliation: Radiología Pediátrica, Hospital General Universitario Gregorio Marañón.C/Máiquez 9. 28007 Madrid. Electronic address: Carlos.marin@salud.madrid.org.
authors.forename: C
authors.initials: C
authors.lastname: Marín Rodríguez
authors.affiliation: Radiología Torácica, Hospital General Universitario Gregorio Marañón.C/Máiquez 9. 28007 Madrid.
authors.forename: M L
authors.initials: ML
authors.lastname: Sánchez Alegre
authors.affiliation: Radiología Pediátrica, Hospital General Universitario Gregorio Marañón.C/Máiquez 9. 28007 Madrid.
authors.forename: Á
authors.initials: Á
authors.lastname: Lancharro Zapata
authors.affiliation: Radiología Torácica, Hospital General Universitario Gregorio Marañón.C/Máiquez 9. 28007 Madrid.
authors.forename: J
authors.initials: J
authors.lastname: Alarcón Rodríguez
mesh_terms: D001775:Blood Circulation; D057791:Cardiac Imaging Techniques; D006330:Heart Defects, Congenital / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D011652:Pulmonary Circulation; D011871:Radiology; D012039:Regional Blood Flow
keywords: Cardiac function tests; Cardiac magnetic resonance imaging; Cardiopatías congénitas; Congenital heart disease; Pruebas de función cardiaca; Resonancia magnética cardiaca