Cardiac quantitative susceptibility mapping (QSM) for heart chamber oxygenation
Because of the difference in electron pairing in heme iron caused by oxygen binding, oxyheme is diamagnetic and deoxyheme is paramagnetic 18. Therefore, blood oxygen saturation (SO2) can be measured using quantitative susceptibility mapping (QSM), which is an advanced phase‐based MRI method for measuring the distribution of biomagnetic sources 19. Furthermore, QSM‐based oxygenation quantification has been demonstrated to be feasible in the brain 17, and QSM has been used to study the mouse heart ex vivo 29, but it has not yet been applied to in vivo cardiac MRI because of several technical challenges: cardiac and respiratory motion, chemical shift effects from epicardial fat, and a large range in susceptibilities from air in the lungs and surrounding tissue. As known from coronary MRI, electrocardiogram triggering can be used to acquire data in mid‐diastole to minimize cardiac motion, and breath‐hold or navigator can be used to minimize respiratory motion 30. Recent advancements in QSM precisely account for chemical shift effects using graph cuts 32, and deal with large range in susceptibility using preconditioning 33. By combining the knowledge from these advancements, this study aimed to investigate the feasibility of cardiac QSM for chamber blood SvO2 quantification.