Free breathing three-dimensional cardiac quantitative susceptibility mapping for differential cardiac chamber blood oxygenation – initial validation in patients with cardiovascular disease inclusive of direct comparison to invasive catheterization

Abstract

Differential blood oxygenation between left (LV) and right ventricles (RV; ΔSaO2) is a key index of cardiac performance; LV dysfunction yields increased RV blood pool deoxygenation. Deoxyhemoglobin increases blood magnetic susceptibility, which can be measured using an emerging cardiovascular magnetic resonance (CMR) technique, Quantitative Susceptibility Mapping (QSM) – a concept previously demonstrated in healthy subjects using a breath-hold 2D imaging approach (2DBHQSM). This study tested utility of a novel 3D free-breathing QSM approach (3DNAVQSM) in normative controls, and validated 3DNAVQSM for non-invasive ΔSaO2 quantification in patients undergoing invasive cardiac catheterization (cath). Initial control (n\u2009=\u200910) testing compared 2DBHQSM (ECG-triggered 2D gradient echo acquired at end-expiration) and 3DNAVQSM (ECG-triggered navigator gated gradient echo acquired in free breathing using a phase-ordered automatic window selection algorithm to partition data based on diaphragm position). Clinical testing was subsequently performed in patients being considered for cath, including 3DNAVQSM comparison to cine-CMR quantified LV function (n\u2009=\u200939), and invasive-cath quantified ΔSaO2 (n\u2009=\u200915). QSM was acquired using 3\u2009T scanners; analysis was blinded to comparator tests (cine-CMR, cath). 3DNAVQSM generated interpretable QSM in all controls; 2DBHQSM was successful in 6/10. Among controls in whom both pulse sequences were successful, RV/LV susceptibility difference (and ΔSaO2) were not significantly different between 3DNAVQSM and 2DBHQSM (252\u2009±\u200939\u2009ppb [17.5\u2009±\u20093.1%] vs. 211\u2009±\u200929\u2009ppb [14.7\u2009±\u20092.0%]; p\u2009=\u20090.39). Acquisition times were 30% lower with 3DNAVQSM (4.7\u2009±\u20090.9 vs. 6.7\u2009±\u20090.5\u2009min, p\u2009=\u20090.002), paralleling a trend towards lower LV mis-registration on 3DNAVQSM (p\u2009=\u20090.14). Among cardiac patients (63\u2009±\u200910y, 56% CAD) 3DNAVQSM was successful in 87% (34/39) and yielded higher ΔSaO2 (24.9\u2009±\u20096.1%) than in controls (p\u2009<\u20090.001). QSM-calculated ΔSaO2 was higher among patients with LV dysfunction as measured on cine-CMR based on left ventricular ejection fraction (29.4\u2009±\u20095.9% vs. 20.9\u2009±\u20095.7%, p\u2009<\u20090.001) or stroke volume (27.9\u2009±\u20097.5% vs. 22.4\u2009±\u20095.5%, p\u2009=\u20090.013). Cath measurements (n\u2009=\u200915) obtained within a mean interval of 4\u2009±\u20093\u2009days from CMR demonstrated 3DNAVQSM to yield high correlation (r\u2009=\u20090.87, p\u2009<\u20090.001), small bias (−\u20090.1%), and good limits of agreement (±8.6%) with invasively measured ΔSaO2. 3DNAVQSM provides a novel means of assessing cardiac performance. Differential susceptibility between the LV and RV is increased in patients with cine-CMR evidence of LV systolic dysfunction; QSM-quantified ΔSaO2 yields high correlation and good agreement with the reference of invasively-quantified ΔSaO2.