A Comparison of Theory-Based and Experimentally Determined Myocardial Signal Intensity Correction Methods in First-Pass Perfusion Magnetic Resonance Imaging

Objectives. To evaluate the impact of correcting myocardial signal saturation on the accuracy of absolute myocardial blood flow (MBF) measurements. Materials and Methods. We performed 15 dual bolus first-pass perfusion studies in 7 dogs during global coronary vasodilation and variable degrees of coronary artery stenosis. We compared microsphere MBF to MBF calculated from uncorrected and corrected MRI signal. Four correction methods were tested, two theoretical methods (Th1 and Th2) and two empirical methods (Em1 and Em2). Results. The correlations with microsphere MBF (n=90 segments) were: uncorrected (y=0.47x+1.1, r=0.70), Th1 (y=0.53x+1.0, r=0.71), Th2 (y=0.62x+0.86, r=0.73), Em1 (y=0.82x+0.86, r=0.77), and Em2 (y=0.72x+0.84, r=0.75). All corrected methods were not significantly different from microspheres, while uncorrected MBF values were significantly lower. For the top 50% of microsphere MBF values, flows were significantly underestimated by uncorrected SI (31%), Th1 (25%), and Th2 (19%), while Em1 (1%), and Em2 (9%) were similar to microsphere MBF. Conclusions. Myocardial signal saturation should be corrected prior to flow modeling to avoid underestimation of MBF by MR perfusion imaging

Three-dimensional left atrial blood flow characteristics in patients with atrial fibrillation assessed by 4D flow CMR

AIMS: To apply 4D flow cardiac magnetic resonance (CMR) for the volumetric measurement of 3D left atrial (LA) blood flow to evaluate its potential to detect altered LA flow in patients with atrial fibrillation (AF) and to investigate associations of changes in systolic and diastolic LA flow with the current clinical risk score (CHA(2)DS(2)-VASc) used for the assessment of thromboembolic risk in AF. METHODS AND RESULTS: 4D flow CMR was performed in 40 patients with a history of AF (in sinus rhythm during CMR scan, age = 61 ± 11 years), 20 age-appropriate controls (59 ± 7 years), and 10 young healthy volunteers (24 ± 2 years) to measure in vivo time-resolved 3D LA blood flow. LA velocities were characterized with respect to atrial function and timing by calculating normalized LA flow velocity histograms during ventricular systole, early diastole, mid-late diastole, and the entire cardiac cycle. Mean, median, and peak LA velocity steadily decreased when comparing young volunteers, age-appropriate controls, and AF patients by 10–44% and 8–26% for early diastole and the entire cardiac cycle, respectively (P < 0.01 for all comparisons except median velocity for young vs. older volunteers and peak velocity for older volunteers and AF patients). There were moderate but significant inverse relationships between increased CHA(2)DS(2)-VASc score and reduced mean LA velocity (early diastole: r = −0.37, P < 0.001; entire RR-interval: r = −0.33, P = 0.005), median LA velocity (r = −0.33, P = 0.003; r = −0.25, P = 0.017), and peak velocity (r = −0.36, P = 0.001; r = −0.45, P < 0.001). LA flow indices also correlated significantly with age and LA volume (R(2) = 0.44–0.62, P < 0.001), but not with left ventricular ejection fraction. CONCLUSION: Left atrial 4D flow CMR demonstrated significantly reduced LA blood flow velocities in patients with AF. Further study is needed to determine whether these measures can improve upon the CHA(2)DS(2)-VASc score for stroke risk prediction and enhance individual decisions on anticoagulation in patients with AF

Abstract 14026: Atrial Fibrillation is Associated with Altered Left Atrial 3D Hemodynamics and Increased Stasis

Introduction: Clinical scores used for stroke risk estimation in atrial fibrillation (AF) have limited predictive accuracy. 4D Flow MRI can acquire blood flow in a volume data set encompassing the entire left atrium (LA) with quantification of blood velocity in 3 orthogonal directions for every voxel at multiple time points throughout the cardiac cycle (4D = 3D coverage + time). Hypothesis: 4D Flow MRI can assess 3D LA flow abnormalities in AF patients, which may potentially be linked to stroke. Methods: We performed 4D flow MRI in 30 volunteers (10 young, 20 older) and 70 patients with a history of AF: 40 in sinus rhythm (AF-sinus) and 30 in AF during MRI scan (AF-afib). The typical LA contained 3000 voxels and 18 phases per voxel. LA flow velocity histograms for each patient were quantified by mean LA velocity, median LA velocity, and the percentage of LA velocities < 0.2 m/s (%stasis). CHA2DS2-VASc scores were calculated for each patient. Results: Mean LA velocity, median LA velocity, and %stasis were significantly different between groups: young volunteers (0.26±0.02 m/s, 0.23±0.02 m/s, 37.3±7.6%), older volunteers (0.21±0.03 m/s, 0.20±0.03 m/s, 52.2±16.0%), AF-sinus (0.18±0.03 m/s, 0.17±0.03 m/s, 67.5±16.9%), and AF-afib (0.16±0.01 m/s, 0.14±0.03 m/s, 78.2±12.9%), p < 0.0125 for all comparisons. CHA2DS2-VASc had moderate but significant correlations with mean LA velocity (R 2 =0.27, p<0.001), median LA velocity (R 2 =0.23, p<0.001), and stasis% (R 2 =0.26, p<0.001). LA flow indices also correlated significantly with age, LA volume, and left ventricular ejection fraction (LVEF) as seen in the Table. Conclusions: Left atrial 4D flow MRI is a novel approach to identify patients with reduced LA blood velocities and increased LA stasis. Further study is needed to determine whether these measures can improve upon the CHA2DS2-VASc score for stroke risk prediction and enhance individual decisions on anticoagulation in patients with AF