Interventional CMR Course
SCMR 22nd Annual Scientific Sessions
Non-invasive estimation of blood oxygen (O2) saturation by cardiac magnetic resonance (CMR) has clinical application in pediatric heart disease, specifically congenital lesions, and may reduce the need for hemodynamic invasive catheterization – the current gold standard. A T2-mapping based, non-linear, multi-parameter method has recently been described to non-invasively determine O2 saturation in the heart and great vessels in specific regions of interest. This study aims to create “oximetry maps” to visualize O2 saturation throughout the cardiac chambers and vessels and provide a visual guide for optimal regions for O2 saturation quantification.
Methods: Ten patients (mean age: 15.7 ± 10.5 years, 5 female) undergoing clinically indicated cardiac catheterization and CMR were recruited for the study in a single tertiary care children’s hospital. For each patient, a series of T2-prepared single-shot steady-state free-precession (SSFP) images were acquired in free-breathing, across T2-preparation (T2p) times ranging from 0 to 200 ms (Figure 1). The corresponding inter-echo spacing (τ) ranged from 0 to 25 ms. Images were acquired in multiple planes depending on the patient’s diagnosis. Data analysis included the calculation of color coded maps representing estimated oxygen saturations based on voxel-wise fitting of the T2 data to the Luz-Meiboom model (S , T , τ , and α). Regional O2 saturation based on oximetry maps were compared to corresponding invasive catheterization results.
Results: The study cohort had patients with multiple diagnoses: post-heart transplant, single ventricle physiology, pulmonary stenosis and hypertrophic cardiomyopathy (Table 1). Oximetry maps allowed for visualization of regional O2 saturation and identification of blood pools versus noise (Figure 1). Foreign material (eg, conduits) made data inaccurate (Figure 1). The left atrium was difficult to accurately analyze in 9/10 patients. The mean absolute difference between saturations measured via oximetry maps and catheterization was 3.6 ± 2.4% (p=0.98). Linear regression (r=0.85, p<0.05) and Bland Altman plots (mean difference= -0.08, limits of agreement= -8.69,8.55) comparing the MRI-derived estimates against catheter measurements demonstrated excellent agreement of CMR map derived regional O2 saturation compared to the clinical gold standard (Figure 2).
Oximetry maps aim to further develop the ability for CMR to estimate intracardiac and vascular blood oxygen saturations in pediatric heart disease. MR estimates demonstrated favorable agreement with the clinical gold standard of cardiac catheterization. The result of this preliminary cohort of patients is encouraging, and ongoing patient recruitment is warranted to optimize image acquisition and analysis.