Novel MRI Technique Enables Non-Invasive Measurement of Atrial Wall Thickness

Abstract

Knowledge of atrial wall thickness (AWT) has the potential to provide important information for patient stratification and the planning of interventions in atrial arrhythmias. To date, information about AWT has only been acquired in post-mortem or poor-contrast computed tomography (CT) studies, providing limited coverage and highly variable estimates of AWT. We present a novel contrast agent-free MRI sequence for imaging AWT and use it to create personalized AWT maps and a biatrial atlas. A novel black-blood phase-sensitive inversion recovery protocol was used to image ten volunteers and, as proof of concept, two atrial fibrillation patients. Both atria were manually segmented to create subject-specific AWT maps using an average of nearest neighbors approach. These were then registered non-linearly to generate an AWT atlas. AWT was 2.4 ± 0.7 and 2.7 ± 0.7 mm in the left and right atria, respectively, in good agreement with post-mortem and CT data, where available. AWT was 2.6 ± 0.7 mm in the left atrium of a patient without structural heart disease, similar to that of volunteers. In a patient with structural heart disease, the AWT was increased to 3.1 ± 1.3 mm. We successfully designed an MRI protocol to non-invasively measure AWT and create the first whole-atria AWT atlas. The atlas can be used as a reference to study alterations in thickness caused by atrial pathology. The protocol can be used to acquire personalized AWT maps in a clinical setting and assist in the treatment of atrial arrhythmias.

Image-Based Computational Evaluation of the Competing Effect of Atrial Wall Thickness and Fibrosis on Re-entrant Drivers for Atrial Arrhythmias

“…The right (RA) and left atrial (LA) geometries of healthy volunteers and patients, respectively, were obtained by manual segmentation using ITK Snap. The AWT maps for all geometries were computed using previously published methods [8]. This involved the generation of epicardial and endocardial meshes from the segmentations and the computation of the AWT maps by averaging the distance between nearest nodes on corresponding meshes.…”

Image-Based Computational Evaluation of the Effects of Atrial Wall Thickness and Fibrosis on Re-entrant Drivers for Atrial Fibrillation

“…Atrial geometries and fibrosis distributions were extracted from MRI to create 3D human atrial models, as described in previous studies ( Varela et al, 2017b ) and shown in the diagram in Figure 1 .…”

“…However, neither the influence of AWT gradients on the RD dynamics in realistic atrial geometries nor comparative effects of AWT gradients and fibrotic patches on RDs have been investigated. Reconstruction of the atrial wall from imaging ( Varela et al, 2017b ) provides basis for computational modeling of the RD dynamics in patient-specific atrial geometries, to understand the role of AWT gradients in influencing RD locations. Elucidating the relationships between AWT gradients, fibrosis, and RD locations can lead to an improved understanding of AF mechanisms, and ultimately help identify patient-specific ablation targets, improving the efficacy of treatment.…”

Non‐contrast enhanced simultaneous 3D whole‐heart bright‐blood pulmonary veins visualization and black‐blood quantification of atrial wall thickness

“…For 1 individual volunteer (subject 2), and for illustration purposes, a 3D whole-heart PSIR sequence 25 was acquired using an imaging protocol similar to that previously introduced for MRI-derived measurements of AWT. 24 Briefly, an IR pulse was applied in odd heartbeats, where data acquisition was performed with a 90° flip angle. The TI was set equal to 360 ms to null the signal from blood, as determined using a 2D TI scout scan that was acquired in coronal view.…”

“…Quantified AWT thickness amounted to 2.54 ± 0.87 mm for the right atrium and to 2.51 ± 0.61 mm for the left atrium, which is in good agreement with MRI-derived measurements previously obtained in healthy subjects (2.7 ± 0.7 mm and 2.4 ± 0.7 mm for right and left atrium, respectively). 24…”