Development of a Comprehensive Cardiac MRI Atlas of Half Fourier-Acquired Single-Shot Turbo Spin-Echo (HASTE) and 3D Balanced Steady-State Free Precession (bSSFP) Sequences Prospectively Acquired From a 1.5T MR-Linac.

Abstract

PURPOSE/OBJECTIVE(S)\nThe 1.5 Tesla (T) Magnetic Resonance Linac (MRL) provides an innovative modality for improved cardiac imaging given its exceptional soft tissue contrast and potential application of real time, adaptive, image guided treatment. A thorough understanding of normal anatomy as seen on the MRL is required for radiotherapy to the heart, such as in treating arrhythmias, thoracic tumors, and breast tumors. To assist radiation oncologists and physicists in further developing and perfecting MRL based radiotherapy techniques, a cardiac MRL based atlas designed for radiation oncologists is necessary. This atlas could also be used for image registration to enhance future adaptive radiotherapy techniques and as a basis for developing novel protocols for treating these diseases. We sought to comprehensively characterize cardiac structures on 1.5 T MR cardiac images.\n\n\nMATERIALS/METHODS\n5 subjects were enrolled in a prospective protocol (NCT03500081) and were imaged on the 1.5 T MRL. Images acquired included breath held Half Fourier-Acquired Single-Shot Turbo Spin-Echo (HASTE) in axial, sagittal, coronal, short axis, and vertical long axis and free-breathing 3D radial stack of stars balanced steady-state free precession (3D bSSFP). These images were then uploaded in commercially available software where cardiac anatomy was contoured, labeled, and confirmed by a licensed cardiologist (JR). Contours of basic cardiac anatomy, the electrical conduction system, cardiac imaging principles, and explanations of the cardiac planes were also created to better prepare clinicians for treating arrhythmias with radiation.\n\n\nRESULTS\nA total of 5 subjects had images acquired with the HASTE sequence, and 1 patient with 4D vane in the cardiac planes. A total of 20 contours were created on each image set for each patient. Contours generated (with respective median volume in cubic centimeters in parentheses) included Left ventricle (LV wall\u202f+\u202fLV interior) (271.95), Left atrium (84.52), Right ventricle (117.06), Right atrium (80.38), Interventricular septum (39.09), Atrial septum (5.77), Atrioventricular septum (11.13), Tricuspid valve (0.16), Inferior vena cava (13.72), Superior vena cava (14.76), Aorta (126.93), Pulmonary trunk (36.4), Left pulmonary artery (15.76), Right pulmonary artery (24.13), Trachea (4.11), Esophagus (25.78), Right main bronchus (2.38), Left main bronchus (2.22), Tricuspid valve (0.16), and Mitral valve (0.21).\n\n\nCONCLUSION\nWe present a comprehensive cardiac atlas using novel images acquired prospectively on a 1.5 T MRL. This cardiac atlas will provide an excellent resource for radiation oncologists in delineating cardiac structures for radiotherapy planning and delivery, with a special focus on providing background information and relevant anatomy essential for treating nearby tumors and refractory arrhythmias using 1.5 T MR guidance.