Three-dimensional (3D) imaging, specifically cardiac magnetic resonance imaging (MRI), plays a crucial role in clinical decision-making for congenital heart disease due to its ability to assess complex cardiac anatomy and function without ionizing radiation. Modern MRI generates 3D and four-dimensional (4D) datasets for dynamic visualization of cardiac activity. However, the segmentation process needed to make these datasets clinically useful is labor-intensive and often impractical, especially in complex congenital heart disease. Although volume rendering is a faster visualization technique used in 3D echocardiography and cardiac CT, it is not commonly used for 4D cardiac MRI. This approach has the potential to enhance visualization of the myocardium and valves while integrating tissue and blood flow information.
This study aimed to develop and show a novel approach for rapid volume rendering of myocardial tissue and cardiac valves using 3D and 4D cardiac MRI and to integrate these renderings with 4D flow data for simultaneous visualization of cardiac structures and hemodynamics. The authors evaluated whether this approach could provide clinically meaningful, Doppler-like visualization of valve motion and regurgitation while preserving full anatomic context and supporting surgical planning in complex congenital heart disease.
This retrospective study was approved by the institutional review board at Children’s Hospital of Philadelphia with a waiver of informed consent and involved 4 pediatric patients with complex congenital heart disease who underwent clinically indicated cardiac MRI between April 2023 and January 2025. Imaging was performed on a 1.5-T scanner using ferumoxytol contrast, which provides prolonged intravascular enhancement and homogeneous blood-pool visualization. Acquisition protocols included contrast-enhanced MR angiography with ECG-gated, respiratory-navigated inversion-recovery FLASH sequences, 4D multiphase steady-state imaging with contrast enhancement (MUSIC) for dynamic valve assessment, and 4D flow MRI with retrospective ECG gating and respiratory navigation to capture velocity-encoded data in three spatial directions. DICOM datasets were imported into 3D Slicer using custom and existing loaders.
Velocity components underwent automatic phase unwrapping and bias correction, followed by the generation of vector fields and streamlines. Custom transfer functions were designed within the Volume Rendering module to emphasize myocardium and valve tissue rather than only the blood pool. Presets were refined using thresholding, opacity adjustments, and color mapping and were stored for reuse. A custom framework projected velocity vectors relative to the annular plane, generating color-coded flow visualizations analogous to 3D color Doppler imaging. Tissue and flow were rendered using multivolume rendering at interactive frame rates. Virtual surgical elements like baffles, patches, and devices were modeled by using established workflows to show applicability for procedural planning.
Results showed that the workflow was computationally efficient and clinically feasible. DICOM parsing required about 100 to 150 seconds, image conversion 10 to 15 seconds, and velocity processing 5 to 10 seconds. Once loaded, rendering occurred in under 0.5 seconds, and application plus refinement of transfer functions required below 3 minutes.
In a 4-year-old boy with aortic valve insufficiency and stenosis, 4D MRI demonstrated a thickened, doming trileaflet valve with a central regurgitant jet and a regurgitation fraction of 39%; these findings were visually analogous and complementary to echocardiography. In a 6-year-old girl with situs inversus, pulmonary atresia, discontinuous pulmonary arteries, and malaligned ventricular septal defects, volume-rendered MRI enabled assessment of potential obstruction in the left ventricle-to-aorta pathway and facilitated placement of a virtual baffle to guide surgical strategy.
In a 3-year-old girl with multiple ventricular septal defects, image-based navigation MRI allowed detailed visualization of septal anatomy and modeling of virtual patches and closure devices. In a 5-year-old girl with Taussig-Bing–type double-outlet right ventricle status post arterial switch operation and neoaortic regurgitation, integrated tissue and 4D flow visualization enabled simultaneous depiction of valve structure and regurgitant flow. Streamline and velocity-projected renderings produced Doppler-like color representations of forward and backward flow comparable to 3D echocardiography, while preserving full anatomical context.
In conclusion, volume rendering of myocardium and valves using 3D and 4D cardiac MRI is rapid, feasible, and clinically informative. This approach enables efficient visualization of dynamic cardiac structures, specifically valves in complex congenital heart disease, often eliminating the need for time-intensive segmentation. Integration of 4D flow data allows simultaneous depiction of structure and hemodynamics, which provides a comprehensive, radiation-free alternative that complements echocardiography and may enhance surgical and interventional planning. Further refinement of acquisition protocols and visualization tools, along with broader integration into open-source platforms, may expand their clinical impact.
Reference: Iacovella J, Vaiyani D, Pressley S, et al. Rapid visualization of valves and myocardium using volume rendering of 3D cardiac MRI, 4D cine, and 4D flow images. Radiol Cardiothorac Imaging. 2026;8(1):e250129. doi:10.1148/ryct.250129
