In western societies, cardiovascular diseases are responsible for at least 50% of the mortality rate. Seen in this perspective, the 3D modelling of cardiac structures based on 2D X-ray angiographic sequences has a strong clinical relevance. At ITIS-ITAB'99, Mr. Nikos Papazis presented a technical overview of the Esprit funded 3D HeartView project. The partners have built an advanced prototype, able to generate 3D heart models with minimal user interaction. The system makes no assumptions on the geometric properties of the model and uses no a priori information. The 3D model is produced in a few seconds since the modelling process has been parallelized on a CCi-3D, delivered by Parsytec. The system enables direct visualization as well as fully automatic measurement of the blood volume in the heart chamber interior. The prototype has proved its medical added value in various clinical cases.
A catheter is inserted into the patient's heart chamber through which a contrast agent is injected. The patient is placed in an angiographic device while the gantries are rotated around the patient's torso. Angiograms are acquired and stored immediately in a digital image archive medium with DICOM-3 format or digitized indirectly by frame grabbing. The cardiac phase is derived from the synchronously recording ECG and associated with every image. The digital images with their corresponding heart phase are ported on the High Performance Computing (HPC) machine to create the 3D model by means of back-projection. The parallel modeller has two components, which are the volume-writer to initialize operations, and the partial modeller which performs the 3D modelling.
The volume-writer first reads the 2D input X-ray images after which the data is broadcast over the 100Mbps Ethernet module to the different instances of the partial modeller. Each instance is responsible for accurately computing the appropriate segment of the 3D volume, which is uniformly distributed. If a task has been completed, the instance transmits the volume segment back to the volume-writer. The total 3D volume is produced after having received all the segments. The CCi-3D Parsytec HPC machine forms the hardware platform, consisting of 4 dual Pentium Pro nodes and using Windows NT as the operating system. As for the underlying software, the choice of the 3D HeartView partners fell on the message passing interface (MPI). In fact, the team used WMPI, a Win32 implementation of the MPI standard.
The acquired volumetric dataset can be visualized and manipulated with the InViVo system. Tests have been carried out on phantom studies to validate the accuracy of the system. The team has experimented with convex static, concave, and dynamic phantoms. Through aggressive code optimization, the sequential modelling time could be reduced to 15-20 minutes, thus providing a better basis for the parallelization task. The 3D HeartView system provides the collaborating physicians with a natural feeling of visualization that might pay large services in various applications, like operation planning assistance, 3D motion studies, and quantitative measurements. The main advantages of the system are that it can be added to any modern angiographer, and above all, that it provides an accurate reconstruction of complex volumes to aid the diagnostic procedure.
Future plans of the team include the 3D modelling of vascular structures as well as further clinical validation with more hospital users involved. Because the structures of the coronary artery and the vessel tree are much finer, the technical challenges will be enormous. The specific issues related to vascular modelling will be tackled in the PATRA project, funded with Greek money. In addition, the team expects to improve the parallelization by implementing a new scheme of data partitioning as well as a new version of MPI. The pre-processing of 2D angio-images before modelling will form another key aspect of the research. A full description of the project can be found at the 3D HeartView home page. We also invite you to read the two related VMW contributions: Fast computers enable perfect 3D view of the heart geometry and Parallel computed virtual heart models form upgrade for existing angiographic equipment.