San Diego —The leader of a bioengineering team at the University of California, San Diego says that using CAD and reverse engineering software to map and analyze the heart could eventually lead to more accurate diagnosis and better treatment for people with heart disease.
Using a chemically fixed pig's heart, Dr. Andrew McCulloch and a group of students, professors, and visiting scholars used a FARO CMM digitizing arm (FARO Technologies; Lake Mary, FL) to take 36,000 measurements from a number of different angles. HighRES STUDIO software (HighRES Inc.; La Jolla, CA) processed the data, and then sent it directly to CADKEY (CADKEY Corp.; Marlborough, MA), a PC-based mechanical CAD system, which created a 3D solid model.
Of particular interest to the team were the atria, the pair of smaller chambers at the top of the heart which take blood in from the lungs and body. Most heart problems occur there, but McCulloch says that typical models of the heart oversimplify their structure.
"Most models represent the atria as spheres with blood vessels attached," he says. "At 1 mm of resolution"–the level of detail in models based on MRI and ultrasound–"you're getting the larger blood vessels, and that's about it."
McCulloch says that the CAD model has a resolution of 0.1 mm, which brings into view such details as the orientation of muscle fibers in the heart wall. This amount of data also necessitated the use of the CAD system to process the measurements.
"The main reason we needed to use reverse engineering and the model was because of the resolution of information on a microscopic level," says McCulloch. "What it enabled us to do was register very large numbers of measurements, and then use the model to do a virtual dissection."
Interestingly, the team has found through the model that variations between individual hearts actually decrease rather than increase as the resolution gets higher. McCulloch says that atria can be categorized into one of four or five different characteristic patterns, a trait that can be used to infer the microscopic structure of a heart, and potentially diagnose and treat problems, without surgery.
"It's entirely feasible that you could make a model of a patient's heart based on low-resolution data from the individual and higher resolution data from cadavers," he says. "This can be done with a high degree of confidence, because when you correct for individual geometry the architecture is quite constant."
The team has now moved beyond measurement and modeling and is feeding the data into a finite element analysis program downloaded from the Internet and modified in-house. In this step of the process the team hopes to learn more about the fluid dynamics, motion, and electrical processes of the heart. Possible uses of the information could include development of better drugs and biomechanical devices for implant, more precise surgeries for given problems, and a more accurate way to tell how and why treatments do or don't work.
As optimistic as McCulloch may be about the the new technology, he stops short of predicting that CAD could entirely replace other diagnostic and research tools.
"Obviously they can't be used for everything–the degree of trust will never be absolute. But," he says, "computer analysis and bioinformatics will make it more feasible for a patient to get a correct diagnosis."