A 3-D motion-capture MRI of the heart
The heart is a dynamic, beating organ, and until now it has been challenging to fully capture its complexity by magnetic resonance imaging (MRI). In an ideal world, doctors could create a 3-D visual representation of each patient’s unique heart and watch as it pumps, moving through each phase of the cardiac cycle. Andrew Powell, MD, Chief of the Division of Cardiac Imaging at Boston Children’s Hospital, and his physicist colleague Mehdi Hedjazi Moghari, PhD, have taken steps toward realizing this vision.
The standard cardiac MRI includes multiple 2-D image slices stacked next to each other that must be carefully positioned by the MRI technologist based on a patient’s anatomy. Planning the location and angle for the slices requires a highly-knowledgeable operator and takes time.
Powell and Moghari are working on a new MRI-based technology that can produce moving 3-D images of the heart. It allows cardiologists and cardiac surgeons to see a patient’s heart from any angle and observe its movement throughout the entire cardiac cycle.
“It’s much easier to appreciate complex anatomy when you can see it in 3-D instead of integrating lots of 2-D slices in your mind,” says Powell.
Moghari and Powell refer to their technology as “3-D cine,” because it creates a 3-D image block that moves as the heart beats, showing ventricles pumping and blood flowing through the chambers of the heart. (“Cine” means “movement” in Latin.)
Simplified data collection, easier for the patient
The technology simplifies the cardiac MRI process for both doctor and patient, and provides a much richer data set for discerning diagnoses. “In our 3-D cine technique, the whole chest is imaged as a 3-D block so there is no need to tailor the position of the images based on a patient’s condition,” says Powell. “This leads to easier, faster planning.”
Another challenge with the standard cardiac MRI is that patients must hold their breath while the picture is being taken because any chest movement will blur the picture. A typical patient must hold his or her breath for 10 to 15 seconds a total of 15 to 20 times. Young children and very ill children often find this challenging. With the 3-D cine approach, they can just breathe normally.
“We track the patient’s breathing motion and only collect data during expiration, when the patient is breathing out,” explains Moghari. “The technical aspects of this are continually being refined.”
Acquiring 3-D cine images of the chest takes less than 10 minutes. Data are then loaded onto a specialized viewing computer that allows doctors to watch the moving heart and blood vessels from any perspective, by “cutting” into the block at various locations and angles. The image can even be rendered with lighting and shadows so it looks real. “In the end, we get much more valuable, richer data,” says Powell.
“If there’s any down side to 3-D cine,” he adds, “it’s that it requires the use of intravenous contrast — a dye that makes the blood brighter and easier to see. In some cases, the impact of this is minimal as we need to give the contrast anyway for other reasons related to the MRI.”
During 2016, Powell and Moghari tested their 3-D cine MRI technique on 30 patients of varying ages with various conditions, comparing measurements with those from standard 2-D cine to make sure they match. Their observations have fueled further technical refinements to find the best balance of speed versus image quality.
“This whole 3D-cine development project is the result of a carefully planned, step-by-step process,” Powell emphasizes. The first step was producing clear pictures without breath-holding for 2-D cine. Next came 3-D still images, and now 3-D moving images. At each step, the work was reviewed by other experts in the field.
Several more development steps are needed before 3-D cine MRI technology is ready for widespread use. Current commercially available tools for measuring the size of the heart are designed for 2-D images; Powell and Moghari are working with several companies to develop software suitable for rapid measurements in 3-D.
Moghari also notes that their technique was designed specifically for a Philips MRI scanner. “If another center uses Philips too, they can also use this technique,” he says, “but it would have to be adapted for a different scanner manufacturer.”
In the future, Moghari and Powell plan to take a similar approach to image blood flow in 3-D. They will develop techniques to combine anatomic and blood-flow data as well as tools for user-friendly visualization and analysis. Polina Golland, PhD, and Danielle Pace at MIT’s CSAIL lab are collaborating in this effort. The result will be a powerful tool for understanding the function of the cardiovascular system and making treatment recommendations for patients with congenital heart disease.
Learn more about cardiac imaging at the Heart Center.