Interdisciplinary collaboration between medical physicists and practicing radiologists has been a critical factor in the success of the field of radiology.
Mistretta
Grist
That was the message of the RSNA/AAPM Symposium presented Thursday by Thomas Grist, MD, and Charles Mistretta, PhD, from the University of Wisconsin (UW), Madison.
According to Dr. Mistretta, it is the medical physicists who leverage advances in technology to solve those clinical problems identified by practicing radiologists. Dr. Mistretta is the John R. Cameron Professor of Medical Physics, Radiology and Biomedical Engineering at UW.
Drs. Grist and Mistretta reflected on their experience working together in vascular imaging, focusing on the development of digital subtraction angiography (DSA) and magnetic resonance angiography (MRA).
The development of these modalities was inspired by clinical need, advanced by technology and engineering, and disseminated through commercial partnerships, they said. “And all of this is made possible by the work and collaboration between clinical radiologists and medical physicists,” said Dr. Grist, professor and chair of the Department of Radiology at UW.
Dr. Mistretta’s early research began the transition from X-ray subtraction angiography to digital in the 1970s. This led to the development of a real-time digital video image processor (DVIP), which Dr. Mistretta and his colleagues adapted for time subtraction, leading to the development of a real-time DSA system that was commercialized in 1980.
“Within one year, there were 30 companies making DSA apparatus, all interested in the intravenous angiographic technique,” Dr. Mistretta noted.
Another significant outcome of the development of DSA was its usefulness for something completely different — in this case intra-arterial DSA.
“People realized this could really facilitate endovascular intervention because images could be obtained rapidly and repeatedly,” Dr. Grist said. “It’s a great example of unanticipated clinical applications.”
MRA Technique Resolves Timing Issues
Timing is one of the major pitfalls in all vascular imaging, explained Dr. Grist.
“We really wanted to time the arterial phase of contrast and the image acquisition at the same time, and sometimes we missed that,” Dr. Grist said. So he partnered with Dr. Mistretta to find a solution.
Their collaboration led to the development of a time-resolved contrast-enhanced 3D MRA technique called 3D Tricks (3D time-resolved imaging of contrast kinetics), which was commercialized by GE Healthcare.
However, with MRA there is a “balancing act” between spatial resolution, signal-to-noise ratio, and contrast-to-noise ratio on one side, and temporal resolution on the other. Thinking about this problem led to a focus on radial imaging.
“Radial imaging has different characteristics from cartesian imaging,” Dr. Mistretta said. “It is basically patterned after the CT acquisition where you have high-resolution radial acquisition. And what we started to do with radial imaging is to sample k-space radially, but only to get limited numbers of samples, and not completely fulfilling the Nyquist theorem requirements. So we developed a series of radial sampling techniques to provide higher and higher speed-up factors.”
The development of a 3D radial imaging technique called VIPR (vastly undersampled isotropic projection reconstruction) helped reduce artifacts, and according to Dr. Mistretta, enabled undersampling factors by between three and 300 without substantial artifacts because they were spread around in three dimensions rather than two.
“It became clear that in some areas of vascular imaging this could be really helpful to accelerate the acquisition and shorten exam times,” Dr. Grist said.
Dr. Grist concluded by emphasizing that another key aspect of radiology/medical physics collaboration is a willingness and desire to work together and function creatively.
“One of the key elements is to have a functioning team,” Dr. Grist said. “However, it’s the entrants who often bring new ideas to the table. It’s extremely important that we welcome graduate students into the clinical environment.”
For More Information:
View the RSNA 2020 session Together We Can Make a Difference: Radiology/Physics Collaboration in the Development of New Imaging Techniques — PS31 at RSNA2020.RSNA.org.
