SALT LAKE CITY - Fine-tuning MRI parameters during vascular intervention can be a time-consuming process that requires the interventional radiologist or technologist to turn away from the procedure and work on a keyboard or mouse. But researchers from Ohio have devised a way to adjust imaging parameters in real-time, using an intravascular catheter.
"If you want to do interventional radiology in the MR, (the question is), is it fast enough? We know MR angiography can be done in 10 seconds or less. For device tracking (in the scanner), positioning and orientation of data takes 60 milliseconds," said Dr. Frank Wacker during his talk on Friday at the Society of Interventional Radiology (SIR) meeting. Wacker and his co-authors are from the Hospitals of Cleveland and Case Western Reserve University.
But interface is more difficult because MR is mainly a diagnostic tool, Wacker added. "Our approach is a much more intuitive interface."
In preparation for the experimental study, an automated scan adjustment plane was incorporated with a 1.5-tesla MR Magnetom Sonata scanner (Siemens Medical Solutions USA, Malvern, PA). This was done to ensure that images were acquired at the tip of the 5 French catheter, which had a single-loop radiofrequency coil. The scan system then determined the current position and orientation of the catheter in 3-D prior to image acquisition, which is presented in an endless feedback loop, Wacker explained.
Localization from multiple time points was used to calculate the velocity of the catheter. This information was then used to adjust such parameters as slice position, imaging resolution, slice thickness, and field-of-view. The tracking device was evaluated in two vessel phantoms and in the abdominal aorta of two pigs.
According to the results, the system collected the tracking data within 40 milliseconds. An additional 20 milliseconds were required to perform localization, velocity calculations, and the image parameters. In vivo, the system was able to accurately localize a motionless catheter 100% of the time and a moving catheter 98%.
"The system successfully responded to changes in device velocity by automatically adjusting specified image parameters in real-time," Wacker said. "Simply advancing the catheter more slowly will automatically improve the resolution or signal-to-noise ratio."
The higher the device velocity, the greater the field-of-view, he added. For this experiment, the FOV ranged from 200-400 mm, with a slice thickness between 5-8 mm, and an acquisition rate of two frames per second.
Another benefit of the system is that it does not require special hardware or software for MR implementation. And it enables more accurate characterization of vessel pathology, Wacker said.
"We hope this is an important step toward the clinical application of MR procedures," he concluded.
A session attendee asked if changing the angle of the catheter, either left or right, made a difference in image acquisition. Wacker said such turns of the catheter did not affect the speed of the system, although it may affect the detection rate as a few frames may fall outside of the actual catheter.
By Shalmali PalAuntMinnie.com staff writer
March 28, 2003
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