Experts speculate on what future will bring for cardiac MR and CT

March 9, 2009

MR systems used in cardiovascular imaging will inevitably have higher field strengths, including 7T, according to a leading cardiac radiologist.

MR systems used in cardiovascular imaging will inevitably have higher field strengths, including 7T, according to a leading cardiac radiologist.

“The future will be about more tesla,” Prof. Matthias Gutberlet of the cardiac imaging unit at Leipzig University and Leipzig Heart Center in Germany told attendees at Saturday’s cardiac categorical course.

Crucial aspects in cardiac MR are the analysis of ventricular function, myocardial perfusion and viability, and imaging of the coronary arteries, he said.

Gutberlet emphasized this point by referring to research from the Society of Cardiovascular MR. The SCMR asked its members: Which is the most important problem in your daily routine with cardiac MR?

A staggering 66% of the respondents replied imaging of the coronaries, whereas 17% cited myocardial perfusion, 14% cited flow quantification, 2% cited functional imaging, and 1% said delayed enhancement imaging.

Switching from 1.5T to 3T improves image quality and doubles the signal-to-noise ratio. It reduces acquisition time and increases spatial resolution. Moving to 7T leads to further improvements in image quality by increasing the SNR by around five times, he said.

The main advantages of 3T are its perfusion/viability, flow measurement, and “tagging”/spectroscopy applications and its effective imaging of the coronary arteries. Conversely, the main drawbacks are its high cost and limited availability.

In terms of image quality, all standard cardiac MR sequences used for functional evaluation of left ventricular function show an improved SNR and contrast-to-noise ratio.

“Image quality of MR flow measurements and myocardial tagging improves without changing sequence parameters,” Gutberlet said. “In steady-state free precession, sequence modifications are necessary.”

Furthermore, “excessive” use of parallel imaging enables improved spatial and/or temporal resolution in all sequences, he said. Reliable flow measurements even in smaller vessels are possible -- for example, in the coronary arteries -- and longer tag persistence allows for a better analysis of diastolic function.

However, 7T systems remain scarce. The first installation of a Signa 7T machine took place at the Laboratory of Functional and Molecular Imaging, National Institutes of Health, in Bethesda, MD, in 2003. It was followed by installations at the University of Niigata in Japan, University of California, San Francisco, and Stanford University. He predicted further 7T units in the future.

The development of dedicated cardiac MR systems is also a real possibility, said Gutberlet, when he was asked about this topic by session moderator Prof. Maximilian Reiser from the University of Munich. Reiser was president of ECR 2008 and is second vice president of the ESR’s executive council.

The future of cardiac CT is not just about more slices and more tubes, Prof. Andreas F. Kopp of the radiology department at Eberhard-Karls-University in Tübingen, Germany, told course attendees.

The first generation of multislice CT scanners (four-row) was launched in 1998. The next generation (16-row) was unveiled in around 2000, and the third generation (64-row) came in 2006. The fourth generation of machines (dual-source, far-field R-wave sensing [FFS], 128-row) is now starting to emerge, as radiology moves beyond the slice race, he said.

In terms of the mechanical design, the latest CT scanners have to withstand very fast rotation. Centrifugal forces acting on the x-ray tube are 75G for a 0.2-second rotation.

Without expanding the limits of physics, Kopp’s “dream machine” would have a wide detector (16 to 20 cm), new dose-efficient detector material, a fast rotation speed (0.2 second), two x-ray sources, and unlimited computing power for iterative reconstruction. It should not cost more than today’s standard 64-row MSCT system, he said.

“Even the smallest screw must be ready for 75G,” he said. “Cardiac CT must be the driving force for innovations in CT.”