A polar map of a landmass resembles a penny that's been squashed by a train: The distance north and south is shorter compared with the longitudinally stretched east and west. A world map with this configuration is able to depict its entire contents on one side, although the representation becomes a bit unrealistic at the edges.

Polar maps of the coronary arteries suffer from the same spatial distortion.

"The problem is that the near vessels are displayed bigger than the farther vessels, particularly around the pole areas and the sides," said lead investigator Dr. Felix Schoth.

As the technique improves, however, it will allow for faster diagnosis, as curved multiplanar reformatted or volume-rendered images of the coronaries are time-consuming to produce, he said.

Schoth and colleagues from Aachen University Hospital in Germany performed a standard CT angiography exam on 10 subjects, using a 16-slice scanner (120 kVp, 550 mAs). Image reconstruction was performed at 60% of the R-R interval.

A newly developed algorithm provides a maximum intensity projection of the myocardium, including the coronary arteries, in 3D polar coordinates. The aortic valve acts as the North Pole.

The images are then "unfolded" into two dimensions as planar projection polar maps. Visibility of the coronary arteries was rated on a scale from 0 (not visible) to 3 (good visibility). Visibility was good proximally, fair medially, and poor distally.

The ratings were as follows:

LAD proximal 2.4, medial 2.2, distal 1.4;

RCA proximal 2.1, medial 1.9, distal 1.3; and

RCX proximal 2.4, medial 1.8, distal 1.3.

Stents and coronary calcifications were displayed accurately, but the ventricles had poor contrast, Schoth said.

A 64-slice scanner would not improve the distortion, which originates from the planar projection; further perfection of the algorithm and data acquisition will accomplish that. But since the temporal and spatial resolution are much better with a 64-slice scanner, smaller vessels would be visible and artifacts would further be reduced, Schoth said.